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Thread: JWT 9.5:1 On 8.5:1 Motor Timing Question

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Posts: 1-10 of 24
2009-07-25 15:07:32
JWT 9.5:1 On 8.5:1 Motor Timing Question
So I've been using my JWT 9.5:1 compression programed ecu on a 8.5:1 comp motor for a couple of years ( yeah I know lazy ) I have the timing set at 15 degrees. And I know the lower compression program would have more agressive timing. So would it be safe to bump it up to 17 degrees?? Or more ?? Or does it not work like that?? Any info is appreciated guys. Thanks
2009-07-26 05:57:28
it would be safe on stock boost levels, but I would just take advantage of more boost if you can support it, and leave the timing alone.
2009-07-27 21:36:57
Turn up the boost and leave the timing alone, enjoy the increase in torque.
2009-07-28 04:44:31
Just run a wide band or have it dynoed to make sure your air fuel ratios are good. It shouldnt matter too much i have ran a stock det ecu on a de and also used a det ecu with a hks rwd fcon hooked up as well it ran fine and pulled hard.
2009-08-04 03:26:41
Wait a minute, so let me get this straight, you can run an ECU programmed for 8.5:1 cr and run it on a 9.5:1cr motor and vice versa with no ill afffects, as long as your air/fuel ratios are good?

How come this is possible? will something go wrong eventually?
2009-08-04 03:45:36
You can't (or at least shouldn't) do the 8.5 on a 9.5 part. Think about it this way- less compression is more resistance to detonation. Generally, lower compression maps run much more aggressive timing. On the flip side, higher compression maps have more conservative timing, which is what this post is talking about.

The only problem with running a 9.5 map on an 8.5 motor, is that it is too conservative. I'm doing it right now. It's OK, but it runs a little rich. You shouldn't try to run an 8.5 map on a 9.5 motor though. That's running more aggressive timing on a motor that's already less resistant to detonation.
2009-08-04 13:10:30
you would think given the ecu is tuned for higher compression that the ignition maos would be more conservative, but could be slightly on the aggressive side for 9:5:1 becuase even though higher compression it doesnt mean the map HAS to be conservative, it could be slightly aggressive...but even if it were to be SLIGHTLY aggressive, it still mild be very mild for standards of a 8:5:1 engine ignition map that might be looked at as overly aggressive for a 9:5:1 engine, but perfectly fine for a lowr compression engine.

the fuel maps might be 100% the same, but the iginiton is going to be 100% different to compinsate for the engine compression
2009-08-04 14:57:43
This thread got me spending hours looking for DE vs DET bins. When I finally found a Calum made map (aka safe as oem, without crazy random numbers that tuners add themselves).

On a DE+T map the timing would be around 15 at 6800 RPM and 88% Load (TP).

On a DET the map is on timing would be around 23 at 6800 RPM and 88% Load (TP).

Fuel maps are identical, but I didn't check the Injector K value, which is really what you should first modify before touching the fuel maps.

What does this translate to?
You can get away with running a 9.5:1 CR map on your 8.5:1 CR motor, it will be weak. Especially in the torque department. But if you run DET 8.5:1 timing on DE 9.5:1 your asking for trouble. It might not knock while it's cold outside, but if one day it temps get high you will probably knock.
2009-08-04 15:49:37
i most defiintly wouldnt run a lower compression iginiton map on a higher compression motor, there isnt any reason to be lazy and not do 1 of 2 things, have it tuned, or learn how to tune it and tune yourself.

bumping the timing in one spot and not have it tuned in other areas will do you nothing.
2009-08-04 16:52:58
i've been running a 9.5:1 JWT tune on my DET for a couple years now. last year i advanced the base timing to ~19-20*BTDC without problems. maybe this year i'll keep it between 15-17* and crank the boost since i got a new head gasket and studs...
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