Getting a Custom Chip for my 1987 3.4 Street Rod - Should I go 91 or 93 octane?

[polizei]

Guys,

I'm nearing the end of the build on 1987 Carrera. I'm punching it out to a 3.4L, running twin plugs, Elgin Super C2 cams, 10.0 to 10.5:1 static compression and stock induction/Motronic.. I live on the east coast where there is an abundance of 93 octane fuel, but I do plan on taking road trips eventually where 91 octane may not be available. I'm planning to drive this 90% on the street with some DE events.

I'd like to extract the optimal performance from my engine without compromising reliability, and it would just be satisfying to know that after spending an absurd amount of money on an engine rebuild that I haven't left anything on the table My understanding is that there is more risk regarding the ignition timing relative to a particular octane, than in the actual octane itself. Is that correct?

If so, then as long as prudent ignition timing is used at 93 octane, is there really any more risk than running 91 octane with prudent ignition timing? By the way, I'll be running a J&S Safeguard to help mitigate knocking.

Thanks!

[Canada Kev]

I would likely go for the 91 chip. I have a Euro car and it's running on the ragged edge with single plug, 10.3:1 compression and North American gas. That being said, I haven't had problems at higher altitudes where I live using 91, but whenever I travel to the coast I am sure to fill with 94 available locally. Altitude/elevation plays a part in this, even though I forget exactly why - atmospheric pressure or something... I was kinda nervous when I went down to WA and OR states last spring, as all that was available was 91. I didn't experience any obvious issues.

I have a 91 octane SW chip, BTW. I think the 91 octane chip will give you some piece of mind after spending a fistful of cash on a new engine.

[petevb]

Originally Posted by polizei

I'm nearing the end of the build on 1987 Carrera. I'm punching it out to a 3.4L, running twin plugs, Elgin Super C2 cams, 10.0 to 10.5:1 static compression and stock induction/Motronic.. I live on the east coast where there is an abundance of 93 octane fuel, but I do plan on taking road trips eventually where 91 octane may not be available.

Get two chips, one for each gas. Probably won't cost much more than one.

On my VRam there was a 10 hp difference between 93 and 100 octane chips. This was nominally an 11.3:1 motor, in practice more like 10.5:1 or 10.7:1.

On my GT3 Cup motor I made ~400 hp on 91, ~418 on 94 (this could probably be more if we optimized for this) and ~435 on 100- I have a switch on the dash to flip between the different maps for when I need to use lower quality gas. This is a 12:1 motor nominally, but water cooled and 4 valve single plug. In any case it can be tuned to run safely below 91 octane, but as you can see you're pulling lots of timing out and leaving a lot of power on the table. Also note both of these motors have good integrated knock sensors for safety, so one can tune much closer to the line.

If I were you I'd burn a 93 chip and use race gas with it for the track, then have a lower octane backup chip for road trips. I'd guess you'll find a ~10 hp difference between 91 and 93 depending on how high your compression is, and you'll safely be able to get the best of both worlds.

[scarceller]

Originally Posted by polizei

Guys,

I'm nearing the end of the build on 1987 Carrera. I'm punching it out to a 3.4L, running twin plugs, Elgin Super C2 cams, 10.0 to 10.5:1 static compression and stock induction/Motronic.. I live on the east coast where there is an abundance of 93 octane fuel, but I do plan on taking road trips eventually where 91 octane may not be available. I'm planning to drive this 90% on the street with some DE events.

I'd like to extract the optimal performance from my engine without compromising reliability, and it would just be satisfying to know that after spending an absurd amount of money on an engine rebuild that I haven't left anything on the table My understanding is that there is more risk regarding the ignition timing relative to a particular octane, than in the actual octane itself. Is that correct?

If so, then as long as prudent ignition timing is used at 93 octane, is there really any more risk than running 91 octane with prudent ignition timing? By the way, I'll be running a J&S Safeguard to help mitigate knocking.

Thanks!

You made substantial changes to this 3.2L most notably the twin plug setup. You can not use the stock DME and chip from the 87 car! Twin plug engines don't require as much ignition advance as a single plug engine, if you attempt to run the new 3.4L modified engine using the stock 87 DME and Chip you WILL toast this motor the moment you go WideOpenThrottle! You MUST have proper ignition maps created for this setup.

The other issue is that you increased displacement from 3.2L to 3.4L and the stock AirFlowMeter doesn't have much headroom left at WOT above 6000RPMs, meaning the stock AFM may not properly meter your air flow because it's at the end (MAX) air flow, the meter is pegged out. You may be safe using the stock AFM but I'm pointing out that you need to do your homework here.

[Canada Kev]

Pete makes a good suggestion. You'll normally be driving where there's 93, but sometimes may be away and only have access to 91. Get a second "traveling" chip.

I'd have a chat with SW to get his opinion, too. See what he suggests.

[Joe Bob]

There is a poster that does chips that have dual maps. Flip a switch and it changes.

[scarceller]

If you want ideas for what ignition timing to use, I suggest you start with the ignition maps from the 90-95 964 C2 cars as this engine is more comparable to the 964 than the 3.2L

[petevb]

Originally Posted by Lorenfb

That's it! It's all about the timing and how far you want to 'push' it to the pre-detonation point and what octane MIGHT help avoid detonation. Yes, that's 'performance' tuning. Can't be made any clearer than that.

"All about timing" is once again stretching it.

The answer actually depends on the particulars of the motor. You can't, for example, run a your typical 13:1 motor on 91 and simply pull out timing to run it safely, however you may well be able to get it to run safely by increasing fuel and running it rich in addition to pulling timing. On a 15:1 motor you probably can't safely run on 91 regardless of your tune.

Thus the actual risk of running lower octane will depend on your engine's propensity to detonate (which is governed by a whole bunch of factors- running temps, cam, single vs twin plug, combustion chamber shape, etc). Assuming your build is as described you should be able to find a safe tune down to 91 octane, and your tuner may choose to make that map a little richer that the 93 to be on the safe side.

[polizei]

Guys - Thanks for the great replies. To Pete's point, at a minimum I could get two chips. If cost is an issue, I'm inclined to get the 93 octane-based chip first then the 91 for road trips.

I'm very interested in Ingo's dual-map solution. That sounds great! I actually asked Steve Wong about this a few months ago, and I don't think he has a solution currently.

The nice thing about working with Steve is that he has developed chips for similar engines to mine. I'll probably chat with both SW and Ingo.

Thanks Guys!

[petevb]

Originally Posted by Lorenfb

Great revelation! Like that's not obvious to most. Maybe find some more cut & paste info from other threads.

Obvious or not, you're once again oversimplifying here saying it's all about timing, fuel doesn't make a difference. It seemed appropriate to point out (again) that it's actually not that simple.

Resorting to personal attacks as a response? Not surprising I guess.

[polizei]

Well, I'm an ignoramus then! Pete - I do appreciate your input, as I don't fully understand the interaction of all the factors related to detonation.

Now I just need to find one of those dual-map chips!

[Joe Bob]

Ingo, screen name 'ischmitz' first used them on the 3.6 chip he and I worked with. We both have converted our earlier rides to 3.6/964 motors.

His idea was to use a dual chip with with a toggle on the outside of the DME box. Jack Olsen used it at one time.

His original purpose was to have a stock mapping for low octane availability or street use to comply with smog regs and a modified mapping for 'track' use or 'spirited' driving.

Since Ingo and Steve Wong are acquainted, I assume Steve can get the blank chip vendor information from him, if he hasn't done so already on his own.

[911-32]

Originally Posted by scarceller

The other issue is that you increased displacement from 3.2L to 3.4L and the stock AirFlowMeter doesn't have much headroom left at WOT above 6000RPMs, meaning the stock AFM may not properly meter your air flow because it's at the end (MAX) air flow, the meter is pegged out. You may be safe using the stock AFM but I'm pointing out that you need to do your homework here.

As well as the stock AFM, you are leaving something on the table with the stock intake as well. Should still be a nice motor though

[polizei]

Joe Bob - Thanks for the note on Ingo and SW. I'll see what I can work out with them.

911-32 - You're correct. I needed to draw the line from a cost perspective, so I decided to stick with the stock the engine management and induction (except twin plugs and the J&S safeguard). The engine is being built so that I can switch to ITBs down the road:

1. Dual 993 Knock Sensors
2. Hemispheric-domed pistons
3. Stronger/Lighter valve train components

Going to ITBs would likely mean a cam change as well, but that's not so invasive.

[polizei]

Joe Bob - Thanks for the note on Ingo and SW. I'll see what I can work out with them.

911-32 - You're correct. I needed to draw the line from a cost perspective, so I decided to stick with the stock the engine management and induction (except twin plugs and the J&S safeguard). The engine is being built so that I can switch to ITBs down the road:

1. Dual 993 Knock Sensors
2. Hemispheric-domed pistons
3. Stronger/Lighter valve train components

Going to ITBs would likely mean a cam change as well, but that's not so invasive.

[petevb]

Originally Posted by Lorenfb

Not really! AFR tweaking in itself yields basically nothing when the AFRs are within
the ideal range.

Hold on. All of six posts ago you agreed that it was obvious that a higher compression motor needed a richer air-fuel ratio run, let alone make power. Now you're saying changing air/fuel does basically nothing. Which is it?

Originally Posted by Lorenfb

Without specialized test equipment when 'pushing' the timing and tweaking the AFRs, one can't really determine how close to detonation the engine is.

Wait a minute- haven't you been saying anyone can tune these motors? Now you need specialized equipment or it's impossible to do right? How do tuners tune their engines without blowing them up, I wonder?

[scarceller]

Originally Posted by Lorenfb

"Twin plug engines don't require as much ignition advance as a single plug engine"

Obviously has never seen a twin plug 964/993 ignition map:

RPM Idle 1000 2000 3000 4000
Timing 3.5 13 32 35 38

Those engines used much more aggressive timing than the 911 3.2 because
the twin plugs reduced the likelihood of detonation and because of knock
control.

Really? Have you seen the WOT ign map for the 964 vs the 3.2L?

I'm not referring to low load ignition such as idle!

I'm very well aware of ign maps in both cars, here's the WOT ign for these 2:

89 3.2L
RPM 520 2520 4000 4520 5000 5200 5760 6000 6160 6400
Ign -4 23 26 24 24 23 22 24 23 23

964 1992 C2
RPM 1000 1480 2000 2480 3000 3480 4000 4480 5000 5480 6000 6240
Ign 0 6.8 15 18 21 22.5 16.5 14.3 13.5 14.3 15 15

Look at the 4000-6000 RPM WOT ign the 964 is significantly lower!

I wonder why?

And when you post values please tell us from what year car as the C2 had several different chips.

[scarceller]

Originally Posted by Lorenfb

Those engines used much more aggressive timing than the 911 3.2 because
the twin plugs reduced the likelihood of detonation and because of knock
control.

Loren, this statement is so wrong it's not even funny! You really don't have a clue of the advantages of a twin plug cyl! The twin plug cyl achieves max cyl pressure much more quickly than the single plug because it starts the burn from both sides of the cyl! You really need to get educated on these principles!

Your above statement lets every serious tuner know that you have no clue! Buy some good books then come back.

[petevb]

Originally Posted by Lorenfb

Right, and that's why typical tuning by so-called 'tuners' other than for example Porsche Motorsports is such a Mickey Mouse effort.

Really? Porsche Motorsports knows how to tune? Hmm.

It just so happens that the guy who tuned my engine won the Daytona 24. Overall. Twice. For PMNA then Porsche. The second time they gave him one of the Rolexes.

Exactly what special equipment was he missing when we tuned my motor together on the dyno? And exactly how is it that you seem to know so much more than him on this topic?

[petevb]

Loren?