Hey guys I'm wondering if a 52mm throttle body would work on a stock 350 TPI and not cause it to run funny

 

Yes it will work fine, but no its not needed on a stock engine.

 

cant recommend it. i ran a 58mm throttle body on my stock 305, it ended up blowing my engine. it really wont give you any gains and there are alot better things you can blow 300 bux on. upgrade your suspension instead, stock engine is quick enough unless you got a whole lot of money

 

the larger throttle body won't exactly make your car faster or more powerful... let me try to find a way to explain it.

a larger throttle body will only make wide-open-throttle come quicker. there's less of an "in between". people say they gain huge increases in the car's response, but i'll put it this way-

pretend a throttle body is a ruler... you have two rulers, one stock and one "upgraded" ruler. it takes you 5 seconds to move your finger 5 inches up the STOCK ruler. on the upgraded ruler, it take's you 3 seconds to get to 5 inches. --> you're still going up only 5 inches, but it's now taking you less time. you gain no height in the "upgraded" ruler.

get it? i just read that all over again... jesus man

 

How does a throttle body blow up your engine? I find that hard to believe without more information.

 

I don't think the throttle body blew his engine, I bet because it's easier to reach a higher RPM, it may have over-revved or it just wore out quicker. Maybe?

 

so basically all it does is increase throttle response by a little

 

Yeah, but I can't say it wont make your car quicker though or give you more horsepower (I don't have figures to stand behind as proof).

 

maybe that was a bad word choice. my engine didnt actually 'blow up' or anything, what did happen was the mass air flow sensor went bad the day after i installed the throttle and i can only assume it is to blame. thats an awful big coincidence, and it was a 300 repair that i really didnt want to do plus i put the old throttle back on. so, when i say blew i meant more like ruined, all though its fine now. sorry for the confusion

 

It's not as big of a coincidence as you might think. The throttle body is obviously after the MAF sensor (in terms of incoming air), which would immediately point to possible damage of the MAF sensor (in your case) during the throttle body's installation (MAF's are very sensitive). Even with a bigger throttle body, the intake's plenum, runners, base, as well as the cylinder head ports, are exactly the same. So the concept of such a drastic increase in air, causing any serious damage, is totally unrealistic. Without the supporting mods, a larger throttle body is simply a waste of money. No real harm though....

 

I just read most of the post and a bigger TB will hurt throttle response, the air volume will increase but the velocity will decrease.

The only gain would be in WOT but unless supporting mods are done you will see probably no gain ( more likely to have a placebo effect ). Think of it like this....

Turn your garden hose on water flows but not much pressure (thats the 58mm TB). Now take the hose and put your finger over it, the pressure increases and the water come out faster but theres slightly less flow. ( factory TB)

 

yea, the good news is the car runs fine now. but while were kind of on the subject, and i could start a new thread but everyone here seems to know what theyre talking about, what advantages would a turbocharger add to a tpi? i was looking at the ati procharger and they said it would add 50-75% more horsepower, and i assume its like the last post said, its more air under more pressure (hose with finger)? anyone have one or have anything good/bad to say? also, i have an 85 and all the turbochargers seem to be for 88 and on, and my guess is because you need a serpentine belt system to run a turbo charger and the 85s had the three belt pulley system. but, summit sells a complete delco serpentine system with a new alternator and ac compressor for 700 bux (and i would like to replace both of those anyways), any ideas?

 

A turbocharger and a supercharger are two different things. What you are describing is a supercharger. See the power adder forum for more info on those.

 

I disagree. I honestly don't see how a larger throttle body would hurt the rate of speed in which the air will flow. Obviously, if one's going to adapt a larger throttle body, then porting the orifice of the stock plenum would be mandatory to avoid any possible turbulence. Aside from this, air is still being pulled way before the throttle body, and I just don't see how the larger throttle body would be that much of a hinderance....

But this is being based from the other end of the spectrum though. I could see how this analogy would relate to engine exhaust backpressure, but I can't see how it would relate to incoming air though....

 

 

....OK, removing THE ENTIRE TPI from mix, and only talking about the throttle body, a bigger throttle body (no finger on hose) will slow down air at lower rpms, but ultimately flow more air. ....The TPI itself lives and dies by this. The longer runners (finger on hose) speed up air due to smaller/longer pathways for the air to travel. Hence low RPM torque, but of course, when the engine requires more air at upper RPMs, the TPI just can't handle more air, and the curve flattens out.

....but more to the point of this thread, on this 305 naturally aspirated engine, the heads, exhaust, TPI, cam etc. etc. etc. all dictate airflow, so unless the throttle body is choking the "system" (which the stock 48mTB is not) it doesn't make a difference.

....now add a supercharger or turbocharger, and that all changes. The pressure is now coming from the other side of the equation. Regardless of how much air the engine can handle, if it the blower/turbo can't push it past the TB, it isn't gonna make more power.

....but to bottom line it for the point of this thread, a 52mm should run just fine, and may add a smidge of snot to the motor, it may cost you a snoodge, but ultimately you won't feel it either way.

 

But we're not removing the entire TPI system from the mix, as that was the whole point. You correctly pointed out that the stock 48mm throttle body isn't the bottle neck within the stock TPI system, and I agree with that. It can in fact handle more air flow as it sits. However, the rest of the TPI system doesn't demand the additional air that it can flow, so it, and every other larger in diameter throttle body, becomes irrelevant, and virtually goes unnoticed. No harm whatsoever when upgrading to a larger TB on a stock engine....

If it's a MAF oriented system, the ECM is told before the air even reaches the throttle body exactly how much air has entered the intake. Whether the throttle body is 48mm, or 58mm, the air was already calculated before hand, and provided the plenum's orifice doesn't cause any turbulence (with a larger throttle body), there won't be any problem whatsoever. Speed Density obviously basis it's calculation a different way, but regardless, as already pointed out, the stock 48mm throttle body can already flow more air than it actually does, but the engine isn't demanding it due to the rest of the TPI's system....

Carburetor's, however, are an entirely different story....

 

so what basically if you do anything with a throttle body replace the MAF cuz its junk or replace it and get a better flowing MAF

 

People have achieved very good dyno numbers with the stock MAF sensor, with 1/4 mile runs honestly speaking for themselves. It really depends on what your shooting for though. Most of today's generation of racers are bent on this 800-RWHP, and no less, craze. This obviously calls for a different setup. If your looking for a solid, everyday runner, I would stick with the stock MAF system if I were you. Knowing that the TPI MAF has brought many racers into the nine's (in conjunction with the right setup; boosted etc.), should tell you that it's more than capeable of taking you where you want to go, so stick with it....

Here ( Click Here), not bad for a stock MAF, eh....?

 

Street Lethal: I think we're saying the same thing. Gotta love unspoken communication!!!

DirtyRacing: Regardless what engine you have, it's ultimately one big air pump. At some point, some part is flowing at it's max, and no matter what other parts you have, the engine stops making power. Kinda like a professional marathon runner breathing through a straw. No matter how much conditioning you have, you simply can't get enough air through a straw for a runner to breathe. So one by one we replace the restrictions. Heads flow more air, cams open valves farther, and keep them open longer, exhaust gets rid of MORE exhaust gas, bigger injectors gives MORE fuel to burn with MORE air. IT's all about getting air in, burning it with fuel, and getting it out.

So where' the restriction on a stock 305? A LOT of it is exhaust. That's almost always a FIRST mod to any factory engine. Under the hood, probably the heads or the intake manifold itself. Unfortunately, it's not as simple as a runner breathing through a straw, and there are a LOT of factors to consider. But the stock air intake box flowing through a stock MAF sensor, flowing through a stock 48mm throttlebody will provide enough air for a pretty stout 350. ....it's quite awhile before a 305 needs to upgrade those parts.

 

It's late man, and I'm tired as hell....!

 

lol, this is a good thread.

 

wow this was a great discussion... lol well i see the points of everyone. and i think the general concensus is that you could spend $300 in a better place.

 

I personally do not care for larger throttle bodies on street cars. In most applications (especially mildy modded street cars) they're a complete waste of money. I can tell you for a fact, that installing a larger throttle body on your car will give you NO power increase what so ever. Zip. Zero. Nada. Nothing.

What it will do, is destroy your throttle response and may even give you a "stumble" or "bog" off the line. That is what happened with my LT1 Formula ( http://www.cardomain.com/id/lt1fun )
after installing an Edelbrock/BBK 52mm throttle body and it took me forever to finally figure out what the problem was. It was such a frustrating time trying to figure out why my car developed this stumble, out of the blue.

I kept getting this "bog" off the line, where there was a slight pause between the moment I hit the gas, and the point where the car actually stated to accelerate. The car would always stutter whenever I'd give it 1/4 throttle. At the time, I figured it was ignition related so over the following couple weeks, I eventually ended up replacing ever part of my ignition system which (back then) cost my well over $1000 CAD.

Still didn't solve the problem. It wasn't until I met up with an old friend of mine (who happens to be a mechanic) that I finally figured out the problem. I explained to him the symptoms and he asked me what was the last thing I did to the motor before I started having problems with throttle response. After thinking about it, I finally remembered that the throttle body was the last thing I did to the car and he said "BINGO! That's your problem right there."

He then explained to me about how/why larger throttle bodies often cause drivabilty issues and suggested I remove the 52mm and re-install the stock 48mm. I was hesitant to do so at first, mainly because I had just finished spending $450+ on this new fancy throttle body and it was such a really nice looking piece. But I was desperate to find out what the problem was and willing to try anything. I figured if the 52mm throttle body wasn't the problem, I could always just put it back on.

To make a long story short, immediately after installing the stock T.B. back on the car, all drivability issues disappeared. Throttle response was smooth and crisp. No bog. No stumble. The car was right back to the way it used to be.
I was happy but at the same time pretty pissed. I mean, on the one hand, I finally solved the drivability problems I was experiencing. On the other hand, I came to the sad realization that I had just spend $450 on a part that didn't give me one single horse power and instead ended up costing me over $1000 in ignition "repairs" that were never even needed....

For the record, I did put the car on the dyno after installing the larger throttle body (I always put my car on the dyno after upgrading anything)
and after 4 runs, the car didn't make any more HP than before. This was on a heads/cam LT1 mind you (with a ported intake manifold), and I was putting more than 360+ at the wheels N/A and over 500RWHP on the spray. On both passes on (and off) the nitrous, I gained absolutely NOTHING !!!

Needless to say, i was pretty disappointed with the results and I tried to comfort myself in the fact that even if I didn't gain any HP, at least the new throttle body looked cool and gave the car a "sucking sound" through the intake that made it sound like I had a blower on the car

Looking back now, it was a learning experience for me.

There's was a lot of dumb things I bought for that car that were a complete waste of money. I guess I was just suckered into the magazine ad's and internet talk and just believed a lot of what I read. Now with my IROC, I'm going off of personal experience and only buying parts that I know are actually worth it.

A larger throttle body definitely is NOT one of them.

A stock 48mm TPI TB flows aprox. 780cfm, which is already more than what a stock (or aftermarket) TPI set-up could ever hope to take advantage of. Really, there is virtually no reason to upgrade to a larger throttle body if you're running a TPI intake.

It's your call really but I wouldn't recommend a larger throttle body at all.
I've never seen anybody gain any HP out of a larger throttle body other than those with highly modified motors with power-adders such as a Turbo or a supercharger. A TPI motor will not benefit from a larger TB, I can assure you.

For the money you'd spend on a 52/58mm T.B. you could upgrade to a set of 1.6 roller rockers and pick up a guaranteed 15-20HP.
You could get a custom Chip burned for your car. A set of headers, cat-back etc. etc. etc.

Learn from others mistakes my friend. It'll save you a lot of time/energy/money/grief

Sorry for the long post.

 

hey whats up! i have a 91 z28 tpi i thought i understood that stock tpi throttle body was 52mm and you had to get the plenum bored for the 58mm am i wrong or right??

 

The 58mm will work on a stocker, but it would probably be beneficial to port the plenum and get some high-flow runners while you're at it.
----------
...52mm is PLENTY for a stock motor. The 58 is better for a cammed, possibly FI application.

 

Too many variables though when trying to determine why your stumble was prevalent. Knowing that the stock 48mm throttle body can already flow more air in a totally stock engine configuration's form, but it doesn't though, because the engine isn't demanding any. How can a larger throttle body allow for more air to enter into the combustion chambers, then, when there's plenty more left in the stocker (remember, which isn't being utilized yet)? In your situation, it quite possibly could have been the state of tune....

Also, if the plenum's orifice wasn't ported when the aftermarket throttle body was installed, a whistling noise would most likely be prevalent (turbulence, which sounds a little like a blower), which obstructs airflow, and could of assisted with the slight hesitation you described, although it honestly sounded more like a flawed TPS setting though in your case. The only time I see an immediate problem when installing a larger throttle body, is when you install a bigger carburetor on a stock engine. This is mainly because the ECM can't really compensate for the added air like it can w/fuel injection, as well as the LG4's intake system not being as limited as the TPI's w/air flow...

When installing a larger carburetor, the engine immediately realizes the additional air being presented. When a larger throttle body is installed on a TPI engine, the air isn't immediately realized, because the stock 48mm throttle body still has yet to even be maxed out, due to the stock TPI system's limited air flow potential....

 

Read this thread again. Stock is 48mm. 52mm and 58mm are aftermarket upgrades. If you put on a 58mm, yes you should get the plenum ported to match the larger throttle body.