355,383,396 effeciency per cube?

This is going to be kind of long so bear with me:
I am in the process of sorting the pros and cons of my next engine build. I have maxed out the "stock" longblock setup and need to move on. The choices I have in displacement is the real question now. I have the heads, exhaust, and cam that I am going to use for the project. (FLP longtubes, CC306, and reworked LT1 stockers that have been very well done).

My question lies in the effeciency of each engine. I am wondering about the power production per cubic inch of each engine (assume equal compression, the same flow from the heads, and exact same cam and exhaust). I am imagining on a budget I can squeeze more hp per cube from a 355 than from a 383, and more hp from a 383 than a 396. If I can squeeze 1.3hp/ci from a 355 (461.5hp), and I can get 1.2 from a 383 (459.6hp), and maybe 1.15 from a 396 (455.4hp) then wouldn't building the 355 make more sense?

The cons to the smaller engine would most likely be that the engine is more 'peaky' and would develop less torque, but that shouldn't be too big of an issue (M6 car used for racing).

The pros to a bigger engine would be more torque and less rpm for the peak output.

What is the difference in output per cubic inch of each engine (355vs383vs396)? Is there a huge difference?

I do have to limit my $ expenditures. Like a $350 oil pan makes a difference if it dosn't get me down the track faster.

Thoughts?

BBB

To answer your first question, yes the 355 would make more sense. Any time you can keep piston speed to a minimum and make the same power, go for it.

Like you have hit on already, the smaller engine will be more "peaky". However the "hp per cubic inch" differences are very little when you are talking about 355 to 383 to 396, anywhere from 4-8% maybe, which you can make up for in another area of the engine.

However the longer stroke motors will make more torque on the lowend and throughout the powerband, but will be running a higher piston speed which can be an issue if you plan on revving this thing too high.

Piston Speed @ 6000 RPM
355 - 3480ft/min
383 - 3750ft/min

I don't remember the stroke on the 396, but just take it X 1000.

Ok, if everything is the same (heads, cam, headers, etc) how do you plan on getting more power from a smaller engine? It just doesnt happen...

Anyways the "rule of thumb" is to always build the biggest engine you can afford. Generally speaking you can count on at least another 1hp and 1lb/tq from each additional cube provided your top end is up to snuff.

Considering a cast Scat 383 crank runs ~$200 cubes are cheap power. Where else are you going to pick up ~30hp/ and 30lb/tq for $200 all other things equal?

I wouldnt worry much about piston velocity, not at the level you're talking about anyways. Plus given the same cam a 383 will peak lower than a 355 so you wont need to rev it as high (which will reduce piston velocity).

IMHO a 383 is the sweet spot on the "cost vs CID" curve. Cranks are cheap and plentyful plus i'm pretty sure you can get away with the stock oil pan after some massaging. For a 396 the only 3.875" cranks I've seen are forged so they're going to run 3x-4x more than the aforementioned Scat crank. I'm not sure a stock oil pan will work with the 396 either.

Originally posted by Soma07
Ok, if everything is the same (heads, cam, headers, etc) how do you plan on getting more power from a smaller engine? It just doesnt happen...

Anyways the "rule of thumb" is to always build the biggest engine you can afford. Generally speaking you can count on at least another 1hp and 1lb/tq from each additional cube provided your top end is up to snuff.

I'm not sure a stock oil pan will work with the 396 either.

Thanks for the feedback. Here is some more food for thought.

First: I am not trying to get more power from a smaller engine (although that would be cool). I am just wondering how they respond to the same parts (like with heads you are limited on valve size because the bore diameter is the same for all three engines, therefore with heads that flow adequately for the cubic inches valve shrouding should be more of an issue for a 396 than a 355).

Second: I want as many cubes as I can afford (ther is no replacement for displacment.) , but there has to eventually be a downside to increasing inches by only increasing the stroke. Horsepower per cube has to fall off somewhere (like the 500ci NHRA Pro-Stock vs 800ci IHRA Pro-stock). If I can make more torque and even hp in a 396 vs a 383 then the 396 is the better choice if it dosn't cost a fortune; however, if the 396 makes less hp per cube than the 383 (say 1.2 vs 1.3) then the 383 is the better choice.

Third: Oil pans are a prime example of my concern. A stock oil pan won't fit a 396, but it will on a 383 (with work). If the 383 hangs right with the 396 then the extra expense is not worth it.

By the same token 355 parts are more readily avaliable than 383 or 396 parts. I would think you can get better rods, cranks, and pistons for a 355 than a 396 for less $$$

Am I thinking in the right direction?

BBB

Originally posted by BBB
Thanks for the feedback. Here is some more food for thought.

First: I am not trying to get more power from a smaller engine (although that would be cool).

I see, thats sorta what it sounded like with your talk of hp per ci though. My point was given the same heads and cam it would be very unlikely a 396 would make the same power as a 355.


valve shrouding should be more of an issue for a 396 than a 355).

How do you figure? Only two things shroud the valve, the combustion chamber and the bore itself. If you're running the same heads, and the bore is the same how does a 396 shroud the valves anymore than a 355?


Second: I want as many cubes as I can afford (ther is no replacement for displacment.) , but there has to eventually be a downside to increasing inches by only increasing the stroke.

I'm sure you're correct, but I doubt you'll reach that point on a production LT1 block. Well at least not before you run out of money :) Building anything larger than ~396 gets pretty expensive. That said the gain in cubes going from a 355 to a 383/396 would more than offset any loses incured with a longer stroke.


By the same token 355 parts are more readily avaliable than 383 or 396 parts

There are tons of "of the shelf" parts for 383's just waiting to be ordered. True you probably wont find them at the local Autozone store but you shouldnt be building a hi-po motor out of those parts anyways :D Stuff for a 396 (namely the pistons) are harder to come by but they are out there if you look around.


I would think you can get better rods, cranks, and pistons for a 355 than a 396 for less $$$


Cant say I agree with you, the only difference is the crank really. There isnt any difference in the rods. More than likely you'll end up running a 5.7" or 6.0" which will be the same on all 3 motors. 355 and 383 pistons are about the same price too. A 396 may require a custom pistons but that isnt much more expensive.

As far as cranks go you can get the 383 Scat crank I mentioned earlier for $200 and it will be more than strong enough for the combo you're building. For a 396 you'll need a forged crank (since they dont make cast ones in a 3.875" stroke) which is stronger but much more expensive.

a stroker shoudln't cost more than 355
just the machining for clearing the longer stroke is all...
maybe an oil pan? i know both myself and kmook used our stock oil pans...
there is no replacement for dispacement:)
396 = +.7L :)
or ~13% more displacement:bow:

cheers :)

Originally posted by Soma07
I see, thats sorta what it sounded like with your talk of hp per ci though. My point was given the same heads and cam it would be very unlikely a 396 would make the same power as a 355.



How do you figure? Only two things shroud the valve, the combustion chamber and the bore itself. If you're running the same heads, and the bore is the same how does a 396 shroud the valves anymore than a 355?





Valve shrouding: I was thinking that valve shrouding would be more of an issue for a 396 solely from a 'feeding extra inches' issue. The bore would be the same so all the clearances would be the same etc. And thinking on it further it should be a cam issue rather than a valve issue. (That is why I asked, good responses make me think things through better.)


HP/CI effeciency: from any current responses nobody has said anything leading me to believe that there is much to be lost effeciency wise with the bigger engine (although I have seen some debate between 396 vs 383 in other threads before)

Thanks for the responses, they have helped clear up my decisions a little.

BBB

i'm emailing you jason
I have one question of my own-

what crank is used in a 396 and does it impair its revving capabilites significantly when compared to a 400 crank?
(is it a 427 crank :confused: )

mr G- Racenet dicked me over too :mad:

Now returning to our original programing already in progress...

Originally posted by treyZ28
what crank is used in a 396 and does it impair its revving capabilites significantly when compared to a 400 crank?
(is it a 427 crank :confused: )


A 396 uses a 3.875" stroke crank. Sorta like a 383 crank just with a little more stroke. To my knowledge its not used on any production motors.

Theoretically the longer the stoke the worse the rode/stroke ratio gets and the less it likes to rev. In reality I dont think its a problem unless taken to the extreme. For instance take a look at jimlab's dyno sheet for his 396:

http://home.earthlink.net/~jimlab/images/dyno1.jpg

7600rpm is plenty fast enough for me :D

Yes, and I understand that it's somewhat popular to use a 6" rod in a 396, but my friend told me he worries that the piston is then too high into the ring lands.

I think there is a 5.8x rod/piston combo.

I emailed JE about a .060 over 5 7/8" stroke piston and they said it would be a custom piston...

HP/cu. in is probably better at 302 even, eh?

treyZ28: they said to me that they had never had a problem with that combo, I have gotten 4 people now that say otherwise :rolleyes:

I'm no expert with strokers, so maybe I shouldn't be in here :D but I'll post my thoughts as I'm starting to work on what I want to do when the 147k stock engine finally pumps it's last ounce of oil :)

I've read that as the rod/stroke ratio gets lower, the crank has a tendancy to pust the piston into the wall of the cylinder, and I think that's where your efficiency goes down. Also, (just a thought) you are "dragging" the piston/rings further, so you have more friction, losses of heat, etc... Also you are getting the piston away from the combustion chamber quicker, thereby reducing the pressure exerted on the piston top during the power stroke. If you have a big rod/stroke ratio, the piston "dwells" near TDC longer, allowing the pressure to push the piston down for a greater angular displacement.

Lately, Hot Rod has been praising high rod/stroke ratios advising that they make more power and spin faster.

Having said that, I'm looking into a NA 396 myself, but I'd want 6" rods, which some have said puts the piston ring too far into the ring lands, which = more blowby and weaker pistons.

The stock engine has 5.7" rod w/ 3.48" stoke, so you're looking at a r/s ratio of ~ 1.64.

A 383, with it's 3.75" stroke is as follows:
5.70" rod; r/s = 1.52
5.85" rod; r/s = 1.56
6.00" rod; r/s = 1.60

A 396 :metal: , with it's 3.875" stroke goes like this:
5.70" rod; r/s ~ 1.47
5.85" rod; r/s ~ 1.51
6.00" rod; r/s ~ 1.55

Here's an idea:
A 302, with a 3.00" stroke w/ impy 6.00" Rods; r/s = 2.00 :bow:

I think you have to decide between cost/forced induction/rev capabilities.

I think a 383 can be built nicely both ways, cheap, NA, medium rev = cast crank, 6.00" rods, high compression

expensive, Blown/NOS, high rev = forged crank, 5.85" rods, low compression

Unfortunately, I don't think a 396 can be as versitle, because it's expensive any way you cut it.

Da*n it, I think I just talked myself into a 383 :(


If I may ask one question though that I'm not clear of, how much hp/stroke can stock 2 bolt mains take? If I'm not mistaken you can upgrade the bolts to ARP, or are the mains held by studs? I notice that 4-bolt/splayed conversions are pretty expensive, and so is the required labor.

See now that is the kind of thinking that has started me to back away from the 396 :(

Dwell time, angularity, sidewall loading, and piston ineffeciency all should contribute to small losses in hp production. The issues can be overcome by more expensive parts, but gee if that was no problem I would buy a 550ci prostock carbon fiber car.

The 355 with 6" rods has the best rod ratio (I have always heard that a 355 and 377 make great acceleration engines due in part to rod ratios).


What do the engine builders say(like Nu-tec/Nick Norris). Someone who regularly builds both and sees dyno time every week should be able to enlighten us.

BBB

OK.... I think I have pruned out the irrelevant material..... I apologise if anyones relevant post got cut... this was my first adventure with the new software..... But I think it was done correctly.

Fred

I went with the 355 6" rod set up why?
I was on a budget as well, instead me spending more money on a 383 or 396 crank i put that money towards the rods and pistons and stayed with a stock crank. And another reason for the 355 i thought there whould be alot less tuning like to the fuel curve, spark etc. that is needed for the 383 or the 396. i think i spent around a 1000 dollars for the rods, pistons, machine work and of the other little things gaskets, oil etc. And i think with the AFR LT4 195cc heads with the LT4 intake and a CompCams nitrous cam 224/236 534/555 114lsa w/ 1.6 rr's and all of the other bolt-ons like the Hooker LT's, 3" Y pipe, Mufflex 4",TH-350, and etc.. I think my car will make some where around 430 to 450rwhp and thats not bad for a little 355c.i w 6" rods
Just my .02 cents

My94RedZ28A4 and Soma07 is who I would listen to.....bigger isn't always better...if the rod/stroke ratio is no good the more problems you will have.

Some interesting aspects of engine design are being brought up, but the bottom line is that for a street or street/strip motor the stroker is the way to go. If you don't want invest in a forged crank, the 383 is the best option. If you are going to a forged crank anyway, go for the 396. All the other parts will cost ~ the same for a given quality between the three combos and the larger motors will simply make more hp. But exceeding 396 gets expensive quick.

Rich Krause

if everything in motor is right, a smaller motor will make as much power as a bigger motor you will just have to turn it more RPMs...for example i know a guy who ran competition eliminator in NHRA and IHRA and me and my dad were talkin to him one day and he said when his motor was 49X C.I. it made 1050 horsepower, he de-stroked it and made it a 477 and it made 1050 horsepower...he just had to turn more RPM's...a smaller motor will be more efficient you just have to be willing to turn it more RPM's, if 6000 RPM's is gonna be peak RPM then goin w/a 396 would prob be the smartest choice, but if you could turn it up to say 8k the 355 will prob run faster than the 396 using the same cylinder heads...

Don't want to start an argument, but it's patently untrue that "if everything in motor is right, a smaller motor will make as much power as a bigger motor". If it were, why would every engine in a displacement limited racing class be built right up to the limit?

Now, if we are talking about an NA 355 v. 383 v. 396, the differences in hp are not proportional to displacement. If the heads are identical, there will be a less than proportional increase in airflow (and hence power) as the stroke gets longer. But there's no question the stroker will be faster, even if the peak power is only marginally greater, due to greater area under the torque curve. Acceleration is a function of power applied over time, not just peak hp.

For a SC setup, the stroker's advantage is even more pronounced.

Rich Krause

Me and A buddy have two 1971 nova's 308 gear's a3 same heads; cam; intake;headers;carb; My nova has A 406 his has 355. In 1320' he smokes me buy 6 car's.smaller moter on same air and gas I gess. You tail Me.

Don't want to start an argument, but it's patently untrue that "if everything in motor is right, a smaller motor will make as much power as a bigger motor". If it were, why would every engine in a displacement limited racing class be built right up to the limit?
the reason is because with a bigger motor, you can put the bigger head to turn the bigger motor the same RPMs as the smaller motor, a motor with high horsepower that turns RPMs will run faster than a torque motor that turns less RPMs...Look at NHRA Pro Stock, why would they turn their 500 c.i. motors 10,000 RPMs??? also compare that to the IHRA Pro Stock cars, they run 815 cubic inch motors and turn them 8000 RPMs! thats 314 more inches and they only run two tenths faster? explain??? what im sayin is to a certain extent a smaller motor that turns RPMs will run as fast or faster than a bigger torque motor with same heads/cam setup because its a more efficient motor cuz there is more head flow for a smaller motor, believe me, ive seen it too many times...

Originally posted by WickEdSix98
the reason is because with a bigger motor, you can put the bigger head to turn the bigger motor the same RPMs as the smaller motor, a motor with high horsepower that turns RPMs will run faster than a torque motor that turns less RPMs...Look at NHRA Pro Stock, why would they turn their 500 c.i. motors 10,000 RPMs??? also compare that to the IHRA Pro Stock cars, they run 815 cubic inch motors and turn them 8000 RPMs! thats 314 more inches and they only run two tenths faster? explain??? what im sayin is to a certain extent a smaller motor that turns RPMs will run as fast or faster than a bigger torque motor with same heads/cam setup because its a more efficient motor cuz there is more head flow for a smaller motor, believe me, ive seen it too many times...

2 tenths is a buttload of power dude!

and at their power levels- their speeds are tire limited

they can spin their tires through most if not all of the 1320.
They make more power than they can put down.

its like having a 60 ft race on street tires with a 900 hp and 1200 hp car.
who cares?
both are traction limited

2 tenths is a buttload of power dude!

true it is but with 314 more inches and heads that flow 80-120 cfm more you'd expect them to run faster...


they can spin their tires through most if not all of the 1320.

they prob could on a typical local unprepped track but on the tracks they run on they will spin off the line a little bit but the rest of the ways down the track they dont...they have computers on the cars with sensors that show RPM's of the motor during a pass, if the graph shows the motor peaking more than its supposed to on a shift, they will take clutch out of it so that it will not spin...

also, i think NHRA Pro Stock cars make around 1300 hp and the IHRA pro stocks make around 1500-1600 hp and when you do the calculations, the formula will show that it takes more power than they have to run what they run due to the efficiency of the tranny's...

Originally posted by WickEdSix98
true it is but with 314 more inches and heads that flow 80-120 cfm more you'd expect them to run faster...




they prob could on a typical local unprepped track but on the tracks they run on they will spin off the line a little bit but the rest of the ways down the track they dont...they have computers on the cars with sensors that show RPM's of the motor during a pass, if the graph shows the motor peaking more than its supposed to on a shift, they will take clutch out of it so that it will not spin...

also, i think NHRA Pro Stock cars make around 1300 hp and the IHRA pro stocks make around 1500-1600 hp and when you do the calculations, the formula will show that it takes more power than they have to run what they run due to the efficiency of the tranny's...

1500hp? LMAO

1500 hp is like 7 sec range.

Look at NHRA Pro Stock, why would they turn their 500 c.i. motors 10,000 RPMs??? also compare that to the IHRA Pro Stock cars, they run 815 cubic inch motors and turn them 8000 RPMs! thats 314 more inches and they only run two tenths faster? explain???

NHRA Pro stock cars are 500ci because thats the limit according to the rules. If they were allowed to build a bigger motor I assure you they would. They spin them to 10k rpm because thats what it takes to make power they need to be competative.

Also as someone else mentioned when you're running in the mid 6's two tenths is a huge difference in power.

None of that really matters since a Pro Street motor is not even remotely similar to the type of buildup we're discussing here.

what im sayin is to a certain extent a smaller motor that turns RPMs will run as fast or faster than a bigger torque motor with same heads/cam setup because its a more efficient motor cuz there is more head flow for a smaller motor, believe me, ive seen it too many times...

If you've seen it "too many times" then prove it. Show us an example of a smaller motor running faster than a larger one all other things equal.

Originally posted by Soma07
NHRA Pro stock cars are 500ci because thats the limit according to the rules. If they were allowed to build a bigger motor I assure you they would. They spin them to 10k rpm because thats what it takes to make power they need to be competative.

Also as someone else mentioned when you're running in the mid 6's two tenths is a huge difference in power.

None of that really matters since a Pro Street motor is not even remotely similar to the type of buildup we're discussing here.



If you've seen it "too many times" then prove it. Show us an example of a smaller motor running faster than a larger one all other things equal. [/B]

isn't it physically impossible for a smaller to make more power "all things being equal?"
I'm fairly confident it is :think:

if power= work/s
and you do more work in the same second- isn't your power higher :think:

and 1/2 sec tenths is 250ft at their speeds ;)
winning by 250ft in a 4 sec race is pretty good IMHO

Originally posted by treyZ28
isn't it physically impossible for a smaller to make more power "all things being equal?"
I'm fairly confident it is :think:

if power= work/s
and you do more work in the same second- isn't your power higher :think:


Yes, but what is work?

Work = Force x Distance

But thats for linear motion. For rotational stuff (like motors) we use torque to represent force and revolutions for distance.

Now we have Power = (Torque x Revolutions)/Time

Now its easy to see if we want more power then we need to increase torque, or increase the number of revolutons the motor performs for a given period of time.

Granted thats a pretty simplified explination but it gets the general idea across.

So in the end, yes, it is possible for a smaller motor to make more power than a larger one. It just needs to apply more force (torque) than the larger motor or it needs to apply its force at a higher RPM. However since torque is relatively proportional to engine displacement (generally speaking) if you want to make a smaller motor match a bigger one you're going to have to spin it faster to make up for its torque deficit.

This is getting pretty unfocused, but there really should be no doubt that if we are talking about a 355, 383, or 396ci LT1 with LTx head castings and otherwise comparable parts the 396 witll be fastest, the 383 next, and the 355 slowest. The 355 will be more "efficient" in the sense of more hp/ci. It will not be more efficient in terms of performance/$, as there is very little cost difference when comparable parts are used.

Rich Krause

Originally posted by rskrause
This is getting pretty unfocused, but there really should be no doubt that if we are talking about a 355, 383, or 396ci LT1 with LTx head castings and otherwise comparable parts the 396 witll be fastest, the 383 next, and the 355 slowest. The 355 will be more "efficient" in the sense of more hp/ci. It will not be more efficient in terms of performance/$, as there is very little cost difference when comparable parts are used.

Rich Krause

Agreed, I'm not even sure I was awake when I wrote my last post, lol...

Maybe I missed the boat, but what's this big stink about efficiency anyhow? Power is power, or else we'd all drive 1.95HP/CI Honda S200's based on efficiency alone:)

I think this was a good discussion as it has brough tto light alot of questions i woul have eventually posted on. :)

Originally posted by Injuneer
OK.... I think I have pruned out the irrelevant material..... I apologise if anyones relevant post got cut... this was my first adventure with the new software..... But I think it was done correctly.

Fred

You sure play "God" a lot in this forum. What qualifies you to decide what the rest of us should and shouldnt see as far as posts go?How can you know someone else wouldnt find some relevance in them?
If you decide to leave a thread in Advanced forum, you ought not to prune the replies.
Kind of miffs me that I take the time read all the way thru this, and then find out someone has edited others posts.

Just my opinion. Now I guess I`ll find out if the mods here can take constructive input or not......................

Originally posted by SSkindog
You sure play "God" a lot in this forum. What qualifies you to decide what the rest of us should and shouldnt see as far as posts go?How can you know someone else wouldnt find some relevance in them?
If you decide to leave a thread in Advanced forum, you ought not to prune the replies.
Kind of miffs me that I take the time read all the way thru this, and then find out someone has edited others posts.

Just my opinion. Now I guess I`ll find out if the mods here can take constructive input or not......................

Amazing.... you read a 4 month old thread, and out of the blue decide that I pruned out things you might have thought were relevant. As I recall the thread was pruned for one of the following reasons:

1 - There were duplicate threads, both with valid responses, the two threads were merged, and duplicate posts were eliminated.

or...

2 - Two people got in a very personal pissing contest that had nothing to do with Advanced Tech, including the posting of some ethnic slurs. These inappropriate posts were eliminated.

What is your specific complaint... What relevant material do you feel would have been deleted by the above actions?

By the way, please e-mail me, since board rules (not mine) discourage direct posting of complaints about the moderators decisions.....

If you are unhappy with the job I do, send a complaint to Jason Debler or Chris Frezza and let them know your concerns... I'm sure they will give you a fair hearing.

I personally don't consider myself playing "God", but you are entitled to your opinions.

Have a nice day.... :).

Fred
Moderator

Originally posted by SSkindog
You sure play "God" a lot in this forum. What qualifies you to decide what the rest of us should and shouldnt see as far as posts go?How can you know someone else wouldnt find some relevance in them?
If you decide to leave a thread in Advanced forum, you ought not to prune the replies.
Kind of miffs me that I take the time read all the way thru this, and then find out someone has edited others posts.

Just my opinion. Now I guess I`ll find out if the mods here can take constructive input or not......................

hes a moderator ;)

Down said the crack pipe! down!

Originally posted by SSkindog
You sure play "God" a lot in this forum.
What qualifies you to decide what the rest of us should and shouldnt see as far as posts go?

What qualifies us? The position as a Moderator given to use by the Admins.
Want some info from the admins, here you go-

What Are Moderators?
Moderators oversee specific forums. They generally have the ability to edit and delete posts, move threads, and perform other manipulations.
Oh and from the rules form that you agreed to when you signed up-
We reserve the right to close or delete any message for any or no reason whatsoever.
Ken
Moderator

Originally posted by SSkindog
You sure play "God" a lot in this forum. What qualifies you to decide what the rest of us should and shouldnt see as far as posts go?How can you know someone else wouldnt find some relevance in them?

with the advice i've gotten from him, and the things i've learned about my car because of him, Injuneer may as well be God. I probably have more respect for him than anyone else on this board.

Sorry..........maybe I spoke too soon.

And I do know that a moderators job is seldom appreciated.

4 month old or not, still a good thread, and didnt want to miss something that might have been relevant.

And I dont question any of the mods automotive expertise at all. Have read the forum enough to know better .....

I do appreciate being able to voice my opinion, wrong or right, without repercussions.

With that said, I think it would be appropriate to put an end to this discussion.

Originally posted by Soma07
I see, thats sorta what it sounded like with your talk of hp per ci though. My point was given the same heads and cam it would be very unlikely a 396 would make the same power as a 355.



I think that given the same cam the 383 will make less power than a 355 up to a point...


A 383 needs a bigger cam because it has more space to fill and thus needs more time for the air to come in..

the higher the rpm the more velocity and the longer it needs to keep the valves open because there is a lot more velocity in the incoming charge due to the piston speed and thus creating more vaccuum inside the cylinder that has to be filled and the way is via 1) more duration 2) more overlap...

rod length also determines what type of cam and a cam for a 383 will not be ideal for a 355 and viceversa...

Originally posted by Jim S. '95 Z28
Maybe I missed the boat, but what's this big stink about efficiency anyhow? Power is power, or else we'd all drive 1.95HP/CI Honda S200's based on efficiency alone:)

I dont know where you get the word efficient...

The S2000 consumes more gas than an ls1...

Originally posted by The Highlander
I dont know where you get the word efficient...
The S2000 consumes more gas than an ls1...

I think in this case "efficient" applies to the hp per ci ratio.


Just to keep the discussion going, Fred, would you mind commenting on why you went with your setup (3.75" crank) vs a larger (or smaller) one?
My next project will be either a 383 or 396 and I'm looking for as many opinions (hopefully based on knowledge/experience;)) as possible. Things like rod length, piston ring lands/wrist pin location, etc. are all concerns for a given setup.

Yes... always wondered how ARE makes so great MPH on just 396 MOTOR... around 120+mph with just a 396.. I know that also here the climate is a LOT more humid and Hotter... so that has an impact.. but anyways...

Stock bottom guys can run 120+, even on the "crappy" LT1.

Its a bit "late" but BBB if your going to race your going to want to swap that pan anyway.

Originally posted by Serial Thriller
Just to keep the discussion going, Fred, would you mind commenting on why you went with your setup (3.75" crank) vs a larger (or smaller) one?


Easy..... nitrous.

I just thought the 3.75" stroke and 5.85" rods would give me pistons that could survive a 300-shot. Giving up .125 off the top of the pistons didn't seem worth the extra 12.7 cubic inches.

Well consider this the 4th gen fbody is no light weight, so the more cubes the more torque to move the mass, the car will be quicker with less gear. Also the killer of engines is rpm more than piston side loading and unless you are going to switch to a solid roller cam you are going to be sort of rpm limited with a heavy hyd roller aren't you.

I know of streetable hydralic motors turning 7500, so not TOO limited in revs ;)

these days, even low rev apps(<7k) are running solids due to there better streetablity.

Originally posted by JordonMusser
I know of streetable hydralic motors turning 7500, so not TOO limited in revs ;)

these days, even low rev apps(<7k) are running solids due to there better streetablity.

Agreed.
In a stroker especially, a solid in the 240-246 range @.050 is plenty livable. Manual trannied cars make it that much more "streetable".
And yeah, guys are turning 7500 with hydraulics but that's where the hydraulic to solid swap needs to be made in my opinion. Lose a lot of valvetrain stability with hydraulics in that range.

-Mindgame

With the same setup, as far as h/c and such take it, the larger motor should be faster bcuz of what was said earlier about power under the curve. The hp/ci effeciency is going to drop with a bigger engine all with the same setup, but the largest should go the fastest bcuz of power under the curve. Guys with a 350 LT1 making 400rwhp are in the 360-385rwtq range, one guy I saw uped that displacement to 360 cu in and suddenly he was at 400rwtq with a smilar setup as a 350 but without loseing hp. Sure his hp/ci went down, but does that mean the car will be slower? NO, it should be faster.

If I was looking at effeciency, I would be looking at tq/ci, I would think that would give you a better idea of what the motor is capilable of.

Originally posted by mastrdrver
With the same setup, as far as h/c and such take it, the larger motor should be faster bcuz of what was said earlier about power under the curve. The hp/ci effeciency is going to drop with a bigger engine all with the same setup, but the largest should go the fastest bcuz of power under the curve. Guys with a 350 LT1 making 400rwhp are in the 360-385rwtq range, one guy I saw uped that displacement to 360 cu in and suddenly he was at 400rwtq with a smilar setup as a 350 but without loseing hp. Sure his hp/ci went down, but does that mean the car will be slower? NO, it should be faster.

If I was looking at effeciency, I would be looking at tq/ci, I would think that would give you a better idea of what the motor is capilable of.

For a larger motor to make as much hp, you have to remove the restriction..... in other words, the bigger stroker is gonna need alot of cylinder head and an intake that doesn't cost you in airflow. That's why alot of race engine guys stick to some of the smaller displacements... so they can get enough cylinder head on the motor to turn more revs.
Tq/L is all cool and fine but there's only so much torque you can make anyways. Let's say its 1.55 lbs-ft per cid. So you have the choice to make your 1.55 lbs-ft/cid at 4500 rpm or make it at 5500 rpm..... one will make quite a bit more hp than the other. One will also be quicker at the track than the other and it aint the lower reving (lower hp) one. So you make as much torque as you can but to be the fastest at the track, you place that peak higher in the rev range and gear the car accordingly.

-Mindgame

Well said Mindgame! :bow:

Then a better effiecency would be avg hp/ci wouldnt you think?

Yes a larger engine should make more power given larger heads and/or cam, but given everything the same they should all make roughly the same hp except that the larger motors will make more tq. Larger engines just have more potential to be "unlocked" with larger h/c.

Avg Hp/Ci would be good but with the same set of heads that equations goes down the more cubes you add. Well at least there is a point of diminishing returns like every curve.

Say 1.5 ft lbs per cube and 1.75 HP per cube. That's 530 ft lbs and 610HP on a 350. Then a 383 is 575 ft lbs and 670 HP. You need alot more cylinder head for that. 610hp is nothing to sneeze at but 675hp doesn't just happen because of the cubes. It's possible to do both but they are entirely different engines.

Mindgames point is good, but remember that RPM cost $. A 6K engine is easy but a 8K engine is going to cost some money if you want it to live. RPM kills things in the engine. A cube class all depends upon the engine designer. Smaller cubes and max power are going to cost you the same as a big cube engine making alot of power and tq, but the small cueb engine might be better because of things like weight. It all comes down to Lb per HP and traction. If you give me the same heads and less weight I'll take the smaller cubes, because of RPM potential and Lb per HP.

Most of you guys aren't talking about a max effort drag engine though. Nobody wants a 10,000rpm engine that you have to change the valve springs in every run and makes over 2.6 HP per cube, well at least on the street.

Guys, cubes are cheap to a point. On a LT1 a 383 is cheap and is never going to be overstressed on a street/strip application so why go to a 7500rpm 355 when you can have a stronger engine that's a 383? It's all going to cost you some cash anyways.

Bret

Originally posted by SStrokerAce
Guys, cubes are cheap to a point. On a LT1 a 383 is cheap and is never going to be overstressed on a street/strip application so why go to a 7500rpm 355 when you can have a stronger engine that's a 383? It's all going to cost you some cash anyways.

Bret

Not to mention the fact that on the street, torque is key. Your car will be fastest if you build your motor to be strongest in the RPM range where the motor will spend most of it's time during a run. So on a street car, I would say building a car with over 6000 RPM peak power is probably not necessary.

It is really cool to see my thread alive and well over 6 months after it started. It seems like we have struck a chord here.

A little update on my engine progress. I originally posted this topic starting in late Sept last year. On the first Saturday of October our car club had a dyno day where we all ran to see how the summer mods had improved our cars. My car is a bone stock long block! That includes the 120,000 mile stock cam. I dynoed 343 rwhp/ 356 rwtrq. Not bad for a stock 350/m6.

Now for the fun part. On the same dyno three 383s (2 LT1s and one carbed) pulled much worse #s.

The best one was 360hp, the next best was 318hp, and the saddest was 275ish hp.

Both the LT1s were cammed (the 360hp had the cc305).

What was the difference between my engine and their strokers? I believe they were seriously undercammed and needed much more head work. I did some serious home porting over the summer that totally woke up my combo. Their heads obviously were not up to the task of filling up a stroker.

I am more convinced that unless you go with very well built top end parts you can't extract power potential out of a stroker like you should. Plus for those of us limited to factory intakes, there is ounly so much cfm that you can get them to flow without boost.

I also am leery of building too much torque. Too much torque = no traction. No traction = no acceleration. I would rather sacrifice a little torque down low for additional midrange torque and high end hp. It give me a better top end charge and better control/consistency on launch.

BBB

Hey Jordan and Mindgame I agree with you guys that there are hyd rollers turning 7500 rpm, but the original question stated that he wanted to keep his CC306 cam right, so I don't think he'll make 7000 + rpm without a hydra rev kit or something. Especially in a 383 or 396 without a big head like AFR 220 or 227 fully ported and then the stock intake or 306 would probably become the restriction.

Originally posted by SStrokerAce


Nobody wants a 10,000rpm engine




speak for yourself :p

Originally posted by The Highlander
I dont know where you get the word efficient...

The S2000 consumes more gas than an ls1...

I don't know where you get your definition of efficient either. Used car salesman trying to sell you a Metro:confused:

In most automotive circles, you know the SAE types, efficiency refers to specific output. In other words, HP per liter/cid.
On the other hand, since you brought up gas mileage, sounds like you're thinking of economy.

Thanks for the opportunity to help clarify your confusion:D

Originally posted by Jim S. '95 Z28
I don't know where you get your definition of efficient either. Used car salesman trying to sell you a Metro:confused:

In most automotive circles, you know the SAE types, efficiency refers to specific output. In other words, HP per liter/cid.
On the other hand, since you brought up gas mileage, sounds like you're thinking of economy.

Thanks for the opportunity to help clarify your confusion:D :lol:

Efficiency is output/Input... Right???

If both cars weigh the same and to do the same one needs less fuel than the other to have the same HP which is more efficient????

The S2000 could be more efficient per CI, but that is it...

Originally posted by The Highlander
Efficiency is output/Input... Right???

If both cars weigh the same and to do the same one needs less fuel than the other to have the same HP which is more efficient????



:confused:

I think you've been reading too many of Trey's posts:D


The S2000 could be more efficient per CI, but that is it...

That was my point exactly. Read my original post again. You basically disagreed with something we agreed on in the first place.

Originally posted by Injuneer
Easy..... nitrous.
I just thought the 3.75" stroke and 5.85" rods would give me pistons that could survive a 300-shot. Giving up .125 off the top of the pistons didn't seem worth the extra 12.7 cubic inches.

Thanks; that's what I thought you'd say.;)

Yes, Mindgame has a good point and although it seems to be more geared towards racers, much the same is true on the street.

"Torque is king"

Where have I heard that before?:)
Of course it's "king" but the question is, torque where? You have to look at more than the engine for that answer. If you want torque off idle, for pulling boats, small houses, whatever. Then stay with short period camshafts or build engines with as many cid as you can afford. Even then you are giving up potential horsepower for a small degree of durability.

If you are building a street engine that peaks at 6000 rpm then you are giving up some 1000 rpm of potential power. 7000 rpm is a reasonable rpm limit for any street engine given the correct valetrain componentry and attention to buildup tolerances. The 434 in my 4th gen revs to 7000 makes over 700 bhp, idles like a well tuned CC306 LT1 (350 cid) and is minimal maintanence... I check the valve lash every other oil change.

So, build the biggest engine you can afford and know what your goals are before you get started.

Take care