I am ordering the rest of the parts needed to convert the alcohol BBC in my race car to EFI. Any reason not to go with a 2000CFM TB? I am probably using a Holley. I can get these at a very good price and the two choices are 1000 and 2000CFM. The motor is a mild 60 over 427 turning 6,500rpm. So, it doesn't need a huge amount of air. However, I am also building a new motor for the year after next that will be in the 550ci range turning ~7,000rpm. It would be nice to buy this once and not have to get another one next year.

Thanks for any insight.

Rich

 

I don't see any reason not too... the TB doesn't need a minimum vacuum to get any air fuel atomization.

Bret

 

That's what I am thinkin'. About the only downside I could see would be a sensitive throttle at small opening angles. But for a race car this wouldn't be relevant, I suppose.

Rich

 

Aren't there just 2 throttle positions? Closed and Wide Open?

You could always put (benign) "tumors" on the back side of the throttle plates like GM did on the 4.3 V6 which used the 5.7 L TB. I'm only half kidding. Look at a 4.3 TB. On your mild engine you could use "tumors" to adjust the total CFM and tip-in, and remove them for the wilder engine. Some clay and a few hours on a flowbench and you could probably tune the flow vs. throttle position fairly well. Sounds like a fun winter project.

Just a thought.

 

Too bad there isn't something like those venturi sleeves you see on those Demons.

 

Ive got a 90mm on my 383. Only problem is have is that it lets in so much air so fast, the car goes lean. Havent had any luck tuning it out.

Im sure an aftermarket EFI system would be better at this since most I have seen have a delta TPS and delta map tables, which dont exist in the lt1 computer. I would just make sure your EFI system has similar tables in it.

 

I came across this the other day. It's about carbs but TB is the same thing. It's how much air gets into the engine. When I built my engine I went with 2 850's instead of one large carb.

http://www.truckpulls.com/Carbs_How_Big_Is_Too_Big.htm

 

Well, there are a lot of differences between a carb and a TB. The TB doesn't need a vacuum signal, which is the primary reason a carb can be too big. The point of the question was to find out if people were aware of any other reasons.

On a related note, why are TB's so expensive? I was pricing them out tonight. Holley sells their Dominator (4500 base) TB's for very little less than they sell a complete carb. This makes no sense to me. After all, the carb consists of a TB PLUS a lot of other stuff. I am a little tempted to make my own TB out of an old carb! Turn out I can get an ACCEL (1550CFM) for just a bit more than $500, about $300 less than the Holley. I may go that route.

Thanks for the opinions so far.

Rich

 

On a side note to what I posted above about throttle tip in issues...

Many of the 4bbl type throttle bodies i have seen have a progressive linkage that acts much like the old secondary carbs. So light throttle you run off 2bbls and WOT you get 4bbls. Should help lots with throttle tip in issues. I didnt mention it first because my mindset was stuck on large single bore TBs.

 

Rich, I have run 2-1060CFM 4 hole TB's on a 408 with no issues. It drove fine. The 4 holer's will make it have better manners on the street vs a mono blade. They were not progressive.Tried it with one 1060 and it didn't run up to par but 2 woke the b**** UP. It was a trailer queen that ran in the mid eights with hose, low 9's on motor,but it has been street driven.
Did ya look at Ron's Fuel?

 

No, but thanks - I will. This is for a race car, so the tip in issues may be irrelevant. The ACCEL is a monoblade with progressive linkage. The Holley is remarkably like the TB from a Dominator carb! Which is why the price ticks me off.

Rich

 

Jared,

I think you found your problem. The linkage, or the mechanical portion of the throttle response might be the problem. A throttle cam like the one on the side of the stock and aftermarket LT1 TB's is probably the issue.

Bret

 

Bret-
Ive got a stock LT1 throttle cam on there right now. But i think you may be onto part of the problem too. How is the orientation of the lobe going to effect things? Im having a hard time picturing it in my head right now.

Heres a pic of how i did it. To be ideal it would need to be turned 90* clockwise right? Will that effect that delta TPS to slow it down?
http://home.cinci.rr.com/atljar/Intake/PICT0052.JPG

 

I think your close now... at least that's what a LS1 TB looks like. Funny thing is they dont have a issue with a 90mm TB with the same throttle cam.

It also could be the orientation of the IAC too... there are a lot of odd things with the accufab compared to the LS1 stuff.

Bret

 

A lot of the LS1 guys i have seen have tip in issues with the 90mm TBs. They however have some tables that I dont have that allow them to fix it. :/

Thanks for thinking about it though.