Carl Fausett

Here we get a little lucky. The 928 motor has never liked a lot of valve overlap, in fact, even increasing the exhaust valve diameter has led to a decrease in torque in most cases. The combustion chamber design is very efficient - ideal really - so valve overlap has been kept to a minimum as a lot of combustion chamber scavanging is not needed.

This helps the SC cars too - as boosted engines also do not prefer a lot of valve overlap.

So we get lucky. The best cam grinds on the NA 928 motors do not have a lot of valve overlap and that suits the boosted motors just fine. This is not common with all engines - but it is with ours.

I should pick up in the next day or two a complete set of stainless steel valves for the 928 that we have had made. I also have Titanium valves for the 928 (shown in photo below).
Intakes are 39.5mm (larger than 36mm stock) and exhaust are the same size.
These will compliment the camshafts very nicely. We have a couple choices of springs, and titanium spring retainers.

More coming soon -

Carl Fausett

Yes. When larger intake valves and seats are installed, they need to be unshrouded to fully benefit from their larger diameter.

IcemanG17

Carl
do you have weights of the Ti cams vs the stock 36mm cams?

BC

Brian's radar gun usage has fried his brain. He means valves.

Carl Fausett

...on pushrod engines. Any lifter that has a crown does need taper on the cam lobe. But most buckets (including our 928 buckets) are flat and have no taper on the cam lobes. The lobe is offset on flat bucket setups like ours to rotate the lifter.

if you did put a taper on a flat tappet engine, the load would be high on one edge of the lobe, the lobe wear would be accelerated, and the lobe would fail.

IcemanG17

Brendan is right...... where did I put my coffee

largecar379

Correct---big difference between overhead cams and pushrod motors.....


Carl--have you also considered offering a solid lifter cam for the 16V? a little larger dims than the big hydraulic you are offering?






--Russ

Lizard928

Russ,

Solid lifters on the 16V are going to be really tricky. Because you will have to remove the cam housing everytime you want to reshim it.
I have talked with Greg Gray about an alternative method which would allow adjustment without removing the housing. He is still working on getting that sorted.

largecar379

I too, have consulted Greg about this......still in the works last time I heard.

thanks--






--Russ

BC

I saw a pic of a 951 with 2 inch threaded "plug plates" on the side of the cam box. You removed them and did...whatever the person arranged in there so you could shim the lifter... somehow.

Lizard928

Brendan, Lindseyracing has this, but you have to remove the camhousing in order to shim.

slate blue

Colin is right, the Lindsay racing system is lighter but would be quite tiresome to use, if you want to use this system you can modify the existing lifters and the weight is 64 grams. I have a set I can part with quite cheaply as i do think I will be using Colin's suggestion with the allen key adjustable tappet. It is 20 grams heavier than my modified stock lifters but miles ahead in usability. The Lindsay Racing system lifter weight 57 grams and then you need to shim it which will probably weigh around 5 grams, so I just hope I can live with the extra weight.

To all I am sorry this job/project is taking so looooong it has been a painful exercise for us all, there has been a few set backs which are to be expected but there is a lot of R&D in this engine especially in regard to the heads and valve seats suitable to use with titanium valves and unleaded fuel. I am currently porting my latest design and I have high hopes that we will exceed 300 cfm at 0.550" on the intake, the exhaust is under control. The port is not that big in area at around 2.6 sq inches, this may be enlarged but I always start small.

Deciding on throttle body sizing is another difficult issue, as I am sure most of you realise bigger ports are not always better, the higher the airspeed the better the engine response, I can get 46 mm motor bike throttles from a Kawasaki, these are quite nice and have sealed throttle shafts with bearings, or if anybody has seen this site, www.extrudabody.com these guys are really nice guys and I should have probably bought the 45/50 tapered throttles but I thought they might be too small, I was offered a sample body to test but I was in hospital with a back operation and then the financial crisis hit and our dollar lost about 40% of it value in a couple of months, if you can believe it, it went from 98.5 c to 65c which it is today but a low of 59c was also achieved, that upset the apple cart.

Personally in regard to the Ti head shown in this thread I can't see the use of it, you have to remember that the GT3 uses bigger intakes and exhaust valves with more lift and very aggressive cams and uses steel, its rev limit is 8,400. I just say this because before Carl puts in a lot of effort and or money into this idea I can't see it as being a winner. Much easier to do something with steel valves, I achieved around 350 cfm from 39 mm intake valves at 0.500" so for all the dramas with dealing with Ti I just wouldn't do it, also if you cut the seats they should be cut under water and you need to wear a very good mask as the dust can KILL YOU!

Greg

Big Dave

Carl...they're definitely shorter. That's why I'm not using them. They were ground down when my tensioner came free from the head.



They're from cyls 1-4 on my '85 S.

I've refrained from putting them in the trash due to a hope that they may be worth something to someone.

mark kibort

wow, and that still ran???? i thought my 7 teeth missing was bad.
carl, where are the pics of your teeth on the cams?

yes, there is a guy in canada that has a process to replace sprockets. did some 968 cams.


mk

Carl Fausett

Valve Weights:

Stock intake = 2.1 oz
Titanium intake = 1.45 oz

Stock exhaust = 2.3 oz
Titanium exhaust = 1.4 oz