|02-02-2004 11:45 AM|
|Robinson Robin||Yup I'd be a little concerned about that compression too you are gonna be getting real close to detonation territory. Your elevation will help alot but its gonna be close. you will probably have to retard you timing some and run a slow advance curve.|
|02-02-2004 10:50 AM|
that is interesting about the cams.
I do think that it will have trouble with 10.8:1 compression, and a thicker head gasket is probably not the answer. One important thing to think about when building a motor is quench distance. This is the area from the top of the piston to the deck of the head. It is calculated by adding the distance that the pistons are in the hole + the compressesd thickness of the head gasket. The optimum quench is 40-60 thousandts. If you go above 60, your fuel will not atomize properly, and the motor will preignite worse than with the thinner head gasket even though you have less compression.
|02-02-2004 09:53 AM|
|slonova||10.8:1 still too much at 4500ft elevation? could i get away with just running a thicker head gasket?|
|02-02-2004 06:54 AM|
10.8 with iron heads will be to much for pump gas. I would take the deal on the heads, turn it into some cash and get some larger CC iron heads or some aluminum.
|02-02-2004 05:44 AM|
|cool rockin daddy||Go to Comp's website. They have torque and horsepower curves for all the cams mentioned. You will be amazed at how similar the power curves are. Really makes you wonder why they even have the different grinds. The only thing these different grinds do is move the powerband up or down. No real difference in total torque or horsepower numbers.|
|02-01-2004 12:27 PM|
I understand wanting torque and driveability out of the motor, but the 274h cam will just flat outperform the 268h. It will make more torque and horsepower. Your motor will be much more fun to drive.
Good luck with whatever yoou decide though,
|01-30-2004 08:11 PM|
I went ahead and ordered a complete Comp Cams xe284h (.507/.510 lift) kit. comes with cam, lifters, timing chain, valve springs, retainers, locks, and seals.
i called up my machine shop and they said itd be about $130 to enlarge the spring seats and add screw in studs and guideplates and put the heads back together.
thanks for the input, guys.
|01-30-2004 04:29 PM|
firestone, you read my mind.
I would also run the 274xe if your staying hydraulic.
|01-30-2004 01:38 PM|
Your new compression will be 10.8 to 1 with the vortec heads.
The spring pads will be OK you don't need to machine them for the 268 comp cam but you will need to get other springs. You will also need to machine the top of the valve guide down because any more then .450 lift and the retainer can hit the top of the guide. I would machine the heads for screw in studs and guide plates. this will eliminate the need to run guided rockers, plus your getting close to the limit where pressed in studs will work without pulling out.
|01-30-2004 12:50 PM|
The first thing to think about is your springs. You will probably need to take them to a machine shop to get the spring seats enlargend to handle a bigger spring; in stock form they are only rated to handle around .450 lift. I dont think it would cost too much to get the seats enlargend. I would use the xe274H cam at least. I had a 355 with the xe268h cam and vortec heads, and although it ran very well, it could have benefitted from the 274h. On a 383, a cam will operate at about 300-500 rpm lower than what it is rated to operate at. If this car is not going to need to be a mild daily driver, I would recommed using the ex284h cam in a 383 with the vortecs.This cam is testing the limits of the vortec heads as far as lift and flow goes, but the vortecs can still handle the lift of this cam. You would be looking at near 500 ft lbs of torque and 430-440hp with the 284h. If you are totally against doing the spring upgrade, in my opinion, the only other head to go with is the AFR CNC ported 195cc. They are expensive ($1250), but not compared to what you would have to do to any other unported head to get them to flow like the AFRs. With a decient cam and the AFR's, you would be looking at 500 hp and 500 ft lbs on 10:1 compression.
Here is a motor you might be interested in.
|01-30-2004 12:27 PM|
383-- use the vortec heads? what cam?
hey all.. i purchased a set of complete brand new vortec heads.. a few days later i got an amazing deal on 383, so i had to jump on it. the 383 is about 9.5:1 w/ 76cc heads. the only cam specs i know is that its .490" lift hydraulic flat tappet (its coming out).
should i use the vortec heads on this motor? i dont mind the compression bump, and i want this motor to be pretty streetable. i figure i'd go with the comp cams xe268. will this be too small of a cam for the 383? im kind of limited on the cam with the vortecs, and if i spend the money to get them machined to run a bigger cam, i might as well have bought an aftermarket head.
i could just try to resell the heads and get some dart iron eagles or something..
what do you guys think?
the rest of the setup.. going in a '77 Nova, with a built 700r4, 4.11 gears w/ posi