Chevy86 IROC-Z

iTrader: (17)

I found this article on an other messageboard which focuses on the flow rate of a 48mm TB and how getting a 58mmTB is a waste of money. Is there anyone out there that can verify is this message below has any truth behind it?

"I get asked frequently if installing a larger than the stock 48mm TPI throttle body will significantly help on a corvette engine, Ill save you some reading right off if you want, yes a 58mm can potentially increase hp if your engines highly modified and your still useing a stock 48mm throttle body but the restriction a stock 48mm throttle body represents is not as significant and the gains to be had are not that large in most cases, your intake manifold and cam plus your heads are the major restrictions. the stock 48mm throttle body flows about 700cfm and has more than enough flow to support about 475hp-500hp, bored to 52mm it will support about 500hp,-525hp, a 58mm can support about 600hp, but keep in mind theres lots of factors other than just throttle body size that determine potential hp

using or modifying a throttle body to flow more than 1000cfm -1200 cfm like a 58mm twin bore potentially flows is a waste of money, heres why
the largest displacement sbc your likely to build is a 434cid, that requires a 4" stroke crank and youll be limited to about 6500rpm even with top quality parts if you want the engine to last any time at all, now you might not realize it but the time necessary to fill the cylinders gets limited very quickly at higher rpms and the volumetric efficiency falls off quickly after about 5000rpm simply because theres just not enought time to allow the cylinders to fill completely. at 5000 rpm theres 41.6 intake strokes per second, per cylinder, by 6500 rpm its up to 54 intake strokes per second, per cylinder thats only 0.018 seconds for the intake port to flow into the cylinder per intake stroke. but theres yet another factor!!! thats the time for the full intake stroke!!!, while theres 720 degrees in the repetitive cycle and Ive given you a full 360 degrees worth of time, the truth is that your cam/engine combo, seldom allows anywhere near that duration!!!! even a radical race cam seldom exceeds 250 degrees in effective duration for port flow, so youll need to knock about 45% off that time, now your down to only about 0.012 seconds or less of effective flow per intake stroke per cylinder, is it any wonder the cylinder can,t fully fill at high rpms??
now the theoretical 434 were working with here even if it could fill its cylinders 100% at 6500rpm which is totally impossiable at that rpm would require 434 (the displacement) x 3250(the number of intake strokes)=1410500 (the full 100% in cubic inches /1728(to change to cfm) = only 816cfm.... now even if you could ram tune the exhaust and intake pulse perfectly and get the cylinders to pack the cylinders to 120% (a total impossability without a supercharger or turbo) thats till only 979 fcm
but in the real world your volumetric efficincy falls off fast after 5000 rpm with a 4" stroke and youll be exceptionally lucky to pull 80% efficiency at over 5000rpm
drop your displacement to a more comon 383 and your rpm limit to the fairly comon 6500rpm and youll drop even the theoretical air flow requirement to below 875cfm

http://users.erols.c...ss/calchpaf.htm

http://users.erols.c...ss/calccarb.htm

heres the ramjet ZL1 454
http://www.sallee-ch.../ramjetzl1.html


yeah you might not believe it but it got a stock 48mm twin bore TPI style chevy throttle body feeding that 454 engine, do you think chevy would do that if it was a significant restriction to hp production??

the restriction is not the throttle body its the port size, valve size and flow the heads have and intake manifold runers restriction,and cam lift and duration... install an intake manifold,cam and heads that can flow 300cfm and the 58mm aftermarket throttle body will still effectively feed the engine, remember that while even 300cfm ports at full flow only pull air about 250 degrees out of 720 degrees in the cycle and are spaced 90 degrees apart, that means that 1000cfm can feed all 8 cylinders a full 833cfm they could in theory flow ,and that 300cfm per port can support roughtly 600hp"


Found here http://forums.hybridz.org/index.php/...to-make-power/

TTOP350

iTrader: (8)

Wow, my head hurts.
I will tell ya a stock motor wont see much if any power gain. but if it makes you warm and fuzzy and your going to mod the crap out of it you may need it..
modify your motor. leave the 48mm tbody on. run it at the track. borrow a 58mm or mono blade tbody. If your car goes faster with the 58 or mono, you need it. If it doesnt you don't.
fairly simple to find out, Don't be a part of the keyboard commando group..

Orr89RocZ

iTrader: (20)

A 48mm will feed alot of setups. Going larger wont necessarily help or hurt sometimes. It may help get the plenum vacuum at 0 on some setups and may see a few ponies but generally 48-52 is all you need.

Some LSx guys are showing 90-92mm TB's flow plenty for 600hp and 90mm flows around 1100-1130 cfm. Going larger to the 100+ mm stuff havent hurt power but havent gained either.

But like said, theres alot of factors involved, more so than a simple equation for cfm to determine hp sizing. A good engine will make 2.0-2.2 hp per cfm of intake runner flow. 500 hp would only require a head that flows 227-250cfm, but then again it depends on the head design. A 250cfm sbc head will have a hard time getting to 500hp compared to a stock LS1 head that also flows only 250cfm on the same bench. On the real time running engine, the altered valve angle makes the difference, so its hard to judge what each CFM will produce on the running motor.

Same would apply to TB's. IMO, 6500 rpm and over, 383 cubes +, 58mm is best choice since its the same price as aftermarket 48-52's. It wont hurt power and it wont be a restriction. Lower rpms and lower hp requirements, you dont need a 58.
Then again, my buddy with a 6200 rpm 360" motor only made 330whp before valve float ran a 58mm I think. Ran fine on the street and had good throttle response. Didnt hurt power IMO. Ran 12.2's and would have been high 11's if the springs would hold the cam.

Chevy86 IROC-Z

iTrader: (17)

If there was a track and especially if I had a friend with a 58mm tb, I would ask. But since that's not the case, then it's out the window. Thanks for the info Orr89RocZ

Orr89RocZ

iTrader: (20)

If it came down to what mod for my money, I'd put all my money into other mods first to complete the motor, then look at the TB when it comes down to it. Do not skimp on intake/heads/cam/valvesprings modifications. Spend money there on good parts. After that look at the intake components like TB. The factory airbox and MAF would likely be more restrictive than the TB anyway. I ran 3.5" air intake on my car and didnt see much of a gain on my setup. I think my intake and heads were just about limited for the rpm range i was shooting for.

Chevy86 IROC-Z

iTrader: (17)

So then my stock 48mm will be fine with a Edelbrock TES exhaust, lt1 cam, descreened maf sensor, Edelbrock hi flow intake manifold, and SLP runners?

Orr89RocZ

iTrader: (20)

Yes

Chevy86 IROC-Z

iTrader: (17)

Sweet. Thanks man.

1989GTATransAm

iTrader: (3)

Here are my thoughts on the subject. It is air distribution in the plenum. The slower the air is in entering the plenum the better it is able to make turns such as feeding cylinder #1. Also the slower the air it will not rush into the plenum as fast and back up against the far wall. When this happens cylinders 1 & 3 will run richer and cylinders 6 & 8 will run leaner.

Also with every restriction in the air intake system it becomes accumulative. The bottom line in my opinion is if you have a well built motor I would run a 58mm throttle body. Like Orr said it won't hurt a thing having a larger throttle body but you may gain some power.

Chevy86 IROC-Z

iTrader: (17)

Good point.

Jim85IROC

iTrader: (2)

When the 58mm throttle body that was on my corvette started to stick, I replaced it with a stock 48mm unit. WOT power was no different, but it felt a bit soggy at part throttle when I went down. The bigger throttle body allows more air for a given throttle position, so it is essentially like having the throttle farther open. I liked the extra throttle response from the bigger throttle body, but it definitely didn't make the car faster.

Chevy86 IROC-Z

iTrader: (17)

Better throttle response but no increase in power? I think throttle response is enough to invest, especially since I'm planning bigger than stock.

TTOP350

iTrader: (8)

On top is a 58mm monoblade I made from a twin 58mm TB.
on bottom is a stock housing 52mm mono blade I did in 1992.
Neither helped make power.

Jim85IROC

iTrader: (2)

Right. The motor only takes in so much air, so having more available does nothing. But, at part throttle, obviously the motor is being restricted by the limited air available. With the bigger throttle body, more air goes into the motor at a given throttle position. Essentially all you're doing is changing the throttle rate.

burnout88

So true, a lot have forgotten that hotrodding is about actually trying things out and experimenting. Sometimes you get surpised by results other times disappointed but the only why to know for sure yourself is to actually try it. All applications and motors are different.

Also, just for the record I tried a 52mm on my 305 TPI car and it made no difference. The car was not slower or faster. Ran exactly the same time at the dragstrip with the 48mm or the 52mm TB. Right now the 52mm is still on the car.

Chevy86 IROC-Z

iTrader: (17)

If I had the money and the time, THEN I would consider "testing". So due to my financial status, I'm not able to do what other members do who are gifted with money. So please, enough with the "testing", "swapping" and "try out". Makes my "head hurt".

burnout88

Then don't ask

Reid Fleming

iTrader: (2)

I would have thought it would be the opposite at part throttle, in that the smaller TB would be the one with more throttle response. I see it sort of like having proper/correct sized headers vs having slightly larger than necessary headers.

I know when I changed from stock intake and TPI to Accel manifold and SuperRam, that I lost a bit of power below 3000 RPM. Made more above 3000 though.

Chevy86 IROC-Z

iTrader: (17)

Don't ask? What's the point of TGO?

TTOP350

iTrader: (8)

You are starting to make my head hurt.
I was maybe 19 years old when I did my "testing" I was NOT nor am I gifted with money now. I did all my stuff with my own money then as i do now.
My parents bought me 1 set of plates and a month of ins when I was 16 and I was very greatful they did that much.(24yrs ago)
If you dont have the time or money to play then don't. Stop crying about time/money, get another job, better job, educated and make it happen if you want it.
You are lucky, 99% of the parts to go fast are all ready made. All anyone has to do is read about a proven combo and follow the build. When I was doing it not much at all was made yet..

Chevy86 IROC-Z

iTrader: (17)

Well on my way to a better job. 65 units in the book and all I need is 6 more credit hours needed to achieve my major in computer info systems. There. Are you happy? Good for you. Your parents had your back. Felicidades, quires un galleta? Eres como lo demas, una persona que no tiene nada mas que hacer. Si no tienes nada mas bueno que dicir, pues sientate y lavanta tu mano quando tienes algo que dicir. I for one am gifted in being bilingual. Try speaking Spanish then tell me how easy it is. I've invested well over $4000 in 2 years and I make only a disappointing $9.70 an hour. At that pay, I still manage to support my family and play with my Camaro. So what's the problem? Do you have something personal against me?

TTOP350

iTrader: (8)

I have NOTHING against you. Your the one jabbing at quite a few of us about you not having this and that.
I'm glad your asking ?s, its a great way to learn. Buut when people throw ideas out don't come back with I can't, I don't. If you cant now be paitent things will come around.
Please speak english if you live in the USA.
P.S. I'll have a chocholate chip cookie while I sit on my *** and try help people that don't want it.

Chevy86 IROC-Z

iTrader: (17)

It's my right to speak any language I want (1st admendment). If your gonna curse or use slang, don't bypass by using symbols such ******. But thank you for understanding me about asking questions. I didn't say anything about you saying "keyboard commando". You've helped me in the past and I'm thankful for that. But when members throw stuff in your face ( not once but twice), it does get a bit annoying. Just like how you told me to borrow another tb, I was cool with that. But when I ask a question and the. Another says try this and try that, well that wasn't in my topic at hand. Help and advice is what I'm here for, not try this or try that. So can we get back to the topic and quit stepping our toes?

Orr89RocZ

iTrader: (20)

Just save money and buy a used 58mm for 200 bucks or less if your lucky. Try it, and if you dont like it, sell it off. TB is a quick and easy change and easy to test. I dont think its worth your time however. Your setup will not see anything with a 58. I dont think you'll notice the difference in throttle response either. You want some throttle response, get underdrive pulleys

Chevy86 IROC-Z

iTrader: (17)

.. Yeah. I decided that perhaps a 52mm may be the way to go since I have no plans to do forced induction. I also thought about getting a smaller pulley system but then my altenater will suffer the charging capacity because Im running a 1800 watt mono block amp for the 2-12's. So 52mm it is. Is there a difference between the Summit brand and others such as BBK, Holley, and Proffesional Products?
http://www.summitracing.com/search/Y...?Ns=Rank%7cAsc

Orr89RocZ

iTrader: (20)

FI is even more of a reason not to change TB. I run stock LS1 78mm single on mine and it makes near 800hp.

And underdrive pulleys wont hurt alternator performance if you overdrive the alternator while underdriving the crank pulley. You need a smaller alternator pulley as well as the smaller crank pulley to keep the alternator working the same speed. Its all speed ratios, if you slow down the crank rotation, you need to increase the alternator and you get that with a smaller alternator pulley kit. Look at March Power and Amp kits. I ran those without any charging issues.

Chevy86 IROC-Z

iTrader: (17)

right on. Thanks for the pulley tips Orr89RocZ

TTOP350

iTrader: (8)

I have a set of black powdercoated march UD pulleys that I would part with.
no belt with it.
I wouldnt use their alt pulley, its bigger and not good unless your a road racer. I use a waaay smaller than stock alt pulley from a fox body 5.0mustang.

Chevy86 IROC-Z

iTrader: (17)

Interesting. Does the UD pulley use the very same style of the early serpentine belt? My 86 is not a full serp like the late Camaro's. Also where could I find the tiny alternator pulley?

Tuned Performance

iTrader: (92)

Ive got a few 58mm accel/lingenfelter throttlebody's left Too sell for anyone interested in the classifieds 89-92 linkage billet aluminum.

TTOP350

iTrader: (8)

I'm a retard, didn't see yours is a early car.
None of this will work for your car.

Orr89RocZ

iTrader: (20)

My setup was full serpentine setup. Not sure if they offer it in a v-belt type setup or not. Have to browse the March catalog. Chances are, someone makes a smaller alternator pulley for v-belt setups tho.

watajob

iTrader: (29)

http://www.gmtuners.com/flow/index.htm