125250

I have turbocharged a 89 S2. The cams reprofiled for the turbo.1500 miles later the cams and lifters are shot.The cam maker thinks it is valve float. I am using stock springs.Only 14 psi boost. Has anyone had this problem? Do I need stiffer springs? Can anyone recommend a spring supplier.

mumzer

i think if the cams were regrinds that they were not re hardened to the correct spec.

Alan C.

Did you use the old lifters with the new/re-ground cam? I'll assume the cam was hard welded. Care to mention who did the work? Not as a slam but as a point of ref.

If the cam is hard welded and properly treated it should last. We hard weld rolls on our cold mills and those things take a lot of abuse.

What do you plan to do with the cams?

Alan C.

Sean Hall

944/951 cams need to be nitrided(hardening process) when re-ground.

-Sean

superjet.1

Not only that, you want to verify that the base-circle diameter doesn't exceed the maximum extended-height of the lifters. A cheater way to obtain more lift on re-ground cams is to grind down to a lower base-circle. But your lifters must be able to take up this slack with out exploding.

125250

The lifters were all new ,the cams were hard welded for a shorter duration higher lift,.030 higher intake and exhaust.

superjet.1

Oil supply issue possibly.Were all the lifters and loabs ruined ? If not which ones ?

TonyG

Dump the re-grind cams.

Everytime I've used a re-grind, I've had problems.

Your best bet is to contact either Huntley Racing or Devek (928 guys) and get some cams that have been ground on virgin billets.... and of course, you're going to have to buy new lifters.

This will eliminate the problem for good.

Good luck,

86944turbo

I agree, never regrind. It is a fairly common practice with these motors to increase boost for more power. The cam is critical. Most who develop them do not reveal all the specs. Too much R&D invested. Changing springs, keepers, etc. is very important. Last summer I spen some time at different shops that build race motors for circle tracks. Most of these were 350CID chevies. All shops had plenty of customers and a valuable reputation. All, w/o exception replaced springs at a very regemented time frame, about 3 races. Partly because of the High rpm's. Partly to maintain a rep. for reliable motors. Mainly because they are not aware of engione harmonics and how to eliminate/reduce. These are not the Cup cars that spin 9000. More like 7800-8000. Jon Milledge, constanly works on harmonics, cam profiling, springs lifters, etc. Never totally satisfied. He told me that no customers (inc. me) have experienced any spring problems, since the harmonics that the cams were producing was reduced. I have 10k+ miles, regularly at 7000 and springs are fine. The alst cam installed was almost identical to the one it replaced in terms of lift, overlap, duration, etc. It produced approx. 20-24 more h/p and is easier on the valve train. The ramping was changed and now the valves do not bounce as much. He told me that one of the main reasons his motors are relatively expensive is due to the high cost os machine work he requires.

Now his heads have been redesinged, with new intake port shaping and are all CNC'd. They flow 14% more on the bench then previous. He's trying to develop more H/P w/less boost. Sizing the turbo for a 3L motor to approx. 680 H/P, 8 valves, solid lifters, dry sump, 8000 rpm.

Jon relayed to me that when he was at the Sebring races earlier this month, A Kelly Moss 944 (I think it's called a GTR. It's the one that ran in the Trans-Am.) with a 6L 928 N/A motor, producing 815 H/P and weighing in at 2300, or less lbs., would go by all 911 bodied turbos down the straight like "they were tied to a fence post".

Side note: I burned out several Throttle position switches anf Jon finally installed one that has no metal to metal contact. Not a simple install. Supposedly, F-1 technology (Ford team). Just as long as it works.