Effect of increasing plenum size?
Effect of increasing plenum size?
(OP)
I have an engine that I've done the following on-
airbox
ecu
cams
ported head
headers
high flow cats
exhaust
This has brought the HP/TQ at the wheels from 201/198 stock with a redline of 6500 to 249/232 currently at a redline of 7300.
There are no other commercial parts available to get anything more out of this engine. The porting of the head gained nothing in real life even though the flowbench #'s seemed very promising.
The only other thing I can think of to do is modify the intake manifold.
The intake manifold is plastic with a normal plenum feeding long runners and a valve that opens a secondary short set of runners to another plenum/resonance chamber at around 4300.
This 2nd set of runners/resonance plenum doesn't bring in air from anywhere, it just changes the pulse of existing air that still comes through the long runners.
I've picked up a spare manifold and the only modifications that can be done to it due to design and fitment would be to cut the tops of the plenums and increase the chamber size.
Any thoughts on how much larger I should go VS the factory considering the engine is making 25% more power and reving 800rpm more?
Should I just enlarge the main upper (real) plenum or also include the resonance chamber?
airbox
ecu
cams
ported head
headers
high flow cats
exhaust
This has brought the HP/TQ at the wheels from 201/198 stock with a redline of 6500 to 249/232 currently at a redline of 7300.
There are no other commercial parts available to get anything more out of this engine. The porting of the head gained nothing in real life even though the flowbench #'s seemed very promising.
The only other thing I can think of to do is modify the intake manifold.
The intake manifold is plastic with a normal plenum feeding long runners and a valve that opens a secondary short set of runners to another plenum/resonance chamber at around 4300.
This 2nd set of runners/resonance plenum doesn't bring in air from anywhere, it just changes the pulse of existing air that still comes through the long runners.
I've picked up a spare manifold and the only modifications that can be done to it due to design and fitment would be to cut the tops of the plenums and increase the chamber size.
Any thoughts on how much larger I should go VS the factory considering the engine is making 25% more power and reving 800rpm more?
Should I just enlarge the main upper (real) plenum or also include the resonance chamber?





RE: Effect of increasing plenum size?
The trade-off of increasing plenum size is slower throttle response.
Depending on the means at your disposal you can either experiment with hardware, or model the engine in software, and iterate to find the solution you are seeking.
RE: Effect of increasing plenum size?
Yes I am aware of runner length and diameter tuning, but as mentioned above due to packaging there isn't anything I can do to that.
To simplify it, basically I just want to know if enlarging the plenum sizes alone will have a positive benefit. I am OK with slower throttle response and possibly a TQ loss at one RPM as a trade off for a gain elsewhere..
RE: Effect of increasing plenum size?
Quick suggestion, put a small housebrick in the current plenum and see if it degrades the performance. If not then a small change in plenum volume is not significant.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Effect of increasing plenum size?
Larry
RE: Effect of increasing plenum size?
on the air flow to the head, we have done a fare amount on airflow work on plastic intake/plenum and found as much as
20% restiction to flow so it may pay to test yours before you get to plenum volume.or make any radical change
RE: Effect of increasing plenum size?
Larry
Larry Coyle
Managing Partner
Cylinder Head Engineering, LLC
CNC Porting
De Soto, KS 66018
RE: Effect of increasing plenum size?