andy-gts

awesome, I have a spare gts engine that would love to have increased hp and torque!!!!

ptuomov

That original GTS engine is probably going to be worth a lot down the road. instead of hot-rodding it, I would pick up S3's or S4's for fun projects like that, since they are going on ebay for $1200-$2500. For example: http://www.ebay.com/itm/85-86-PORSCH...83a0e4&vxp=mtr.

Who knows what an S3 engine would unleash with head work, cams, headers, and ITBs?

ptuomov

I went with stock size valves on the second engine (another 5.0), now I am not sure whether that was the right choice.

In the universe, outside the 928 bubble inside which the laws of physics are suspended, bigger intake valves allow for more flow and make more power -- 5.0 or not. If the cams and ports are matched to the larger valves, why wouldn't the largest possible valves make the most peak power? I guess theoretically one could be rpm limited and slow down the air speed at lower rpms and lose torque for minimal top end gain. If so, it's high time for the community to figure out how to spin these things like Hondas.

AO

Great job! Looks good too! And to think of all those out of work strippers... Oh well.

Hilton

My statement was based on gut feel from reading too much of rennlist over the years, coupled with comparison against S3 heads and dyno results - so its pretty much like reading tea leaves.

The S4 has larger valves than the S3 - but can't be as aggressive with the timing - so my assumption is that the difference is largely port velocity, and hence keeping the S4 valves with greater flowing cams will push velocities higher and combat detonation.

Of course, I'm just still in the parts gathering and idea-tossing phase - and trying to avoid the expensive parts-tossing phase

For shorter-term kicks I have some S3 cams to drop into one of my S4's (with the collar mod. by that guy in California) to go with an X-pipe I'll stick on it.. while I continue to slowly gather bits for another 5L engine.

daveo90s4

Tuomo, you say that bigger valves allow more airflow and therefore make more power, or words to that effect. In the 928 and other universes this is not always so. Air velocity makes a big difference in both purging the cylinders and refilling with the new charge. If valves are too big for the application then air velocity can fall, leading to a loss in power. In essence there is a compromise between volume and velocity that needs to be met.

Randy V

It really comes down to volume and stoichiometry.

Cheburator

running factory lifters and new factory GTS springs (had them lying about the workshop) ... interesting comment about the valve springs hitting bind before full lift...

cams are Stage 2, normal flow... now I wish I went with stage 3...

ptuomov

I agree with the velocity being important, and that's why I added the caveat for cases where the rpm is limited for some reason. If the rpm is not limited, I think you will make the most peak power with the largest possible valves (that still leave some unshrouded flow area near the bore.) The cams, port, and runner will also have to match the larger valve size.

The velocity is important, in my opinion, mainly because higher velocities produce stronger pulses. But I think you can get the velocity up on any port by just running the engine at a higher rpm (and cams and runners matched to that).

Rick Carter

Is your dry sump easy to duplicate? Are you going to do more for oil control, if so what?

Cheburator

The dry sump system is easy to duplicate if you are a good welder - we use a custom pan. Everything else is pretty much off the shelf stuff. Ok, custom pulleys and a pump bracket, but they are not exactly rocket science. The pan is a bit more complicated as we use dual pick up - one on each side of the crossmember.

I ain't doing anything more about oil control - the previous engine run plenty good with the same drysump. It pools oil in the heads - so what? There is plenty in the oil tank, even at 6000rpm, so I would live with it. The most important thing is that I always have constant oil pressure

LostInSpace

Very solid numbers, as a baseline you must be pleased - congratulations.

Peak HP near the redline will be good for racing. Look forward to tuning updates, stick the long runners back on and take the 70 torques

Lizard928

Alex,

I'm not sure about GTS springs, but I know that S4/GT springs see bind just over .400" lift. The cams you have are .437" lift.

I will send you an email we may be able to get you up to stage III

FredR

A,

Well done mate you must be quite chuffed.

Regards

Fred

justaguy

Nice work!. I would be very interested in your dry sump design if you are willing to share.

I will be in London for a few days this summer. Do you accept visitors from this side of the pond? Are you located any where near London?