SBC anyone here well versed?

[WolfLMM]

Im building a SBC 350 Marine engine. Have a couple of questions.

Runnig cast crank and rods.
AFR 180cc with 65cc combustion chamber.
4.00 bore with 3.48 stroke.

What style pistons for max quench with these heads? I have heard .040 is a good number, but what about piston type and style?

Any other suggestions are welcome

Thanks,

Wolf

 

[Grizzly5531]

Check these out http://www.summitracing.com/parts/SLP-H618CP/ I figured since your running a cast bottom end your not trying to go to crazy with the power, So these should be plenty strong for your application they also disperse heat better then a forged piston. (good for marine purposes). They also come in .020, .030, .040 and .060 over. I run these pistons on my 350 bored .040 over with AFR 195's. Are these the 75cc or 65cc heads?

 

[S Phinney]

C/R should be your main concern. What type gas you plan to run etc... Low CC chambers means high C/R and race fuel etc..

 

[ZeroGravity58]

if you run a 65CC chamber with them pistons posted, with a zero deck and a .040 gasket your looking at roughly 11.3:1 compression. Flat tops are your best bet. id run these http://www.summitracing.com/parts/SLP-H631CP/ pistons. With those with what you have listed you would be around 10.2 which is pretty comfortable. If it is zero decked or not i wouldnt run any thinner then a .040 head gasket. Either way you would stay around 10:1

 

['03duramax]

What's your goal with this motor? What are the cam specs?

 

[WolfLMM]

C/R should be your main concern. What type gas you plan to run etc... Low CC chambers means high C/R and race fuel etc..

I know quench is more important that CR. With a tight quench I should be able to run higher CR without pinging. At least thats the way it was explained to me. Wanting to stay around 9.5:1.

 

[ZeroGravity58]

Cam specs wont change static compression ratio but will change dynamic compression ratio. What changes dynamic is where the intake valve closes ABDC ( At Bottom Dead Center ) I have a feeling he wont be running a huge came with lots of overlap anyways. BTW ive always had great luck with Comp Cams Xtreme energy grinds :thumb: You dont want to push it to close. I ran a SBC that was zero decked with H beam's with .040 gaskets and after turning 8,500 down the track i pulled it apart and you could see where the piston was just kissing the head from the rods growing. that motor was so tight that if i didnt index the spark plugs the piston would bend the ground strap down on the electrode. I was also running a 14CC dome with 58CC heads which puts it right around 16:1 and a custom cam that was .725 lift and 286/292 @ .050 lift she loved RPM's

 

[WolfLMM]

Goal is: A pretty reliable, good running engine, LOL.

Specs:
AFR 180s 65cc with inconel ext. valve
Comp cam XM270hr 214 and 224 and duration. 495 503 max lift 114 LSA
Cast steel crank and rods (whatever Merc put in them in 1987)
650cfm carb
air gap intake
CMI headers.

Hoping to make 400-425 horse. idle to 5500rpm operating range.

 

[ZeroGravity58]

i like the cam thats the Xtreme marine cams. Id go with the Speed pro flatops i posted with the .040 head gasket. right around 10.2 with a zero deck. Be around 9.8-10 with a stock deck. You wont be disappointed.

 

[WolfLMM]

So is keeping the quench at .040 important with these heads? My deck height is stock (new block) Whats the piston to deck height with a stock block?

 

['03duramax]

It varies. Best to get it decked to a "0" deck height. The increased efficiency would offset the higher (slightly higher) comp. AFR are efficient heads, plus being aluminum, you won't have problems running pump gas. Why inconel exh valves? Unless you run high heat like a turbo application, the added valvetrain mass will just hurt performance.

 

[WolfLMM]

It varies. Best to get it decked to a "0" deck height. The increased efficiency would offset the higher (slightly higher) comp. AFR are efficient heads, plus being aluminum, you won't have problems running pump gas. Why inconel exh valves? Unless you run high heat like a turbo application, the added valvetrain mass will just hurt performance.

Because the engine is going to run wot for extended periods. Like possibly hours, without a break. Not to mention it corrosion resistance, since I am running a wet exhaust, there is always the possibility of moisture remaining in the exhaust after shut down.

Thanks, hopefully I'm not to far out, have to call the shop today.

 

[Stingpuller]

Engine

If you have a virgin block you will probably be .015 to .020 in the hole. You are correct on wanting to run the motor tight on piston to head. .030 to .035 would be nice with the lower rpm, under 5500. I would also run a high silicon piston with a tight piston to wall so it will not rock much over TDC. That would also help with a tighter clearance. I personally like to run a piston with the rings moved up to kill to dead space. AFR 180 head will work verywell with your setup. Jeff

 

[Steve W]

Why not just change head gaskets and save some money and time?

 

[Trippin]

Tighter piston to cylinder head clearance has been shown to reduce detonation.

I would run a minimum of .018 total piston to cylinder head clearance for the tightest quench. Compression will be above your target though, with flat tops.

Need to watch piston to valve clearance as well.

 

[WolfLMM]

Tighter piston to cylinder head clearance has been shown to reduce detonation.

I would run a minimum of .018 total piston to cylinder head clearance for the tightest quench. Compression will be above your target though, with flat tops.

Need to watch piston to valve clearance as well.

Thats what I was told. .018 though, Man that is close. I am running a slight dish piston, ordered them today. 7cc dish so not much, with .040 quench that put me IIRC 9.8:1 CR. So you are telling me to tighten it up some? I wonder, what's the thinnest gasket I can get?

 

[Trippin]

Thats what I was told. .018 though, Man that is close. I am running a slight dish piston, ordered them today. 7cc dish so not much, with .040 quench that put me IIRC 9.8:1 CR. So you are telling me to tighten it up some? I wonder, what's the thinnest gasket I can get?

Been a while since I sold my portion of the ownership in AFR (2006). I'm a little rusty on the SBC gasket #s.

Nothing wrong with .040 quench at that compression ratio.

Neat thing about marine engines is you have an almost unlimited amount of cooling system.
Keeping the water temp down will raise your resistance to detonation.

 

[WolfLMM]

Been a while since I sold my portion of the ownership in AFR (2006). I'm a little rusty on the SBC gasket #s.

Nothing wrong with .040 quench at that compression ratio.

Neat thing about marine engines is you have an almost unlimited amount of cooling system.
Keeping the water temp down will raise your resistance to detonation.

Does the dish of a piston have any real affect on quench, these pistons should have a flat rim around the edge. Or should I just stick with flat tops with valve reliefs? Not to late to cancel and go with a flat top:spit:

 

[WolfLMM]

Just did the math, I will end up with 9.92:1 on 7cc pistons, 65cc head volume, .040 quench. Seems a bit high??

 

[Trippin]

Just did the math, I will end up with 9.92:1 on 7cc pistons, 65cc head volume, .040 quench. Seems a bit high??

Yep starting to get up there for pump gas.

Flat tops and 75cc heads looks like an interseting set up. approx 9.12.

Are the heads new?