LO3 91 RS 305 TBI

Im limited in a lot of things, mostly EFI knowledge.
Ive looked and looked for a new throttle-body and easy mods to do for this puppy but to no avail. I called TPIS and they said the 52mm TB was too much for my 305...is my present TB a 42 or 48mm?

I live in CA so SMOG OK is a must...

im inquiring on replacing the TB with a more efficient one, or perhaps the injectors (how difficult is that?) what kind of performance gain can i expect from these respective changes?

TIA

 

Two totally different animals brother. You've got throttle body injection which sits up on top of your intake manifold like a carb. You've got two large injectors firing fuel into a normal intake where it then travels down the 8 runners into your heads.

The different sized throttle bodies that you are referring to are for Tuned Port Injection; which injects fuel directly through 8 injectors to each separate intake valve. The throttle body for a TPI is the air metering device which contains the butterflies (or butterfly as the case may be) - again, you can't swap between the two types as they are completely different.

However, you COULD swap a bigger TBI setup on your engine - just not sure it'd be needed on a stock 305. I think school is still out on that one...

Steve

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Steve's Trans Am Temple

 

thanks for the lesson Steve, but as i said TBI is what im looking for, im familiar with the semantics of it, just cant find much of anything to do with TBI other than the articles listed on this site (radius drilling, dremeling out the edge, and a spacer)

go with bigger injectors? what does anyone recommend?

I plan on taking it apart and ChemDipping it so what can be done while its dismantled?

 

a site for you to check out is www.turbocity.com

they have some tbi product lines

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91 camaro RS
- 305 TBI
Mods: Performer TBI intake, 1" TBI spacer, K+N, jet fan switch ,160 thermo,Accel control module, Jet Stage 2 chip, edelbrock TES headers, Compleate 3" Flowmaster exhaust, Edelbrock springs, KYB struts and shocks, 700R4 built by TSI, SLP tq converter, b+m trans cooler, white guage faces, megashifter..
next month: spohn LCA's and panhard rod, BMR relocation brackets,posi 323 , lt1 cam and new valve springs

 

What have you done to increase air flow to use the extra fuel that injectors would provide? Headers, exhaust, intake, cam, heads, what?

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91 RS 5.0 TBI....LT4 cam....Edelbrock headers....3"Dynomax exhaust....5spd.... 3.08.....Ultimate tbi....afpr...ZR 255-50's...Koni's

 

thanks for the responses

I checked turbocity out and noticed a few things like spacers and such..thanks

As far as mods

Headers, original cat, edelbrock muffler (3" system)

no engine mods at all, just the headers and exhaust. I do plan to get an adjustable fuel-pressure regulator so i can make any necessary changes.

no cams, intake manifold, heads, or even dress up valve covers!

my JET Stg-2 just showed up, along with a lowtemp stat,
-as of right now im going to increase spark gap to .045 or a bit lower, install the low temp stat, and the chip.

[This message has been edited by TBIfly (edited October 25, 2001).]

 

Only increase spark gap if you've got a better than stock coil. If the coil is stock then don't think it'll like having such a far gap under high rpm with load. Keep it where it is until you get a new coil.
Don't bother with the metal TB spacers, just the injector spacer! The TB spacers are only good for gas milage, some tuning, and for keeping away the heat. Make your own from a kitchen cutting board plastic (just test to make sure it doesn't react to gasoline).
The cheapest and best mods for a 305 TBI:
open element, exhaust work like headers, fuel pressure reg, injector spacer. That along is good for low 15's with a 5 speed. Next mod would be gears. Next I would do an intake manifold and Lt1 cam swap at the same time. Done, that's as far as I personally would go with a 305. Now if you want to be different like Tim, Brian Felts, and Camaroracer1992, keep going onto heavy suspension and traction mods. Then get heads

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, Jon (350 TBI!)
91 Red My website

 

Thanks Jon, that was one of the more direct and crack-free responses i have seen posted, especially for us rookies


I have the coil, so i will fiddle with the gap a bit, and find a liking, im just gonna hit .045 and leave it i think.

Im working on full suspension redo now, just installed the chip and 160* stat....definitely more power! it was a JET Stage 2

Thanks again JP

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not fast....not pretty....but has great potential for both.

 

Word has it that you can install a Holley 670 TBI unit on there with minimal work. You'll need a new TBI manifold for it's 2" bore though, and some special connector to make one of the wires plug in, and maybe a little computer reprogramming if you stick with the bigger injectors.

These go for about $300, and I would think it'd make a pretty big gain, especially if your engine is going to be heavily modded.

As far as emissions legality, it would retain all your smog equipment, so I guess it'd be legal in CA. I doubt they'd even be able to tell.

Jason

[This message has been edited by 89BlwnRs (edited October 25, 2001).]

 

JP you said and LT1 cam and intake? What intake's do you have in mind? I'm pretty much doing what you have said. I just need to install my 3:42's/torsen and choose an intake. I'm hearing from some that the Performer RPM intake is too large for the stock TBI/TPI heads and some have hood clearance problems.
Thot's?

Thanks

Darrell


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91 RS 5.0 TBI....LT4 cam....Edelbrock headers....3"Dynomax exhaust....5spd.... 3.08.....Ultimate tbi....afpr...ZR 255-50's...Koni's

 

Yes, hood clearance is an issue with the RPM intake. I've tried everything and there is no way I can fit a 14x3. I have to modify my adaptor plate to give the "ramp" of the carb mounting surface more of an angle. This angle should look more like the angle on the hood, this is how I plan on making mine fit under the stock hood but it's just a PITA.
So with that said and yes, stock TBI heads are pretty bad for intake port flow. They love N2o but what head/engine doesn't .
I'd go with either a holley low profile or performer intake. Tim (NJSpeeder) got his car into the low 14's with his stock Lo3 cam and edelbrock heads.
If you plan on going to a cowl hood and a lager engine or one with more hp say ~250+hp then an RPM intake might be better in the long run. The RPM intake is a great design, I love mine and Brian likes his too. My friend has the air-gap RPM on a built 327 with a 600 double pumper making 370hp with Dart Iron Eagle heads. His limitation isn't the intake manifold yet, it's the carb and cam. So I would have to say that the performer is a good choice for under 300hp and under 350ci staying a daily driver.
The Lt1 cam is better matched with the performer anyways. The best part about the Lt1 cam is it's cheap, it's a roller, and it works well with the Lo3 in general.

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, Jon (350 TBI!)
91 Red My website

 

JP you seem to be well-versed in this area.

I presently have a 4" cowl so clearance isnt really an issue...

Im considering the Performer TBI intake (edelbrock) and a Comp Cam's Compucam. All is stock with regards to engine and throttle body, as i have come to understand it, my present throttle body bore is 1 11/16" (just a halfwitted guess). What intake do you recommend if i were to stick with the stock TB..or should i opt for a different intake than the Performer and try out the Holley 670 idea?
thanks Jon
blain