LS4 Intake and Exhaust Modification
Thread Starter
Joined: Feb 2010
Posts: 906
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From: Champaign, IL
LS4 Intake and Exhaust Modification I picked up a couple more LS4 dropouts for 2 more Fiero swaps. One will be an auto, the other a manual, but both will keep the stock LS4 intake and exhaust from a cost/simplicity standpoint.
I have been a large advocate of the stock LS4 intake and rear exhaust manifold being crap, but I am curious how much potential there is for some low cost gains to them (they still probably will not be as good as an LS6 or headers, but will be much, much cheaper as well).
The intake just needs the OPSU relocated to the oil pan cap off plate, the boss trimmed down some, and the notch opened up to increase air flow. It won't help the plenum volume issue, but should provide some hp increase on a stock camshaft LS4:
The rear exhaust manifold could be cut open and have more metal welded in to make the runners larger. The portion where the 5 cylinders flow through is about 14% smaller than the main log on the front manifold with 4 cylinders. Also, the rear 2 cylinders run through a log that is 16% smaller than the front one after 2 cylinders.
Thoughts?
I have been a large advocate of the stock LS4 intake and rear exhaust manifold being crap, but I am curious how much potential there is for some low cost gains to them (they still probably will not be as good as an LS6 or headers, but will be much, much cheaper as well).
The intake just needs the OPSU relocated to the oil pan cap off plate, the boss trimmed down some, and the notch opened up to increase air flow. It won't help the plenum volume issue, but should provide some hp increase on a stock camshaft LS4:
The rear exhaust manifold could be cut open and have more metal welded in to make the runners larger. The portion where the 5 cylinders flow through is about 14% smaller than the main log on the front manifold with 4 cylinders. Also, the rear 2 cylinders run through a log that is 16% smaller than the front one after 2 cylinders.
Thoughts?
Better off just capping the rear manifold to crossover port and welding a true y after the rear port.
As for the intake, moving the opsu to the cover is sketchy. The oil pressure readings off that threw codes for me.
Here's what I did
And where I started porting the inside
As for the intake, moving the opsu to the cover is sketchy. The oil pressure readings off that threw codes for me.
Here's what I did
And where I started porting the inside
