I'm helping a friend (I know, I got lots of friends doing winter projects and I'm their answer guy??)put his 427 together and need a little help. We're pretty much wide open to suggestions as far as CR, pistons and cam (roller hydraulic). He's using the GMPP 12363410 signature series aluminum rectangle heads (2.19/1.88 valves and a 120cc combustion chamber) and a stock 427 425 HP 3 two barrel corvette carb setup. The motor is going back in his 69 Corvette mated to a Muncie 4 speed. He is after something with respectable power and still run on 94 octane fuel. The pistons he's looking at will yeild about 10.3 to 10.6 CR but no choices have been made yet. Anybody out there have a good combonation they would like to share?
Thanks
Jim

[ 12-18-2004, 07:56 PM: Message edited by: GMJim ]

Do your home work on dynamic compression ratio to keep youselves out of problems with octane. I would shoot for less than 8.5 to one. In other words...engineer your combustion chamber and process.

Do a search...alot of web calculators for DCR. YOu can start with head chamber size and of course keep the quench close to .040 as you can stay. Then work backward into the DCR and it will tell you how much static you can have with what duration cam.

GMjim, your compression is right on the money, srp makes that piston for that head, That gmpp 12363410 is the exact same head as the edlebrock rpm If you bought that from gm complete the you will get 2.25 1.88 valves. But 2.19 is better for you. I would go with a cam that has around a 530 lift about a 240 duration@50 with a 112-114 lobe seperation for that set up, your gonna have to search threw catalogs for that cam. Did you buy the heads already?...mike

[ 12-19-2004, 08:33 AM: Message edited by: 69camaroralleygreen ]

Steve
Thanks for the advice. We are working on all the numbers.

Mike
Yes he already owns the heads. They are GMPP heads bought at a GM dealer. I didn't actually measure the valves but the specs in the GMPP catalog say they have 2.19/1.88 valves. He has a Comp roller hydraulic cam in it now (at least he did before we took it apart) I have to get the specs from it to see what it is, but it didn't perform as expected. I'll find out and post it. We took this motor apart because of oil consumption and found .010" piston to wall clearance, a seized roller lifter trunion among many other major and minor screwups from the previous engine builder.
Thanks
Jim

Check the spring pressure as that inportant on a hyd roller, and too much can cause lifter failure.
Heads are on the big side, but since you have them, use 'em. Keep the cam small, since a hyd roller is usually good for around 6500rpm, or a bit more - if set up right. Look into Lunati hyd. rollers, since their lobe design will let it rev, which it will wanna do with rect. ports.
Some thing between 230-240s dur. will be good for 6500rpm with a 427, use a tight LS around 108-110, (but run the DCR) and throw some lift at it around 550-600 is what the Lunati lobes will give you. Call and talk to Harold.

I would agree with 502.
The biggest drawback is that carb set-up.

Thanks for the replies.
Here is what he and the engine builder has come up with so far. Pistons #212134 SRP's and the cam is an ISKY #396275/284. http://www.iskycams.com/iskypartnumber_search.php?partnumber=396275%2F284&x=9&y=4&compid=69&dealer=no
I don't know a lot about this cam but it seems a little much.
Jim

Some added info.
The valves are confirmed to be 2.19/1.88. To achieve 10.5 CR the heads were milled to 115cc. chambers. I'm not the best guy to choose a cam but the one mentioned above I think is a little much for the street???
Jim

You might want to go over to Big Brother, (Team Chevelle), and look up 427L88, (Gene), and ask his opinions/thoughts..
He likes "trips"!!!!

pdq67