IcemanG17

My racer has a stand alone SDS Digital-Crane ignition system that allows spark and fuel to be adjusted every 250rpm... Quite handy I found out....

1981 4.5L L jet engine (9-1CR) with 34 hours of porting in 1993 early Euro S (187-188) cams, MSDS headers into a Y pipe and single 3.5" exhaust....

When I got the car the timing was set to 30' from 3000rpm up.....here is my original dyno chart

I increased timing this winter to 34' (max recommended by Porsche at 5000) from 3000rpm up.....recently I developed an odd miss-studder between 4-5k rpm.....after changing EVERYTHING (plugs-wires-cap-rotor-coil-fuel filter-checked fuel pressure and flow) I pulled the timing back to 31' from 3000-5250 and left it 34' from 5500-up.... Here is the NEW dyno chart that is plus +22whp & 32 ftlbs we really didn't change AFR much...it looks a bit lean on the chart since I had a slight leak at my Y pipe.....

928Shane

Nice!

Ducman82

whats the timing chart look like?

Lizard928

He doesn't have a timing chart like you do Jake.

Did you listen for knocking or look of extra oil ejection?

Ducman82

me or him? :-P

LT Texan

1 deg advance made that big difference from 3k to 5250?

Ducman82

Sure does. I went to 29 and had a stumble. 28, none

Lizard928

If you had a stumble at 29, I'd back it down to 27 or 26 in that area to give more of a safety threshold.

IcemanG17

I don't have a chart......every 250rpm I can set it however I like, so at 3000rpm it hits 31'....hold that until 5500 where is peaks at 34'...whats funny is stock spec under the hood is 31' at 3000rpm....

On oil ejection, I always keep a close eye on the breather-separator and when it stumbled at 34' between 4-5k it never increased oil ejection-consumption..... Once I have my wideband installed that data logging will help quite a bit, with out having to pay for a dyno.....

I wonder if I can increase more timing 5500+ to extend the torque curve a bit higher-later....

Lizard928

I would not recommend that.

IcemanG17

34' is the factory recommended maximum for 4.5L L jet engines (9-1 CR)

Lizard928

More aggressive cams than factory will require less timing.

For the track car, at 9:1 CR and euro cams, I would be stopping at 32 in the upper range.

LT Texan

Almost a 20% increase in HP at 5k with a 1 degree increase in timing?

Call me a skeptic.

But in the infamous words of Hillary, "what difference could it possible make now?"

Great result on tuning!

The Fixer

Makes you wish you had a Dyno doesn't it, I'd be worried about burning a piston though. LT Texan, thanks for the Hillary image before bed. I guess i can't Blame Bill, yuk. Hope I'm not audited.