head porting flow

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CrashCade

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Mar 28, 2007
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so i just got my stage 3 head back for my 12v from laroy engines and the flow numbers are out of control. i have 230 CFM of exhaust flow out of each cylinder, the intake is flowing 210 CFM through each port. i had a custom triple intake horn made and a step header. the point im getting at is, am i going to drop in boost numbers since i have more flow over stock. i am running a GT4202 if that helps at all. thanks
 
yes boost will drop it is the measurement of the build up of pressure which is due to the restriction of the intake ports.
 
What was the valve lift at when they got those numbers?
 
the lift was with the stock cam numbers at .300 lift. the higher the lift the exhaust flow started to drop. so im just staying with the stock cam. the step header goes from 2'' tubing at the exhaust port stepping down oin size a few times to 1 1/2" to create a turbulance effect. more pressure at the turbo to spool faster
 
CrashCade said:
so i just got my stage 3 head back for my 12v from laroy engines and the flow numbers are out of control. i have 230 CFM of exhaust flow out of each cylinder, the intake is flowing 210 CFM through each port. i had a custom triple intake horn made and a step header. the point im getting at is, am i going to drop in boost numbers since i have more flow over stock. i am running a GT4202 if that helps at all. thanks
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That's their stage 3? (230 exhaust and 210 intake)

You mentioned the 230 was at .300 of lift. What was the 210 @

Seems a little low.
 
the intake was at the same lift. the intake might be more, i cant remember what he said. i will find out. i will take some pics as soon as the part has a patent. laroy engines will be building the triple intake horn to sell after we work some more bugs out for the 12v. they are working on building one for the 24v also.
 
the step header goes from 2'' tubing at the exhaust port stepping down oin size a few times to 1 1/2" to create a turbulance effect. more pressure at the turbo to spool faster
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how does that work out for port matching?
 
CrashCade said:
the lift was with the stock cam numbers at .300 lift. the higher the lift the exhaust flow started to drop. so im just staying with the stock cam. the step header goes from 2'' tubing at the exhaust port stepping down oin size a few times to 1 1/2" to create a turbulance effect. more pressure at the turbo to spool faster
Click to expand...

wouldent the step down hurt your top end performance? and about the cam lift I would think more lift would help the flow not hurt it?
 
as far as the exhaust tubing diameter goes, It should match the port outlet and remain constant until merge/flange/etc.
 
In the gas motor world you don't limit the valve lift to where a head stops increasing flow numbers. I don't think it would be any different in the diesel world. Just food for though:)
 
Hurley said:
as far as the exhaust tubing diameter goes, It should match the port outlet and remain constant until merge/flange/etc.
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thats what I was thinking makeing it smaller should help spooling but would cause you to lose top end and make more heat.
 
NickTF said:
In the gas motor world you don't limit the valve lift to where a head stops increasing flow numbers. I don't think it would be any different in the diesel world. Just food for though:)
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well, if the numbers actually started to drop, it's not beneficial to open it furthur, but you have to look at area under the curve... sometimes you sacrifice some flow at the peak of the lobe to get more area under the curve due to ramp rates.
 
Hurley said:
as far as the exhaust tubing diameter goes, It should match the port outlet and remain constant until merge/flange/etc.
Click to expand...

have you tested step-up, step-down, and constant diameter headers in a turbo application so see which performs best?
 
Forrest Nearing said:
well, if the numbers actually started to drop, it's not beneficial to open it furthur, but you have to look at area under the curve... sometimes you sacrifice some flow at the peak of the lobe to get more area under the curve due to ramp rates.
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Area under the curve is exactly why you lift the valve past the point of no gain on the flow bench. Remember, duration at peak lobe lift is very small which is why it's typical to see cams lift valve past the point where a head stops showing additional gains on a flow bench, to increase duration at that peak flow point.

I had some c5-r heads which flowed 370 cfm at .650. Erik Keonig, instructor at School of Automotive Machinists, flowed them and assembled most of the long block these heads went on and indicated the heads were not done at ..650 even though the flow bench showed a small drop past .650. Cam we ran in this motor had .750 lift, made around 750 hp naturally aspirated on pump gas at 434 inches below 7500rpm, not too shabby. The flow bench does not tell all. :Cheer:
 
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