McGehee/Forza Supercharger Install!!!

Mike C,
I think the answers to these are in the thread, but darned if I could find them:

1) What clutch are you running?
2) Noticed you're keeping the stock belt cover. How much did it have to be modified?

'Gards,
Verell

 

still has the stock clutch and the cover on the 328's is left untouched.

 

Did you order the tiny 3" pulley yet ?

 

another thought is the BOV, if it's leaking then you'll never build the boost you should. there is a way to check, call me and i can explain. I'm also playing with an adjustable one at the moment, we'll see how that goes.

 

There are a couple things at work the best I can tell. I’m not sure how much of a 2v vs. 4v thing it is, I just haven’t seen enough 2v data. The cams on the late 2v are almost exactly the same as the 4v cams.

I know that the heads on most cars are exhaust flow limited. The lets the cylinder fill pretty well without losing air/fuel out the exhaust so mileage and emissions are better.

The 308 heads are intake limited. It seems like Ferrari got the intake flow as good as they could, the simply opened the exhaust up until the hp stopped going up. The exhaust ports on all 308 heads are way to big. I know at least on the later 2v engines they actually offset the headers a bit on the head to help the problem. For a boosted engine, that makes it really hard to keep the air in the cylinder.

My heads are getting ported now, the intake took days to figure out how to get the air in, special valves, new intake manifold, much higher lift cams and that gets the flow up about 25%. But on the exhaust side, it’s basically just getting a good valve job and stock cam….the flow only had to come up about 5% to make it match the new high-flow intake. The stock exhaust flows WAY too much to work well with the stock intake.

The second thing going on is the lobe separation angle the cams are installed at. The US cars are 107 degree, the euro cars are 109 degrees (mine are currently set to 109). A good turbo/blower number is 114, which is where I’m going to try my cams when the engine goes back together. The smaller the number, the longer the intake and exhaust valves are both opened at the same time…which lets the intake charge escape out the exhaust.

Combine the excessive overlap with the excessive exhaust flow and a lot of air/fuel goes out the exhaust pipe. I’ve found I need to pump about 50% more air than I should need to make any give boost number. In theory, when I install the re-flowed head and re-time the cams, that problem will be gone…but I’m still buying a blower big enough to deal just incase……

 

The cam timing is a tough one really. I know Ferrari spent a lot of time on the dyno deciding what to do. The 109 euro spec makes a wider torque curve (probably the widest possible) and the 107 us spec makes the highest peak hp.

You read a lot of stuff about how if you advance a cam it does x or retard a cam and it does y. I’ve never really found any of that to be particularly true. With Lobe separation angle (LSA) it seems that about 109-112ish works pretty good on all naturally aspirated engines. Less LSA and you lose low-end torque, due to blow down I think, but may gain a higher peak hp. More LSA and you start to lose top end, I think because there just isn’t time to fill the cylinders. Modern engines tend to be closer to 112 than 109 in general, probably for mainly emissions reasons, but it does generally work well on the dyno.

On my car, changing from 107 to 109 moved my torque peak down to about 5000 for 5500 where it was with the cams at 107, but didn’t do anything measurable to my boost pressure. So, if you want to get the boost up, you’ll need to go more than 109. 111 or 112 might be worth trying, but I don’t think 114 will be too much and it definitely won’t hurt bottom end and will probably help, but will certainly cost a bit of top end…I’m just not sure how much.

Any top end lose cause be increasing the LSA should be more than offset by the increased boost, if the engine will stand more boost. I’m honestly not so sure it will though. 5psi is safe. 8 psi is probably ok for a street car, but I’m not sure about track use, you really need to watch the mixture. 10 psi might work on the street, I’m not sure you’ll have the mixture control for it though….maybe. The point being, it looks like you’re going to get to the 8-10 range with your pulley change, so I don’t know how much you’ll gain by messing with cam timing….you might find 107 LSA=2.87 pulley, 114 LSA=3.5” pulley, but the hp is similar. The higher LSA will give more bottom end, so maybe it's worth it.

 

Have you installed any kind of knock sensor?

 

some tech notes:

the 4v and 2v share the same cam events (according to the WSM):

the base version -read Euro- calcs out this way,
Overlap = 30*
Duration = 244* both
Intake centerline = 106*
Exhaust centerline = 108*
LSA = 109*

and now the US version,
Overlap = 26*
Duration = 244* both
Intake centerline = 106*
Exhaust centerline = 112*
LSA = 107*

some more info, the area of the valves works out as,
2v:
Intake = 1371.58 mm/2
Exhaust = 1063.07 mm/2

4v:
Intake = 1320.37 mm/2
Exhaust = 1061.32 mm/2

 

I don't have my WSM in front of me, but there are a couple more key variables.

The valve seat ID area minus the valve stem area is key to flow along with the area of the valve perimeter times valve lift. Ideally, the valve lifts far enough so that the seat/port are the flow limit, but on the late 2v, if I'm not mistaken, the limiting area is the perimeter times the lift…Ferrari knocked something like .050” of lift out of the cam so the valve never opens far enough to get it out of the way.

Also, on both the 2v and 4v, the seat areas aren’t actually the smallest flow passage like they should be. The port at the manifold flange surface is a smaller area on both head…bad, bad, bad……

 

I am not sure you hear it if it were happening. That is the part that would concern me right now, especially if you have both those exhaust inserts out.

I am no mechanic but I am not sure just how dependable an aftermarket knock sensor would be for our cars since one was never designed by the factory. I would imagine it would need two sensors at the very least - one on the front bank and one on the rear. Then someone would have to decide where to put them and then drill two holes in the block to put them in. After that, we would have to figure out the correct torque values. I think it would be tough not just installing it but getting it to act properly.

The best insurance is probably just to stick with premium fuel ALWAYS.

 

right, that's just the area of the valve face. the stem cross section based on the WSM specs,
2v: 47.76mm/2
4v: 36.29mm/2 each or 72.59mm/2 combined

 

okay, if these settings work without smacking the pistons this would be ideal, it's on the extreme end though. exhaust adv 6* and intake retard 6*, idle quality etc unknown...

IO = 10*
IC = 54*
EO = 56*
EC = 8*

this works out to:
overlap = 18*
duration = 244*
Intake centerline = 112*
Exhaust centerline = 114*
LSA = 113*

 

For some reason, it almost always seems to work out better on the dyno when the numbers all match. SO 10/54 - 54/10 giving 112/112 centerlines with a 112 LSA is probably good and so would 8/56 - 56/8 giving 114/114 and an LSA or 114.....but some engines are different and it's a small change.

 

Mike,

What's going on??

I had to look deep for this thread.

So, how's that SC doing? The 308 running strong? And how's that new WUR doing?

Cheers,
Chris

 

I'm running the timing at 8/56 56/8, runs great! I bump'd the timing up to 16*, that's 2V though. i'll work on what the 4V can take.