JordanRAdams

I'm in need of a new throttle body. The one to be removed is stock, and it was recommended that it be replaced with a 60mm BBK for a 350 (I've looked, and I can't find a 60mm one, so I'm thinking he just rounded up the 58mm, but I'm not sure). I have an 89 IROC-Z28 305 TPI bored .30 over, and completely rebuilt engine (I bought it that way, and probably don't deserve it, but I want to learn). Really my only concern is, will the timing, fuel pressure, or anything else need to be adjusted to compensate for the additional air coming in, or will the computer take care of that by itself? I think I can handle putting on the new TB, but I'm not comfortable messing with any of those other items at this point. Reason I'm considering doing it myself is the guy that I'd have do it is 35 miles away and since gas hit $4 a gallon today, I'd rather not take it out and back 6 times (2 vehicles, of course). Of course, if I put it on and then it doesn't work, I'd have to tow it, so basically I'm trying to decide on the most cost effective solution. Thanks for any advice.

tonys91rs

iTrader: (17)

is the only reason you need to replace the tb is because it is stock? based off your listed engine modifications, you dont need a larger tb. the stock one will work. however, there is a 58mm tb available. four bolts and its off. you wont need to make any other adjustments. you can swap it out at home.

before you spend the money, do a search on the site and read where others have asked and answered this question.

vetteoz

iTrader: (13)

By who ?

No MORE air will come in to your engine with a larger TB;
the engine only sucks what it wants and in your tiny little 305 the stock TB is more than adequate

Waste your $$ on something useful

JordanRAdams

The dude said it should be replaced because "the plates are worn to hell". It's got 136k some miles on it. The TB, that is. The block was bored over, and has all new parts, including a cam, high compression pistons, and 30lb injectors, among other things. So it is a higher performing engine than stock, and he thought since it's got all that stuff it would benefit from a bigger TB. It runs wild sometimes cuz the plates stick open, so I do need something done to it. That's all. I hate spending money if I don't have to, but if I'm going to, I might as well make it well spent. Thanks for the input.

blackroc68

iTrader: (2)

You will only have to adjust The iac and the tps sensor.

ASE doc

If I remember correctly, you have to open up the the front of the plenum to accept the 58mm throttle body. If you go with the 52mm this isn't necessary. I run the BBK 58mm TB and I believe it comes with instructions for opening up the front of the plenum to match the larger thottle bores. Otherwise the plenum may interfere with the throttle plates. You will need to remove the plenum to bore it larger.

VincentZ28

iTrader: (2)

If you car is not making over 420whp or over 500fwhp then all you need is a 52mm throttle body. The 58mm will not help your performance at all. Also you need to bore the plenum to accept the 52mm.

ASE doc

Thanks for the correction. I know you have to bore for the 58mm, was wrong about the 52mm. Either way, the plenum needs to come off.

JordanRAdams

Hmm, well, is there a good/easy way to figure out if I'd really benefit from having a larger one? I was thinking it was just kind of like slapping it on, and I don't really want to get into drilling holes in things. =) Or paying someone else an arm and a leg to do it for me. Thanks

vetteoz

iTrader: (13)

Can you read?
You have already been told in your case you are not making enough Hp so there is NO benefit

But if you have a new one only buy a 52mm

You can also get your stock one rebuilt for around $170
http://www.ebay.com/itm/TPI-LT1-Thro...b40bf1&vxp=mtr

JordanRAdams

I'll take it under consideration.

BTW, are you saying I'm not making much hp because it's a 305, or because of the only mod listed? I very much doubt that it even makes 300, but still, there's a lot more done to it than just that one.

hellz_wings

iTrader: (2)

Jordan,

I have a 305 as well making a little over 206RWHP and 284RWTQ. I have more mods than you and I still have the 48mm throttle body. It's also somewhat worn out and it needs to be replaced. I figured I would just wait until I drop the 383 in there that I'm planning. If you really want to replace it, there's some 52mm TB's on EBAY that are just stock TB's that have been ported and rebuilt with new throttle blades and such. You should also get a new Idle Air Control valve and a new Throttle Position Sensor while you're at it. These will ensure your throttle body is brand new and functioning properly, and has 52mm capacity in case you decide to upgrade your cubic inches later on (as I am planning to).

Also it was mentioned above, but the plenum will need to be ported to match the 52mm opening but isn't easy to do properly and you need the tools to do so. If you can't do it yourself there are many places on EBAY that will do it for you and/or send you a unit that's already complete. Just make sure you get the right plenum for your year of TPI (there were different variations over the years).

It seems to me though a stock replacement without worn throttle blades is really only what you need rather than all this upgraded stuff lol.

87zjeff

iTrader: (4)

i ran a 52mm BBK throttle body for years with a factory, unported plenum. only thing i ever did to the factory opening was grind down the ridges right behind the throttle body but that was several years after installing the 52mm TB.

vetteoz

iTrader: (13)

I'm saying your mods don't change anything enough to require a larger TB
Physics 101
The engine is a air pump, every time it goes around it sucks in only so much air

Use this online calculator to see how much air your engine requires
http://www.carburetion.com/calc.asp

then look here to see how much cfm a stock 48mm TB flows
http://www.gmtuners.com/flow/index.htm

GM used a 48mm TB on a crate big block chevy for a reason

JordanRAdams

Ok. 507 is what the calculator came up with, and 600 is the 48 mm TB. So you're right, I don't need a bigger one. Like I was saying to a friend that used to have an IROC, I guess I just don't know enough about it to know what to do, I was just going by what someone told me. I'm going to try to find someone with a dyno that can check it out and really tune it up properly.

hellz_wings

iTrader: (2)

This probably hurt performance actually, because with the 48mm, there was no obstruction for the air to enter the plenum, with the 52mm, some air will be obstructed as a result of those walls inside the plenum blocking. Unless you port them out (as you did years later as you said) then you would lose power as a result of the air not flowing as smoothly as before with the 48mm TB.

vetteoz

iTrader: (13)

Stock TPI/LT1 48mm Throttle Body w/o airfoil -- 783.0 cfm

but note the MAF on your car is much more restrictive
Stock TPI Bosch MAF sensor w/ screens -- 517.8 cfm

so having a larger TB doesn't change intake restrictions

JordanRAdams

My car: should need 507 CFM
stock 48 mm tb flows 783.0 CFM
Bosch MAF w/o screens flows 658.4 CFM

So it's getting enough air.
But too much fuel.

It's got a thermal chip for street performance, so it's injecting more fuel? Or not, IDK.
It's got 30# injectors to handle that fuel.
30# injectors will comfortably supply 384 hp (http://www.gmtuners.com/flow/index.htm)
My car MIGHT make 250 hp, didn't have it tested so that's a guesstimate.
The throttle blades are worn, the plenum is FILTHY, seems like fuel getting in there, but I don't know.

So enough air, too much fuel.
I didn't get different spark plugs.

What should my first step be?
It seems like it has plenty of power.
I'd just like the effing thing to run PROPERLY. It doesn't run BAD, it's a lot better than it was when the timing was off, but it's probably not right. It rips, but could it rip more? Possibly.

I'm just writing all this stuff because it helps me to remember things if I write them and read them, so if I ever actually get around to taking it somewhere I'll have some idea and not sound like a total moron. I apologize for not knowing what I'm talking about. I usually like to research things before I blow off about them, but I got excited and just started typing. Plus sometimes I can reason things out if I do this. You've all been a lot of help, and helped me realize that I know absolutely jack **** about engines. Being able to admit that will probably be the most useful tool in this endeavor.

JordanRAdams

And could someone tell me how to completely delete a post?

vetteoz

iTrader: (13)

You think?
Guys are running 383's with 24 lb injectors and you have 30's in a basically stock ( for airflow purposes) 305 with stock fuel tuning

the aftermarket off the shelf chips only play with engine temps and timing ; fuel is still based on stock 305 19 lb injectors

JordanRAdams

Well, I didn't know, so that's why I asked. Just trying to figure out what to do in what order so I don't have to take it to a garage multiple times. But if it's injecting based on 19# injectors, why does it seem like it's getting too much fuel? Just because the 30s are capable of putting more in doesn't mean they are, does it? And how about the maf screens?

hellz_wings

iTrader: (2)

30lb injectors are way too big for a 305, even for mine. I still have stock 19lb injectors making 206WHP. That's wheel horsepower. On a 305 I wouldn't go higher than 21 or 22, which is what I'm getting, but you have to tune the PROM to accommodate for the injector size change otherwise you will have fuel problems.

And I highly doubt you will make 250 wheel horsepower with a NA 305. I have all the bells and whistles and I'm making only 206 wheel horsepower (maybe a bit more by now but not by much).

Tuned Performance

iTrader: (92)

Man you need to call up southbayfuelinjectors and get a set of bosch 3 19#hr on order A.S.A.P your running so rich and washing down the cylinder walls.

http://www.southbayfuelinjectors.com...o_305_TPi.html

hellz_wings

iTrader: (2)

Agreed. Those are the ones I was going to get but I'm going to opt for a little larger ones: The 22lbs injectors. My engine is at the 19lbs injectors theoretical limits of power so I'll go a little bigger and tune the PROM for them.

These are the ones I'm getting: http://www.southbayfuelinjectors.com...esign_lll.html

JordanRAdams

Will do.

vetteoz

iTrader: (13)

You have 2 water hoses ; one is 1/2" ,the other 2" connected to same pressure tank
The computer knows it needs to turn on the 1/2" hose for 30 sec to fill a bucket
; if it turns on the 2" hose for same 30 second period , does more water come out ?????

Until you tell ( tune ) the computer you have changed the injector size it will continue to add fuel based on the stock inj size

Tuned Performance

iTrader: (92)

vetteoz

iTrader: (13)

I find it better to explain auto tech with analogies rather than baffle newbies with science

Tuned Performance

iTrader: (92)

maybe you should just put it simple bigger hole more fuel !

JordanRAdams

Sorry for the stupid questions, but I guess if you really hated answering them, you wouldn't. I appreciate the advice/answers/criticism.

I'll be getting new injectors, changing the oil, and then taking it to someone who can tune it and burn a new chip. Then I'll find another way to make an *** out of myself with it

Tuned Performance

iTrader: (92)

Just Change the oil install the 19#hr injectors and if its a mild cam you will not need a tune. The nice thing about maf

hellz_wings

iTrader: (2)

Don't be shy to ask questions, after all that's how we learn. That's how I learned what I know today! I doubt anybody dislikes answering questions, but rather it's just that most of us are used to answering more advanced questions or solving more challenging problems. You gotta start somewhere tho

Southbay 19lbs injectors are good. Get those. Your car will run much better. You won't need to tune the injectors if you have 19lbs replacements since that is what the stock size was. Also, make sure to use the best oil you can afford (I use Royal Purple synthetic with zinc additive and it performs great).

So I would say just get injectors, change oil + filter, and get a 48mm TB replacement with new TPS and IAC and it should run very well (provided there aren't any other problems.)

JordanRAdams

That's what I'll do.

Thanks again!

Funny how it went from fast, uneven idle to all this, that's how I found out that the TB was worn.

JordanRAdams

Alright, I said it's got a mild cam. I was basing that on the fact that the guy I bought it from bought 2 different ones, and returned the one in favor of the milder because he thought it would be too much. Now, I'm not so sure. It's got a gross lift of .480/.480, but it has 1.6 rocker arms, so that makes it .512. Is that mild or not? for a bored over 305? Would a dyno test and chip burn be more practical knowing that? I was thinking it was a .32 lift

This is the cam that's in it:

http://www.summitracing.com/parts/CCA-08-302-8/

Stock was .4035, so I guess it is quite a bit larger, but I'm not sure if it's big per se.