Craig Moates

Folks,

A little help here from the experienced engine builders please.

SCAT 4340 forged I-beam rods, cast SCAT 9000 crank, .030 over 350, World Iron Sportsman 2 200cc heads, Fluidampr, 350/500# springs, 1.5 Roller rockers, 1-3/4" long headers, titanium retainers etc., flat-top Powerforged pistons press-fit, file-fit moly rings, etc etc.

Anyways, the rods are a bit meaty and since the whole thing's been balanced to +/- 1gram I want to go ahead with a small-base-circle roller cam. With those springs, it's gotta be solid roller. Need suggestion on lifters also, std offset & bore. The 64cc chamber, plus a little decking I had done to even things out, should bring the compression in above 10, so I was thinking about some overlap on the cam to avoid detonation. That along with EFI control, which is why the post is here.

So, two ways I could go with this engine. Either in a drag Camaro with TH350, 4.56 gears and a 4000 stall converter or in the street T/A to replace the present 305 for street use with 3.23s and 700R4 /w/ 2200 stall. Either way, with this build the way it is, I'm shooting for no more than 6500rpm really. No plans for nitrous (well, maybe..) or forced induction.

Present plan is for the drag application initially with MAF-based EFI. I'll work the issue with MAF maxing. Might try a carb first just to get started. But I need a cam that will do well detonation-wise and be EFI manageable on 93 octane. Lifts of like 0.625 at the valve with durations of 280+ have been suggested, but without more porting (have some already), I can't see the benefit with this lower-RPM engine. An alternative cam is likely for the street app.

Any thoughts on the subject would be helpful, looking particularly for lobe separation / lift / duration / centerline / base circle advice or words of experience. This is the first full-build I've done.


Many thanks,
-Craig

I8AStang

I tend to agree with you in that 280 @.050 is alot of duration, I would think there is no benefit to going that high. If I were you I would call a good company like compcams and see what they suggest. I would guess that something in the 240 to 250 ish duration and around a 112-114 lob separation, but they could probably be more helpful. After all, that is a SERIOUS motor (at least to me, and my pair of pansie 13 second rides:hail: )
I'm pretty sure that they will suggest a pretty high lift figure, so the over .600 range is probably a good guess.

doc

Please check out the various cams offered by Comp Cams.

For a 383 and 200cc heads, I would think that a cam with 218*I/228*O (@ .050 lift), 0.510"/0.525" lift (1.5 ratio rockers), and 114 LSA would work pretty nice for a MAF EFI engine.

But, hell, what do I know about cams!!

Just my 2 cents worth.

Doc

Craig Moates

Those .510/.525 numbers sound much more streetable.

What about being able to use pump gas with iron heads above 10.5:1?

Is a closer lobe separation viable for accomplishing this?

Is it just unwise to try and design a higher-compression pump-gas iron-head engine and then try to compensate with cam spec?

Guidance is appreciated.
-Craig

I8AStang

IMO, building a high compression engine and trying to compensate with the cam (if that is necessary) is a band aid solution when you are buiding the engine fresh. Also, if you picture the valve events during the overlap period (exhaust valve is closing, intake starting to open, piston just going down) you will waste energy to reduce cylinder pressure. Either way, 10.5:1 with iron heads is alot for pump gas. You could probably reduce it enough with a thick head gasket (or 2). Keep in mind the 383 will tolerate more cam than a 350. When you said 200cc heads, I assumed a "wild" engine was being created. I think you would be better off to drop compression to around 10 and select a cam that is optimized for what you want to do, instead of bleading off presure. Good luck.

MR.HP

I have a 421 cu.in Iron eagle heads 10.8 comp.Ratio with comp cams 224/230=110 L/S Runs good on street with 355 Gears in 3700 pd car. Made 528Hp on my Dyno, Put it in on a 109 intake C/L
It will not ping Keep deck .040 to .045 will ping more 9.5 c/r and
.060 Deck than 10.5 with .040 [ count head gasket too]

Hope it helps Dale

SATURN5

From what I have read, on average each point of compression = 16 HP gain, 10.5 comp with iron heads is rather steep with pump gas I would drop a point of compression or run alloy heads.

"For a 383 and 200cc heads, I would think that a cam with 218*I/228*O (@ .050 lift), 0.510"/0.525" lift (1.5 ratio rockers), and 114 LSA would work pretty nice for a MAF EFI engine."

thats a fairly tame cam...should work very nice on a 383.

TRAXION

Cam it big and give it some converter

How about a 240/250ish solid roller on a 112 LSA with lift in the 550-600 range. Get it with 4deg of advance ground in. This would be a sweet cam for a 383 with lots of topend power. Only problem is - it doesn't really match with those heads ... so, you'll have to buy some new heads Some ported Track 1's or some AFR210s would be sweeeeeet

Seriously though ...
If I could do it all over again I would definitely go solid roller. They offer a really substantial increase in power. You just need to make a decision regarding powerband and maintenance. If you don't mind adjusting the valves once a month then definitely go solid roller. If you don't mind spinning it high then go for the big boy cam. It takes some getting use to but the rush is amazing. Just depends on what you like - torque or horsepower.

Tim

junkcltr

iTrader: (1)

There is a good article at www.speedomotive.com that talks about compression, cam, and quench. It is worth a look if you haven't already seen it.

BTW, Would the knock sensor pick up solid cam mechanical noise and trigger false timing retard?

Cheers,
J

Blackened

Desktop Dyno says you'll make 421 HP and 402 TQ at 5500 RPM with a cam in the 240/250 range, hydraulic roller with a 112 LSA. Going with a lower duration like 220/230 only makes 374 HP but 475 TQ. It all depends on what you want... more HP or more TQ. I always opt for more HP on top, becase I got way more TQ then what any tire can handle! LOL


p.s. Do this with a carb and a single plan intake and DD2000 says you'll make 466 HP at 5500 RPM and 445 TQ. Kinda shows why I went with a carb for my 406 and sold my hi-flo TPI.

Craig Moates

Well,

I think I'm going to go kinda high on this one. Maybe skip the FI at first. So here's the combo:

AFB Carb /w/ hi-rise single plane (got a setup waiting to go)
10.5+:1 tight quench
4000 stall, 4.56 12-bolt, 12" patch slicks, TH350
2800lb 75 Camaro /w/ 71 split nose (glass doors, hood, lexan)
350/500# springs, solid roller cam, roller rockers etc.
Sportsman2 iron 64cc heads, extra porting
Cam: 250I/260E .575I/.590E 112lsa small base circle

Now I've just gotta get this thing together and quit talking about it. If we need high-octane, then we shall have it. Maybe take a split off the Alky unit over at the Refinery...

-Craig

junkcltr

iTrader: (1)

That looks better. I would try to keep it as cool as you can to help with detonation. Also, I was planning on putting a TPI on an engine with a solid lifter cam (it seems you are too). I am not so sure how the knock sensor will deal with it. Might want to give that a thought.
J