Anyone KNOW what is the most lift I can put on GT40P heads (even with spring swap)

I am looking into swapping springs and putting in a new cam, but with 1.7 rockers, it is very difficult to buy a decent cam and stay under the .500 lift that the stock P head springs allow. I was thinking if I put new springs that would allow .600 travel, how high could I go with the valves before they start to mess up?

I would be happy with a cam with lifts near .550 so I don't think I need to push them to .600, but would rather have springs that can go safely with my other components. I don't want to do a THIRD cam swap anytime soon

 

I believe you'll regret not getting that monster cam when you're at the track, or when that Mustang GT pulls up beside you.

This is my 3rd cam in my engine. Mine is a hydraulic cam and it has a .601"/.605" lift. I spent a LOT of time and money finally getting there. I wish I'd gone straight to this one in the beginning.

I know it's hard to understand and get the mindset, however, I recommend bearing down and saving up for the parts you'll need for that monster cam. You won't regret it (IMHO).

Good luck.

p.s. can't you just get shorter pushrods to accomodate the 1.7 rockers? Plus, you should be able to get a grind that will work for the rockers/push rod setup you currently have (please jump in anyone to correct me or elaborate on that).

In fact, I'll bet there's folk out there who will swap you even stevens for some 1.6's if you're stuck on using them.

P.S.S. To answer you're original question, "I'm sorry. I do not know."

 

If I spend the $325 and my heads/valves can take it, I will put on springs good for .600 and put the biggest cam that I can fit in there. But I am not sure that the valve travel can take it. I KNOW the springs will, once I swap them, but not necessarily the valves.

If they can...:evilsmile

I will be the one-of-a-kind running .750 lift on an 8.0:1 compression engine...(for a while, at least...until I slap on the 6-71 blower)

 

Go to comp cams website,and go to cam help icon,they will ask you for your complete combination then they will email you they're best recomendation for a camshaft.I understand what Rick is saying about a big cam,but you don't really want a overcammed slug while you are waiting to do more upgrades.

I'm not sure exactlly what you mean when you say your not sure the valves can handle the lift.What you need to be concerned about is piston to valve clearance.Sometimes stock pistions do not have large enough valve reliefs in them to clear huge lifts.Thays why i sugesst CAM HELP they will know what will work

 

Well, my pistons are 8:1 stock pistons with pretty deep dishes, so at this point I am not all too worried about piston to valve clearance (I am one of the lucky few who doesn't need to worry about this...benefits of a very low compression engine)

So at this point, it is probably safe to run .550 lift and a pretty bizarre cam...

AND...I have emailed comp with all my specs and a question on what would be a quick easy and CHEAP fix (ie, no spring swap) and what would be a typical mid-budget upgrade (new cam, springs, etc.) for my heads.

But I didn't email them until late friday night so I don't expect an answer until monday or tuesday.

 

Uh, it doesn't work that way. Shorter pushrods have nothing to do with the lift increase from using 1.7's over 1.6's. The only time you want different length pushrods is to correct the rocker arm geometry.

 

The only other dimensions you have to take into account in going bigger on the lift(other than what the springs are rated for) is the distance between the bottom of the retainers (at the installed height) and the top of the valve guides. Any competant machinist can measure that for you. The retainers hitting the guides & coil bind, are the limiting factors, not the valves themselves.

 

And you can now forget about running a .750 lift cam, that ain't gonna happen with GT40P heads.

 

Oh and don't forget non adjustable valvetrain will limit your "big cam" choices.

 

Don't forget how duration, lobe separation and cam timing affect valve to piston clearance.

Since you have the intake off, you might as well pull a head and check valve to piston clearance once you've installed the new cam. It's not that much more work to do the job right.

 

Good advice. My cousin is building a really hot nailhead Buick. He has an early ISKY cam with some ungodly lift numbers, and brand new forged pistons. First time he ran the engine, he knew it didn't sound just right, had a strange tapping/ticking sound. He suspected the cam had too much lift, so he pulled a head, every valve had hit every piston enough to leave a mark! He was lucky, none of the valves bent and none of the pistons were damaged. He then pulled the motor back down and measured the pistons, they were .040 oversize bore and .040 oversize deck height! He had them custom made, and got in a hurry and didn't check them before installing them. He has since had them cut down .040, and flycut for the valves. Should be a hoss when he gets it finished.

 

The 40p heads are about done flowing (flatten out) above .500 lift for both intake and exhaust. Check the flow charts for these heads.
Going much farther accomplishes little because the rise in flow is very little per increased lift and just causes needless valve spring pressures.
Increasing cam duration on a low compression motor just keeps losing more and more low and mid range power making the motor come on late at higher rpm. This is what is called over camming a motor.
Unless you like this kind of result, you need to increase compression to gain back low and mid range with longer cam durations and keep the 'net' lift to about .550". They tell you in the cam discriptions that longer durations need more static compression.
In between all this, the changes must be checked for clearences at the springs and the piston to valve clearences checked if pistons crowns are raised to deck height and flat tops with valve reliefs are used.
Leave the push rod lengths stock for the late valve train. The only reason to change push rod length is a change in rocker height/ head height and/or valve stem length for some reason, which a stock unalterd head does not get into.

Photos show a 2001 long block with 40p heads, FMS headers, Crane 1.7 rockers and two different plug wrenches that can be used.
Cam is a 95 Cobra roller with 490" lifts on stock springs.
Second photo show a dial indicator mounted to check /set lifter preload.
Should be between .020 and .040". Shim or alter stands to get between those limits or adjust stud height and lock in place.
CR = 9:1 stock.

 

Yeah, but I just figured I would say "valves" and everyone would understand what I was asking.

I was just kidding I am really hoping for somewhere closer to the .550 range.

And Bluegrass, as always, thanks for the great information. So my .550 is not a bizarre goal to shoot for...

 

Hey Scooper...keep in mind too that the cam choice for a blower motor and a normally aspirated one are different also. So if you are planning to go pressurized one day, you will either be making another change or you need to consider it now. Good luck!!!

 

I would like to add a blower, but that is WAY down the road. WAAAAYYYY down...

This engine will be long gone by then.