I have a 360 stroked to a 408. Next week I'm going to weld in a X pipe.
Also I'm going to take out my radiator fan "no clutch" and install a electric fan.

How much HP will I gain? I'm thinking 25hp give or take a few.
15hp from the new electric fan & 10hp from the Xpipe

 

I actually see very good gains from dumping the water pump fan and adding the E fan. There was very little inprovement in peak hp but the power came on quicker in the curve and stayed around later. And the motor was very responsive. It feels very much like adding beehive springs. Very revvvvyyy. ( If that makes sense).

25 HP? I hope you get that, but without knowing your build I would say 3-5 percent bump.


I think X pipes and H pipes really help restrictive exhaust. Stuff with tons of bends, small headers, cats, small diameter pipe, etc... does very well with equalization.

If your system already has the right size pipe and header diameter the x or h smoothes it out alot IMO but not a ton of hp gain. You could certainly get 10.

Make sure you re tune the carb or the ccomputer

 

The biggest thing the X-pipe will do for you is help equal both sides fwith backpressure. Well worth the investment in a mild - full built motor in my eyes.

 

I'm rebuilding the tranny right now. Next week I will put the X exhaust on, then wait a couple of weeks & install the elect fan. That will give me a chance to evaluate the X exhaust & the elect fan.

 

Good for you! As far as the electric fan goes, PK1 is right, more revvy! There will be less mass to accelerate. The penalty will come from additional drag caused by the alternator. However, that is a result of magnetic fields, and will be slightly lagged behind your acceleration. For simplicity, and weight savings, I would use one. Have they gotten reliable enough these days to use on a driver? I see a + of 5-10 hp with a crossover. The point of tuned headers is that after the pressure wave from an exhaust pulse, there is actually a vacuum behind it! Tuned headers, and cross-overs, take advantage of this as the prior exhaust pulse can actually help the next cylinder with better evacuation of spent gasses. An X-pipe can also do the same thing downstream.