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Compression? or Ignition Advance? 

 

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 Post subject: Compression? or Ignition Advance?
Posted: Mon Apr 19, 2010 4:32 pm 
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Many of us have advanced our ignition timing to improve power and economy. The usual method seems to be to advance it until you get light pinging under load, then back off a couple degrees.

Another way to improve performance is to increase compression, eg, shaving the head, using a MLS head gasket. But the higher the compression ratio, the less ignition advance you can give it before it pings.

In the collective wisdom and experience of Fordmods members, has anyone worked out an optimum mix of the two? That is, is it better to have more compression and less advance, or less compression and more advance? Or, is there a balanced combination where power is maximised but drops off as you move away from it? Clearly, changing fuel octane, cam, air charge temperature, etc will affect the outcome, so assume all other factors are unchanged.

This seemingly theoretical question has a practical purpose. I'm trying to determine if I can wring more power out of my engine by increasing the compression, or would I just end up giving all the gains away because I have to pull out some ignition advance? Right now it's advanced to just short of pinging.

Thanks for your help.

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Mon Apr 19, 2010 5:38 pm 
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I'm not sure how much mechanical knowledge you have, so I apologise if this sounds too simple.

If the engine is unmodified and tuned correctly, it won't benefit much from advancing the timing. Factory settings have been determined after extensive testing and we tend to rely on them rather than use guesstimates. Distributor timing is usually altered as a result of an engine modification (eg. increased compression or a different cam). This is where a dyno is useful to see how it affects the torque curve and air-fuel ratio when altered.

Have you modifed you engine at all?

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Mon Apr 19, 2010 6:06 pm 
Getting Side Ways
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Thanks, Shortshift.

The car has a cam one step hotter than XR6, 15-thou shaved head and AU MLS head gasket for compression, headers, no cat, mandrel-bent 2.5" exhaust, SS Inductions and modded airbox exit. The TI Performance J3 chip is custom-programmed for as much ignition as it will handle without pinging on 98 octane (as well as correcting the over-fuelling).

If I shave another 10-15 thou off the head, I will have to take some timing out because it is on the edge as it is. What I'm wondering is: will I gain more from the compression increase than I would lose from retarding the ignition?

On the issue of factory settings, I'm pretty sure they are less than optimal. They have to allow for the owner who doesn't maintain their car, drives at 2500rpm max, engine full of carbon deposits, 45 degree ambient temperature, worn out spark plugs and leads, a dodgy batch of 91-octane gas, clogged radiator and running hot, etc. The car still has to be capable of starting and running without blowing the engine. They must need to allow a generous safety margin. I would be surprised if they base their settings on people like us who maintain our cars and try to wring every ounce of performance out of them.

Cheers

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Mon Apr 19, 2010 10:15 pm 
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OK, I can see where your at now. I doubt you're going to pick up many more rwkw with 10-15 thou of the head. A more radical cam will give better results.

Was the J3 programmed using dyno results, or purchased pre-programmed? When I had my J3 chip tuned, the first thing I was told was "Don't change the dizzy timing". I guess the spark & fuel settings are all tied to it and the tune will be stuffed.

I've got much the same setup as yours, but also have ACL race pistons & 25 thou off the head.

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Mon Apr 19, 2010 11:57 pm 
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Jason custom-programmed my J3 chip from actual dyno results with AFR. Because I'm running the stock EF coilpack, all the timing had to be done on the chip. Out of the box, the timing was a bit too radical, and there was significant pinging even on 98 octane. Jason had me send the chip back, and he took a few degrees out. When I first put the chip back in, there was still a small but detectable amount of pinging, but it gradually went away over the first few kms. Now it's sweet. I have to think that it has ignition timing trim and adjusted the ping out, or maybe it richened the fuel trim a bit to get rid of the ping.

Anyway, it pulls hard right up to 5700rpm rev limit - the breathing in and out must be working pretty well. It's especially strong from about 3500rpm. It's not particularly torquey off the line, but I'm using the stock torque converter which stalls at 2100rpm. A more radical cam wouldn't give me much more at top end unless I increase the rev limit - which I am reluctant to do on 280,000km factory internals. And it would make it weaker off the line. As it is, when I have to replace the torque converter, I plan to go about 2400rpm stall to put more snap in the launch.

What I am actually looking for is a bit more poke particularly in the 2000-3000rpm range. Launch is very tricky. If I floor it from idle (a real world launch), it's unimpressive for the first second or two. If I stall it against the brake (a drag launch), it just liquefies the tyres through first gear. Will more compression help up to 3000rpm, even though it will allow less advance? I'm thinking I might need to break down and get the full-house programming kit with WBO2 sensor from TI Performance and do my own optimised tune, especially for low-rev or part-throttle conditions.

Thanks.

BTW, that's one seriously tidy engine bay you've got, and decent power too.

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Tue Apr 20, 2010 3:08 pm 
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Sorry, I been off with the fairies... here I am rabbiting on about distributors & you've got a coil pack. I don't know much about coil packs so I can't advise whether fiddling with the timing is a great idea. Are there any people over there who can tune J3 chips while the car is on a dyno?

I had the same sluggish takeoff when I had a 4 speed auto. I changed to 3.7 gears & that fixed it. But changing to a higher stall, as you mentioned, might be all you need if you already 3.45 diff gears.

The engine bay is just standard with a few things painted. The tuner spent about 4 hours trying to wring out that power. He reckons it's got a bit more but needs a 256k Moates chip instead of the older 64k chip I have now. Something to do with not being able to store enough settings or something.

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Tue Apr 20, 2010 3:33 pm 
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Hey efxr6wagon, are you running an adjustable cam gear? If you do, you could always have a muck around with the cam timing, advance it to bring on torque a little earlier etc.

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Tue Apr 20, 2010 3:36 pm 
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Sorry to hijack but keen to know if anyone programs J3's over here too :)

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Tue Apr 20, 2010 3:41 pm 
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Deff wrote:
Sorry to hijack but keen to know if anyone programs J3's over here to


You could try these guys. http://www.torqueperformance.co.nz/index.php

They apparently tune just about any ECU, controller, piggy back (Quote from website). I guess if you bought a chip and burner from TiPerformance and took it to them they would be able to work it out.

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Tue Apr 20, 2010 3:51 pm 
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KWIKXR wrote:
Deff wrote:
Sorry to hijack but keen to know if anyone programs J3's over here to


You could try these guys. http://www.torqueperformance.co.nz/index.php

They apparently tune just about any ECU, controller, piggy back (Quote from website). I guess if you bought a chip and burner from TiPerformance and took it to them they would be able to work it out.

Dude you are an encyclopaedia of information! Cheers again.

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Thu May 06, 2010 3:34 pm 
Getting Side Ways
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Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
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A quick update.

I got my wish in a roundabout and expensive way. The car started making an almighty rattling/knocking noise especially when cold or idling, that settled down when warm and cruising. We narrowed it down to the flexplate, so took it to Dr Trans in Glenfield (top blokes). It seems I was a bit of a clutz when reinstalling the engine last year and broke the flexplate and snapped the nose off the torque converter :oops: Don't know how it carried on for so long with no problems. It's a miracle it didn't do more damage when it finally let go, and that it was still driveable.

Anyway, as the converter had to be repaired, I had them increase the stall at the same time. I have about 2500-2600rpm stall now, and it jumps into the power band much quicker. Launch is great! :twisted: And the effect on normal low-rpm driveability is hardly noticeable. Problem solved. Hmmmmm....maybe I should go for more cam now. :lol:


efxr6wagon wrote:
Jason custom-programmed my J3 chip from actual dyno results with AFR. Because I'm running the stock EF coilpack, all the timing had to be done on the chip. Out of the box, the timing was a bit too radical, and there was significant pinging even on 98 octane. Jason had me send the chip back, and he took a few degrees out. When I first put the chip back in, there was still a small but detectable amount of pinging, but it gradually went away over the first few kms. Now it's sweet. I have to think that it has ignition timing trim and adjusted the ping out, or maybe it richened the fuel trim a bit to get rid of the ping.

Anyway, it pulls hard right up to 5700rpm rev limit - the breathing in and out must be working pretty well. It's especially strong from about 3500rpm. It's not particularly torquey off the line, but I'm using the stock torque converter which stalls at 2100rpm. A more radical cam wouldn't give me much more at top end unless I increase the rev limit - which I am reluctant to do on 280,000km factory internals. And it would make it weaker off the line. As it is, when I have to replace the torque converter, I plan to go about 2400rpm stall to put more snap in the launch.

What I am actually looking for is a bit more poke particularly in the 2000-3000rpm range. Launch is very tricky. If I floor it from idle (a real world launch), it's unimpressive for the first second or two. If I stall it against the brake (a drag launch), it just liquefies the tyres through first gear. Will more compression help up to 3000rpm, even though it will allow less advance? I'm thinking I might need to break down and get the full-house programming kit with WBO2 sensor from TI Performance and do my own optimised tune, especially for low-rev or part-throttle conditions.

Thanks.

BTW, that's one seriously tidy engine bay you've got, and decent power too.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Thu May 06, 2010 6:35 pm 
Getting Side Ways
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efxr6wagon wrote:

Anyway, as the converter had to be repaired, I had them increase the stall at the same time. I have about 2500-2600rpm stall now, and it jumps into the power band much quicker. Launch is great! :twisted: And the effect on normal low-rpm driveability is hardly noticeable. Problem solved. Hmmmmm....maybe I should go for more cam now. :lol:

Hmm, how does one increase the stall? I always thought the whole converter had to be changed for a higher stall model?

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Thu May 06, 2010 6:49 pm 
Getting Side Ways
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Power: 148 rwkw

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Apparently, up to a certain rpm they can simply adjust the angle of the blades inside the torque converter. Egan at Dr Trans farms the converter work out (only takes one day) and charged me NZ$255+gst to modify the converter. The expensive bit was the labour getting the transmission out of the car and back in. If you can remove and install the converter yourself, it's a very reasonable cost. I tested the converter properly tonight, and found it flashes to 2900rpm - WOW! - yet drives pretty normally. I'm very happy with it.

I think if you were going to build a car mostly for drag racing, you would go to a smaller (and lighter) high stall converter. For example: http://www.transgear.co.nz/Torque-Converters.html

Cheers

Deff wrote:
efxr6wagon wrote:

Anyway, as the converter had to be repaired, I had them increase the stall at the same time. I have about 2500-2600rpm stall now, and it jumps into the power band much quicker. Launch is great! :twisted: And the effect on normal low-rpm driveability is hardly noticeable. Problem solved. Hmmmmm....maybe I should go for more cam now. :lol:

Hmm, how does one increase the stall? I always thought the whole converter had to be changed for a higher stall model?

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Thu May 06, 2010 7:01 pm 
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Good to hear you got the mechanical problems sorted out? Are you still planning to alter the ignition timing, or get the J3 tuned while on a dyno?

 

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 Post subject: Re: Compression? or Ignition Advance?
Posted: Fri May 07, 2010 11:25 am 
Getting Side Ways
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I don't know of anyone in the Auckland area that does a J3 tune at a reasonable cost. I have to keep the spend on the XR6 under control. Torque Performance were helpful years ago, but the last time I contacted them, they seemed to only be interested in teenage ricer drivers with $10k to spend on their turbo WRX or Evo.

First I have an idle issue to sort out. Then the plan is to get another dyno run done and send the chip back to TI Performance for fine-tuning. At AU$100 plus the cost of a dyno run, that's a bargain.

I think I will be leaving the compression alone, and just push the ignition advance as far as it will take on 98 octane when I get the chip re-tuned.

Shortshift wrote:
Good to hear you got the mechanical problems sorted out? Are you still planning to alter the ignition timing, or get the J3 tuned while on a dyno?

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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