lets figure this out for the last time- Throttle body size vs performanec

please discuss

how can a bigger TB hurt?

i'm tired to al this speculation in LT1 tech:o
lets get an advances answer here:alert: :bow:

Yes too big of a TB can hurt a NA car. However I am pretty sure it cant hurt a boosted car.

CAN WE GET MORE OF AN EXPLANATION PLZ :p

the only logical thing i can think of in my head and visualize utizilizing my inutituion :o, is that bigger TB = less velocity

maybe deprive back ports of air in high rpm driving?

Way too big hurts driveability. Imagine a 102 mm LT1 TB bores which flow about 4 times as much air as a 48/52 mm bores. At highway speeds, it would only take a fraction of a degree of blade rotation to make a big airflow change. Your right foot or your cruise control would go nuckinfutz trying to hold a steady speed, and traffic driving would be challenging.

If an engine actually eats 800 cfm at max power, a TB which flows 1000 cfm or so @ 1 in. Hg. will probably produce max power. More TB won't increase power, but neither should it reduce it. It will be harder to get a good idle also.

To paraphrase the old saying, anything more than what's useful is wasted. ;) Well, maybe it looks good to the other guys!

This has been discussed ad nauseum in LT1 tech. Examples were given.... stuff was debated and good points were made. Might want to search but I recall you participating in those discussions.:think:

Velocity through the throttle body...... well it's always gonna be high at slight throttle. So what are we talking here.... WOT?

I agree with OS on the drivability issue. I don't think the throttle body is gonna make some magical hp gains if it's not needed but if the current system is a restriction then yeah..... rocket science says we're gonna see a gain with less restriction.

-Mindgame

Originally posted by OldSStroker
Way too big hurts driveability. Imagine a 102 mm LT1 TB bores which flow about 4 times as much air as a 48/52 mm bores. At highway speeds, it would only take a fraction of a degree of blade rotation to make a big airflow change. Your right foot or your cruise control would go nuckinfutz trying to hold a steady speed, and traffic driving would be challenging.

If an engine actually eats 800 cfm at max power, a TB which flows 1000 cfm or so @ 1 in. Hg. will probably produce max power. More TB won't increase power, but neither should it reduce it. It will be harder to get a good idle also.

To paraphrase the old saying, anything more than what's useful is wasted. ;) Well, maybe it looks good to the other guys!

how can i "figure out" how many cfm i need:confused:

Drivability issues aside, it's probably less of a sin to put too big a TB onto an FI motor than too big a carb onto a carbureted motor. TB is is just an "air door". A carb you also have to have sufficient velocity through the venturis to generate enough booster signal (vacuum) to pull the fuel out of them cleanly and evenly to get it well atomized, even if you whack the pedal to the carpet at low RPMs (or suffer a bog and other tuning headaches). TB/FI: not nearly so much of a problem from low velocity since the fuel is mechanically squirted in under pressure from the injectors downstream.

I'm no expert on the subject, but I thought I'd throw that in since the questions about too big a TB seems to spring from the old question about too big a carb. The two situtions aren't quite that directly comparable.

Trey,

Aren't you an engineering student?

CFM = rpm x displacement / 2 x 1728

or CFM = rpm x displacement / 3456

Then you calculate the velocity through the throttle body bore and determine at what velocity a restriction occurs. Covered in the "other" threads.

-Mindgame

Originally posted by Mindgame
Trey,

Aren't you an engineering student?

CFM = rpm x displacement / 2 x 1728

or CFM = rpm x displacement / 3456

Then you calculate the velocity through the throttle body bore and determine at what velocity a restriction occurs. Covered in the "other" threads.

-Mindgame

my intuition told me that... but i doubted it :(

for some reason i thought it would be max intake flow x4 or x8 or something

:irk:
Shibby

this is what almost got me failing phys-
i knew the answer, tried to do it in his BS way and got it wrong every time:mad:
edit:

where does 3456 come from?

HP and TQ gains have been proven many times over with the larger TB.

Large TBs make tip in brutal at times but I am working on a throttle cam to ease this problem. for those who can not wait TPIS has a new TB with new design.

I can count how many times I have had to stop and explain to people that you can not go to big on the TB with a port injected car. There is no need for High velocity over any of the sensers. There is no ventury velocity needed like in a carb to get the right mixture.

As long as you have correctly tuned your car you will benifit from the TB. Your TB is more of a restriction then your MAF and everyone on earth seems to be hacking the hell out of those LOL

Chris Bennit(sp), Jordon Musser and my self have all show VERY measurable gains with larger TBs.

Originally posted by OneFlyn95z28

1. Large TBs make tip in brutal at times
2. but I am working on a throttle cam to ease this problem.
3. for those who can not wait TPIS has a new TB with new design.


Ellis can you further on these points?

If bigger is better (I’m not saying it’s not, just why and how much?)…….. Then exactly what are the hp gains at what level engine, what level TB? Does anyone have objective dyno data or corrected 1/4th mile documentation?

The world is black and white. The only reasons you see shades of gray, is because someone hasn’t figured out how to measure it yet.

FYI…. Documented gains/subjective losses I’ve seen:

On a bolt on LT4 making 331 rwhp, there were no gains in a 58mm TB over 48mm TB even after computer/dyno tuning.

In a 398ci solid roller engine, I personally saw no gains from a monoblade over a 58mm TB. But….. I’ll also admit there were other problems that interfered with the engine making power.

Downside to a monoblade…….. I experienced very quick initial throttle opening making low speed maneuvers a bit tricky over a 58mm TB..

Believe me, wish I could say I did see gains. How about some objective data from those whom did!

Originally posted by treyZ28


where does 3456 come from?


Not to flame, but I see why you might be having some trouble in physics. 'Game's equation was the theoretical cfm needed to feed an engine @ 100% volumetric efficiency with the units corrected.

rev/min X inches ^3 x 1 intake stroke/2 revs x 1 ft. ^3/1728 in.^3 = ft^3/min (CFM)

revs cancel, inches^3 cancel, and 1728 is 12^3. The 3456 was the (2 x 1728) below the line. What's left is CFM. I hope they are teaching that kind of stuff in physics nowdays. If you can't do the "units" correctly you won't get the correct result.

So, as an example, a 383 peaking power at 6200 at 100% VE would consume 6200 x 383 / 2 / 1728 = 687 CFM. That doesn't sound like much, but CFM is normally rated (for 4-bbl carbs anyway) @ 1.5 in. Hg. pressure drop and that engine is probably running a 1.0 to 1.2 in. Hg. Using the 1.0 in. Hg., you'd need a carb or TB rated at least 22% more (square root of the pressure ratios, if you are curious) or about 840 CFM @ 1.5 in. Hg. to flow 647 CFM @ 1.0 in. Hg.

As others said, going somewhat bigger on a TB ain't bad like it can be with a carb.

My car went quicker with a 52mm throttle body, and my junk was stock heads/cam/bottom end. Didnt care what a dyno said, my car was faster...2 tenths and 2 mph. Also picked up the same amount on 3 of my friends cars too. If I had a bolt on car to do again, I would really want to see if the 58 was any better or worse, since I've yet to see that anyone has proof other than in an equation.

Originally posted by OldSStroker
Not to flame, but I see why you might be having some trouble in physics. 'Game's equation was the theoretical cfm needed to feed an engine @ 100% volumetric efficiency with the units corrected.

rev/min X inches ^3 x 1 intake stroke/2 revs x 1 ft. ^3/1728 in.^3 = ft^3/min (CFM)

revs cancel, inches^3 cancel, and 1728 is 12^3. The 3456 was the (2 x 1728) below the line. What's left is CFM. I hope they are teaching that kind of stuff in physics nowdays. If you can't do the "units" correctly you won't get the correct result.

So, as an example, a 383 peaking power at 6200 at 100% VE would consume 6200 x 383 / 2 / 1728 = 687 CFM. That doesn't sound like much, but CFM is normally rated (for 4-bbl carbs anyway) @ 1.5 in. Hg. pressure drop and that engine is probably running a 1.0 to 1.2 in. Hg. Using the 1.0 in. Hg., you'd need a carb or TB rated at least 22% more (square root of the pressure ratios, if you are curious) or about 840 CFM @ 1.5 in. Hg. to flow 647 CFM @ 1.0 in. Hg.

As others said, going somewhat bigger on a TB ain't bad like it can be with a carb.

come on now "ace" :p
I only have 28 credits, i dont think technically a sophmore yet :o

Originally posted by treyZ28

I only have 28 credits, i dont think technically a sophmore yet :o

Perhaps you should change your siggy picture. ;)

AE was my Physics I teacher. I've always wanted his hairdo...I finally got the color right, but not the style.

Originally posted by OldSStroker
Perhaps you should change your siggy picture. ;)

AE was my Physics I teacher. I've always wanted his hairdo...I finally got the color right, but not the style.

:o

if you hung out in the lounge more often, you'd understand the underlying humor :lol:

and in school i got the hair doo, thankfully not the color yet. Although i'm losing the hair rapidly :(

8am classes = no shower, no combing hair, no getting dressed up

8 am classes = cap, sweater, shorts, sandals- maybe underwear depending on what happened last night:bow:

Originally posted by OldSStroker
AE was my Physics I teacher.

Damn now thats pretty cool :)

Originally posted by kmook
Damn now thats pretty cool :)

I'm old, but not that old. ;) AE was an associate professor of physics at the University of Zurich....in 1909! He died in '55 when I was just realizing girls were more than round boys (6th grade as I fondly remember).

Originally posted by OldSStroker
I'm old, but not that old. ;) AE was an associate professor of physics at the University of Zurich....in 1909! He died in '55 when I was just realizing girls were more than round boys (6th grade as I fondly remember).

girls still had cooties till i was in 7th grade :o

I was a slow one :( Ohh well, High school was a blast when you could blow $20k on your car in your senior year and not worry about girls:bow:

college = :irk:
too many :eek: looking girls:cool:

I hear ya trey, i find myself wearing shades (even when its raining) between classes so I cant see how hot the women are......

Damn 18 year old hormones....;)

On to the topic though, the four barrell air door's may be a larger restriction to the airflow, but I think they are much easier to control and smoother when driving around town than a 100mm single blade TB.
My friend's 70 Challenger has a fuel injected (and blown) 383 big block in it and he was using a single blade TB, but he switched over to a 4 barrell from Force Fuel Injection when his broke.
I rember driving his car with the monoblade, you had to have the softest foot or the rearview mirror would be full of smoke. Now the thing drives like a dream. Also 4 barrells could have progressive linkage hooked up kinda like secondaries on carbs to further smooth out throttle feel.

Just my 13 cents

Hunter

For those guys saying that a larger TB shouldnt reduce HP on a stock car.... I agree but this is one time that theory doesnt quite explain reaility. I attended a Tech school Where we had 5 LT-1 F-bodys to toy with and dyno. Each student had a list of mods to try BBK 58mm TB BBK 52 TB and Holley 58mm TB were all tried and dynoed. ON all 5 cars. 2 bolt on cars / 1 supercharged / 1 cammed with ported heads / one stock. All saw losses from all 3 throttle bodies. The instructor of this course (who is one of a few LT-5 Certified GM techs said that he has run them at least 500 times and never seen a gain on a car that was still a 350. Apparently the N/A stroker guys are the only ones that benefit from it. IT should be noted that all except the N/A cammed were mounted on a stock (non-portmatched)intake. That may have been the reason for some of the losses. There was very little if any loss on that car. I run a 58 milBBK on a portmatched LT-4 intake, If I ever get a chance i can throw the stock one back on for a dyno run, but because my car is a N/A stroker im shure the extra air is needed.

Originally posted by treyZ28
I only have 28 credits, i dont think technically a sophmore yet

Wait until you have 60 credits and see how much of your sanity is still intact. Mine has all but left, and hangin' on by a thread.

Or better yet, wait until you hit Statics and Dynamics, those two classes are like Physics on steroids/crack/speed, etc. Then Thermodynamics and the Fluid Mechanics classes are right after that.

Just bend over and take it like a man :irk: :D

Originally posted by Fast Caddie
Wait until you have 60 credits and see how much of your sanity is still intact. Mine has all but left, and hangin' on by a thread.

Or better yet, wait until you hit Statics and Dynamics, those two classes are like Physics on steroids/crack/speed, etc. Then Thermodynamics and the Fluid Mechanics classes are right after that.

Just bend over and take it like a man :irk: :D
I usually do really well in hard classes and fail easy crap :confused:
I almost failed art in highshool:(


I'm looking foward to fluids though :D

and just for the record, i lost my sanity and dignity a long time ago :o

Originally posted by treyZ28
I'm looking foward to fluids though :D



Tell us how you liked fluids and thermo after you take them. :)

Ya' gotta love statics and dynamics. It's how things work. Isn't that why people become eingineers...to learn how the world works?

Best cam designer I know is a Particle Physicist by training. He's top designer at a very well known CCam company, and one fine teacher.

See Avatar for my Throttle Body. Probably double what the engine needs (~1000cfm), but then again, anything less then WOT is unimportant on that car. ;) I didn't even bother with an IAC. :)

Funny thing about it..... even a carbed engine will make more hp with a larger than "theoretically acceptable" carburetor. Especially a slightly warmed over small block chevy. So what's the point?
Well, if you can shear fuel and atomize it properly (booster signal and metering) the drivability will be there along with less restriction at high rpm and WOT. All equals more hp.
Just look at the carb recommendations a shop like Pro Systems makes. A well tuned/developed carb can be (should be) larger than "theoretical" for max power.

So, now that we take the fuel atomization and metering aspects out of the equation...... who's to say it aint the same for a throttle body?
And I've seen numerous gains on mild (stock stroke) LT1's with a change to 52-58mm tbs. Usually something like 6-10 rwhp.

-Mindgame

Dyno tested? IF sowas the intake matched to the throttle bores?

Carbs aside and EFI the point its not a matter of bigger is better nor vice versa..The problems with a larger TB effectively tuned out..The transition stumbles can be bad but from a 52 to a 58 isnt much..Ive worked on more stangs with bogs and stumbles because of the large 65+mm TBs they seem to like.Off idle stumbles and severe hesitations are other problems ive worked with..HP gains not much because think about it..The most popular carb out there is the holley 750.You can support 700 hp with one..The throttle respose will be killer when compared to a big ole HP950 carb.The 950 carb will make a few more ponies..If im correct a car rag did a carb shootout and found the same out recently..Think about and remember that im talking about tuned here and not out of the box...A 650 DBL pumper will loose a few hp on a dyno when compared to a 950 on the average hot small block. Then take out the fuel part of it..Then you just have air..On top of that you are working with a rather large plenum just behind the TB blades..So to me its really hard to compare with a carb when the whole intake tract is different.

The only gains ive seen from going to larger TB is driveablity quirks..Seems to be when the point has come to upgrade the TB is in the 650HP range..From my experence thast when the 58mm TB helps out on a sub 400cid smallblock. N/A of course..On anything but a race car i would stay smaller.6-10 HP on a stock LT1 with bolt ons is pretty common but the tq from what ive seen is more like 2-5 ft lbs. if any..

I always thought the reason a larger TB hurts carb cars because you don't emulsify the fuel well when you loose velocity at the TB, the more vacume there was at the TB the better the fuel was immulsified therefore having a better burn thus making HP, noone told me this I just kinda assumed when I learned about carbs & how they worked. With fuel injected cars it wouldn't matter since the immulsification happens at the injector, & when you put a bigger TB on a fuel injected car it always & I mean always in my understanding should make more power. Think about it, port velocity happens at the heads, so the bigger the TB the less you disrupt the port velocity at the head, think about it, you syphon a gas tank, now the velocity of the water keeps it comming & comming, now restrict the tube & then let it go, you can acctually stop the flow of fuel :)! I always imagine the engine in my head, I never use formulas unless you need them like calculate HP etc...

Also, one way to tell your TB isn't big enough is when you see your MAP increase at WOT when you switch TB's, I would get 92-98 for MAP at WOT, with a 58mm I keep my MAP pretty constant at 99-101, the 92-99 fluctuation tells me too things, the end result map is low & the fluctuation represents the flow / port velocity is being disrupted at the heads.

If you don't understand I can explain my explenation a bit further.

By definition, a throttle bod is a restricter. By this i mean an engine withOUT one with want to accelorate untill i guess it blows up.

So you put one on and you control the engines speed. It really has nothing at all to do with hp theoretically. BUT when the throttle body does not flow enough to sustain the engines air needs, then a bigger throttle body is needed.

More hypothetical talk. if you car needs 1000cfm and you have a choice of 3 throttle bodys:
20mm 500 CFM
50mm 1000CFM
Garage door 10000000 CFM

Of course the 20mm will still restrict HP AND the other two will make THE SAME MAX horse power(WOT[duh])

But with thing like throttle respons, cruise control and space, the 50mm is best.


Now for the lt1, i think its just based on both personel preference an engine CFM needs.
I currenly use a 58mm body on my bolt on LT1. I do this for personel preference. The amount of time it takes to go from 1000 rpm to 6000 rpm is so much faster then the 48mm that its great for me for downshifting witch i like to do.

Now my new engine with IMO need the more CFM becuz with a huge cam, ported heads and 500 hp it will raise the CFMs my engine needs.




TO sum it up, Neglecting your PCM, there is no way a bigger TB would HURT HP just possible driveability

Dyno test - 48mm vs. 58mm TB on a fairly stock LT1 (http://www.ws6zxr.com/showthread.php?s=&threadid=20095)

Originally posted by Injuneer
Dyno test - 48mm vs. 58mm TB on a fairly stock LT1 (http://www.ws6zxr.com/showthread.php?s=&threadid=20095)

Its about time someone had some actual numbers.:bow:

Originally posted by Injuneer
Dyno test - 48mm vs. 58mm TB on a fairly stock LT1 (http://www.ws6zxr.com/showthread.php?s=&threadid=20095)

Though you cant really accept that as proof as he states that he did the dyno runs almost 5 months apart, so conditions could defintaly change.

SAE corrected?

Originally posted by Injuneer
SAE corrected?

Ah ok.... helps if i didnt skim the thread. I saw his reply saying they were.

Originally posted by KTamez
See Avatar for my Throttle Body.

That's a damn fine looking TB there, Mr. Tamez! :) I still want to try a 4bbl TB on my car with a "conventional" intake, but the time required to make this happen just hasn't appeared yet.

Something to keep in mind when considering theoretical maximum TB flow - the engine does not consume air in a steady, consistant fashion. Those same pulses that seem to get everyone all riled up when discussing manifold design also affect the TB, and with the small plenum volume of the LT1 manifold I feel that this is somewhat significant. So, while you may have an engine that only consumes an average of 650 CFM, it may have instantanous demands that exceed this number. Of course, there's a ton of variables that will determine the relationship between instantanous and average airflow demands, such as, oh, just about anything that sits behind the TB and regulates airflow in the engine (intake, heads, cam, exhaust).

There's also the velocity element that someone mentioned early on. A gentleman in the Impala world did some flowbench testing and found that the TB size does indeed have an effect on intake port velocity, but I don't know the specifics of his data nor have I pursued this sort of testing on my own. When someone drops off a Superflow 600 in my barn, I'll be happy to work on this ;)

So, to summarize, I think that TB selection is more than just a consideration of the theoretical average pressure drop across the bore diameter, and I think that TB selection needs to be done when considering a lot more than expected RWHP numbers, displacement, FI vs. NA, etc. Now, since we don't seem to have the info required to calculated optimum TB size, it would seem that duplicating known combos or testing various TBs on your particular combo would be the way to go.

Back to back track results coming in about 2 weeks :cool:

-Shannon

good idea Shannon. Which TBs are you going to dyno and on what car? What mods have been done to it??

Originally posted by NOMAD
Back to back track results coming in about 2 weeks :cool:

-Shannon
i'll test one for ya ;)

I had a 52mm throttle body and had the engine on a dyno engine.
I then put a monoblade on the engine. The engine made a bit more hp (like 5hp) but the interesting thing was that the back cylinders EGT's were greatly improved, even at idle which was surprising.

you can see my motor buy looking at my sig.

Rob

Originally posted by 96Z28SS
......EGT's were greatly improved, even at idle which was surprising

Rob

At idle, wasn't most of the air coming from the IAC system, or was that eliminated, or somehow altered by the design of the monoblade?

I know the IAC is different on the monoblade, it maybe that they somehow modified it, i know we were surprised when we saw the EGT's on the dyno.
I don't have any data from the egt's cause they don't normally record that data but i know it was significantly better at wide open throttle. I want to say 60 degrees better.

My 396 is pretty basic, GTP stage 2's with a cc306 cam.
11:1 compression. I think it made pretty good power.

Originally posted by AdioSS
good idea Shannon. Which TBs are you going to dyno and on what car? What mods have been done to it??

Running one of my 52mm ones against a stock 48mm one. Car has long tubes, heavy cam, port/polish, elec water pump... On down the line. This car is very quick, so i'm hoping these gains seen on this will be detrimental to how we look at this whole subject :)

-Shannon

your site shows you're running the LT4 hotcam. Is that current?

Is there any chance that anybody around you might let you borrow a 58mm to compare?:confused:

Originally posted by AdioSS
your site shows you're running the LT4 hotcam. Is that current?

Is there any chance that anybody around you might let you borrow a 58mm to compare?:confused:

Lol, I didnt' realize how uncurrent that is. I have a CC305now with some more headwork. I'm thinking everything else is current.. Maybe time to update the page :p

I don't even know anyone with a 58mm on their car, so until I get it figures on on how to make one from a stocker, it prolly won't happen.

-Shannon

Originally posted by LT1 1980 malibu
The most popular carb out there is the holley 750.You can support 700 hp with one..The throttle respose will be killer when compared to a big ole HP950 carb.The 950 carb will make a few more ponies..If im correct a car rag did a carb shootout and found the same out recently..Think about and remember that im talking about tuned here and not out of the box...A 650 DBL pumper will loose a few hp on a dyno when compared to a 950 on the average hot small block. Then take out the fuel part of it..Then you just have air..On top of that you are working with a rather large plenum just behind the TB blades..So to me its really hard to compare with a carb when the whole intake tract is different.

Is that right?

Ok, compare two wet-type manifolds on a 350 that makes 500 crank hp. You can easily run a 1300 cfm 4bbl type throttle body on that engine with excellent drivability. Air is not the problem... and air aint the problem with the larger carb either. A 750 on a hot 350 is a loser.... I'd run no less than 850 cfm, then I'd use a booster and tune the metering circuit to get the signal and drivability. Worth power in every hot 350 I've ever seen. Then again, if you're building something for a 4000 lb 3 speed auto car, there would be better choices.
So I have to disagree there.

-Mindgame

Originally posted by NOMAD
Running one of my 52mm ones against a stock 48mm one. Car has long tubes, heavy cam, port/polish, elec water pump... On down the line. This car is very quick, so i'm hoping these gains seen on this will be detrimental to how we look at this whole subject :)

-Shannon

Shannon-

Im still fighting vacuum issues over here with that cam. Im gonna tear down the motor again and make sure all the timing is correct. heads/intake are still stock, but you got the rest of the mods down pretty well. Hows my TB comming :cool:

Anyways, hes going to get me a set up TB, and i was going to switch them at the track. I will also do some logs to see where the 02s are before and after the TB. That should let us know if more air is comming in or not. Then i re-tune, and get the 02s back to where they were. So its basically a 3 step deal, before, after, after + tune. I figure about 2 weeks? Will let everyone know.

Mindgame, i stand on that ..I was refering to the wet and dry comparo..But let look at your point..Ive tried to smae as you stated,in the end on the dyno the smaller carb still had way killer throttle response when compared to the bigger unit.After tuning remember..Why would we say that we can tune the larger carb and not the smaller one..I can understand that you are speaking from experence though..On the engine that im recalling here the smaller carb still made the same power in the nids as the bigger one and lost less than 2hp up top..That was with a well know PA carb guy doing the work..Theres a thousand things that one can play and adjust on a carb to egt it to work but myself id rather make the better choice for the intended aplication 1st off and be closer to optimum to start with..In the comming weeks as with today Im gonna be playing with a 412 stroker and a small tiny dual plane (hood clearance issues)and several carbs at the track to see what works best..Ive made many a dyno run at a local engine shop to see what makes the est power.Now we all know on ther is a different story..It should be fun to see what happens..

Still to me one cant compare wet manifold to a dry inatek..The runners are differ completely as is the plenum area.

Originally posted by atljar
Shannon-

Im still fighting vacuum issues over here with that cam. Im gonna tear down the motor again and make sure all the timing is correct. heads/intake are still stock, but you got the rest of the mods down pretty well. Hows my TB comming :cool:

Anyways, hes going to get me a set up TB, and i was going to switch them at the track. I will also do some logs to see where the 02s are before and after the TB. That should let us know if more air is comming in or not. Then i re-tune, and get the 02s back to where they were. So its basically a 3 step deal, before, after, after + tune. I figure about 2 weeks? Will let everyone know.

It's together now. I've polished and everything. I've just been having a problem out of my legs. I dunno whats wrong, but I can barely walk at times.
I'm gonna pull the plates off an do some IAC passage work and we will see if it helps your idle:)

-Shannon

Sounds good. No rush, as i said i still have to tear down the motor and re-assemble.

Also, that sounds serious. Might want to head to the docs and make sure all is ok.

So what was the result of the comparison? :)

Bringin up the :death: !!

Here's are some variables to consider when changing from one TB size to another...

Assumptions:
1) A 350 ci engine will demand 175 Cubic inches (2,868 ml) of air per revolution (100% efficiency, zero compressibility, no restrictions) ...on any given revolution, 4 of the 8 cylinders are drawing air.

2) at 7000 RPM, the throttle body ports will flow 1,250,000 cubic inches of air per minute, or approx 8506 CFM (700,000 / 12 x 12)

3) If the throttle opening is a twin 48mm, then the maximum area available is 3617mm, wheras with a 52mm it is 4245, and with a 58mm it is 5281 mm during WOT (100% TPS)

4) Fact: you can draw 10,000,000 Cubic feet of air through a 10mm opening. It will either be very slow at a low pressure/vacuum, or if you want all of the air within 2 seconds, the velocity will be extremely fast. As the velocity increases, compressibility and fluid dynamics begin to exert restrictions. Real world dynamics says it's going to be a problem. Restrictions will mean that additional power must be exerted to overcome and air not received is air not converted into power. A larger throttle body will reduce the power necessary to overcome the restriction, allowing the cylinders to fill quicker, and air received is air available for power.

Now the downside.

If you install a larger throttle body, your PCM will assume that 50% throttle position should equate to a specific air flow, but the MAF will countermand that instruction with the correctly measured air flow (GPS) and the PCM will "correct" the assumption. This "correction" consumes time, and will probably induce fuel delivery oscillations. Otherwise the PCM could care less about the throttle position and simply read the MAF for all fuel/air delivery equations. Such is not the case.

Also, your intake port velocity will be reduced. Possibly resulting in a poorer air/fuel mixture inside the combustion chamber. This will probably not be a big issue during WOT, but during initial throttle opening (tip-in) your port velocity will drop and subsequent air/fuel mixing may be impaired, resulting in less power.

SOme of you old-timers may remember the reasoning behind a high-rise manifold, that being the weight of the air falling through the manifold increases intake port velocity...

Originally posted by Ultra_Dog
Here's are some variables to consider when changing from one TB size to another...

2) at 7000 RPM, the throttle body ports will flow 1,250,000 cubic inches of air per minute, or approx 8506 CFM (700,000 / 12 x 12) I don't follow. I don't know where you got the 1250000 ci per min stat, but I'll take it at face value. That means the engine needs 723 CFM (ci per min divided by (1 ft / 12in)^3)

If you install a larger throttle body, your PCM will assume that 50% throttle position should equate to a specific air flow, but the MAF will countermand that instruction with the correctly measured air flow (GPS) and the PCM will "correct" the assumption. This "correction" consumes time, and will probably induce fuel delivery oscillations. hmmm... I dunno about that. injector pulsewidths hit 5 to 10 ms... CPUs are A LOT faster than that... even the OBDI computers can do fuel delivery corrections without problems (OBDII PCM's are even faster). The other issue is that sensor tests like this are only run ever 100 rotations or so in the LT1 PCM. Unless there is a MAF failure in one of the tests it goes through, and a flag is triggering in the algorythim, the MAF data is taken at face value. While out-of-range voltage tests are tested frequently, I belive the test your refering to would only be used every 5 or 6 seconds, and if it did fail, it would be monitored for future compliance... at high rpms I'm not even sure this specific test is used (in the LT1 at least).

Otherwise the PCM could care less about the throttle position and simply read the MAF for all fuel/air delivery equations. Such is not the case. true, the TPS is nessesary for every car that has an 4L60E, or even for others that are running speed density due to a MAF failure.

Also, your intake port velocity will be reduced. Possibly resulting in a poorer air/fuel mixture inside the combustion chamber. This will probably not be a big issue during WOT, but during initial throttle opening (tip-in) your port velocity will drop and subsequent air/fuel mixing may be impaired, resulting in less power. TB air flow has little to do with port velocity or air flow in a specific runner.

SOme of you old-timers may remember the reasoning behind a high-rise manifold, that being the weight of the air falling through the manifold increases intake port velocity... your kidding right? People actually belived that?

Consider this:
A) What does Barometric pressure measure?
b) Will barometric pressure change if you put a 3 foot tall cylindrical wall around the sensor? of course not.

350/2 X 7000 = 1,225,000 cuin/min

1,225,000 / 12^3 = 708.9 cuft/min

When you start your arguement off with an sloppy calculation, it sort of loses credibility. :)

lol... guess I need a new calculator. :p

but you get my point I guess... no 350 needs 8500+ cfms (not unless it's putting down 4000+hp :))

Originally posted by Steve in Seattle
lol... guess I need a new calculator. :p

but you get my point I guess... no 350 needs 8500+ cfms (not unless it's putting down 4000+hp :))
My comment wasn't directed at you.... except to explain where he got 1,250,000.... which appeared to be a typo.... and it went down hill from there.... :)

My typing wasn't much better in my post.....

Ahhh... that makes sense now. Also explains why I got 723 instead of 709 ;) (I started with 1,250,000)

Dyno test - 48mm vs. 58mm TB on a fairly stock LT1 (http://www.ws6zxr.com/showthread.php?s=&threadid=20095)

I cant get this link to work. It goes to a 3 post thread? Thanks.

-Dustin-

That's a pretty old link!


I remember they had quite a few dyno comparisons on that site a while back.

Running one of my 52mm ones against a stock 48mm one. Car has long tubes, heavy cam, port/polish, elec water pump... On down the line. This car is very quick, so i'm hoping these gains seen on this will be detrimental to how we look at this whole subject :)

-Shannon

Well? Lets hear it.

-Dustin-