Bill Ball

Daryl: I think your measurement is good. It shows the filter and intake tube up to the MAF is not a restriction. Since the MAF and throttle body are narrower than the distal tube, they are an essentially (without a lot of extra parts and work) unavoidable restriction. It would be easy to T into one of the throttle body vac sources and see what it does at speed. I think it goes essentially atmospheric. If so, seems there is enough air for the engine pump at these boost levels even with the stock MAF and throttle body. I could temporarily move the source for my boost gauge there.

Daryl

Hi Bill,
Thanks for clarifying that. I think Tony is interested in the numbers after the throttle body. I think DR has him thinking about a larger throttle body.

I think Jim was concerned that the filter location may not be getting enough air. I think this test shows no problems at least at 8lbs boost.

Just to follow up on that idle issue. I have my bypass vacuum set up exactly like yours. Off the throttle body and appears to be working very well. After another round of checking each cylinder drop etc I am convinced that what ever issues there may be will clear up after tuning the air/fuel ratios. All cylinders are about the same including numbers 6, 7, and 8. The best way I can explain it is at cold it runs perfect and I am seeing 13s on my A/F gauge. When hot the A/F is 14s and the engines idle is a tad off. The kind of thing that would be fine tuned using the air adjustment screws on a carbureted car. Of coarse that is not an option for us but thanks to John, Louis, and Dave’s work those answers will come out shortly.

bd0nalds0n

Daryl,

I really like your intake system. Did you mention that the pipes are 3.5"? Where did you source the straight pipes and the 90 degree elbows? What material are they made out of, and how thick are the walls?

Tony:

I'm very interested in the Murph SC pulley, not only because it would allow us to run higher boost, but also because we could go back to using the "regular" belts in all the other places.

Most of the other TS guys should be happy, too, because we wouldn't have any problems with the PS belt rubbing on the alternator, nor problems with cutting the radiator hose.

Can someone do the calculations to find out how much more boost we'd generate by increasing the crank pulley size? Or else who's going to be the first guinea pig to try it out? I've got several pullies--the one on my car does around 9psi, and I have one bigger and two smaller.

Bill Ball

I second Brian's request to calculate the effect of the Murph pulley on boost. I could measure the the pulley on George Suennen's Murph'd car, but I'm not sure when I'll be going over to his place next.

BTW, Daryl, my idle is so close to perfect now, cyl 7 is no longer dropping out. Seems like you no longer have 6 more affected than other cyls, as well. All I did was change the vacuum source to the bypass from manifold to throttle body instead. Weird, but I'm happy.

Daryl

Brian,
I got the pipes from a heavy truck parts store. They are two 90s 3 1/2" exhaust pipe. You can get them in aluminum or steel. I got the one end stretched to 3 3/4 to accommodate the larger MAF to intake pipe hose. Email me at daryllmiller@hotmail.com and I will send you a complete parts list, instructions, and pictures of the install.

mspiegle

Hmm... someone else may be able to answer this better, but I think our question is "Where to test the intake for restrictions?".

It makes more sense to me that measuring closer to the SC unit (like at the SC inlet) would be a more accurate test of restrictions from the filter back. After all - it is the SC which is sucking in the air, so it would be most undesireable to have a vacuum right at the SC inlet.

The first thought that comes to my mind is tee-ing off the connector where you hook the brake booster because that is very close to the SC inlet.

mspiegle

This is 100% UN-SCIENTIFIC, but when I went from a large prototype pulley to the smaller production pulley (on the crank), I lost 1psi of boost. IIRC, the pulley was between 0.5 and 1.0 inches smaller. For some reason this doesn't sound right to me (math wise), but those are the numbers i can remember off-hand.

Jim_H

As I recall every 3mm increment will yeild 1.5 to 2 psi. Sound right?

Bill Ball

Jim, that's in the SC pulley diameter, right? 3MM on the crank pulley is a small change and probably would do much at all.

Jim_H

Correct. I figured somoeone could use some trigcalcunomitry and figure it out with those numbers. Either that or pm Tim...

Bill Ball

Hee, hee. Trigcalcunomitry is Tony's specialty, but we still need to know the size of Tim's pulley. He's posting on the board. I'll ask him.

Tim Murphy

Okay,
For the record my sc section of the crank pulley is 7.25"

Now, before I will consider selling anyone a pulley (since then I will be involved) I would need to known about your intensions. The guys that run my systems have the same questions about running more boost (it's addicting!). I know the centrifugal forced induction effect on our cars WAY BETTER and I can offer better advice and guidelines with respect to the risk involved. Running 10 psi peak boost in a centrifugal system is not the same as 10 psi peak boost in a positive displacement system.

mspiegle

Tim's 7.25" pulley with the largest (i think?) autorotor pulley of 73mm would make 10+ psi of boost. Any upper pulley larger than this would *probably* hit the hood.

mspiegle

This is definately uncharted territory for anyone who even thinks about attempting this. The kit itself should have no problem in this department, but it hasn't been done on a 928 motor. You probably shouldn't attempt this unless you have injectors larger than 30#, standalone management (or maybe the sharktuner?), access to very high octane for initial testing, a very good grasp of boosting/tuning, and some ***** of steel. But otherwise... good luck.

Bill Ball

Ah, The Man! Hey, Tim, I assure you my intentions are nothing but honorable, sir.

In my case, I'm thinking it would be nice to run all the stock accessory pulleys, which your crank pulley would permit. I want to make sure that the boost change from using your pulley wouldn't be much at all - maybe a lb. I don't want to have to change all kinds of other things.

So, we need to do the math versus Andy's pulley.

Mike, I see your post that even with the largest top pulley Tim's crank pulley is so much larger than Andy's that we would make huge boost. So, Tim's pulley has more than TWICE the circumference of Andy's pulley, if my trigcalcunomitry is right?