Exhaust

[courtholl]

I have a new engine being built and need to figure out my exhaust. My old engine froze and the block cracked. I have what appear to be older dry gil exhaust. The manifolds are polished aluminum and I have not seen any online like that look like these. We are scrapping these, as they might have cracked and my mechanic here hates them and says they are old. The exhaust pipes are still good and are dry pipes.

I am having a 454 stroked and bored to a 496. Engine builder is thinking it will pull 500-525 hp. He does have a big cam in the engine and he likes to try to go to dry exhaust to eliminate the possibility of reversion. He is going to have it idling at 800 RPMs and said at idle the big cam could pull water back in, etc. I am not sure how concerned I should be about this. I am trying to figure out 3 different options for our exhaust set up.

One would be to buy gil replacement manifolds and use my existing pipes (stick with complete dry system that I already had on the 502). Or go with 2 different EMI options. One he has EMI build a complete dry exhaust for about $2,500.00. The other is EMI with the water jetted towards the back when it is introduced into the exhaust – he has it introduced later and force back towards the transom (about $2,100.00). Would be able to use some flexible tubing in the second EMI option, but the first would be a solid dry pipe like I had with the 502. I wanted to try to use my existing Gil pipes, but will not be able to, as they said it would cost more to modify everything to use those (if just get gil replacement manifolds, then would be able to use them). Gill replacement manifolds alone are around $2,000.00.

My questions are: Should I be worried about reversion? What is my best option? My engine builder and my local mechanic come from two different schools of HP. Builder likes big cams with good intake, and my local guy focuses on intakes for big HP gains. Any feedback would be greatly appreciated. Oh yea, this will be going in a 24 pantera (89).

[MILD THUNDER]

As for your local mechanic focusing on intakes for big HP, concerns me. There is only so much power you can make. The worlds greatest flowing intake isnt gonna do jack for you if your cam isnt spec'd right, or heads and exhaust cant flow. Its a combination of alot of stuff, like carb, intake, cam, compression, heads, and exhaust to make a reliable marine engine.

500HP should be easy out of a 496CI. We need to know more about the cam specs, heads, etc to give advice on whether your gonna NEED dry pipes. The fact your engine builder is familiar with the reversion issue, is a good thing.

[courtholl]

Here are the basic specs I was able to get over the phone:

Dart Cast Iron heads 345

2.30 intake valves
1.88 on the exhaust

Cam is hydraulic roller
547 lift
230 intake
236 exhaust

Hope this helps for additional info.

[MILD THUNDER]

Those heads are a bit too big for a 496 for my likeing. I'd think they are better suited for 540+ cubic inch mills. I think something in the 310 size would be better suited, and make more power pretty much thruout the RPM range.

Cam wise, i'd say long risers should be ok, but would prefer dry tails. Do you know if the cam is 110, 112, or 114 LSA?

Keep in mind I am no engine builder. I am sure someone with more knowledge will chime in here.