1 day ago in News
We hit the track with Flyin' Miata's latest power adder.
So I've got a 79 Porsche 924 with the 2.0L SOHC Audi lump in it.
It is currently the low-compression 95hp jobbie with an Integral Stage 2 camshaft, 45mm throttle bodies from TWM, EDIS-4 distributorless ignition and MS1 w/extra code and a LC-1 wideband to tune it all.
I've finally got it running fairly well after debugging some wiring issues, etc. However, between the cam, the low compression and the way too big throttle bodies, it doesn't have much low end torque. I'm ok with that as I still have either a turbo or a supercharger to add to the motor down the road (which is why I didn't up the compression when I had it apart), but I'd like to help it as much as possible.
So, one of the things I can do to help broaden the power curve is to add a neat product from back in the day that I picked up. A Franco automatically adjusting timing gear. It works like an old mechanical advance distributor with a set of weights inside of it to adjust timing based on engine RPM. Its a pretty cool product and I've heard a few good things about them from the research I've done. The trick however seems to be adjusting the ignition timing to compensate, I've only ever heard references to this without any further information on what those adjustments might be. So I turn to the braintrust here to get some ideas on what settings to change as a start before I head to the dyno and fine tune them.
Here's some specs on the cams (stock on top and Stage 2 bottom):
Seat Duration, .015" .050" Duration Cam Lift 255° 223° .472" 276° 239° .520"
Here's some info on the Franco timing gear:
And my current timing curve:
Let me guess: That map wasn't tuned on a dyno.
As a general rule, you need less advance where you have more cylinder filling. So theoretically you would need less advance down low, and if the cam retards to the same amount of advance at the top end as stock, the same advance up top.
That assumes the spark map you have now is actually optimal for the engine.
Is the table base on Kpa or???? If it is KPA and you are idling between 70 and 80 you have a vacuum leak some place. It should be down around 25-30Kpa at idle. Your bottom end power issues may be vacuum related and not so much cam related.
What is the static compression ratio of the motor?
I have large ITB's and a larger cam, therefore very little engine vacuum at idle. I've confirmed with other 924 owners with ITB's that they idle at similar amounts of vacuum at idle.
And the ignition curve is based on the stock distributor curve, just adjusted to compensate for the narrow amount of vacuum I have in the motor. So no, not dyno tested on this motor and this configuration.
Trust me, I've been through the vacuum system 4 times on this car, the best I've been able to pull is around high-60's on decel.
just a thought....(looking at your ign timing map) you might change your rpm cells... add more in the lower rpm range, remove a few of the higher rpm ones... I'd do something like 4000, 5500, 7000, that will give you 3 additional cells to help with tuning in the 600-3000 range...
concerning the mechanical advancing/retarding camshaft gear.... it would be best to tune it on a dyno to know the best ignition points for mechanically varying cam timing
Dredging this up since I went ahead and installed the gear today due to a timing belt issue. Set it to +10/0 and it helped the bottom end quite a bit and the top end didn't change.
Need to tune the accel enrichment, but it's a marked difference.
Do you know how much the gear moves and at what rpm?
On that motor I would be using alpha-n or itb mode in any case.
I do use Alpha-N and since its MS1 there's no ITB mode.
I just modified the ignition table to use MAP for better throttle response and it did help.
The gear moves 10 degrees at 3500rpm. It starts at +10 and moves to 0.
It shouldnt be snapper with map load for ignition. If you tuned tps load you should be able to get better response. What did your tps based map lool like before?
For intake vvt I usually take 10deg ignition out from base for 25deg of cam advance. Not sure how much your exhaust events moving with it change things but it is a place to start.
The problem is that the TPS based ignition map sucked when the load changed. The car would fall on her nose with any elevation change and since I'm surrounded by hills I couldn't tune the car since it would just stop when it met a hill.
Changing to the MAP based ignition table fixed that as well as the low speed stumbling as recommended by others running ITB's and are looking for better drive ability.
Also, trying to stick to a more or less stock ignition map while I tune the fuel table. The only table available for me to reference is the stock one from the manual and someone was nice enough to make that available as downloadable table file.
At this point this is getting frustrating and I'm either going to go back to a single throttle body solution (which is a huge pain in the ass) or save up my pennies and try and find a dyno and a tuner with MegaSquirt experience to try and fix something that, according to you guys, is complete crap and is completely wrong.
I have a bunch of stuff on msruns for setups like yours, some off map some off tps. I can send you a spark table, shoot me an email kandpperformance at gmail dot com. Most itb driveability problems are fuel not ignition related. You have any logs?
The alitudet issue you can fix with constant baro but the ms1 implementation isnt adjustable like ms2/3.
For getting fuel right just use fixed angle and 30deg. You will be surprised how well that works until you try and start it lime that ;)
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