My head feels like a twisted wedge right now so need to write some stuff down and let people take a go at it. All comments appreciated. Well, been doing a lot of research on cams and think I might have the perfect cheap solution to go with my gt40p heads. Erson makes a couple at .504 lift with 228 and 235 duration at .5. Since I had seen the stock gt40p's were good to .500 lift, I was thinking this was a good way to avoid new springs(my heads are new with new springs), just throw in the cam and off I go. Been looking at whole combination decisions and this is where I'm going so far: My ported heads should make peak HP around 6800 rpm based on flow, so I want to be able to run to at least 6500, just occasionally. Ok, 6800, REALLY OCCASIONALLY. I really need the 235 duration to get to at least 6500, and my heads are not going to flow much, if any, better at higher lifts than approx. .500. Have actually seen info saying the stock springs will go to .520 but am worried about float at higher rpms. If anyone knows the stock springs specs. that would be greatly appreciated. Thinking the Weiand Stealth intake, they claim good to 6800 rpm, have seen some good feedback on this intake. The Erson 235 duration cam is claimed good to 6500, the 228 only to 6000. Both the Erson cams are single pattern cams. Why do I want that? Because all the build combos I've seen of 400 horse 302's, non stroked, have used single patterns. I think this is because once you overcome the lousy exhaust flow, single patterns are better for overlap and make more HP at higher rpms, don't know if that is correct, but the high HP motors I've seen ARE single pattern, and measured results are good enough for me. Now, I include the 228 duration cam because I'm starting with a 289, not a 302 and am not sure just how much duration will work. Now all that said, what has my head really twisted is that my heads have double springs in them already and I don't think the stock spring setup is double. Any one know the stock spring setup, with tensions? I'm thinking I got some upgrade springs along with the porting but it wasn't mentioned(ebay). I'm going to ask, but it's been a while and it was through an ebay clearing house, and if nothing else I'll get them measured. Sooooo.... that makes me think I can probably support higher lift, which is available at the same duration, BUT, do I really care? I could avoid piston clearance issues at .504 I would imagine, be happier with lower spring tensions, and be happily back on my "how cheap can I do it" program. I have a build combo list making 400hp with only .517 lift and less flow than I have at .500, duration 232, single pattern. Also, I'm thinking 270-280 whp with this setup, 340-350 crank, non roller or I would be expecting more. Starting with a Holley 600cfm, just because I have it but that may go to 650 or 700. Headers will be 1 5/8, however I end up with them. Probably a 3000 stall converter, 9.5 to 9.8 compression, 3.5 to 3.7 rear. I do want to drive it on the street. oh, ps, checked the tach on the exploders with gt40p heads and they go to 6000 with no redline on it. Anyone know the real stock redline on these motors and lift?
The stock GT40Ps came with single springs for use with a hydraulic roller cam. They'll also work fine for a flat tappet cam. If you have dual springs somebody else must have installed them. A machine shop can measure seat pressure, available lift, and open pressure. If the open pressure is too high you could collapse a hydraulic flat tappet lifter or damage a camshaft. Cam gear manufacturers can then tell you what pressures work with their hardware. Your correct about better breathing exhaust ports only needing a single pattern cam. When exhaust-to-intake flow is around 75% or less a dual profile cam is suggested. Once exhaust flow gets to about 80% or higher of the intake flow a single pattern cam is better. To get P heads to flow more air with higher valve lifts and durations you need to not only open up the runners and ports but also the "hourglass" venturie above each valve. These keep velocity up for great low rpm torque. If you grind them out the head will flow more air at the cost of losing some low rpm grunt. With my own GT40Ps I'm running an Edelbrock Performer Plus cam with 1.7:1 roller rockers for valve lifts of .478/.502.
Redline depends on balance and valve spring capability. It varies. Stock balance is suppose to be good to 6250.
cool So I'll have to get the springs measured and see what I've actually got. Hope they work, expect they will, maybe I made out even better than I thought. Since the heads were already ported when I got them, someone probably set them up for a project that never got done. If they weren't going for a lot of lift I should be good. What duration is your cam BMC? And are you running stock springs, and if so, any float problems?
204/214 duration @.050". No problem with float, the roller cam springs are a little stiffer than normal factory flat tappet springs.
The problem (as I see it here) is that you're more concerned with upper rpm (6000 and higher) than you are with low/mid range power. How often is the engine going to see beyond 6000 rpm? Now then, how often is the engine going to see 4000 rpm? Or 5000 rpm? Or 5500 rpm? The engine will see 4-5000 rpm much more often. Especially after a gear change. If you tunnel-vision your way into high-rpm power only you're going to end up with a real pig on the street. Especially with 3.5-3.7ish gearing. With this type of application you really should not go higher than 226 degrees of intake duration at .050". I don't care how well the heads flow or what power numbers they promised you at 6500 rpm. Down low...on the street...when you nail the throttle it's going to be a dog if you over-cam the engine. Single pattern cams: they're easier to grind so they're cheaper. They also make good bracket race cams because of consistency. There are some good single pattern cams out there that make good power but a majority of them use a single pattern on the lift and a split duration. I don't use straight lift/duration cams because they do not come close to maximizing the combination like a well selected dual pattern camshaft will do. Something else to think about.....cam grinders give you an rpm that the camshaft is "good up to here". Generally speaking, the cams will rpm higher than the number listed. If it's the money you're concerned with, then why not try Speed Pro? Just as good a cam as anyone else and they're priced nicely. Here are some suggestions for your combo: CS1020R .472/.496; 214/224; 112 c/l CS1141R .496/.520; 224/234; 112 c/l (My choice for your combo) CS1162R .496/.520; 224/234; 110 c/l Your combo: Stealth intake: great manifold. Will run to 6500 with a bit of work. Makes excellent power up to 6500 but will fall off rapidly after that. Holley 600: Too small for your combo. Headers: 1 5/8" is good size. I have seen combinations such as yours with 1 1/2" primaries that hauled ass and had killer throttle response. Converter: At least 3000 rpm stall speed. Gear: Minimum 3.7ish gears. Preferably 4.11. PS: If you're really worried about price then PM me. I might be able to help you find something since I get a pretty good discount at most places here in Houston. Just trying to help.
not quite yet, but yeah. 2 or 3 weeks away from actually buying what's left, and I didn't mention any pistons, still have to research that. Suggestions for the c/r I'm after? The car is going to be a toy, and I'm more interested in having the hp when I really want it over civilized daily driving, it will only go out for fun, not to work every day. I realize the carb size will be my weak link, but probably just starting with that 600cfm and a couple months later something really nice. The build combo I'm sort of imitating makes great torque numbers, 370lbs, I'm sure it will still have some usable torque down lower, that duration really isn't all THAT high. Don't know if my throats are ported as BMC mentions above but if they aren't I'll leave them that way to help with broad torque. Flow is supposed to be 218/156 which is believable, the build I'm following had 190/146 with early 289 heads and makes 401hp at 6500/370torque at 5000, so the torque peak wasn't too high. And that's the 232 duration single pattern with .517 lift, Joe Sherman build, so I'm sort of decided on that already. C/r on that motor is 9.54/1, and I want a little more to make up for the fact it's a 289, and my combustion chamber should handle it fine. It doesn't say, but I've been thinking it is probably a roller block, but with that cam I'm not so sure now. ....Probably just wishful thinking. If so, I'm down 30-40 hp right off the bat. Bottom line I want high hp and I've got to go up in the rpm range to get it. But i think I'll still end up with a fairly broad range motor. My bike(FJ12, yeah it's really different) has a huge hit at 7-10 k and if you just looked at the dyno sheet you would automatically go "whoa, real high end motor", and it is, the hp curve takes a big turn almost straight up at 7k, BUT it still makes 25 hp over a stock one from 3 grand to 7 and lots more torque too, I think it's perfectly driveable on the street even though there's no grunt under 3 grand. Hoping for the same kind of effect, at all lower rpms of course, and I just don't mind the real low end loss to get the high end power. And I think this combo is going to have a pretty smooth curve anyway, i.e. no light switch point like the bike has. Thanks for the comments and the offer to shop around for me, I'll definitely pm you when I'm ready with a list.
You won't be able to go too much higher on the CR with iron heads and still run pump gas, 9.5:1 is usually about the limit. But a cam with more overlap will lower the actual cylinder pressure, so you could go a little higher and not detonate. One thing to remember about P heads, because the spark plug is located in the center of the chamber as opposed to the side of the chamber with "normal" Windsor heads, they don't need as much ignition advance. The flame front starts in the center and goes outward. Other heads have the flame front moving from one side of the chamber to the far side. Takes longer (needs more advance) and has more time to cause detonation. I used to run 14* advance with the 351W heads, my Ps seem to like about 10*. That fact may help keep you out of trouble with detonation, too.
