Lemming

Chris,

Glad you had a good weekend. There is definitely a flat spot shortly after 3,500 rpms. If you look in my other thread, you will see that the A/F tends to go rich in that area. We tried to lean that out but could not without making it too lean on top. The solution, don't drop below 4K when you are having fun

edz968s

Update.
Car and SC been running good, still only 4-4.5PSI, though on max throttle.
The larger fully knurled pulley is getting constant boost all the time, but a downside is an alarming wear on the belt.
I have fitted a DAYCO HD belt and gone for 1570mm in length down 5mm to shorten the turnbuckle adjustment.
It`s the crank speed and how you use it that accelerates the belt wear.
I suppose and that`s what gets the belt to wear with throttle application and a heavy right foot. Can`t be gentle though.
The flat spot between 3250-4250 hopefully will be eradicted with the fitting of a Pormax chip, which I`ve fitted but not run yet.
This has a more enhanced fuelling map and with the larger pulley, I hope to compensate this with the larger pulley, I think 2.55" from the origional 2.25" so will spin the impeller up to a comparative RPM for enhaced boost.

What is the formula for crank pulley speed X SC head pulley size/RPM?

Carl Fausett

I have a pulley size calculator for you.

Here is the link: http://www.928motorsports.com/servic...eed_Calculator

UPDATE: saw the 968 Stage II crank pulleys yesterday, they are close to finished and look fantastic!

nick_968

Have you considered having a custom map done by someone like Wayne Schofield so the fuelling is actually spot on for your requirements?

Eric_Oz_S2

You would be better off with a custom map. Running the Promax will probably result in too much advance at higher boost levels and knock issues.

Lemming

A custom map is the way to go. I have been trying to gather the information for Rogue Ant, I just have the WOT fuel and timing to figure out. Hoping to do it this weekend at the track in the daily driver 968. Once done, all you will need is an ostrich and free software to remap.

edz968s

A full live re-map is on the card, just as funds allow.
The crank pulley is around 5.00" plus head pulley at 2.55" and at 7100, would be around 41700 impeller speed, roughly, correct me on the sizes, difficult to measure with the belt on.

Carl Fausett

A good tune is essential. Superchargers are safe, but only when they are not allowed to run lean. Don't do it.

After a supercharger kit is installed, a good tune by a qualified person is essential. Well worth the money spent.

Lemming

Chris,

You do not want to run your 968 engine to 7100 rpms on the track. I killed two NA engines doing that, don't go there unless you blueprint your engine and want to spend even more money. After lowering my limit to 6600 rpms, my engines stuck around for a bit!

edz968s

I was running the 7100 a while before the kit as n/a with no probs, the engine has been completely rebuilt, just thinking that the extra 300rpm over stock, will get the impeller speed up, now the pulley is larger.
If you think I`m barking up the wrong tree and advise against it then point taken, I`ll replace the OEM chip.

nick_968

Dont do it, especially not with a chip that is not designed for your extra boost. Most engines seem fine until that split second when they go pop!

86 951 Driver

Engines run their best right before they blow up.

Lemming

Tell me about it, I was leading two races and blew two motors

edz968s

But this chip with more aggresive fueling map has got to be better than running the stock chip, so no issues with it going lean.
With the stock chip and FMU, it goes nicely rich on boost, so by installing this and 300rpm extra to the cut off, depending on my a/f guage and the bigger pulley, should equal it out and still be richer on boost

nick_968

Its not the fuelling that will cause you a problem its more likely the fact that the timing will be way too advanced for a boosted application. Running too much advance is a lot more dangerous than running slightly lean. Its a very dangerous game to play.