10:1 cr sbc
 

Guys, is a 10:1 CR workable on a marine sbc with aluminum heads, 270 cam, and on 93 octane?? I assume the 10:1 would be too much for a vortec headed engine? thank you

Yes you will be fine with a reasonable timing curve and consistently good fuel. I've built several with similar cam and alum. heads at 9.5 up to 10.2:1 running on 91 no ethanol premium. Most aftermarket heads have efficient chamber shapes that only need about 32 degrees of full advance. I've seen AFR, Profiler, and ProMaxx heads all on the dyno not pick up anything from 32 to 34 or even 36 degrees with the limited cam profiles we need with wet exhaust. Bring your full advance in no earlier than 3000 but by 3500 rpm and you won't have any issues.

I'm currently talking with Skip White..They have a 383 kit with 12cc dished forged piston and was gonna use their NKB heads...I think it works out to be 10:3 which I don't love....I wish it was a little lower...Anyone make .050 headgaskets for a marine application? thank you..

I doubt you're going to be zero decked just to get the block deck squared up. .010" in the hole at .030" over bore is only 10.03 with a std. .039" head gasket with a -12cc dish and 64cc chamber. That will work fine. Any thicker gasket or if the piston is further down in the hole and I'd start to worry about quench pad efficiency and detonation from too large of quench distance. Lots of other piston options like the Mahle power pak with a 16cc dish if they are zero decking the block. Those have a great low drag ring pkg. as well.

Dude, you seem to know your stuff..Can you look at what I'm doing and see if I'm screwing up please? That 383 kit from Skip White with the 12cc dished pistons, comp 270 roller lifter cam, the NKB 200cc heads, 1.5 roller tip rocker, performer intake, and a QJ....Don't bust my chops on the QJ...The guy at quadrajet power knows these things in and out and jetted for the 383...I know a QJ....I have no experience with a Holley etc...and it wasn't cheap at all....You ever seen a 900.00 buck QJ?? This isn't a total performance boat....No tubing and spends 99% of the time at idle and 3k...thank you...Jason

Good combination overall. I've tried with Q-jets. Holleys are just too easy to tune. Guys that can make a Q-jet work deserve a lot of credit. I'd go with an rpm air gap intake and a spacer adapter to adapt the spread bore Q-Jet to the air gap intake. The straight performer will be your choke point in the mid 4000's if not a little before and while it will still climb and make power, your torque curve will suffer compared to the rpm air gap port volume. That combination will give you great docking manners, solid hole-shot and 450+ ft. lbs. of torque at cruising rpm and carry out to about 5200 rpm peak.


Run a 7 or 8 qt. oil pan and put an oil temp gauge in. A good pan with windage tray and / or crank scrapers will be a great investment. More power will create more heat and higher rpm when up there will create more windage. Most guys building their first non-stock marine engine neglect this and burn up the bearings running hard for too long of a duration. It doesn't take too long on the throttle to see 250+ oil temps. You shouldn't need an oil cooler until you get closer to 450-500hp which is much harder to do with a marine small block.


I'd also recommend a fuel pressure gauge so you can verify your pump and plumbing is keeping up with the increased fuel demand. Simple things such as restrictive tank pickups have caused months of frustration for some of us trying to diagnose engine problems.



My current build has been well documented on here if you do a search. 530hp /520 tq. 394 cu in. sbc. As far as carbs, I'm running a Pro Systems 850 with annular boosters to improve low rpm atomization. The larger boosters hurt a little above 6000rpm as it starts to pull about 2"+ of vacuum again in the low 6's but I don't spend much time up there.



Good luck and reach out with any questions. SB on here is also a great resource on the small block stuff.

I already have the spreadbore performer intake..A real one and not Wuhan...Trying to not go crazy with cost..Gonna run a 3/4 " phenolic spacer...I appreciate your help Sir....Jason

Are the NKB heads available with 68cc chambers ? That would put you closer to 9 1/2 to 1. A lot friendlier.

Yes, but I'm coming up with different numbers than you...10:3 is what they say with a 64cc chamber and zero deck...The 68 is 10:1....They deck their blocks to zero deck height I want to say...I definitely would like to lower the compression some more to get some more safe area...You just don't see a lot of marine 383 strokers online running 10:1, but that being said most all vortec cast iron heads....thx...Jason

dumb question but based on what you say the boat is used for why the need to spend money on an aluminum head 383? if it is going to idle or run 3k most of the time why not just replace it with a vortec head 350 and save the money for fuel.