I'm wondering At what point is the factory throttle body going to be a limiting factor? With my current setup I know it's not worth doing. But when I eventually put a new top end and valve train in the engine I just want to know if it's one of the first things I should do or one of the last. In the end I'll be looking for maybe 350-400HP out of the engine as it will probably never see the track. So I don't want to waste the money on it if it's not going to make any sort of demonstrable difference.
Thanks in advance

 

You'll be fine with a stock one

 

Thought so. Just wanted to confirm. Thanks!

P.S. I notice you also have an 89 Formula 350 T-top car. Very nice!

 

Not sure what the limits are for the SBC throttle body. Fuel makes HP and there's only so much fuel that you can push through 2 injectors. I do know the the BBC throttle body is bigger and can flow more fuel through the OEM injectors. NHRA gave a HP rating of 310 HP for stock eliminator for the 90-93 454SS pickup trucks which used a 2 injector throttle body.

Aftermarket injectors can provide a little more fuel but again there's only so much fuel that can be pushed through the 2 injectors. That's why the 8 injector system with 1 injector per cylinder has a much greater power potential.

For the average street driving where most of the time, you're under 3500 rpm, you'll be fine since you won't be driving around at the limits of the injectors. Don't expect WOT performance to be what you anticipate.

 

His info under his avatar and screen name seems to indicate he has a stealth ram TPI. Pretty sure he is asking about this throttle body and not a TBI system.

 

I do, I also have an 89 formula 350 asc vert, Fun car too.

 

OK. That's entirely different. That throttle body is bigger than the TBI throttle boby which will allow more air in considering fuel doesn't also need to go past the butterflies. It should not affect your predicted HP levels but there are still limits to using OEM sized throttle bodies.

 

When the existing TB becomes a restriction.

Fortunately the TB isn't in the running for being a restriction on a TPI style engine. It's low hanging computer friendly fruit. A simple upgrade with few negatives, that simply has to be better than stock. Just look at how much bigger the holes be. Yo.

 

Very easy to know if your TB is "The Restriction":

Put a vacuum gauge on it, hooked up to the plenum; measure the vacuum during a WOT run; it should stay the same all the way, at basically 0" of vacuum (atmospheric pressure). Tape it to the windshield so your assistant can watch or video it. This would indicate that air is flowing INTO the plenum, via the TB, at the same rate that the engine is pumping it OUT OF the plenum. You might be able to datalog the MAP readings if your ECM is fast enough and gets/outputs its readings often enough. (i.e. if it's a 0411 or something, NOT the original TPI one)

Instinct tells me though, at 400 HP, you're not likely to have run out of TB just yet.

 

I always thought 52mm was where the TB was maxed out and 58mm was the "pointless" upgrade for a bolt-on ( Cam / Headers ) upgraded 350 ?? A 52mm TB really isn't worth the expense with a bolt-on modified 350 ?

Is there EVER any use for a 58mm BBK TPI TB ??

 

Well, I guess if you're BBK, and you spot a real thick wallet somewhere in the pocket of somebody with TPI and a poor understanding of what makes a car "faster", … could be hard to resist.

Beyond that, I don't know. The vaccum at WOT test will tell the truth, more than marketing materials will, for sure. The Stealth Ram has higher flow potential than TPI but I can't tell you how much, at the TB. I do know that the runners won't support very much past 425 HP in a N/A motor on modern pump gas, as they're about the same cross-sectional area as typical good GM heads from back in the 70s (292 for example), since that's what the Street Ram, the product that eventually got turned into the Stealth Ram, was built for. It had 2 little bitty plenums on top that you would put something like 500 or 600 CFM 4-bbl carbs onto. I really wish I had a photo of those, but all I have is this.

 

IIRC, the 502/502 ramjet big block setup used a stock 48 mm T-body and a some of the stock class LT1 racers use them too and they are around 600hp

 

Look at map kpa data. See what your key on, engine off kpa is. It'll be around 100, but it varies depending on sea level and other conditions. Do a nice 3rd gear wot pull while data logging. If your kpa is lower then the "baseline" koeo, you have an intake restriction ( throttle body to air filter). If you have a mildly built stealth ram engine, you probably have a small drop. I had a 2-3 kpa drop on a ~400 hp miniram engine with a 52mm tb. That same tb on a ~550 hp engine netted an 8 kpa drop. Disappointingly enough, a 58mm still has a 5 kpa drop. Being as you have an 89 however, your maf flows less then a 52mm. My advice if you're planning on making more power in the future and maximizing your combo, ditch the stock maf, there's a few options there, and go big on the throttle body. I guess I'll edit this by saying if you do in fact still have the 89 ecm, you won't be able to do the kpa test. But a good quality, large vacuum gauge will do the same, just not in as much detail.

 

That's the fanciest way I've ever heard someone say "Never".

 

I was simply presenting facts and data for others to determine if they have an air inlet restriction. I've been logging this data for years throughout a few different combos. It does become a restriction as your power goes up. If you are looking to maximize your combo, it's worth it, especially if you can find a used unit at a cheaper price. There are no driveability drawbacks, I actually regret getting a 58mm instead of a monoblade.

Every 3.3kpa is 1 inch of vacuum. My koeo kpa was 101 on this log. 7kpa drop is a little over 2" of vacuum at wot.

 

Yeah i would say short runner intakes, turning 6400+ rpm will usually want more tb

on a tpi deal? Maybe on a big cubic inch motor using welded up aftermarket bases and custom runners lol far outside most ppls builds

 

You're good. I can neither confirm nor deny the accuracy of your statement, since it might as well be written in Chinese to my level of understanding, but it sounds good in theory. Consider my reply an attempt at levity and simplification.

 

I guess that rally says it all. The stock MAF (even de-screened) flows less than the stock 48 TB for cryin' out loud,.... !

TPI / LT1 flow #'s: http://www.gmtuners.com/flow/index.htm

I realize the TPI parts will require porting to gain anything from a bigger TB. I've got a 58MM BBK and was going to sell it off to get a 52mm because I figured the 58mm was better suited for someone going a bit more radical than a 350 with ported heads, headers and other bolt-on mods. Never thought about it till I read this thread . Seems like I should just use what I've got and drill a couple holes in the throttle blades if I need to rather than wasting the time/effort selling the 58 and buying a 52.

 

beat me to it....mos that have large TBs dont need em
Its like the guy who puts headers on his 350 then insists he needs a 750

 

Here’s a neat cfm write up on tpi parts

http://hobracing.com/tech/tpi_flow.asp

 

my buddies old 350 vortec motor with an lt1 cam and rpm air gap intake ran best with a 750 carb lol

my 555 bbc i guess should be nearer 750 hp with a single 102mm tb was only seeing 93 kpa na. 99-100 was atmosphere. Exhaust was small for the turbos however and cam wasn’t exactly optimal for na but shows you need more intake side mods when you see low map readings.

my 383 maf car made 400 whp 6500 rpm range and used a 58mm holley. I throw on a custom 3.5” cai and maf and didnt pick up anything. So the maf wasnt a restriction on that setup. The snorkel tpi filter box will flow 775 at 16” depression. The maf is said to be 650’s. Thats a fair amount of airflow but remember whats upstream compounds downstream to reduce flow across the entire tract. So the bigger tb may help remove some restrictions across the induction package. Reallly need to see an entire induction system flow tested