915 valve question

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kempkan

kempkan

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I know I had a thread on the 915s I got already but a buddy of mine wants to try out his new machines and offered to build the heads. I buy the parts at cost. He is experienced with the new machine but finally got one. He asked what valves I wanted in it and told him 2.02 valves all day. Then he sked if I wanted a 1.625 exhaust valve put in too and shave the heads .045. Like I said before I'm running a 318 right now. He wants to fit me with a .525 cam and m1 intake and a little rebuild with some kb pistons. Is it ok to take off .045-.050 and will the 1.625 exhaust valve fir with the 2.02 intake valve in that head? Any opinions?
 
You better have a ton of compression to use that head and cam on a 318. Start shopping for a set of tall gears too. What do you plan to use this motor for? If it's a street motor I think you'll be very dissappointed.
 
The problem I see will be compression and that cam. Which ".525" cam? hydraulic, solid? You won't notice a down side to the valve size if those two can be better matched. But with them a little mismatched the loss of response and low end will be more noticable.
 
Holey Moley do it. The valves will fit and unlike others here I do not think it will hurt the bottom end, I think it will help. Cut the guides to clear the retainers at that .525" lift and go with the cam and pistons. I think I would go with the air gap style dual plane.
 
don't forget taking that much off the heads you may have to machine the intake a little bit to help it seal with the change in the head seating angle. cant remember the actual formula but it was posted here several times. for every so many thousandths taken off the head the intake needs machined x number of thousandths to match
 
I had 915 heads on my 318. With a 2500 stall converter and 4.30's, it wasn't any faster than my 318 heads. I learned 3 things 1) You need at least 3000 stall converter. 2) 9:1 compression isn't enough 3) You need to use a dual plane to get any decent throttle response.

The bigger ports ( intake) really hurt port velocity and without some big changes they won't help. When in doubt use the smaller of your cam choices with tight LSA.
 
The car is strictly for the strip. He wants to port match everything. I'm running 4.56s with a 28in tall tire now with a 3000 stall converter so I'm not worried to much about loosing bottom end snap. He wants to see what my chamber size is now and get me as close as we can to the 10:1 mark. I realize the intake will need cut also I just don't know how much yet. As for the cam I'm undecided yet. He recommended the .525. I have a 85-86 318 block. Didn't those come with roller lifters? I'm getting this done labor free just buying parts I couldn't pass it up and if it doesn't work I will have the other heads still. Should I look into the eddy airgap or stick with the m1 intake?
 
Racin'? Now we're back to the M1 single plane.
 
Instead of milling the intake have him mill the intake side of the head. that way you can always change intakes later. On a small block mill .0095 off intake side for every .010 off deck side.
 
Ok I didn't know the amount to take off the intake or intake side of the head. Thanks mopar sam. Any suggestions on a cam around the .525 lift? I was thinking solid just to eliminate floating the lifters at high rpm in a 318. I will more than likely being shifting between 5900 and 6200 with this set up. We will see when its done when I run out of cam but that's a guess.
 
I see you trapping around 6100-6200 depending on the slippage. I'd make it higher than 10:1 by whatever means you have to use. Milling's fine so long as it's done right and there's the understanding that things like pushrods will need to be replaced and the intake and heads will be a permanent package. I think the M1 would work if you have it, but I think the RPM would be a better power producer. Not by much, but more torque and with only 3K stall you still need torque. If you can get a race convertor up around 45-4200 that would help. As for a cam, I'd use the XS274S, and get a set of 1.6 rockers for it.
 
I found a timing set from comp cams. K20-248-4. Includes everything but pushrods and rockers. Decent cam or should I stay away from comp? If so what should I look for?
 
I also found the xs274s in a kit from summit. Thanks moper. Its part # K23-231-4. Only 15 bucks more. So many choices its unreal. What to do?
 
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