Does anyone know what is the most lift one can run on a cam with the stock crank and heads?

I'm looking at one with .568/.592 with 1.6RRs, and am wondering if I could get by with 1.7RRs for .604/.629. I will probably port the heads somewhat in the future, so stalling the stock ones is not a big issue for me.

Anyone know for sure if this will work?

 

it's more a function of duration than it is max lift

you should measure to be certain.

however with that kind of lift you will need great springs and lifters as well.

You do know that cam will not work well with stock heads.

 

BPS is correct... CHECK!



The piston to valve clearance Will be dependant upon the individual shortblock/head setup, and lobe profile along with where it's ground.

Some use clay, we use feeler gauges or a dial indicator, but any method is preferable to none

Good luck

 

So there is no way to know ahead of time?

Because, I need to know whether to buy 1.6 or 1.7RRs. I know the 1.6RRs work fine, as someone else had that combo. But not sure if the increased lift from 1.7RRs will work.

This is the GTP6 cam, 236/245 @ .050.

 

I'd ask other people with the same grind (lobes/lsa/icl) & see what kind of clearance they're coming up with to at least get an idea. Headwork etc. will all change it a bit however, so you will eventually just have to check IMO.

 

You can only be completely sure by checking, but depending on your LCA simular cams have been used in LT1s with stock configureated pistons and stroke and never touched or cam close.

I am running a GM 847 in my 383 with 18cc dish pistons, 2.02 valves (5.7 rod) with 1.6 rockers my lift is 595 on the exhaust, I had almost a 1/4 an inch clearnace between my piston and the exhaust valve, the intake never really came close. On assembly we didnt take any off the rod bolt head, but I turned it over several times and they never came too close to the cam lobes.

 

Solomon,

One thing to keep in mind is that you will need a different spring that can handle the increased lift (above .600). I'd stick with the more common 1.6 ratio as the gains would be negligable, in my opinion.

Ryan

 

That sounds like a pretty big cam for stock heads. I hope you plan to port the heads soon or get aftermarket ones. The healthy duration of this cam is going to move your powerband way high up in the RPM range. People with CC306 cams are spinning near 7000 RPM; you might want to find out where this one makes power. Stock heads become a restriction at speeds like that, with the result that you will trade quite a bit of low end drivability for not-so-fancy gains up top.

To answer to your original question, the generally accepted limit for max valve lift on stock without any machine work is 0.600". Any more and you will need to get some work done to use different springs. Also, when you get a cam that moves your powerband so much higher in the RPM range you also need good hardware, such as new springs, lifters, possibly pushrods if you don't have hardened pushrods already, lightweight retainers & locks, etc. You don't want a weak valvetrain robbing power and setting your engine up for potential destruction while spinning at 7000 rpm. Of course, all of this assumes the bottom end is capable of spinning to those RPMs.

 

It's on a 114 LSA.

 

Yes but LSA is different from LCA, the LCA is usally tighter, the tighter the LCA the closer the exhaust valve will be to fully opened while the piston is at the top.

 

Yeah, and most LT1 cams tend to have 4* advance ground in, so that would make the LCA 118, correct? EDIT: I see I did it backward, so it would be 110 ICL.

 

do you mean ICL?

LSA - advance = ICL

So a 114 cam with 4 degrees will have a 110 ICL

I'd stick with the 1.6RR, if you really wat that high of a lift then go solid roller.

I have a set of new springs and Ti retainers and cups that will nicely support that cam up to .6 lift - pm me if interested

 

PTV Clearance is like Pushrod Length, you just have to measure and check it.

 

Listen to this man!

Rich Krause

 

LSA is the Lobe seperation angle in degrees ( crankshaft degrees)
ICL is what I was refering to instead of LCA which I beleive is also the same thing.

And yes you can sutract the advance to get the ICL.