Ok I've scoured the past 6 years of cz28.com's posts concerning 58mm use on NA 350 LT1 applications. And I have yet to find someone who posted actual dyno results comparing the two. Everyone has an opinion. And yes the calculations show a 52mm is plenty for a H/C LT1. There are a few guys showing increase in track times, they didnt elaborate on temp, same track, variables, etc, so thats not a controlled test. Lingenfelter has a 58mm TB on their Heads/Cam LT1 350 package. Now why would lingenfelter use a 58mm when a 52mm is is cheaper and just as good? Question to ponder.

Now I have a 52mm TB on my car with a gasket matched to head intake manifold. Im about 2 seconds away from buying a 58mm and ported intake to resolve this debate by dynoing them back to back. I'm happy with my power but I'm wondering if my relatively flat HP peak is a result of inadequate air supply.

If anyone wants to lend me one that would be great too. I'd pay for shipping and give you a collateral deposit or something.

 

I used this formula:

http://www.csgnetwork.com/cfmcalc.html


As for a dyno result, none to date...

 

I'd be interested in the results just to end the debate. I couldn't find any solid information either when I wanted to upgrade from my stock 48mm, so I just bit the bullet and got a 58mm AS&M. Let me know what you have in mind for collateral and maybe I'll send mine over for a dyno test. I've even got a stocker 48mm and air foil I could send over.

-Dustin-

 

Bersaglieri that would be great if you could. I dyno shop a couple miles from my house and they charge me next to nothing for pulls... 10 bucks a pull.
My LT1 is probably one of the best test engines we could use since every single mechanical piece is basically new, along with the fuel system and ignition system. No tuning issues and no exhaust leaks... so results should be very accurate for H/C package. I'll have to port my intake bore to a 58mm or pick up a similar intake (gasket matched). Would rather port mine to keep things very consistent.

 

Only concern though is that ASM has different port positions than the Holly, BBK, Edelbrock, and Summit. The ports are off center I guess compared to the others. This might be a concern when matching it to intake that I port prior to borrowing or purchasing a 58 tb.

 

bolted it up to my 58mm ported intake tonight and it looks fine. I guess I'm not following what your saying? A guy in Texas ported my intake, didnt say anything about AS&M being a problem.

-Dustin-

 

Check you pm. I'll see if i can get a loaner ASM 58mm from ASM today but if not I'd like to use yours.

FYI for those following this. I will be doing a controlled experiment. Pictures will be taken, a write up will be done, Data master logs will be available, dyno graphs will be shown, all variables kept constant.

 

We ran my stroker on an engine dyno, measuring air and fuel flow. At 496 flywheel HP, the engine was getting adequate air flow through my 58mm Holley TB at only 77% throttle position. Opening the throttle further did not increase air flow. If you work backwards, using the square of the diameter, it would appear that a 52mm TB would have provided enough air for my engine.

Its a matter of pressure loss through the orifice, represented by the throttle blade diameter. Making the diameter larger will always reduce the pressure drop, but you reach a point of diminishing returns, where the tiny difference in pressure loss does not materially affect the air flow.

 

IMHO the larger throttle body has less air speed going through it at WOT and that allows for the air to makes turns easier. This also allows for better air distribution among the cylinders in the smaller than desirable LT1 plenum. The air has a tendancy to rush to the back of the plenum. Anything you can do to help the situation is a plus.

 

Why would you think that? The air is pulled through the TB by cylinder vacuum. If it was pushed in as it would be by forced induction then I could see what you mean.

What goes on in an intake manifold is pretty dynamic...Air flowing in many directions, suddenly stopping, reversing direction, etc....

 

Let's just say air has mass and wants to go straight. It is the atmospheric pressure that is pushing the air into the plenum when the pistons create a depression.

 

I'll be receiving a 58mm TB from ASM next week for testing.

Also found this article in GM high tech. But they installed 1.5 roller rockers at the same time they installed the Summit 58mm tb
http://www.gmhightechperformance.com..._manifold.html

 

My datamaster findings with 52mm vs. 58mm Tb and Lloyd Elliot Intake porting:

52mm stock intake - MAP reading 94kPa at WOT until reaching apprx. 5500rpms then MAP would drop to 89 and 90kPa up to 6300 RPM's gradually.

Holley 58mm and Lloyd Elliot ported Intake - MAP readings stay at 97kPa all the way up to 6000RPM's with a slight dip to 95kPa up to 6300 RPM's.

Unknown on what the hp differance is but I did pick up 3mph in the 1/8th with this and some skinnies up front compared to street tires on a mail order tune. I'm sure once I get my tuning squared away and get a good run at the track this spring I'll see better times still.

 

so the 3mph.. was it at the same track? same temperature out?

Also Lloyd recommends a monoblade TB on his LE3 set ups per his website where according to the math a 52mm is enough.

 

Air sure does have mass...a 1" x 1" column 60 miles high weighs 14.7 pounds.

The atmospheric pressure you have pushing it is pushing it towards the area of lowest vacuum. There isn't any obvious reason why the are wouldn't follow the path of least resistance. Anyway, I guess this test will prove it out.....

Peace.