Inlet length tuning

[tpepmeie]

Little slow this weekend, so I thought I'd share some simulation results of various intake lengths. The stock runner length is a little long, but offers a very good torque curve, yet still allows peak power at 7000 rpm. Here is a simulation showing volumetric efficiency of my 427, using the stock inlet tract length. The green line is volumetric efficiency.



Volumetric efficiency peaks at 6400 rpm, and 5200. The latter being close to the torque peak.

Here is a simulation with a very short runner, sheetmetal type intake. Runner length is some 4.5" shorter than stock. VE peaks at 7200, and again at 6100. The overall peak VE is substantially lower, about 7.5% less. In this config, I would expect hp to peak around 7500.



And here are the two graphs on top of each other.



To better isolate the intake tuning peaks, I have performed this simulation with a "stub" exhaust length, rather than full headers. The headers and collector would smooth out the troughs, and pick up VE by about 3 pct at peak.

So what does it all mean? We'll the stock intake length is about the best for a peak power speed at 7000, although even the best ported setups have at least 20-25cfm flow loss. If we could get the minimal flow loss of the fabricated manifold, but the tuned length of the stock system, that would be as good as it could get.

Todd

[Paul Workman]

Originally Posted by tpepmeie

Little slow this weekend, so I thought I'd share some simulation results of various intake lengths. The stock runner length is a little long, but offers a very good torque curve, yet still allows peak power at 7000 rpm. Here is a simulation showing volumetric efficiency of my 427, using the stock inlet tract length. The green line is volumetric efficiency.



Volumetric efficiency peaks at 6400 rpm, and 5200. The latter being close to the torque peak.

Here is a simulation with a very short runner, sheetmetal type intake. Runner length is some 4.5" shorter than stock. VE peaks at 7200, and again at 6100. The overall peak VE is substantially lower, about 7.5% less. In this config, I would expect hp to peak around 7500.



And here are the two graphs on top of each other.



To better isolate the intake tuning peaks, I have performed this simulation with a "stub" exhaust length, rather than full headers. The headers and collector would smooth out the troughs, and pick up VE by about 3 pct at peak.

So what does it all mean? We'll the stock intake length is about the best for a peak power speed at 7000, although even the best ported setups have at least 20-25cfm flow loss. If we could get the minimal flow loss of the fabricated manifold, but the tuned length of the stock system, that would be as good as it could get.

Todd

Question for ya Todd... Is this model run with stock cross sectional runner areas, or cross section dimensions you now have?

P.

[tpepmeie]

Originally Posted by Paul Workman

Question for ya Todd... Is this model run with stock cross sectional runner areas, or cross section dimensions you now have?

P.

Its my current configuration. Different areas won't change the location of the peaks, but may change the strength of the pulse. Taper, on the other hand, will change the effective length. More taper = tunes like a shorter runner, but loses a little strength.

[Pete]

Originally Posted by tpepmeie

=
So what does it all mean? We'll the stock intake length is about the best for a peak power speed at 7000, although even the best ported setups have at least 20-25cfm flow loss. If we could get the minimal flow loss of the fabricated manifold, but the tuned length of the stock system, that would be as good as it could get.

Todd

Todd,stacks might be a happy medium

What was the loss with the sheet matel intake?


Pete

[tpepmeie]

Originally Posted by Pete

Todd,stacks might be a happy medium

What was the loss with the sheet matel intake?


Pete

We'll find out soon. I have to pack it up with a mile of bubble wrap and send it out for testing. The sims above suprised me a little. Granted, I did not account for the added flow from the fabricated manifold, I was only trying to account for the runner length. Maybe I'll try that today. ... Just tried it with zero flow loss on the fabricated manifold, and it made little difference. picked up the curve by about 1% VE, but still well behind the longer intake. Appears that wave tuning is more important that outright flow.

[XfireZ51]

Todd,

THanks for sharing that information. What would you speculate is the effect of siamesing the runners?

[tpepmeie]

Originally Posted by XfireZ51

Todd,

THanks for sharing that information. What would you speculate is the effect of siamesing the runners?

Siamesing, in our case, has the effect of increasing cross-sectional area. I would expect pulse strength to be reduced. The Gen II LT5 and import 4-valve heads had siamesed runners, but were designed that way...therefore the overall cross section was controlled using one mono-runner. In our case, the port spacing was set using 2 separate runners, so siamesing from there results in really big cross-section areas, IMO.

[4DSZR1]

Question

When you talk about intake runner length and tuning and the importance of it when looking at torque and HP Is this why some of the old hillborne injection systems had the tall stacks?

Thanks

Rick

[flyin ryan]

Originally Posted by 4DSZR1

Question

When you talk about intake runner length and tuning and the importance of it when looking at torque and HP Is this why some of the old hillborne injection systems had the tall stacks?

Thanks

Rick

To a degree, Yes.

[tpepmeie]

This time with full length headers and exhaust, and showing the effect of Flat Plane crank 180 degree firing order. You can see VE and BMEP up almost across the board. Std firing order is the plain line.