The cam duration is to small and the LSA is to tight causing a lot of cylinder pressure and on 93 octane it pings. I can not retard the timing enough to stop the pinging. So I mix 2.5 gals of 110-112 octane a tankful to stop the pinging. I was thanking about changing the cam to the Summit 2801. A lot of people like it and may cure my pinging problem since it can relive some pressure in the cylinder with a longer duration. The summit 2801 specs are here. https://www.summitracing.com/parts/sum-k2801.
The valve lift is almost the same. xe262h -.462/.47 vs 2801 - 0.444/.466. If my valve springs were set up for the XE262 would I need to do anything with the valve springs if I installed the 2801? Can I just install the cam and align the timing gears back up?
Need to know what exactly the springs are set up at now in your heads. Spring specifications in the catalog do not represent actually what they are in real life. Just had new springs installed in my heads today and I can tell you they were off from what they are advertised as far as the seat pressures at the installed height. If you know what the installed height of the springs are now and you know what height the springs come into coil bind you should be able to figure that out and if it would be a problem. I did not see what the seat pressure should be on the comp website for your current cam. Will have to search a bit more. Hope this helps some.
Comp recommends 988-16 springs for you camshaft. Do you know if that is what's installed now? If not you'll have to check your spring's load force with a spring tester then check height, clearance, bind, etc when they are installed with the new camshaft. Like Bigchief, I couldn't find the specs on the comp site but Jegs has it: ID outer-1.060"; id inner-0.804"; seat load 232 pounds at 1.600"; open load 232 pounds at 1.100" coil bind-1.000"; rate-230 pounds per inch.
You'll have to go to Summit and ask what the recommended springs are for their camshaft and compare them to yours. But as stated above, just because Joe Blow says his springs have specs 'A' don't be surprised if they are not specs 'A'.
That XE camshaft lobes seems to have a rather quick opening and closing ramp. Advertised duration is less than the 068 but it's more at 50. I'm sure the 988 springs would have suitable load and rate for the Summit 2801, but you will have to check the clearance to the valve seals and for coil bind with the new camshaft.
If you really get into it you would check the installed height of all the valves and shim the springs to match the shortest to within about 0.020". But for a basically stock build as long as the retainers don't hit the valve guides and the coils have clearance, I'd say your good to go.
Thanks for the information. The springs they installed were the SPI brand. They are inner \ outer springs. 60-1136 and 160-1137 Rates seems a lot less then the Comp brand. More like a stock spring. Unless you add the two pressure together. Not sure how the two specs compare. I was kind of looking at both valve lift which are real close and since they are, would I have to worry about them. I guess the cam will have specs that I will just have to look at and see.
That will give you a closed rate of 93 pounds, I don't think I've ever heard of a spring that low, and that's at a lower height than the 988 specs. If it's 93 new what would it be after five years? I know the spring is supposed to keep it's rate but we all know they, just like people, get weak with age. I wonder the reason such a weak spring was installed? Maybe to keep the studs in the head.
Summit also recommends the 988 spring for the 2801 camshaft. Looks like the springs you have are on the weak side. Pressed in studs should be good up to 275-300 pounds spring pressure, 988 springs are only 232 at 1.100". Do you have screw in studs and poly-locks?
I think the 16 heads have screw in studs don't they? I don't know why they used those springs. I thick they are standard replacement. I guess when I get my replacement cam. I should just plan to replace the springs. I don't have a tool for that but I guess I can get one. Like to do it leaving the head on the block in car but if it becoms to confusing, I guess I can remove heads and take to machine shop.
Just checked my cranking compression and I have two cylinders hit 200 PSI. Most are 185-200 PSI. No wonder it pings on 93 octane.
Dished pistons are the only way to solve the problem. Drop the compression to 9:1 - 9.5:1 Last 400 I built with 670 heads was 9.4:1 using dished pistons and 2802 cam. That engine runs 87 octane all day long.
