please discuss

how can a bigger TB hurt?

i'm tired to al this speculation in LT1 tech
lets get an advances answer here

 

Yes too big of a TB can hurt a NA car. However I am pretty sure it cant hurt a boosted car.

 

CAN WE GET MORE OF AN EXPLANATION PLZ

the only logical thing i can think of in my head and visualize utizilizing my inutituion , is that bigger TB = less velocity

maybe deprive back ports of air in high rpm driving?

 

Way too big hurts driveability. Imagine a 102 mm LT1 TB bores which flow about 4 times as much air as a 48/52 mm bores. At highway speeds, it would only take a fraction of a degree of blade rotation to make a big airflow change. Your right foot or your cruise control would go nuckinfutz trying to hold a steady speed, and traffic driving would be challenging.

If an engine actually eats 800 cfm at max power, a TB which flows 1000 cfm or so @ 1 in. Hg. will probably produce max power. More TB won't increase power, but neither should it reduce it. It will be harder to get a good idle also.

To paraphrase the old saying, anything more than what's useful is wasted. Well, maybe it looks good to the other guys!

 

This has been discussed ad nauseum in LT1 tech. Examples were given.... stuff was debated and good points were made. Might want to search but I recall you participating in those discussions.

Velocity through the throttle body...... well it's always gonna be high at slight throttle. So what are we talking here.... WOT?

I agree with OS on the drivability issue. I don't think the throttle body is gonna make some magical hp gains if it's not needed but if the current system is a restriction then yeah..... rocket science says we're gonna see a gain with less restriction.

-Mindgame

 

how can i "figure out" how many cfm i need

 

Drivability issues aside, it's probably less of a sin to put too big a TB onto an FI motor than too big a carb onto a carbureted motor. TB is is just an "air door". A carb you also have to have sufficient velocity through the venturis to generate enough booster signal (vacuum) to pull the fuel out of them cleanly and evenly to get it well atomized, even if you whack the pedal to the carpet at low RPMs (or suffer a bog and other tuning headaches). TB/FI: not nearly so much of a problem from low velocity since the fuel is mechanically squirted in under pressure from the injectors downstream.

I'm no expert on the subject, but I thought I'd throw that in since the questions about too big a TB seems to spring from the old question about too big a carb. The two situtions aren't quite that directly comparable.

 

Trey,

Aren't you an engineering student?

CFM = rpm x displacement / 2 x 1728

or CFM = rpm x displacement / 3456

Then you calculate the velocity through the throttle body bore and determine at what velocity a restriction occurs. Covered in the "other" threads.

-Mindgame

 

my intuition told me that... but i doubted it

for some reason i thought it would be max intake flow x4 or x8 or something


Shibby

this is what almost got me failing phys-
i knew the answer, tried to do it in his BS way and got it wrong every time
edit:

where does 3456 come from?

 

HP and TQ gains have been proven many times over with the larger TB.

Large TBs make tip in brutal at times but I am working on a throttle cam to ease this problem. for those who can not wait TPIS has a new TB with new design.

I can count how many times I have had to stop and explain to people that you can not go to big on the TB with a port injected car. There is no need for High velocity over any of the sensers. There is no ventury velocity needed like in a carb to get the right mixture.

As long as you have correctly tuned your car you will benifit from the TB. Your TB is more of a restriction then your MAF and everyone on earth seems to be hacking the hell out of those LOL

Chris Bennit(sp), Jordon Musser and my self have all show VERY measurable gains with larger TBs.

 

Ellis can you further on these points?

 

If bigger is better (I’m not saying it’s not, just why and how much?)…….. Then exactly what are the hp gains at what level engine, what level TB? Does anyone have objective dyno data or corrected 1/4th mile documentation?

The world is black and white. The only reasons you see shades of gray, is because someone hasn’t figured out how to measure it yet.

FYI…. Documented gains/subjective losses I’ve seen:

On a bolt on LT4 making 331 rwhp, there were no gains in a 58mm TB over 48mm TB even after computer/dyno tuning.

In a 398ci solid roller engine, I personally saw no gains from a monoblade over a 58mm TB. But….. I’ll also admit there were other problems that interfered with the engine making power.

Downside to a monoblade…….. I experienced very quick initial throttle opening making low speed maneuvers a bit tricky over a 58mm TB..

Believe me, wish I could say I did see gains. How about some objective data from those whom did!

 

Not to flame, but I see why you might be having some trouble in physics. 'Game's equation was the theoretical cfm needed to feed an engine @ 100% volumetric efficiency with the units corrected.

rev/min X inches ^3 x 1 intake stroke/2 revs x 1 ft. ^3/1728 in.^3 = ft^3/min (CFM)

revs cancel, inches^3 cancel, and 1728 is 12^3. The 3456 was the (2 x 1728) below the line. What's left is CFM. I hope they are teaching that kind of stuff in physics nowdays. If you can't do the "units" correctly you won't get the correct result.

So, as an example, a 383 peaking power at 6200 at 100% VE would consume 6200 x 383 / 2 / 1728 = 687 CFM. That doesn't sound like much, but CFM is normally rated (for 4-bbl carbs anyway) @ 1.5 in. Hg. pressure drop and that engine is probably running a 1.0 to 1.2 in. Hg. Using the 1.0 in. Hg., you'd need a carb or TB rated at least 22% more (square root of the pressure ratios, if you are curious) or about 840 CFM @ 1.5 in. Hg. to flow 647 CFM @ 1.0 in. Hg.

As others said, going somewhat bigger on a TB ain't bad like it can be with a carb.

 

My car went quicker with a 52mm throttle body, and my junk was stock heads/cam/bottom end. Didnt care what a dyno said, my car was faster...2 tenths and 2 mph. Also picked up the same amount on 3 of my friends cars too. If I had a bolt on car to do again, I would really want to see if the 58 was any better or worse, since I've yet to see that anyone has proof other than in an equation.

 

come on now "ace"
I only have 28 credits, i dont think technically a sophmore yet