Testing for Intake Restriction...
 

Im trying to figure out whether my motor requires a larger throttle body. I read somewhere that if I hooked up a vaccumm gauge to my intake manifold and remove all the ducting in front of the TB and then ran it on a dyno (somewhere the gauge could be watched) that i could tell if there was an intake restriction in the TB. I think the gauge should read 0 at wide open throttle and if there is still a vaccumm then the TB is restrictive.... Is this method correct? Does it rule out intake restriction due to the heads/cam? Has anyone tried this?

That method will work. A vacuum gauge connected to the intake manifold will only show the pressure loss between the filter and the manifold. It will not be materially affected by head/cam losses.

If you have a scanner or scan software, you don't even need the vacuum gauge. A scanner can read "manifold absolute pressure" (MAP), and can tell you what the local barometric air pressure (BAR) is. Vacuum = MAP - BAR.

You also need to pick a specific RPM to take the vacuum (or MAP) reading at, since air flow volume will affect the pressure loss in the intake track. Start by removing the filter, then work your way toward the TB. Of course you can't go past the MAF as far as removing things.

If i went past the MAF to eliminate that from possiblities and allow the car to run on speed density would this method still work?

sorry ddr.. need to ask injuneer a ? and his pm box is full..

Injuneer...Shoebox mentioned your name so i figured id ask ya a ?... How can i make sure i did my cam install right? It runs fine.. i want to make sure there are no internal problems.. How do i do this? I have felpro head gaskets too.. They dont need to be re-tightened do they?



Nick

I guess you could pull the MAF and go int speed-density. Just trying to think if that would cause any changes to things that would affect vacuum, like the timing.

"CoUnTry...."

I emptied my PM box.... its full of nasty notes from people who's posts I move off Advanced Tech, and I like to keep them so I can remember who I don't like to deal with.... :D.

Send me a PM, but I'm not sure that I can answer your questions. Not something I know a lot about.

Fred

Thanks for the help Injuneer, I know its probably the oldest question in the book but would you run larger than a 52mm on a 383 w/ AFR 190 Comp ported heads and a XE 230/236 .544 .555 112lsa cam? Thats what im running right now and i have a feeling im starving the motor,
Dan

Most people with your amount of displacement and heads have a 58mm tb. Hell, people with mildly ported heads with a cam use a 58 as well. Though, i have read somewhere (possibly from posts here, not sure), that someone dyno tested with a stock tb and 58 tb and actualy lost power.....this was done with around stock displacement. What i am basicaly saying is that at your point i doubt there will be any draw back at all with switching to a 58, though the gains from a 52-58 may be small.

I'm running a 230/242 114LSA 0.590/0.590 solid roller on a 381ci motor. 290+cfm LT4 heads. I have the Holley 58mm TB. No MAF.

When we were tuning it on an engine dyno, with all the instrumentation connected for air and fuel useage, we found that the engine reached peak air flow at 77% throttle opening, and didn't really gain appreciably after that point no matter how far the throttle opened. If you work it out, 77% TPP is a little less open area than a 100% 52mm throttle body. So I really doubt you are starving it with a 52mm TB. I understand GM uses the 48mm TB on their 502ci/502HP RamJet crate motor.