After having done all the ultimate mods, full exhaust, no cat, eddy intake, upgraded ignition,1.6 rollers (not on), and every bolt on there is there any advantage using a bigger throttle body???have the afr, and tpi pump.TBI.com stage 2 chip. Seems like it runs out of fuel, and or air the car runs solid `14's now..2400 stall,just reminds me of a motor with too small a carb on it....89 LO3...Thanks for any suggestions..The car has all the good suspension pieces..No AC, no pollution stuff..Oh yes, and a cold air package with ram air.Thanks in advance for any help...Tom Shaw

 

well where does it seem like it need more air above 4500 rpms? the factory heads are holding it back anyway....

 

Yes, it does seem to lay down on the big end....I do have head change plane in the future, but i have a 454 throttle body, and was just wondering if it would be worth the time to change it, keeping my injectors...Could it hurt performance??? Is there chance it could help, even with the lame heads???? Thanks again for any thoughts on this...Tom

 

With a larger TB, the engine will just go to full load sooner, when all is properly tuned. I have a 1000 CFM TB, and I can jamb it all the way open off idle w/o any issues. The engine doesnt really care what causes the air to come in. The only issue you can run into is that it becomes harder to control the engine as at low speeds, 40-50% throttle will result in full load.

With the stock heads, its not worth it yet. With better heads, then you will want to switch over. You may need larger injectors, or more fuel pressure. One driving factor will be AE. The larger throttle body will like to have a lot of TPS AE on tip-in, and a better manifold will want more MAP AE when its cold. These requirements can easily force a smaller set of injectors to 100% DC on transients when AE is active.

 

What do you mean by full load???....Also AE??? Thank you very much for your reply...Tom

 

Basically I mean the manifold pressure going to around 95-100 kPa. At this point, the engine will basically be at "WOT" even though the throttle is not open all the way.

AE is acceleration enrichment. Do some searches. There is a lot of info on here about how AE works with TBI. Much more than I could regurgitate here.

 

One way to tell if your engine needs more air is to datalog the WOT or PE event. You monitor the MAP sensor. Key on read the log, lets say it is 97 MAP. So that is atmospheric pressure. then LOG WOT. Say it is 87 MAP. That tells you a restriction BUT not necessarily in TB. Could be air cleaner.

Not sure if head restriction will cause a lower MAP as map sensor is at TB. Dim can you comment on that Q?

 

Need a cam that actually opens the valves. The moniker 'peanut' referring to the cam in the L03's is being kind.

When it comes to throttle body bore, use a data log to see what level of drop there is. And size the TB accordingly. On a stock cam'd L03, the stock TB is plenty large.

RBob.

 

RBob, am a little scared of the cam changed due to tuning issues...I do have a set of 1.6 rollers tho, that could perhaps help a bit......On my motor tho the pushrod holes are too small, must drill them out......Thanks everyone for the answers, I will look into what you guys say...Tom

 

You wont see this. It will only show up in the VE. You will see low engine VEs at high RPMs (the cam will play a big part as well). Conversely, a good set of heads and cam will produce good VEs. At high RPMs (5000-5600), my combo has VEs of about 95%, which would be an example of heads that arn't a restriction.

 

You should change it. Its tiny. I think the specs are a duration of 190 degrees at the intake. Unless you have LS1 heads + 1.7 ratio rockers on there, your going to have a hard time going past 4500 RPM.

If your changing heads, the pushrod holes will no longer be an issue (your new heads will have different holes/slots cast/machined in). I assume that you currently have the TBI heads that have the guide slots in them?

 

Whats the biggest injectors available these days for TBI ?

-- Joe

 

I think the largest was the mythical 90 pph ones for use in gasohol setups in south america and early BBCs, or so I hear.

The next largest size is 80 pph for the large injectors, and 61 pph for the smaller FWD delphi injectors.

Heres a list of some available:
http://www.diy-efi.org/gmecm/compone...injectors.html

 

Hard as it is to believe the little motor really likes to rev....I will look into a cam change...I have a B body LT1 laying around.....Wonder how that will run with the Chip I currently have in the car?? TBI.com Stage 2...Thanks again everyone.....Tom

 

Cool. So yeah, 4bbl TBI is the way to go to support 500+ hp cars.


-- Joe