Thread: Engine kit question

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I found a Federal Mogul SBC rebuild kit from www.spdc2000.com part no. MKF630C. It looks pretty decent for what I need. It says with 76cc combustion chambers it would give me a compression ratio of 8.6:1. I was told an 11:1 ratio would be good for me. I plan on using GM L31 Vortec heads, with a vortec intake manifold and a holley 750 carb. What would be good cam dimensions to get me close to this CR?

11 to 1 seems high unless it is a drag motor. 64 CC chambers will rate you around 9 to 1. Cam dosen't give you compression, your pistion cc along with the head chamber size does that. The cam I guess in a way could work with compression as hot cams bleed off compression so you need a high compression ratio for them to work right ( so they maintain a safe compression ratio, otherwise, stalling at idle could occour and so on ). We do need to know what the engine will be used for, this will assist with cam decision, but the bottom line with that is, only run a hot cam on the track, run mild cams on the street/ strip situations. and as a baseline for the hot cam would in fact be at least a 11 to 1 or 12 to i engine min where as a mild cam, probably 9 or 10 to 1 baseline. And if running a blower, 8 to 1 static compression is probably the best.

im looking for a strip/street motor. i would like 350-400 HP out of it.

Originally posted by muteboy49
im looking for a strip/street motor. i would like 350-400 HP out of it.

Probably gonna want 9 to 1 compression, which with the 64 cc chambered vortechs you will have that, run a mild cam, other than that, a set of headders and a good intake and 4bbl carb will probably run 350 horse or so. make shure that the RPM's match on the cam and the intake, like if the cam goes out at 4,800 and say you have a single plane victor jr that runs to 7 grand but dosent come in until 4 grand, that is severly mismatched . Somthing like an edlebrock performer manifold will come in at 1,500 and go out at 5,500, get a cam that runs 2,000 to 5,500 and that is matched pretty good. You should look at edelbrocks carb cam and intake kits, there designed to work togther so it is almost perfectly matched

That seems very close to the kit I used for my 350 but are you sure you want that high C.R.? For strictly racing that would be good but if you plan to run on the street it is a bit high. In my case I had the heads "resurfaced" quite a bit to cc out at 73 cc and the best estimate I can get for my C.R. is 9.0:1 hoping to run on 87 octane or maybe 89. On the other hand there is not much percentage difference between $2.90/gallon and $3.20/gallon so if you have to run 93 octane that may not make much difference. One way to handle high C.R. is to use aluminum heads or set the squish close to about 0.030" by decking the block and careful machine work. Admittedly the Vortec heads are a cheap way to get good flow but they are iron so maybe someone else here on this Forum can tell you the correct directions to setting the squish to the optimum value. The tradeoff is that a closer approach of the top of a piston to the inside of the head the better turbulence and resistance to detonation, but if the piston pin and the bearings get a cumulative slop equal to the squish, the piston will destructively hit the inside of the head and great damage will occur. If you plan to do this check with Tech1 as to what is the safest squish to use and have the machine shop deck your block accordingly. The list of possible cams is vast and different folks have different preferences. My rough guess would be that you should look at Comp cams XE286 for all out performance, but a Comp Cams 268 might be better for the street. I also like the Crane cams low rpm street cams for torque (and mileage), but I don't really care about 1/4 mile E.T. I'll bet you get at least six different cam recommendations here before this thread is done!

Don Shillady
Retired Scientist/teen rodder

my friend showed me this and said it would be good for me on a budget www.summitracing.com part no.SUM-K1109

Originally posted by muteboy49
my friend showed me this and said it would be good for me on a budget www.summitracing.com part no.SUM-K1109

That cam is way to hot even for your 11 to 1 comp, this cam would require 12 to 1 comp at the min, this is a race only cam. K1104 is better suited for what you want as a street/ strip cam. even K1105, you would be able to run to 5,700 with that 1 and if you have like 3.73's, you will cruise ( 65 MPH ) at the 2,200 approx so you will always be in full power.

ahhh i see i do appreciate the help

Stock Vortec heads are good to about 5,200 RPM and then they go flat. You can not run a high lift cam (anything over .480-.500) because the valve spring retainers will hit the valve guides. You can machine Vortec heads for high lift cams and better valve springs but after you have paid for this aftermarked performance heads start to look affordable to.

I like Vortec heads. I have a set on the motor in my roadster. These heads complemented my over all build plan. A simple motor for street use. One that had good torque and power from zero to 3,500 RPM, the range that I drive in 99% of the time.

I used a tight quench (.038, about as close as you want to go on the street), and Edlbrock Performer intake and matching cam. I recon I have 300 hp. Nothing to brag about. But I run all day on 87 octaine and I can get rubber off the line and a nice, satisfying cherp going into second.

Built some radical motors in my younger days. Most of them were expensive mistakes.

how much of a difference is there between a 8.6:1 Cr and 9:1 CR?