I finally got the cam specs out of my engine builder.....now if only I understood them!

Can someone explain what they mean? I'm assuming they are about right for my engine, since it is running sweetly and making loads of power. (Not measured yet, but it was enough to total the gearbox during the 2nd WOT run on boost!)

Specs:

Duration st .006 tappet lift 280 degrees intake and exhaust
Duration at .050 tappet lift 224 degrees intake and exhaust
Gross valve lift .525 intake and exhaust
Lobe separation 110 degrees

TIA
Steve

 

.050 : The valve is open for 224 degree's, when measured from .050" of lobe lift points.
Use this number when comparing cams's.

.006" : The valve is open for 280 degree's, when measured from .006" of lobe lift points.
This number is not as important as the .050" number. (It doen't say as much about the cam/lobe.)

Lift : Lobe and vavle What you have here is valve. The total amount the valve will open (w/o bounce). .525" of lift is a lot for a SBChevy.
It is typically speced w/ 1.5:1 rocker arms. (If other it should be stated.)

LSep the number of degree's between the Intake end exh lobe peaks
LSeperation of 110' is very small for a SC application

 

That's a Comp Cam 280 Magnum roller. Not really what I'd expect with your combo.

After you get the transmission taken care of and the car tuned out, I'd think about trying 1.6 rocker arms on the exhaust side.


[Modified by SloRvette, 5:07 PM 11/19/2002]

 

Thanks Zyla - I actually understood that!

Hi Slo - Buddy's shipping me the new trans any day now, so this project might finally be finished soon (well, it'll never be finished, but you know what I mean!). He's found me a nice Precision Industries multi-disc convertor that will lock up at WOT too. Stalls at 2800, which will suit my mini-ram better. Turns out I have the 3.07 gears, so I'll probably stick with those for now. Had to count driveshaft turns to dicover this, as I have no build sheet for the car.

Hmm - seems perhaps I got supplied with a cam that was 'lying around the shop'? (Bit like my 'new' heads :mad ). I'd be interested to hear why it's wrong for my combo, and why 1.6:1 exhaust rockers would be better - apart from the obvious bigger gap flows more exhaust, how do you determine the optimal ratio?

Cheers Steve
(Still learning :) )

 

I think id go a little bit bigger than that actually. With a 377 and MR, you could go up to about 230/230 or thereabouts. I'm also wondering if the AFR 220s would be a bit on the big side? Seems like youll have very low port velocity.

But that combo will make plenty of good power.

 

I'm no expert but....."Lobe separation 110 degrees" and not having a split intake/exhaust duration and lift #s doesn't sound much like a blower cam. :nonod: :crazy:

 

The cam sounds like it might have been a lying around piece.

Extra exhaust duration on a blower cam is there since the intake is being forced in.

There's a period while the exhaust valve is closing that the intake is opening. The wider the lobe seperation angle the smaller the overlap period. With the intake pressurized you can blow some of the intake charge out of the exhaust. These are just a couple of generalizations about cams.

Those heads can be more streetable with a smaller duration cam. The destroked 400 (377) likes to spin high rev's. With more cam and more blower you could have an absolute rocket ship. It'll be more racecar than street car. Check out Keith Brownlee's numbers in drag and northeast (Eastcoast Quick 4). That'll give you an idea of what's capable.

Personally I wouldn't mess with anything you've got until you get it all dialed in. I would make sure I've got a super high flow exhaust system. Long tubes and dual 3" exhaust. Then have fun knowing that you've only scratched the surface.

:cheers:

 

The motor setup looks good. I suspect the AFR 220 heads are a bit overkill. The intake duration on the cam looks fine. I would think the engine builder would have spec'd a wider lobe spacing 112 vs 110 and 10 degrees more exhaust duration vs intake because of the blower.

Blower motors actually do very well with stock cams or one step upr from stock like cranes 210 224 112 LSA roller cam.

 

Actually the AFR220's are a killer set of heads when used with forced induction. A friend upgraded from AFR195's to the 220's with only other change was I rejetted his carbs, he gains 58hp and 43tq at the rear wheels! This was on a 379ci small block in a chevy 4X4! He is running a around .540 lift, with .230dur@ .050 and 112 lobe seperation. His last dyno pulls showed he was making 542hp@6800rpm and 529tq@5100rpm. Those AFR220 heads are unported also. They do make serious power with a blower. :cheers: