Cylinder Heads (350 Chev)

[Riv]

I'm considering changing the original cylinder heads on my 82 Century, to newer fast burn or a high quench head for more efficency and power. I have looked at the Edelbrock performer heads and intake. I will have to change the exhaust valves, as the stainless valves that come with the heads aren't compatible for marine use. I would also be using Comp cams magnum roller rockers. The heads, intake and rockers will work in the rpm range from idle to 4800 rpm. I want to basically increase efficency, performance and fuel economy. The short block is rebuilt, balanced, blueprinted and clearenced. The cam is stock, and should worrk with the heads and intake. The exhaust is IMCO power riser with through hull only exhaust. The Edelbrock heads are aluminum. Boat will be used in fresh water only. Would Dart or World iron heads be better?

 

[John_S]

Re: Cylinder Heads (350 Chev)

What pistons do you have? and was anything taken off the deck? what was the bore?

Keeping in the low to mid 9's on compression ratio, and having a good quench, can be a challenge, especially if the pistons are not quench style.

Most of the aftermarket heads, are geared to produce power above the 5K range. If you have flat-top pistons, though, a vortec style chamber in aftermarket (7x cc head) might be the best combination. Something with intake runners in the 170-180 cc range, instead of 200+.

 

[Buttanic]

Re: Cylinder Heads (350 Chev)

Exactly why would you say the stainless steel valves aren't compatable with marine use when many marine engines come with stainless valves.

 

[79Glastron]

Re: Cylinder Heads (350 Chev)

Yeah, I don't see why the SS valves won't work for marine use. Are your old ones sodium filled? SS valves are top shelf stuff, I wouldn't have a problem using them.

 

[ron7000]

Re: Cylinder Heads (350 Chev)

stainless steel valves are top shelf stuff, that's funny.

you might want to first understand the definition of stainless steel,
unless you like getting boned out of money for something that is not that special.

 

[Riv]

Re: Cylinder Heads (350 Chev)

Don't remember piston manufacturer. (shortblock at machine shop) They are forged and the top is ceramic coated. took .010 off deck and bore is .030 over. Heads are Edelbrock rpm performer with 170 cc intake runners, 65cc D shaped exhaust ports, 64cc dual quench combustion chambers, 2.02 intake and 1.60 exhaust valves. Intake I will be using is Edelbrock Performer air gap (designed for power from idle to 5000rpm) Compression ratio should be arround 9.4 to 9.5 to 1. I have a friend with a flow bench, and cc measuring beaker, we got the heads (intake and exhaust) within 1/8 cc of specs.

 

[Riv]

Re: Cylinder Heads (350 Chev)

Its not a stainless valve in general, it's the type of stainless valve. Most marine heads with stainless valves use whats called an Inconel stainless valve. The difference is heat compatibility, or the ability to wiyhstand heat for extended periods of time. If you consider automotive high perf, you are wot for a short period of time (14 seconds or less) and then you are off the throttle, alowing the exhaust valve to "cool down". In marine use, you usually cruise arround 2200 rpm to 3000 rpm (on plane). At wot, you will be there longer than an automotive engine would be (except for NASCAR), from 5min up to 30min or longer, generating more combustion and heat. This type of stainless valve is designed to withstand these conditions. Edelbrock puts this valve in their big block marine head, butt doesn't offer it in the small block head. They also manufacture marine heads for other marine builders and manufacturers. Hope thih helps answer the question on "stainless valves. And yes, all of you are correct, stainless valves are first class. Valves are not sodium filled.

 

[John_S]

Re: Cylinder Heads (350 Chev)

Pistons would need to be quench style "D" w/ -12/-14ccs. (assumes 0.040 quench - w/deck and head gasket)

With the stock marine hyd flat cam, you are probably approaching 300hp at prop. If you went with 1.6:1 rocker and adj timing on the cam, you can get another 10hp. Given all the other pieces, you might want to just go with a better cam.

PS: I am not crazy about all the alum, but know there are many people that do it with raw water cooled - running in freshwater.

Keep us posted on the project.

 

[wire2]

Re: Cylinder Heads (350 Chev)

Well, I learned something about valves here, although we seem to be a bit off topic.

Riv, part of the gain of aluminum heads will be the reduction of 50 lbs of weight. In a car, weight is only inertia, in a boat, it's inertia AND displacement, the latter adding wetted area and friction.

Typically, you can bump up 1 on compression ratio with the same fuel because aluminum cools so much better.

A cast iron to aluminum intake swap will also benefit by 50 lbs.

 

[mtnrat]

Re: Cylinder Heads (350 Chev)

Riv are the pistons flat top, D dish, or smog dish? And what cc is the dish or valve indentations?

 

[Riv]

Re: Cylinder Heads (350 Chev)

pistons are as you described. I have decided to replace stock cam with a comp marine cam. Specs pn 12-262-4, lift in 464, ex 470, duration@ 0.50 in 218, ex 224, lobe separation 114. this is a hydraulic cam.

 

[Riv]

Re: Cylinder Heads (350 Chev)

Pistons would need to be quench style "D" w/ -12/-14ccs. (assumes 0.040 quench - w/deck and head gasket)

With the stock marine hyd flat cam, you are probably approaching 300hp at prop. If you went with 1.6:1 rocker and adj timing on the cam, you can get another 10hp. Given all the other pieces, you might want to just go with a better cam.

PS: I am not crazy about all the alum, but know there are many people that do it with raw water cooled - running in freshwater.

Keep us posted on the project.

John, Forgot to mention that I had the heads and intake Marine hard annozided.