mark kibort

I have a chance to do a comparison with a GT computer on the Holbert car. is it worth the time, or should there be no difference except a higher rev limitation? (and will all the funtions work. in otherwords, are the GT computers drop in replacements?)

Mk

FlyingDog

With the modified 85-86 cams in your car, I would think there would be an improvement. I'm surprised you don't already have GT maps in you LH/EZK.

the flyin' scotsman

I have/had GT eproms in my S4............makes a diff in where the pwr comes in and SOTP impressions were good.

Downside is there's no provision for the transmission so back in went the S4 prom in the LH.

AO

I'll bet you already have a VERY customized fuel and ignition map in your car (assuming it's the original). The higher rev limit might be nice, but I doubt you'll see much, if any, other benefit. However, if you're running the stock S4 chipset, you would be better served by the GT chips.

Garth S

I have both a set of '91 GT chips and '91 GT EZK/LH modules complete, the latter which I had used in my '88 auto, before selling it with the original computers..
The GT EZK clearly appeared to have a more agressive ignition map - more 'snap', and I much preferred it to the S4 EZK. There was a less marked difference when using the GT LH .... but to be fair, it was not used solo with the S4 EZK: perhaps had I done so, its contribution would have been easier to determine.
The modestly higher idle never bothered my auto - lucky, I guess.

the flyin' scotsman

Its not the high idle thats of concern with GT proms in the S4 but the fact that a GT hasn't to compensate for an auto transmisson when its in gear. The LH brain GT chip fail to hold a strong enough idle and allow the car to almost stall.

Best combo in my experience is the GT chip in the EZK and the stock S4 chip in the LH brain.

Hilton

Hmm.. this is a VERY good point.

Has Mark ever taken a backup of the car's ECU chips? Given the car's history, its reasonable to suppose that Andrew's probably right and Mark's car is not running the same maps as other cars.. potentially any other 928.

The LH and EZK existed in separate versions for even small production runs like the Clubsport, so providing a custom map for a one-off production world speed record isn't beyond belief.

Would be great to get a copy of the Holbert car's LD and EZK firmware put up on Chris Ford's site to add to the other ones there (www.928s4.com).

Edit: Mark - if you're putting in GT LH/EZK as a trial, it would be a great time to take your originals to someone with a shark tuner and get them dumped to a computer. Would also give you a means to replace your original chips with the same map if one of them ever fails.

brutus

I remember reading that the brains are not what was used by Holbert the originals had external ports for quick chip changes.

John Speake

There's so little difference in the fuelling between the GT vs S4 LH EPROMs that we didn't bother to have them seperately listed in the SharkTuner menu.

If you just want a higher rev limit then that is easily done with a SharkTuner.

There are substantial differences in the EZK maps. But in fact the GT has slightly less advance in the mid range than S4. This is because of the better cylinder filling with the GT cams.

I thought the Holbert car had a somewhat modified EZF ignition ECU in it originally, (25 pin) and when that failed the car was fitted with an S4 version ? If that is correct then the original EPROM may be lost...

mark kibort

Yes, the Holbert car had some funky, one off, box. however, it was given to me with the car, but it wasnt installled. The Holbert car was fitted with a bone stock set of S4 computers. (right from 928 international) so, ive never run the car with the original computers. I sent the originals to Rich in AZ, and he was able to look at the set up, but i dont think he was able to capture the maps or anything useful.

Is there a set of chips from the sharktuner that i could try on the dyno to see the HP gains of optimized fuel and air in the 4-5000 to 6500rpm range? I would be interested in checking a set out, or even using the tuner if it is cost effective to do so.

thanks for the comments all.

Mark

John Speake

To optimise the fuelling to the Holbert care would require a SharkTuner session. Every car is slightly different. At WOT the stock chips tend to run a little on the rich side (probably for safety) and this doesn't compromise power by very much.

It's the same on the EZK side, but there is something to be gained here with a SharkTune.

What mods to the engine systems are on the Holbert car that make it different to a stock S4 manual ?

I (or anyone else with a SharkTuner) can supply you a S4 LH chip with a GT rev limit, and also a GT, S4 or GTS EZK chip.

drnick

mark, you are better off running a sharktuning session rather than taking a chip from someone elses guess at what your car should be. iirc you have a comletely different exhaust including headers as well as intake/airbox mods and 86 cams, your car would bennifit most from an individualised session. i had the pleasure of sharktuning with john speake in person and there were appreciable gains with both the LH and ezk, my car has only an ott x with dual 2.5" exhaust and a mild cam somewhere between a GT and GTS.

Mako 928

Mark
Why not save some money and wait to do this to the new motor? Or does this mean you will be running the Holbert car W/ the original motor for a While?

mark kibort

Good point. I was more curious than anything.

since my engine makes almost the exact same power as another GT that i saw the dyno run for, i was wondering about the differences in the two boxes. I guess the LH is fuel curves and EZK is spark, right. im wondering which will help more of if all the gains vs stock are pretty subtle.

Looking forward to running the stroker, but its been a long project road. i have to be prepared to race without it, if it doesnt get here in time!

Mk

mark kibort

nothing really. Just a set of headers and the 85 cams with a vented air box

mk