Compession ratio and my planned engine

[RDJ]

Here is the plan for my motor. I used the KB pistons compression ratio (CR) table, but most are about the same.

According to the CR table, and depending on what size the combustion chambers in the Edelbrock heads are (63-65cc), the CR should be somewhere between 10.2 and 10.5. Is this CR good for somewhat unreliable 91 Octane pump gas with an aluminum head? I could just as easily go with a 20 cc dish. I live at 1,000 feet, but any direction I drive except south are mountains with passes up to 7,000 feet. Any comments, positive, negative, or suggestions are welcome.

In a 360 block (408 ):
4" stroke Eagle cast crank and forged I-beam rods, internally balanced.

SRP forged aluminum pistons with 16.9 dish, 4.030, zero deck

Edelbrock 60779 heads, no porting

3.23 8 3/4 sure grip. It will see some freeway travel, so I don't really want to go more than that (a 3.55 might be OK, but I already have the 3.23)

Air gap intake, not sure of carb yet (750cfm maybe?). I have one of the Professional Products Croswinds intakes. Originally, I had planned on a Magnum head. I had already gotten it before I read some of the reviews of it on this site.

Car weighs about 3300 lbs

This will be a street cruiser with occasional track days.

I am willing to get a converter to match the build when finished, but I want it to be pretty streetable. (I have a 727 trans).

BTW, what cam would be best? I plan on getting a Hughes cam or maybe the Lunati 60403 (226/234 @ .050, .494/.513 lift, 110 lobe). I like the lift on the Hughes cams though without having to go real high with the duration. Hughes HEH2832 (228/232 @ .050, .524/.540 lift, 110 lobe)? Or should it be less for my planned usage?

 

[dgc333]

FWIW, I run a 10.6:1 360 with iron magnum heads and it runs just fine on 89 octane. The cam is a 224/230@0.050" and my cranking pressure is 185-190 psi.

A well designed closed chamber head with a zero deck flat top and an 0.04" thick head gasket makes an ideal quench distance resulting in a very detonation resistant engine that does not require a lot of timing to make max power. This means you don't need a high octane fuel and with alumnium heads you could go higher on compression

 

[RDJ]

FWIW, I run a 10.6:1 360 with iron magnum heads and it runs just fine on 89 octane. The cam is a 224/230@0.050" and my cranking pressure is 185-190 psi.

A well designed closed chamber head with a zero deck flat top and an 0.04" thick head gasket makes an ideal quench distance resulting in a very detonation resistant engine that does not require a lot of timing to make max power. This means you don't need a high octane fuel and with alumnium heads you could go higher on compression

Thanks for the response. It seems the choices for pistons for the stroker are the 5 cc flat top, or the 16.9, 20, and 23 dish. According to the CR chart, the 5 cc flat top at zero deck will give me a range of 11.6 to 11.9 CR (depending on 63-65 cc heads), which seems to be too high with crappy 91 octane. Anyway, sounds like the 16.9 pistons will be OK? I guess I would rather err to the side of lower compression.

Did you cc your combustion chambers and cylinder reliefs? I'm curious if the 5 cc flat top area actually measures 5cc, or maybe it measures out to be more?

 

[dgc333]

I cc'd my chambers on the magnum heads and they were 64cc. I did not measure the valve relief in the pistons, I used KB's number of 5cc, I also didn't take into account the area between the piston top and the top ring but I did use the bore of the head gasket and gasket thickness.

 

[moper]

You will want to increase the duration of any cam to 245°@.050. otherwise, even with the aluminum and quench, you will be in detonation range. Also, the 750 carb is too small. I'd go 870VS Street Avenger. Otherwise I think it's a good build and you'll be happy.

 

[RDJ]

You will want to increase the duration of any cam to 245°@.050. otherwise, even with the aluminum and quench, you will be in detonation range. Also, the 750 carb is too small. I'd go 870VS Street Avenger. Otherwise I think it's a good build and you'll be happy.

Thanks. Would the 20 cc dish be a better choice? That brings the compression to a 9.9 to 10.1 range. Or will I still have to run a more aggressive cam with that.

Maybe split the difference? Go with the 20 cc dish and move up one step with the cam instead of two, (Lunati 60404 234/242 @ 0.050, .513/533 lift, 110 lobe), or (Hughes HEH3237AL 232/237 @ 0.050, 540/548 lift, 110 lobe). Does it work like that?

 

[moper]

I would move up in cam. It will not hurt you at all, and you will lose power in that higher altitude driving by going lower static. You have an RV cam for a 4" stoke engine there. Step up to "mild performance"...