big cam + small heads

I've seen lots of posts in here about small cams and big heads or the like. That is obviously a good combo for a wide powerband.

However, there's the other side. Like the saying goes, speed costs money. One of the most expensive parts of building a strong engine is porting the heads. Some of us can't afford AFRs or professionally ported heads yet. That's why you see lots of people going "too big" on the cam. The difference in a 215* cam and a 235* cam is nothing.

You see LT1 folks putting 230*+ cams in stock headed 350s and getting pretty good numbers. You could put a 218* cam in the same engine, but put well flowing heads in and make the same power. Yet LS1 folks can put a 224*cam in with stock heads and kill both the engines above de to their superior heads.


My situation is sorta similar. I picked up a 383 with mild headwork (I was told 230cfm with 1.94/1.50 Manley valves) for CHEAP. I'm not sure of the cam in it, so I was going to pick one for myself. I will probably be pulling the heads and getting them milled for compression (the motor has reverse dome pistons) but I don't want to spend a grand for the porting. I'll need that for headers since Impala specific headers ain't cheap. In a few more months I may have some well ported heads, but don't want to wait that long.

So, I'm thinking of going with a relatively bigger cam that what most would recommend. Something along the lines of 236/248 with around .600" lift. It'll be lumpy for sure, but that's not a bad thing in my opinion. I'm only 23 now, so later I might want something milder.

My car has enough converter (Vigilante 3200+) and gear (4.10s) for higher RPM use, and I'm not worried one bit about losing low end. The current 350 has too much for street tires at WOT in first so with the added displacement and compression, I'll likely have more everywhere.

My goals for the new motor are to run at least 12.41 @ 111.7 with a 4100# race weight. That's 1 second quicker and 10mph faster than my car did a few weeks ago in great weather with just bolt-ons (but no headers!) Smokemup.com says I'll need almost 390hp to the wheels for that MPH. I think that's reachable when the temps hit 30s again next year. Anybody disagree?


:think: :irk:

Um, I think I've strayed from where I started with this thread...

While I'm at it, can you estimate how much power an engine can potentially make just from looking at how much air the heads flow? :confused:

oh yeah, now I remember what I was thinking when I started typing this.


Do you folks see any problems with running a relatively big cam with relatively small heads? Would it be hard to tune? Would drivability suffer? I'm just gonna guess that velocity will be increased, which means more torque?

Thoughts:

1. How do you get an Imp down to 4100 with a driver and a little gas? Mine is a tad heavier than that. ;)

2. IMO there's quite a bit of difference in 215 vs 230. You might think twice about choosing your own cam. If you are willing to spend the $, a very aggressive HR with all the correct valvetrain parts could give you a lot of what you want. It won't completely make up for better flowing heads, but it will help.

3. I seriously doubt you heads want .600+ lift. Maybe so, but probably not. If you are willling to take cam advice, ask a good engine builder.

4. 12.40 @ 111 ain't gonna happen on street tires in the Imp IMO. With stickies, you'll need lots of mid 3s torque to get that Killer Whale moving. I don't think your cam choice will do it.

5. Yeah, given head flow curve, and intake, exhaust system and other engine parameters, you can estimate torque and power curves.

6. Imp exhaust manifolds ain't all that bad. Some hand porting of the outlet, and good pipes behind the manifolds might allow more money for the heads and valvetrain. LPE uses stock manifolds up to about 450+ hp.

7. The big cam kills Dynamic Compression, driveability and low end torque, all things the Imp needs. In my (never humble) opinion, that's the wrong door to be opening. Tuning and port velocity won't solve the problem.

8. You asked.

Why the big cam choice?

The reason I say that is because most setups out there will peak at 6000rpm and die off afterwards, be the camshaft a 218 duration or 240 duration on the intake. The problem is that the 218 lobe makes more power below 6000rpm where it makes the car faster.

You are going to need better heads to get 390rwhp out of a LT1.

Bret

My Imp went 12.5's at 109.X with my 335/30-18 street tires...

Cheston I wish you good luck with this one, my 396 is finally ALIVE and all I can say is - my tires aren't wide enough.....

Can you say 60MPH spin the tires when kicking down into 2nd gear???

Never did that with my 175 shot.

:)

Mike

Originally posted by OldSStroker
Thoughts:

1. How do you get an Imp down to 4100 with a driver and a little gas? Mine is a tad heavier than that.
Last time I was at the track it weighed 4160# with my 320# butt in the driver's seat :) I had a freind drive it that weighs about 160 and it picked up 1.5mph.

Lemme think, 15x5 draglites with 26x7.5 mickey thompson sportsman fronts, 15x8 draglites with 26x10.5 et streets on the back, no swaybars, QA1 12-way adjustable aluminum shocks, took passenger seat out (I just picked up a pair of slightly lighter buckets for the front so I won't be doing that much anymore), took floormats out at track, empty trunk, 1/4 tank of gas or less, 9.5" 3200+ Vigilante converter (flashes to 3800rpm now) instead of stock 12", aluminum driveshaft, gutted cats, no tail pipes, airpump delete, and that's all I can think of right now. Later I'll have aluminum heads (50#!), a T56 and lighterweight tubular cross member and probably a few other weight reduction tricks ;)

2. IMO there's quite a bit of difference in 215 vs 230. You might think twice about choosing your own cam. If you are willing to spend the $, a very aggressive HR with all the correct valvetrain parts could give you a lot of what you want. It won't completely make up for better flowing heads, but it will help.

3. I seriously doubt you heads want .600+ lift. Maybe so, but probably not. If you are willling to take cam advice, ask a good engine builder.

I was looking at Comp XE lobes 3196 & 3318 with 1.6s on the exhaust on a 115 LSA. I've got an AFR rev kit, Comp R liftters, and won't cheap out on the springs. I want peak power around 6500 and good vacuume with decent gas mileage.

The heads might not flow so great at that much lift, but they are still flowing air. This just means the peak airflow will be reached more. Or maybe that's just how I think of things. I might try 1.5s on the exhaust to get "only" .563" exhaust lift.

4. 12.40 @ 111 ain't gonna happen on street tires in the Imp IMO. With stickies, you'll need lots of mid 3s torque to get that Killer Whale moving. I don't think your cam choice will do it.
Like I said, with virtually no engine mods other than MTXPERT's awesome RAISS intake and a good catback exhaust (but no headers!) I got 13.41@101.7 with a 1.949 60ft time (it was his first time to drive it so he didn't know how to launch it best.) I don't run street tires at the track when I'm serious about it. I'll run street tires just for fun sometimes though. I did run a few Marauders with street tires on to try to even it out just a little. ;) I still beat them bad! My best 60ft with the ET Streets was 1.798 with a little tirespin :) I've got a little more suspension work to do.

I dyno'd months ago when it had a vacuume leak and before the 4.10s and alum driveshaft. Temp wasn't in my favor. 255rwhp/320rwtq. After fixing the leak and changing the driveshaft, it defintiely felt stronger.

5. Yeah, given head flow curve, and intake, exhaust system and other engine parameters, you can estimate torque and power curves.

I think I was asking for a way to figure out the max potential horsepower just from looking at how much air the heads can flow.

6. Imp exhaust manifolds ain't all that bad. Some hand porting of the outlet, and good pipes behind the manifolds might allow more money for the heads and valvetrain. LPE uses stock manifolds up to about 450+ hp.

Other stock engine impalas pick up 3-5mph when they put better headers on. ;)

7. The big cam kills Dynamic Compression, driveability and low end torque, all things the Imp needs. In my (never humble) opinion, that's the wrong door to be opening. Tuning and port velocity won't solve the problem.

Dynamic Compression: According to http://www.rbracing-rsr.com/comprAdvHD.htm with 11.5:1CR and with the different cam specs I've temporarily chosen, my DCR will be between 8.11-8.50. I read on this forum that 9:1 DCR should be the max for pump gas. I think a half point should be enough to keep me safe if I can't get good gas somewhere. :)

Driveability: 115LSA, loose torque converter or future stick shift, steep gears, young driver (23) :)

Low End Torque: I'm not at all worried about low end. My car is under 2k RPM almost never (only with the converter locked when cruising under 60mph and around idle) :) I've got more than enough low end power with the converter and 4.10s with the stock 350. Add almost 10% more displacement and increase the compression ratio up to around 11.5 or so and that just makes thing worse on the street.

8. You asked.
I'm a glutton for punishment :) :D

thankSS for your help!

Originally posted by SStrokerAce
Why the big cam choice?

The reason I say that is because most setups out there will peak at 6000rpm and die off afterwards, be the camshaft a 218 duration or 240 duration on the intake. The problem is that the 218 lobe makes more power below 6000rpm where it makes the car faster.

You are going to need better heads to get 390rwhp out of a LT1.

Bret
Bret, I want to give up low end. :D Hooking on the street is one thing I want to do. I don't want to have a ricer pull up beside me and leave me at a light spinning my wheels. I also want to be able to hang with Corvettes on the highway from a high roll :D

I was able to drive just fine with the WEAK TBI 305 in my Caprice with 2.56 gears. We don't need all the low end that people always talk about.



I just thought of something, what are the racing classes that require stock lift cam and stock heads? How do they make the power they do? Lots of duration?

Originally posted by mtxpert
My Imp went 12.5's at 109.X with my 335/30-18 street tires...

Cheston I wish you good luck with this one, my 396 is finally ALIVE and all I can say is - my tires aren't wide enough.....

Can you say 60MPH spin the tires when kicking down into 2nd gear???

Never did that with my 175 shot.

:)

Mike
Glad to hear it Mike! I wish I could've been more help. I finally found those 1.6 rockers. :shame: The box was inside another box here in my room :o

I haven't seen your entry to the impala SS Dynamic ET page yet ;)

http://dan.esteban.com/impalass/ReturnTopET.asp

What kind of 60ft times were you getting? Which track was it at? Have you weighed the car?

If you would've been at Hallsville when I was running 13.4s you probably would've gone 11s with slicks! :D

Originally posted by AdioSS

I think I was asking for a way to figure out the max potential horsepower just from looking at how much air the heads can flow.





Courtesy of David Vizard and Superflow:

Assume everything like exhaust is optimum, which is a challenge:

You need, for a 10:1 350 cube SBC:

1) head flow at full intake lift value at 25 in H2O. If you have 28 in. H2O numbers, multiply 28 in numbers by .89286.

Multiply that number by 2.05 for hydraulic roller, or 2.1 for a solid roller.

If you have a 400, multiply again by 1.1 or .95 for a 327 or .9 for a 302.

For 11:1 multiply by 1.07

Example 1: 230 cfm (at 28 in H2O) x .89286 x 2.1 x 1.07= 461 hp at the flywheel.

Example 2: 290 cfm x .89286 x 2.05 x 1.05 (my guess for a 383) = 557 hp at the flywheel.

Remember, this is with everything spot on.

Originally posted by AdioSS
I just thought of something, what are the racing classes that require stock lift cam and stock heads? How do they make the power they do? Lots of duration?

Usually duration and overlap. That and a very agressive lobe to get the most area under that set lift limit.

That plus making everything in the motor the exact spec it's supposed to be and tweaking everything.

Bret

Originally posted by AdioSS
...I don't want to spend a grand for the porting. I'll need that for headers since Impala specific headers ain't cheap.

Impalasuperstore.com is selling the last of the SLP headers for b-bodies for $469.95.

-Chris

Originally posted by OldSStroker
Courtesy of David Vizard and Superflow:

Assume everything like exhaust is optimum, which is a challenge:

Remember, this is with everything spot on.
With the mild heads that are on my engine now and using these calculations, my engine has the potential for over 500crank horsepower.

In order to run the MPH that I want, I'll need about 375 to the wheels. Since my 4L60E decided to make a big bang on a 4-2 downshift today and I just happen to have a spare T56 bolted up to the 383 right now, I think this is doable when the weather gets better :D

Originally posted by SStrokerAce
Usually duration and overlap. That and a very agressive lobe to get the most area under that set lift limit.

That plus making everything in the motor the exact spec it's supposed to be and tweaking everything.

Bret
I'm using plenty of duration (for a hyd roller) but probably gonna give up some power on the overlap. These Comp XE lobes are pretty dang agressive, but I don't have a lift limit :)

Originally posted by Chrisbequick
Impalasuperstore.com is selling the last of the SLP headers for b-bodies for $469.95.

-Chris
And those are shorties. Like I said, headers for the B-bodies ain't cheap (compared to F-bodies) :rolleyes:

I'm leaning toward the JetHot coated Flowtech Afterburners for under $400 new. They are long tubes with 1 5/8" primaries.

I would prefer the 1 3/4" primary long tubes from ClearImageAutomotive.com but at that price... It's a tough decision.

This is a SBC but the headflow numbers probably aren't too
different.

I run a 240/246 cam on vortec heads that have had a little
work done to them and 2.02 valves. They are protopline 170cc
heads. The cam is .507/.510 or so. The car really needs some
heads, IMO. After feeling the topend pull of my LS1 and comparing
it to this car. It really suffers on drivability at low rpms (which with the
t-56 you will notice) but it feels like it just runs outta breath
past 6k. Don't get me wrong.. it still pulls hard, but it feels like it
reaches a climax at 6k, and just sorta holds steady til 6500-6800.

Now.. my LS1, although the flow numbers aren't ridicously better,
I run a 224/224 cam with it, and the heads are stock LS1 heads.
The car pulls hard all the way to the 6600rpm shift point, and
actually stays pretty even in 2nd gear, but 3rd and 4th the LS1
will just run away from the 84 1-2 cars to 110-120. So you are right
about the 23x still being pulled by a 224 LS1. However, making
it even worse.. even a 24x is still being pulled.. Heads are key.

The 1984 model Z28 has a t-56 6 speed and twin disk mcleod clutch.
The car surges up to 2000-2100rpm on average. However, if you
keep your foot out of it and if your on level ground on the highway
you can sometimes cruise comfortably at ~1900. It idles decent at
1000-1100rpm. Its sometimes a PITA to start, and has made 6th
gear more or less useless except at 80mph+. The car does not pull
very well at all in any gear below 3000 rpm. Lowend is really weak.
I have rev to 2500-3000 and slowly disengage clutch on takeoff in
order to keep from surging, bucking, stalling, etc.
Luckily the twin disk doesn't have alot of chatter or it'd be REALLY
annoying. Hopefully when I get some heads I'll gain enough
throughout the powerband to at least correct for this a little. That
and I have 4.56's on the way as we speak.

If you plan to do heads in the future, go ahead and go for it.. Being
that I'm 21, the drivability doesn't bother me that much. I don't think
it'll bother you either once you drive it a few days.

Good Luck,

so, it's an 84 Z28 with a T56 behind a SBC. How big is the motor? What's the compression ratio? hydraulic or solid, roller or flat lifters? What's the lobe seperation? Advanced or retarded valve timing? One more thing, what rear gear ratio and what diameter tires are you running?

I've got 4.10s in the SS now, but the tire size cam easily be changed. At the moment I've got 255/50WR17s (27") on (stock size), but have considered going up to a 275/50WR17(28") or possibly down to a 275/40ZR17(25.7"). I can fit up to a 28.5" tire in the back right now, but I might be doing a little custom work to allow a 29-30" tire to fit. I've had tires as short as 255/40ZR17s (25"), but they looked a little funny :D

Originally posted by AdioSS
I was looking at Comp XE lobes 3196 & 3318 with 1.6s on the exhaust on a 115 LSA. I've got an AFR rev kit, Comp R liftters, and won't cheap out on the springs. I want peak power around 6500 and good vacuume with decent gas mileage.

The heads might not flow so great at that much lift, but they are still flowing air. This just means the peak airflow will be reached more. Or maybe that's just how I think of things. I might try 1.5s on the exhaust to get "only" .563" exhaust lift.
OK, I've got a chance to get a used cam that's almost exactly what I want. There are only 3 differences.

I would've chosen the 3196 lobe for the intake and this one has the milder 3316.
lobe -- adv - .050 - .20 -- lift - - 1.5 - - 1.6
3316 - 288 - 236 - 157 - .347 - .521 - .555
3196 - 288 - 236 - 162 - .390 - .585 - .624

I would've chosen to get it on a 115LSA and this one is on a 114 (not too big of a difference)

I would've chosen to get it ground with Zero advance and this one has 4* advance ground in.

I just don't know... The price is VERY appealing, but hmm... I don't know... My cam would have top end that meas I'd have a better chance of getting the trap speed I want. :confused: This one would be better for around town driving.

AdioSS

Big diff in lobe area between those two cams. Might want to take that into consideration.

That and I'm not a big fan of that wide of a LSA, either the 114 or 115.

Just my .02

Bret

so, it's an 84 Z28 with a T56 behind a SBC. How big is the motor?

It is a 357.

What's the compression ratio?

~10:1.. iron heads

hydraulic or solid, roller or flat lifters?

hydraulic cam, flat lifters

What's the lobe seperation?

I believe that would be a 110Lsa.. Partly responsible for some of
the drivability issues.

Advanced or retarded valve timing?

Advanced, as to how much I can't remember exactly. The car doesn't
detonate as I believe the cam bleeds off alot of compression.

One more thing, what rear gear ratio and what diameter tires are you running?

245/50/16 right now and 3.42's.. Have had 3.73's.. Not a huge difference
between the 2.. New rear has 4.56's, but haven't had it installed yet.
Not my choice to run 4.56's, because thats what the used rear had in
it I bought.. I will probably try runnin them with a 275/40/17 BFG Drag at
the track until I get some slicks for this car.

As you can see gearing will probably help my probs a bit.. I also just took the
284h cam out in favor of a 274h..Its only a 2-3 hour job to do cam and
lifters.. I figured why not :) The 284 was just too much for now until I get some
better heads.

Peace,

Originally posted by dist0rtion_69
I run a 240/246 cam on vortec heads that have had a little
work done to them and 2.02 valves. They are protopline 170cc
heads. The cam is .507/.510 or so. The car really needs some
heads, IMO. After feeling the topend pull of my LS1 and comparing
it to this car. It really suffers on drivability at low rpms (which with the
t-56 you will notice) but it feels like it just runs outta breath
past 6k. Don't get me wrong.. it still pulls hard, but it feels like it
reaches a climax at 6k, and just sorta holds steady til 6500-6800. Originally posted by dist0rtion_69
It is a 357.

~10:1.. iron heads

hydraulic cam, flat lifters

I believe that would be a 110Lsa.. Partly responsible for some of
the drivability issues.

Advanced, as to how much I can't remember exactly. The car doesn't detonate as I believe the cam bleeds off alot of compression.

245/50/16 right now and 3.42's.. Have had 3.73's.. Not a huge difference between the 2.. New rear has 4.56's, but haven't had it installed yet.
Not my choice to run 4.56's, because thats what the used rear had in it I bought.. I will probably try runnin them with a 275/40/17 BFG Drag at the track until I get some slicks for this car.

As you can see gearing will probably help my probs a bit.. I also just took the 284h cam out in favor of a 274h..Its only a 2-3 hour job to do cam and lifters.. I figured why not :) The 284 was just too much for now until I get some better heads.
OK, now we're comparing apples to oranges :)
My case vs yours
383 --- 357 CID
11.5 -- 10.1 CR
alum - iron heads
roller - flat tappet
EFI ---- carb?

I'm interested in seeing how the 4.56s work behind your motor.

That we are.. but it still relates to the topic.

Peace,

I won't run my mouth alot b/c it's been a while since I've posted but I'll say this, "The faster ya go the more it takes". Low end is your friend, if you don't want to spin buy some tires but @ 4100#s you need all the bottom end you can get. Too much camshaft is only going to make drivability suffer, and put your power where you can't use it. I recently discussed this issue with a gentleman concerning the cc306. Very popular, but he said you'll hate it below 4000 R's. Basically it'll make you not like it very much when you drive it.

later,
Vicious

Originally posted by Vicious95Z28
I won't run my mouth alot b/c it's been a while since I've posted but I'll say this, "The faster ya go the more it takes". Low end is your friend, if you don't want to spin buy some tires but @ 4100#s you need all the bottom end you can get. Too much camshaft is only going to make drivability suffer, and put your power where you can't use it. I recently discussed this issue with a gentleman concerning the cc306. Very popular, but he said you'll hate it below 4000 R's. Basically it'll make you not like it very much when you drive it.

later,
Vicious Just got a buddies car done a few weeks ago. It's a 94 with 11.96:1, balanced 357 with home ported heads, normal bolt-ons and a 306. The idle is choppy, but not obnoxious, and the car pulls like hell from around 2800 to about 6800. With the ceramic coatings, it doesn't detonate at all on 91 octane. This particular car needs tuning and is running pig rich, but the cam isn't really offensive to me. If you like the quiet refined ride of a Lexus over the rumble of a hotrod, you'll not like it.

Originally posted by Vicious95Z28
I won't run my mouth alot b/c it's been a while since I've posted but I'll say this, "The faster ya go the more it takes". Low end is your friend, if you don't want to spin buy some tires but @ 4100#s you need all the bottom end you can get. Too much camshaft is only going to make drivability suffer, and put your power where you can't use it. I recently discussed this issue with a gentleman concerning the cc306. Very popular, but he said you'll hate it below 4000 R's. Basically it'll make you not like it very much when you drive it.

later,
Vicious
I might be totally wrong, but I think the weight of the vehicle shouldn't have near as much impact on building the engine that everybody seems to think. yes, I know my car is pretty darn heavy. However, with the extra 33cubic inches and a good bit more compression, I should have more power everywhere in the RPM range than my stock engine no matter what size cam I go (to an extent!) :D

Others have gone with cams of similar size in smaller engines and loved them! Yes, my car is heavy and needs torque to go, but why not move the torque band to the right where I can also pick up horsepower?

Assuming the only changes to an engine are the duration specs (same LSA, same lift, same everything else in the engine) it should be able to put out X peak torque, right? What's wrong in moving that torque peak up and gaining horsepower at the same time?

If you are right about this being too much cam, then I'll put 4.56 gears in the big boat :cool: