a6t8vw Posted June 6, 2007 Share Posted June 6, 2007 maybe a simple question but i dont know, what is max lift for stock heads? does it come down to just valve springs? a friend said run Z28 valve springs and you can run .550 lift..? so my question is what can i do to my stock heads to run a .500" lift camshaft? andy Quote Link to comment Share on other sites More sharing options...
blueovalz Posted June 6, 2007 Share Posted June 6, 2007 Valve springs would be the first issue I would think, but a .500 lift should be within the realm of just about any spring these days. Pressure and rate must also be considered based upon the cam profile. Lastly, you can always change the rocker ratio if you're looking to keep the same cam, but increase the lift (and duration ever so slightly). Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 6, 2007 Share Posted June 6, 2007 Typically you would need to machine the head to hold larger diameter springs then use high performance retainers which normally raise the spring install height about 0.050" to 0.100". Also the valve stem seals used can effect the total lift. What heads do you have and what cam do you want to run? Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted June 7, 2007 Author Share Posted June 7, 2007 honestly i dont know what cam i want to run, but im about to install a holset H2 turbocharger, i dont know much about it but its about the same as a HX50. Fresh stock rebuilt 195 heads form a 73 truck. i know the're not the greatest but they were cheap.. With the dished pistons that came with this motor - with low 8.5:1 CR led me to the turbocharger. It was either that or i needed to change the pistons. Not that i really wanted a "turbo sbc datusn" because i know i could build a kick ass N/A motor to the same HP but ive always wanted to play with a turbo and since this is my project car here we go. but as far as the cam goes I really just want to move the powerband up quite a bit and get some good lift/duration for the forced induction im shooting for 450hp I was thinking this cam Hydraulic Flat Tappet, Advertised Duration 274/ 292, Lift .487/ .501, Chevy, Small Block, http://store.summitracing.com/partdetail.asp?part=CCA%2DCL12%2D564%2D4&autoview=sku thx, andy Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 7, 2007 Share Posted June 7, 2007 Not a good turbo cam. Turbo cams have wide lobe angle seperation (112 to 116) Plus, turbo cam typically have more intake duration than exhaust duration. Go to Compcams website and check out their turbo cams for the chevy small block. If you build a 300hp engine and then add 7.5 psi of boost then it will make 450 hp. Or if you build a 270hp engine, it will take 10 psi of boost to make 450 hp. Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 7, 2007 Share Posted June 7, 2007 check out these turbo cams from compcam. cam number: 12-252-4 212/212, 112 LSA, 0.447"/0.444", power range 1800 to 6000 rpm or cam number: 12-253-4 218/218, 114 LSA, 0.462"/0.455", power range 2200 to 6500 rpm Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted June 8, 2007 Author Share Posted June 8, 2007 check out these turbo cams from compcam. cam number: 12-252-4 212/212, 112 LSA, 0.447"/0.444", power range 1800 to 6000 rpm or cam number: 12-253-4 218/218, 114 LSA, 0.462"/0.455", power range 2200 to 6500 rpm I was thinking of something more radical... but that second cam 114 LSA should be potient and i could probably swap it in with the stock springs right? Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 8, 2007 Share Posted June 8, 2007 I wouldn't use stock 73 truck springs. However, there would be no need to do expensive head work to allow for the larger diameter springs. A set of the old "z28" springs (stock diameter) would be good enough with that cam. You could try the stock springs but I would bet there will be valve float at 5500 rpm. When you disassemble the head to change the valve springs, that would be a good time to do a little bowl work on the heads. Just spend about 5 minutes smoothing out the area where the head meets the valve seat (about 1 inch under the valve). There is typically a big edge there and some casting marks. You can pick up 20 or 30 hp on stock heads with this simple procedure. But don't hit the top of the valve seat with you grinder or else you will be getting another valve job. 7.5 psi of boost will add 50% more power. So the more power the engine makes off boost, the more power an engine will make on boost. For example, a 250hp engine will make 375hp with 7.5psi of boost and a 300hp engine will make 450hp with the same boost. That 250hp engine would need 12 psi of boost to make the 450hp. So, the power your engine can make off boost is important also. Therefore, cam, springs, intake, head work, ect, can all help make more power with boost. What transmission and rear end ratio are you planning to use? Make sure to use diesel engine oil with your new cam. Quote Link to comment Share on other sites More sharing options...
TravRMK Posted June 8, 2007 Share Posted June 8, 2007 Also, you should figure out how much boost you want to run before you get set on stock springs, especially if they are old truck springs. The more boost, the stiffer the spring. But, I am sure you allready knew that. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 8, 2007 Share Posted June 8, 2007 The big problem with using higher lift on stock heads isn't just the springs, it's retainer to guide clearance! Seat pressures exceeding 100 lb can cause the press in studs to pull out. Old skool method was to drill the studs using a cobalt drill bit and use cold roll pins driven through the boss and stud to "pin" them. The real way to do that is have them machined for screw in studs and guide plates. Another upgrade you need to do with stock heads is retainers, high seat pressures tend to pull the keepers through the retainer. While your at it, have them cut for 2.02 and 1.6 valves and do bowl work. All of this necessary machine work is what makes sportsman 2 or dart iron eagle heads so attractive. You'll get more flow with an out of the box sportsman 2 or iron eagle head than you will with a worked set of stockers and by the time you get the machine work, springs, stainless valves, etc, etc. you'll be about the same $$$ wise. Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted June 9, 2007 Author Share Posted June 9, 2007 Great info there guys. thanks very much... it just so happens i just bought a set of heads off the neighbors! they were rebuilt about 10 years ago and sat ever since, (acually i bought the whole motor) 4 bolt with forged pistons .03 over... but im going to disassemble the heads and do some "bowl porting" like pyro stated. I used to port/polish 2 stroke engines for a living years back so i have alot of porting skills but never a car cylinder head with valves and 100% CAST IRON! uggh. Right now i have more time than money lol so ill dust off the ol Foredom flex shaft grinding tool.... Anyone else got any porting experice/tips? Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 14, 2007 Share Posted June 14, 2007 That's right. The doc has a good point. Screw in studs would be a good idea. And check retainer to oil seal clearance. And yes. you should consider a set new of dart iron eagles or sportsman II's. Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted June 14, 2007 Author Share Posted June 14, 2007 That's right. The doc has a good point. Screw in studs would be a good idea. And check retainer to oil seal clearance. And yes. you should consider a set new of dart iron eagles or sportsman II's. how does the iron eagles compare to the new platinum's? because the iron eagles are really cheap right now! Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 14, 2007 Share Posted June 14, 2007 The iron eagles are about a 70HP increase over stock heads, so it's significant. You won't be sorry. Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 14, 2007 Share Posted June 14, 2007 I use a 200cc dart iron eagle on my Z. They flow very well on the exhaust side. Their intake flow isn't the best but isn't the worst either. I'm sure a little intake bowl smoothing would bring them up into the AFR head range. My engine makes around 435hp with a compcam 292H using those heads (120mph in the 1/4 mile with a curb weight of 2700 pounds). And that is out of the box, I haven't done any bowl work on those heads. And it made 625hp with a 200hp shot of n20 (135mph trap speed). Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted June 16, 2007 Share Posted June 16, 2007 Not a good turbo cam. Turbo cams have wide lobe angle seperation (112 to 116) Plus, turbo cam typically have more intake duration than exhaust duration. Go to Compcams website and check out their turbo cams for the chevy small block. If you build a 300hp engine and then add 7.5 psi of boost then it will make 450 hp. Or if you build a 270hp engine, it will take 10 psi of boost to make 450 hp. So a supercharger cam is different ? Im doing a supercharged 383 and all the cams ive looked at have less intake duraition then the exhaust . But then i looked at turbo/nitrous cams and it was the other way around why would this be as a turbo and a supercharger are the same thing to a point . I dont know to much about cams and duraition . i ended up with a blower cam with a .050 dur of 222 intake and 234 exh with a 109 and 119 lobe center . I even called Weiand and that is what they recomend more exhaust duraiton then intake . Sorry this doesnt have much to do with the origanal question i just saw a response that made me think a bit . Jason Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 17, 2007 Share Posted June 17, 2007 What I've read is that a supercharged (crank driven pump) engine has the pump pushing the mixture into the engine, so less duration is needed on the intake. But with a Turbo, you are feeding the turbine with the exhaust, so more duration can help drive it. Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 18, 2007 Share Posted June 18, 2007 Turbos like less exhaust duration to keep the exhaust flow at high velocity. This helps spool up the turbo. N20 and blower cams are about the same (more exhaust duration). This helps get rid of the extra fuel and air beening burnt. In all three cases, turbo, supercharger, and N20, less over lap is a good thing. So when longer than stock durations are used, wider lobe separations angles are required. In your case, a cam with a 109 intake center angle and a 119 exhaust center angle (LCA) has a 114 lobe seperation angle (LSA), (109 + 119)/2=114 . Which is about right. No over lap at 0.050" with a 222 intake/234 exhaust duration cam Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 19, 2007 Share Posted June 19, 2007 Turbos like less exhaust duration to keep the exhaust flow at high velocity. This helps spool up the turbo. IMO the cam selection should be based on the induction package, which is intake and heads in the turbo application. Area under the curve dictates total mass flow for a given application, not sure what you mean by less duration makes the exhaust flow at high velocity. You still need to evacuate the cylinder no matter what, cutting down on duration won't achieve that with all other things being equal, only a good flowing exhaust port will complement your statement, otherwise a poor exhaust port may benefit from more duration and/or more lift. Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 19, 2007 Share Posted June 19, 2007 Turbos like less exhaust duration to keep the exhaust flow at high velocity. This helps spool up the turbo. Well, a lot of the energy that spins up the turbine has to do with the heat in the exhaust, from my readings, and less on flow velocity. So if that's true, then the less exhaust duration thing doesn't hold up. Not saying I'm sure, but wondering if I am correct. Quote Link to comment Share on other sites More sharing options...
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