Catorce

Friggin gorgeous!!!!!!!!

Kiwi'79

WOW!!!!

They should be facing OUTWARDS!!!

ptuomov

With the risk of derailing the thread a little bit, what are the units of those percentage gains that you are quoting? You probably don't mean that the stock heads and cams with ITBs would make X hp and with "wet flow" porting change only it would make 1.37*X hp? Or do you?

Getting to this thread's build, what kinds of cams are going in with those heads? It's a plenum manifold still, so I don't think one can go nuts with the overlap and expect it to run well in the lower rpms. But then again it's a race car.

Carl Fausett

In short, we are using more valve overlap in these cams because it is a NA motor than we use for our boosted motors. The cam grind we are using for this motor is our 928MS 32vR3 cames INTAKE .432" / 220 deg EXHAUST .398" / 216 deg LIFT/DURATION

The relatively small plenum chamber on the stock '87/'95 intake manifold is the very reason why I have taken the intake shoe to task to open it up, and create a larger plenum area behind the throttle body.

ptuomov

What's more overlap? Those specs don't nail down the overlap. You could have those cams set up with a lit of overlap or with almost none.

If you're planning to use a lot of overlap, then what's the strategy in these heads to manage reverse flow from exhaust into intake when the intake and exhaust are not exactly at their tuned rpms?

Carl Fausett

Yes, as I said, the numbers I posted are valve lift and duration, not overlap.

Cam phasing and cam timing will be adjusted on the engine dyno. So I cannot tell you right now what the final best valve timing/overlap will be. I will be trying several cam phasing and timing combinations to make this motor generate the greatest usable area below the torque curve.

ptuomov

Do you have adjustable center sprocket camshafts to adjust the overlap on the dyno?

Carl Fausett

I don't want to get ahead of myself here, and I don't want to turn this thread away from the original starter post. You know the OEM cam sprockets allow for about 10 degrees of adjustment, and you know that you can change the cam phasing by one link in the intake drive chain forward or back also. Because we are using a stroker crank, and because we have increased the CR to 10.4:1 there are natural limits on what I can do regards cam overlap without interference with the pistons. So there is a range of adjustment that we have to use, and we will use all of it. But I cannot tell you at this time what the best final valve timing will turn out to be, and I don't want to guess. I feel that is what the engine dyno is for, to eliminate guessing. We will change the valve timing and overlap within the range of adjustments we have, and report the results.

ptuomov

Just making the point that in order to vary overlap on the dyno, you need to fabricate camshafts that have an adjustable center sprocket. Adjusting the belt sprocket does not change the overlap. If the cams don't have an adjustable center sprocket, then in my opinion the overlap is cast in stone when the cams are fabricated. One could of course fabricate a number of camshaft sets with different LSAs, but that would be somewhat pricy and it takes a long time to swap cams on the dyno.

Strosek Ultra

Adjustable intake center chain sprocket like this.
Åke

Dave928S

Correct me if I'm wrong ... but how would that be useful, being that it would give a huge LSA change, and take you outside practical and usual 928 LSA range?

ptuomov

I don't think that's in practice useful in tuning.

Without adjustable center sprockets, I think what one needs to do is to burn some computer time and pick a relatively conservative LSA value and forget about it. Conservative value being LSA of say 114, but then again EMC winning modular Ford 4-valve engine ended up winning with LSA of 98...

One of the things that I'd like to do with a set of heads is flowing it from intake to exhaust and separately from exhaust to intake with the both intake and exhaust valves open 1mm and the piston at TDC (or something that simulates the piston at TDC). I say I would like to because I've never myself done anything like that. I feel (not to be confused with knowing) that this would tell me a little bit about how much overlap the engine likes and how much back pressure it can tolerate.

Strosek Ultra

If you change the cam phasing by one link in the intake drive chain forward or back you will change the camshaft position relative to the crankshaft by 19 crankshaft degrees which is huge and cannot be applied for fine-tuning of the cam timing.
Åke

Cheburator

Also, there is every chance that you will have piston/valve contact, particularly on a higher comp/higher lift engine. Don't ask how I know, but I do...

Strosek Ultra

Yes, you are all correct. When putting an engine together it is crucial to check the valve to piston clearance even for the worst case scenario. Also intake valve to exhaust valve clearance during overlap.
Åke