Louie928

I don't know if those are available anymore or not. They do work. I've not checked with a cam grinder, but it should be possible to grind S4 cams to get something like GT+ cams. There is also the '85/'86 cams that can be modified to work in the later 4v heads. I used to be put off by trying reground 928 cams with higher lift, and the requirement for using lash caps on the valve stems and grinding a relief in the lifter next to the oil supply hole. Seemed too much like untried voodoo. After using the B1 cams I'm thinking it's an ok route to go. I have 7000+ miles on my engine now and changed the oil last week. I had 4000 miles on this oil (Redline). Previous oil change was at ~2700 miles. The drain plug magnet had no black residue at either of these changes so I'm thinking cam/lifter wear is zero. I have stronger valve springs too. Probably the key thing is to be sure the cams are properly heat treated after grinding. I'm also watching the timing belt and sprocket wear closely and expect to replace it sooner than normal. So far, it all looks good.

John Speake

Were/are B1 cams just a regrind of an existing 928 cam, or made from a new billet ?

Louie928

Regrinds. Mine were S4 cams in a former life. I've seen some reground from GTS cams which offer about 1mm larger base circle than mine have. My base circle dia requires 2mm lash caps on the valve stems.

andy-gts

Louie,
very informative ...thanks for the dialog...Since you have a monster engine and I think B1 cams...and devek is defunct, do you know the specific grinds on the B1 cam so we can get some ground also to those or close to those specs..
Just a thought.
andy

john gill

From personal experience I reccommend that you look at a set of 85 86 cams & regrind them for as much lift & duration as possible as I have done to my rebuilt GT engine , if you think it goes from stock , you should feel it now , to make the cams fit you only have to make a sleeve spacer which any machine shop could do , these cams in a stroker would be sensational , no lash caps were required. I will have some power comparisons as soon as my dyno house is complete .

mark kibort

How do you regrind the cam for more lift and not use a lash cap? can you take a mm of the low side of the base circle, and have the lifter pump up with more oil to accomidate the smaller "low side" radius, and then suddenly, you have more lift (because the lift is the ratio of the low side and the high side of the cam, right?)

Ive often wondered about this possiblity.

mk

john gill

the cams were done at Elgins , your question was on my mind prior to assembly , however after careful inspection & measurement ,(we made a special set of lifters from old units with light springs to test ) we found that the extra lift we achieved (11mm) was within the capabilities of the orginal lifters , and after running the engine , found to have no issues at all with oil pressure

Dennis K

We're looking at doing something similar on my engine w/ the S3 (85/86) cams. Looking at the numbers, the dynamic compression ratio drops when running S3 cams on a stock S4 head/piston combo. How does the midrange feel? When do you think you'll have dyno graphs? Were there any other mods besides the cams? I'll be extremely curious to see how it turns out.

IcemanG17

It is a bummer that there really isn't any "blank" cams out there for 928's......regrinding exsisting cams has its limits......

But the GT cam in the GTS is the hot setup.....I rode in a 5 speed GTS with this setup and it is quite strong!!

Jim Morton

Brian:

Just wait until Dennis' engine is back together... Lots of folks working hard to make it work much mo' better !

;^)

Louie928

Andy,
You might check with John Veninger. He had his own cams ground and they work very good in his 6.5L, ITB, engine. I don't know what he started with.

Louie928

Mark,
That's how you do it. The lifter can handle < 1mm smaller base circle without lash caps, but any more than that and you run out of the amount of "stretch" the lifter can handle so need lash caps.

Vilhuer

Has anyone measured how much higher in head lifter can be before oil feed to it suffers? Its obviously possible to make feed groove in head wider so this is easy problem to solve.

I can't recall if '85-86 heads have this groove or not. These early 32V lifters have their own groove too so heads might not.

john gill

We're looking at doing something similar on my engine w/ the S3 (85/86) cams. Looking at the numbers, the dynamic compression ratio drops when running S3 cams on a stock S4 head/piston combo. How does the midrange feel? When do you think you'll have dyno graphs? Were there any other mods besides the cams? I'll be extremely curious to see how it turns out.
__________________
Dennis

Engine was a 90 gt , we ported the heads , fitted larger 968 intake valves (928 part no,) ported the throttle body , extruder hone the manifold , machine the pistons to allow the valves to fit , has 944 conrods (early 87 32 v) 180 degree crosover exhaust , fully balanced .

On driving the engine has more torque , more mid range & more urge up top I, intend to increase the rpm cutout to 7200 . It is crnaky to drive around the city as you can feel the cams , the fuel economy is better slightly than before until you use the power , it is very difficult to drive the legally , as the urge to use the power is always there . will be very interested to see what the output will be after I sharktune it .

Vilhuer

Just spoke with machinist who soon modifies S3 cams to fit into GTS heads. Asked him to take 0.5mm away from base circle while at it. Besides resulting cam lift increase also opening times will obviously be little longer, don't know how much longer exactly. He thinks this will move peak hp and tq maybe 500 rpm higher up in rev range. Does this sound right?