bcbaja502

I have a mild 502, GM Performance aluminum heads, Dart intake, 850 cfm Holley, Crane Hi-6 Inition, EMI Thunder exhaust. The motor has been together for a while but the EMI Thunder manifolds and risers, Crane box and intake are all new. The carb is off of a friends boat that has virtually the same motor.

I put it all together, and set it up with 14 degrees base timing and used the #6 curve for the Crane box (Normally aspirated V8). Set the idle mixture a little richer than it was originally but left the jetting the same.

I ran it on the hose for a while and then put it in the water for a test run. It seemed to run strong, no pinging or anything, normal engine temp just under 170 degrees with FWC. Constant stream of cooling water was coming from both pipes. About 20 minutes into the run my 4" rubber exhaust tubing blew out on the starbord side (Brand new). I patched it with a beer can and some duct tape and headed for home running fine. Ten minutes later the port exhaust tubing did exactly the same thing. Both times cruising at around 3100 RPM. Got it home and found both tubes were absolutely burnt to a crisp...like BBQ charcoals that you could crumble with your fingers.

Any ideas on what could cause this??? My firing order is currently 1-8-4-3-6-5-7-2...Could I maybe have a 4-7 swap cam that is dumping raw fuel into my exhaust and catching fire in there?

Any help would be greatly appreciated!!!

picklenjim

You need to check how much total timing your running.Should be about 36 max by 3500 RPM. 14 initial sounds kind of high but that's not as important as your total.Should probably be more like 10-12.You need to have someone run the engine up as you watch with a timing light.See how many degrees it's at when it stops advancing which should be by 3500 RPM.If your balancer isn't marked that high (36 degrees)you will need to get a timing tape to put on it.They sell them at speed shops.You will need to know your balancer diameter.Or buy a balancer that's has marks going that high.

bcbaja502

Thank you for the reply,

Base timing is 14 degrees as spec'd in the Crane manual, checked total at 34 degrees at around 2900 rpm. Everything seems fine as far as timing goes. I know timing being off would make some heat, but I wouldn't think it would completely incinerate my exhaust...especially with normal engine operating temps. Pretty much anywhere from the end of the tailpipes back is so burnt you can stick a finger through it.

picklenjim

Man that's unreal.I assume you used the correct 4" rubber hose made for exhaust. Does all your engine cooling water go out through them. They don't run dry at some point and the water goes out elsewhere do they?I believe ya but it's hard to believe they get so hot they burn up the rubber especially if the engine cooling water is going through them and the engine is only running 170.

bcbaja502

Yeah, it's a mystery...correct marine wet exhaust hose that was brand new before that run, the only time all of the cooling water wasn't coming out of the exhaust tips is when it was spraying through the hole that burned in the side.

CB-BLR

You don't have enough water going thru the exhaust to cool the hoses. Check for blockages or a bad impellor.

Chris

lookinforboats

Ditto - what chris said - not enough water entering the elbows period. Its the only thing that burns them up

tms1155

only lack of water will burn those hoses

Griff

Like was said, lack of water to the pipes. Maybe something is plumbed wrong with the EMI's.

bcbaja502

Thanks guys, I'll check the impellor in the raw water pump even though there's only about 10 hours on the new pump and impellor....is there an impellor in the leg as well, or just the raw water pump?