: 4.0 cam swap/exhaust size



Aurora By Olds
03-09-04, 12:46 AM
I finished swapping the stock LD8 cams back into my 4.0 last weekend. It was pretty easy with the nice set of details I made to hold the cam gears in place.
I installed the 4.6L VIN "9" (L37) intake cams when I did my headgaskets about 2500 miles ago. Just as bbobynski said, the torque basically disappeared with those cams. I had quite the HP gain right on top, as it would set you right back at WOT. I also have the 3.42 final drive ratio, which made things all that much worse. With the stock cams back in it, I can actually pass cars and leave stoplights without having it right to the floor all of the time.
I also noticed a huge gas mileage loss (well about 4 mpg) as well as rougher cold starts and sluggish light throttle acceleration with the L37's.
If you're looking for 4.0 performance mods....go to a 4.6. If I had one, i would toss it in today, unfortunately, when I gaskets were bad, all affordable used 4.6's seemed to magically disappear. I would also like to upgrade to some 3.71 final drives too, that would make quite the difference.
So for now, I was wondering what any of you would agree on for the perfect size exhaust for the 4.0. It will be manifold back, as I am ditching the cat (Yes, I know its illegal and everyone will die from my fumes, so spare me the pep talk). I was going to run true dual 2" with one delta 40 series flowmaster for each side, but after I got to looking at it, it is going to end up being way too much work just to be able to say I have true duals. That, and the bends I will need to fit them both in will probably inhibit too much flow anyways.
So what I would like to do is run a singe straight pipe that Y's off to dual mufflers out the back. I dont care how loud, I just want the best performance. Any suggestions for pipe size, mufflers, or anything else?

BeelzeBob
03-09-04, 01:05 AM
I finished swapping the stock LD8 cams back into my 4.0 last weekend. It was pretty easy with the nice set of details I made to hold the cam gears in place.
I installed the 4.6L VIN "9" (L37) intake cams when I did my headgaskets about 2500 miles ago. Just as bbobynski said, the torque basically disappeared with those cams. I had quite the HP gain right on top, as it would set you right back at WOT. I also have the 3.42 final drive ratio, which made things all that much worse. With the stock cams back in it, I can actually pass cars and leave stoplights without having it right to the floor all of the time.
I also noticed a huge gas mileage loss (well about 4 mpg) as well as rougher cold starts and sluggish light throttle acceleration with the L37's.
If you're looking for 4.0 performance mods....go to a 4.6. If I had one, i would toss it in today, unfortunately, when I gaskets were bad, all affordable used 4.6's seemed to magically disappear. I would also like to upgrade to some 3.71 final drives too, that would make quite the difference.
So for now, I was wondering what any of you would agree on for the perfect size exhaust for the 4.0. It will be manifold back, as I am ditching the cat (Yes, I know its illegal and everyone will die from my fumes, so spare me the pep talk). I was going to run true dual 2" with one delta 40 series flowmaster for each side, but after I got to looking at it, it is going to end up being way too much work just to be able to say I have true duals. That, and the bends I will need to fit them both in will probably inhibit too much flow anyways.
So what I would like to do is run a singe straight pipe that Y's off to dual mufflers out the back. I dont care how loud, I just want the best performance. Any suggestions for pipe size, mufflers, or anything else?

The bigger and more free flowing the better. You cannot make it too big or too low in backpressure. The 4 valve engines just love to have the backpressure as low as possible. But, realize, that the gains are going to be on the top end where the flow is most restricted by the backpressure...it isn't going to make any perceivable gain in the low end. For that you need cubic inches or more compression...or a blower....or NOS.

Aurora By Olds
03-09-04, 09:19 PM
Thanks. I'll plan on going as big as possible more than likely.
I'm happy with the amount of TQ I have now, so top end gains is what I am aiming at.
If I could have kept the TQ I have now with the HP I had wtih the L37's, it would be about perfect.
I think I'll skip other mods for now. I plan on possibly going with a chrfab 4.6 sometime in the future when I make it my project car. But until I'm out of school and it's retired as my daily driver, none of that is going to happen :-)