so i got this nice government economy stimulus and i need to spend a lil of it on my car. i was thinkin 52mm t-body the reason???(and ive heard all the arguments) back in 2003 i tryed changing my TPS sensor and somebody stripped the aluminum on the t-body and right now the sensor is held in with 1 bolt and constantly comes out of adjustment SO I HAVE TO ADDRESS THAT and i was thinking why not at least upgrade to the 52mm t-body(since i do have full ram air thru hiflow filters and descreened maf sensor very soon on top of headers and full custom exhaust with hi flow y pipe and no cats) and why spend money on a stock one ya know. if not does anyone have a mod( and dont say 350 engine or nitrous i love my stock 305 with 130k on it ) that does not require to much install time as im currently enjoying the season after a yrs worth of restoration on her and dont wanna rip the motor apart until i put her away for the winter,, and i have power pulleys and gears on her??? plz help
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i meant original 305 not stock OBVIOUSLY

 

I love my BBK t-body, they look sweet, and function good, dont listen to the B-S people that say they dont help, that's a load of crap, it HELPS, you just really need to make sure and port the plenum, to take advantage of the bigger t-body. DEFINATELY DO IT. I did, and havnt looked back. Plus...later on, you already have it.

 

if you havent done aftermarket runners i would do that and get a stock replacement tb to fix your screw issue, or drill and tap your existing one, i think you will have better gains on runners then a tb

 

The stock throttlebody on your car is nowhere near a restriction on your current setup, or even with full bolt-ons. You can buy a used stock one on ebay for like 20 bucks.

Old my old GTA 350, a 52mm TB was put on the car after headers and runners, and cam. It made no difference at all, and i kicked myself for spending $300 on it. On my new setup that puts 300hp to the wheels, I have a stock TB and no intentions of changing it.

 

If the stock 48mm TB flows, with an airfoil, 709cfm. Then this is equivalent to a carb rated at 787cfm @ 1.5 in Hg.

Stock intake manifold with runner.....................198.72 cfm

Stock TPI-------- 7.250"------1.470" round (1.70 sq inches)

305 intake valves are 1.72" = 2.32 sq in ---- 350 is 1.94" = 2.95 sq in

What would you change first?

 

I think the runners (like SLP) or headers would be a better "stimulas package" for your car than a TB. Yes, they definatly will help IF yours is restrictive. You can find out by putting a vacuum gauge on a full time port and doing some full throttle runs. If you pull a vacuum (over say 2) at the top of each gear, then you may benifit from a bigger TB.

Yeah I hear ya on hating to buy a stock part to fix yours. I also look for chances to upgrade when I can, so if you find a 52 at a bargan- do it. You probably wont see as much of a gain-per-dollar-spent as you would with other mods. I'm currently running a stock 48 with an air foil on my 5.7, HSR, cam, ported heads, headers etc. Turning 8.6 1/8 mi times and it's not a restriction for me.

 

ant man. i have headers,, and yeah im not dropping 300 on a t-body i have a 30 dollar off coupon( as a tax refund market ploy that summit is running) 30 dollars off a SUMMIT 260$ 270$ after shipping t-body leaves me at 240$ for a 52mm t-body now i didnt think you could put a airfoil on and aftermarket t-body,, but yeah i hope the posters here UNDERSTAND WHY I AM CHANGING THE T-BODY as i have no choice but to

and whoever posted that cfm chart im so damn lost haha explain to me a little more it turned my brain into jello

 

If the air cleaner/air box only flows at 499 cfm then that is the max air flow into the engine. So if you install a 52 mm TB (848 cfm) you still only get 499 cfm to the engine. It is like installing a 45 mm restrictor plate on the front of your 48 mm TB, changing to a 52 mm, will still only get you 45 mm worth of air.

You will get air flow quicker up to the 499 limit, quicker but no more max flow (better throttle response or lean bog, depending on the tune).

Drill and tap small replacement screw $10, new TB $250. Worn throttle bores get a new one or rebuild the old $150/200 (machine shop/TB rebuilder).

HTH

 

so what your saying to me,, even if i installed the biggest sickest motor out there and fed it thru my stock tpi inlet nothing after that would matter,, i dont see how this is plausable. bieng that heads alone add some decient power,, if what your saying is true heads should only flow quicker up to 499 cfm its not making sense to me

 

dosent my FULL RAM AIR account for anymore cfm,s???

 

Basically what the flow charts show is the 48mm (stock) TB is big enough to support around 400 or more horsepower. It may not be the most restrictive component in your intake system. (air filter to cylinder)

You gotta get a TB and a 52mm is a good choice regardless of how much you pay. Just look at the data provided and be consirvative on what you expect as far as power increases.

 

I would spend your additional money on new fuel injectors, an adjustable fuel pressure regulator, porting the plenum and have a good machine shop fix the stripped threads on your stock throttle body. Then if there is any money still avaliable buy a cam. You may want to consider an air foil to smooth out the air flow. Consider having a vacuum test done to find any leaks, especially with the stock throttle body, before you dissasemble the induction system.

Your stock 305 does not need a twin 52 mm throttle body even if you intalled a turbo/super charger. As the numbers indicate your 305 can only take in 618 cfm and the stock throttle body will flow 783 cfm. Therfore, it is not a restriction on air intake to your engine.

 

Here is something else to consider. I was recently in the same position of needing a new throttle body because of a vacuum leak through the stock throttle body. So I though as long as I needed a new throttle body why not get a twin 52mm or even 58mm throttle body with a nice BBK or Holley plate on it and everybody could go ooh and aah when I open the hood. Then I removed the rubber bellows from the throttle body and opened the butterfly valves and inserted my finger and found the twin 48mm bores were flush with the corresponding bores in the plenum. So adding a bigger bore throttle body would necessitate porting the plenum bores or you would have a big obstacle to disrupt the airflow as well as the casting ridges behind the plenum bores. Then there was the price to repair my stock throttle body versus the price to buy an aftermarket throttle body.

 

That is exactly it, if you actually spend the time to bore out the plenum, then the bigger throttle body, is actually gonna make a difference, all these people that just slap them on, and get no gains, are the ones saying it aint worth it.

 

AND WHAT WAS THAT PRICE TO REPAIR?????

 

I have never said it "wasn't worth it". But consider this, lordmetalz28, your running a 305. At 565 cfm your motor would be at 6400 rpm, mine at 5100.

I have a mild 383, stock intake/ 48 TB, 24# injectors @ 50# fuel pressure, bigger heads (2.02 valves) mild cam (1k-5k power range), stock exhaust.

Right now the ECM tune (stock $32) is my biggest restriction. Not the Maf, TB, Intake, Ect...

There is a Max Air Flow vs RPM table restriction and a lean idle, 128 blm cruise, and a too rich Wot issue. Until I get "the tune to match the car setup" There will be no true gains.

There is a compensation window that the ECM can Adjust for (give you more HP/torque). When that is reached, your done with any gains, till you retune the "Parameters".

I got my education (30 yrs) "Hot Rodding and repairing" CNC equipment (electric motors, hydraulics, and computers). They always wanted more out of the machines, so you tune to run up in the "safety margin". Trading machine long life, for more power (bigger cuts), and faster part cutting time. The trade off was shorter equipment uptime vs quicker production "Hot Rodding".

Every computer run system (OEM) has built in restrictions on torque and rpm (HP). This is so you (the customer) don't break a bunch of parts during the warranty period. After that you are stuck with this lame tune.

So after the warranty is up (what 20 years ago) we are running this same lame OEM tune in our TPI cars. This needs to be changed (reprogrammed to increase HP), the farther from "stock" you get the more important the "tune".

This is why there is a big discussion about what "adds HP". The first things added to your car will give the biggest increase, when you hit the limit of the compensation "window" all gains stop, till you retune the "chip".

I can take a 500 HP/500 TQ motor and detune it to 250, with only changing the "tune/programing" not touching any "Hard parts".

Restrict air flow (Maf/Map limits) to 200 cfm, drop injector flow (pulse width) from 30# to 19#, rpm limit, mph limit, ect.... by lowering the internal preset (OEM) ECM programing limits (you know like traction control).

 

The stock plenum already has a bore to accept a larger TB.

Camshafts offer the best HP/$$ improvements. Aft that, cylinder heads. Then the bolt-on shiney stuff which offers little gain without other work first.

 

well you really are in depth pandin and you know your sh*t,, i appreciate all the input,, the throttle body issues reguardless has to be solved and bieng( possibly bullsh*t) that it is our job as americans to help make this stimulus check help the economy and for those 2 reason,s i am going to do it. now i also just got another coupon for another 30 dollars off at summit so my price is now 210(including shipping) so whatever it does it will DEFINETLY help the tps problem,, and also im curious about it and lastley this maybe the last mod i do to my 3rd gen,, ive been building it for 6 years now( mostly getting her back to prestine orginal condition) and she needs floor mats, window switches a tranny mount and this here THROTTLE BODY ISSUE and then im gonna buy a 4th gen, but i do appreciate everybodys input and it did not go to waste whatever that throttle body does helps or not theres more reasons involved in getting in right now than not,, mainly curiosity and existing problems,, thank you guys

 

No, it does not. Not mine anyways, it was the EXACT same size as the stock 48mm.

It's not hard to bore it out for a bigger throttle body. There are plenty of good write ups about it. Just take your time.

 

If your selling just try it. Let the next guy perfect it.

 

I am the origianl owner of a 1989 GTA and the twin 48mm throttle body bores match up with the bores on the plenum. I can not speak to other years. I have seen instructions that comes with I think the larger Holley throttle bodies that indicate boring out of the plenum is required.

 

Not counting the EGR humps in the floor (well, they used to be there), this '86 was/is 51.80mm across the bores - In other words, pretty darned close:



I've done a couple of '87s which were the same. I know the plenum changed, as well as the runners, in about 1988 or 89. The later parts had no cold start passages, and may have had machining differences.