What valve springs to use?

hobieboy · 11-15-2005, 06:14 AM

Hi,
I'm rebuilding the engine and am debating on what valve springs to use.
My plan is to go with titanium retainers but am deciding on stock vs stiffer springs.
My understanding is that stiffer spring will both rob HP and put more load on the cam (hence wear).

So, does anyone know what safe RPM can the stock valve springs sustain?
The car is mainly used on track and I can see me revving regularly to 6700.

Thanks...

cstreit · cstreit's Garage

I used the EBS VMAX valve springs in my last motor... Good for 7500 easy with a modified S cam. Used Ti retainers with it as well. 4 seasons and still good with no discrenable wear patterns on the cam (which incidentally is a hard-weld)

HawgRyder · HawgRyder's Garage

Are the old Vasco-Jet springs still available?
We used to use them for the drag cars because they lasted so long.
The regular springs go "soft" in time but the V-J springs used to get "harder" after about 30% of their time.
They would be great for many more hours, then suddenly break after a long time.
We got used to that and changed them about once every 3 seasons.
Bob

Jeff Alton · 11-15-2005, 07:54 AM

Camgrinder who posts here often has two different sets available. Check out his website www.drcamshafts.com

Cheers

camgrinder · 11-15-2005, 08:23 AM

More information is needed. Things like cam selection, valve sizes, rpm range etc. If you miss shifts the performance springs are good insurance on a factory SC or 964 camshaft.
The racing springs are better for 7500+ rpm shift points.

cgarr · cgarr's Garage

I am going to use the New Super Cup cams and performance springs from John when I rebuild this winter, which could be this weekend!! I think these springs are one step down from race springs? good to 7k without any problem

camgrinder · 11-15-2005, 08:30 AM

Craig,
yes they are good to 7k easily.

JoeMag · 11-15-2005, 08:36 AM

I have stock springs on my car. Red line at 6.800 rpm, and go there a lot. 3+ years no problem except a recent over rev way past 7k which broke an exh rocker. car has 964 cam, '82 930

camgrinder · 11-15-2005, 08:40 AM

Yep, the exact application for the performance springs. The SC and 964 cams are fine to 6800 with factory springs, but missed shifts cause problems like broken valve springs, broken rocker arms and dropped valves.

hobieboy · 11-15-2005, 09:43 AM

Hi John,
I have SC cam with a K27HF right now and am going EFI.
I am contemplating going with a 964 or your GT Evo cam with EFI, but as it stands, I feel that my torque is still flat enough all the way to 6500 rpm.

I haven't missed any shifts (so far) but go to & stay at the 6800 redline a lot - in fact, that's the reason why I'm rebuilding the entire engine. I had valve float right @ redline and seriously dropped & bent an intake valve.

I'm leaning on using Ti retainers with stock springs, and maybe shim it up a tiny bit? I thought this set up might cause less load on the cam/valve train but still give me some insurance?

Comments & suggestions?

thanks.

camgrinder · 11-15-2005, 10:16 AM

The Ti retainer with a new stock valve spring would work for the 964 profile. But your only adding a little insurance, not enough in my opinion. The GT2 cam wants more spring pressure for sure.
Shimming the stock spring for either cam will be tricky. Both cams have high valve lift. You will want to keep the valve spring about 1.5mm from coil bind.

hobieboy · 11-15-2005, 10:38 AM

umm... so should I go with your performance spring set up with Ti retainers? If I am not go to rev >7000, I dont think I'd need the racing springs?

How much more spring pressure is there between the performance & stock springs?

cgarr · cgarr's Garage

Cant a high lift cam interfere with the valve guide seals too?

cstreit · cstreit's Garage

Quote:

Originally posted by cgarr
Cant a high lift cam interfere with the valve guide seals too?

OH YES. Particularly the teflon ones... BTDT

911pcars · 11-15-2005, 12:02 PM

For the record, anyone care to contribute some valve spring specs ?

Sherwood

KobaltBlau · 11-15-2005, 02:24 PM

Quote:

Originally posted by cgarr
Cant a high lift cam interfere with the valve guide seals too?

Yes, a UK member recently had this problem with 993SS cams in his 3.2, if I remember correctly.

cgarr · cgarr's Garage

I think I remember reading about that, I think you need to take off about 2mm on the guide for them to clear?

camgrinder · 11-15-2005, 03:09 PM

The factory spring typically installs at 60+/- lbs. The performance spring installs at 90 lbs and the racing spring at 110 lbs.
I do not make a Ti retainer for the performance springs. The factory retainer works fine.

The idea higher spring pressures cause premature wear or failures is valid. However at these spring pressures (110 lbs @ installed height) I am not concerned with these types of faulures.

cstreit · cstreit's Garage

Quote:

Originally posted by cgarr
I think I remember reading about that, I think you need to take off about 2mm on the guide for them to clear?

That sounds about right...

camgrinder · 11-15-2005, 10:12 PM

I wouldnt use 2mm as an absolute guidline. Every combination can be different. If you pulled out an SC cam with .450" valve lift and installed a Super Cup cam with .490" lift, the guide should only require 1mm removed. If you use aftermarket retainers, seals, or new valve guides you will have to measure the clearance.