Carrera Rebuild 10.3 Pistons & Cylinders

[88-diamondblue]

I am considering buying new pistons & cylinders, specifically Mahle 10.3 pistons and cylinders for an 88 Carrera engine with Motronic. These are the PC's that came on the ROW cars of the same year. I have read the rebuild book so many times that when I do anything on the engine I could swear I have already done it and Wayne states that this is a great upgrade but I need more info about it. What are the drawbacks of using these instead of the 9.5 PC. Will 91 octane fuel be enough or can I have the chip programming done to compensate. I have a SW chip now and will have Steve program a chip for the rebuilt engine once I know what I am going to do. Would like to hear from those who have done this. And with the price I have found I can afford new PC's.

[tom1394racing]

I've always read that 9.8:1 is about the limit for CR with single plug and pump gas I would expect that this would be true for the Motronic system. I'll be interested to see what the experts have to say on this.

[dd74]

9.8:1, I think, was the limit for CIS engines. The compression for USA Motronic 3.2s was 9.5:1. I would think if driven sensibly, 10.3 compression for Motronic Euro 3.2s wouldn't be too high for 91 octane.

[88-diamondblue]

I just looked in Wayne's book and one of his top engine picks is the 3.2 Euro upgrade with no other modifications Best option for rebuilding a stock 3.2 engine is what it says. Not much more info than that though.

[Carrera3.5L]

Originally posted by dd74
9.8:1, I think, was the limit for CIS engines. The compression for USA Motronic 3.2s was 9.5:1. I would think if driven sensibly, 10.3 compression for Motronic Euro 3.2s wouldn't be too high for 91 octane.

I disagree. For 91 octane, the CR should be kept under 10:1 and if a big-bore motor using 98's or 100's is built the motor should also be twin-plugged. The rings are thin and just can't and won't take the beating. On a street motor, why take a chance? Less is more unfortunately.

Ralph

[Boxer 6]

Steve Weiner responded to one of my "Race Gas" posts and indicated that compression should be no more than 10:3 using Sunoco Ultra (94 Octane). That's with a twin plugged motor. Like the previous "poster" said less is more.

[88-diamondblue]

OK how do the ROW cars that were imported do with the gas here in the US? They are 10.3 or were the 10.3 PC's by Mahle over rated as to what there true compression ratio.
Ralph if I only had the budget, your rebuild is what I would liked to have done. There some things that I am doing like your fuel line rebuild. Weren't your PC's lower compression than what they were rated at?
The other question is could I use a .5 copper sealing ring to slightly lower compression to the 10:1 number. I have an email in to Steve W to get his experience with dealing with Euro Carrera's and any detonation problems. Thanks everyone for the help.

[Henry Schmidt]

There is a screw on the side of the Motronic brain (ECU) that with allow you to retard the timing slightly.
Although I agree that 10.3 is very high for street gas, if you go with this compression give yourself every change of survival.
Yes, you can reduce compression with increased deck height.

[Carrera3.5L]

Originally posted by 88-diamondblue
OK how do the ROW cars that were imported do with the gas here in the US? They are 10.3 or were the 10.3 PC's by Mahle over rated as to what there true compression ratio.
Ralph if I only had the budget, your rebuild is what I would liked to have done. There some things that I am doing like your fuel line rebuild. Weren't your PC's lower compression than what they were rated at?
The other question is could I use a .5 copper sealing ring to slightly lower compression to the 10:1 number. I have an email in to Steve W to get his experience with dealing with Euro Carrera's and any detonation problems. Thanks everyone for the help.

Some motors are more lenient than others. I have heard of some alledged 10.3:1 motors running fine on 91, others don't like it. I would think the last thing that you want to do on a street motor is build one with too much compression and be "forced" to blend race gas to avoid detonaton issues. Better safe than sorry.

I haven't been blessed to live in an area where 93 or 94 is available at a pump, so don't know what the safe CR would be. I can tell you that the CR should be under 10:1 if using 91 and if longevity is a concern. Andial won't build a 3.0/3.2 based motor over 10:1 with 91 octane.

The Mahle P's/C's have a rep for measuring lower than advertised on some sets, but there are many other variables that affect the static CR as well. I ended up at 9.5:1 with 100's and while another couple of tenths would have been nice it's not the end of the world.

If Steve has detonation issues when programming with the higher CR's and 91, one of the things he will do is back the timing down incrementally to lessen the risk of detonation. On the flip side, with a little less compression many times he can be a little more aggressive with the timing to help compensate.

A few tenths of compression is not a very significant horsepower increase and many may not even notice it.

Ralph

[88-diamondblue]

Henry, Can you tell me more about what you mean by chance of survival. And what if any draw back of increasing deck height.

If I could get the 10 or 10:1 compression then it would be at a point where It should work knowing it is at the edge.

The difference in price between the 9.3 and 10.3 PC is around $2000. The budget would not allow new 9.3's. Was looking for a way to install new PC's. I do have a SteveW chip now and will have him do a new one for me.

[Henry Schmidt]

If you run more compression there are three things you need.

high octane (very expensive)
retarded timing (easy)
more fuel ( simple programming)

A chip can retard the timing, increase the fuel (mixture).

Two out of three will reduce the chance the engine detonate.
No detonation the engine will survive.

Check PM

[dd74]

Originally posted by Henry Schmidt
If you run more compression there are three things you need.

high octane (very expensive)
retarded timing (easy)
more fuel ( simple programming)

A chip can retard the timing, increase the fuel (mixture).

Two out of three will reduce the chance the engine detonate.
No detonation the engine will survive.

Check PM

As Henry suggests with the two of three adjustments, 10.3 is still possible with 91 octane.

[Steve@Rennsport]

Originally posted by Carrera3.5L
I disagree. For 91 octane, the CR should be kept under 10:1 and if a big-bore motor using 98's or 100's is built the motor should also be twin-plugged. The rings are thin and just can't and won't take the beating. On a street motor, why take a chance? Less is more unfortunately.

Ralph

"Brother" Ralph speaks VOLUMES of wisdom on this subject,....

[88-diamondblue]

After getting back a response from SteveW on how he has to program the chip to make them work on 10.3's and all the feed back I have gotten here I am looking at other options since I am not gaining much and risking more, Just need 93 octane back like we used to have. Thanks everyone for their input.

[Steve@Rennsport]

Michael:

It sounds like SW gave you some sound advice.

IMHO, its not worth the risk given the normal variations found in pump gasolines since the consequences can be VERY expensive.

[cgarr]

Is the 93 octane the real holdback here? or is it a twin plug issue? or all the above combined? I am planning on running only 93 in my 3.2 with close to 10.5:1 98mm p&c's but it will have two sets of plugs too, when I talked to Steve he didnt sound like it should be a problem or should I back the compression down a tad?

[dd74]

For what it's worth, my stock 3.0 with 80,000 miles and 9.3:1 compression, occasionally rattled on 91 octane fuel. The CIS system when checked, was flawless and the distributor was set at factory spec. However, even with an occasional octane boost and even an infusion of techron, the engine gave off the occasional ping on uphill grades at WOT on warm days. So, with my options exhausted, I learned to drive through/around it, which, in the end enabled the engine to survive another 20,000 miles until I sold it.

So what's the lesson here?

1) 91 octane is too low for even 9+ compression?

2) A dose of race gas/octane boost should be as commonplace as one taking daily vitamins?

3) Maybe any engine over 8.5:1 compression should be twin-plugged?

I can't imagine #3, but I think numbers 1 and 2 could be a very real possibility in California, unless one wants to retard their ignition to the point the car no longer performs as it should.

Or again, you can just drive "around" the problem.

[lvporschepilot]

I built a Maserati Merak ss engine a couple years ago and used 10:1 pistons in it(276bhp@7400rpm 3.0l v6 engine). It ran fine on 91 octance but, I made sure all the engine components were perfectly balanced so not to subject the motor to added unbalanced stress. I was still reluctant to go 10:1 even after all the balancing. Never go higher than 10:1 on a street engine . 91 octane gasoline at certain places may not be 91 all the time. Too risky if you really want to take advantage of your new compression. You can always lag down the timing like someone else said but, less is more as correctly stated earlier.

Good luck!

[Determined]

There's a lot more knowledgible people on this subject giving great advice than me, but I too am planning to run 10.3 compression on my 84 Carrera without twin plugging. I did invest in thermal barrier coating on most of my internal components, specifically the piston domes and skirts plus other areas. I have read a great deal on the subject and believe that it will help reduce detonation. What does everyone else think? Since my car will not be driven daily I do plan on putting some octane boost with ever fill just in case.

Regards,

Alex

[ChrisBennet]

Originally posted by lvporschepilot
I built a Maserati Merak ss engine a couple years ago and used 10:1 pistons in it(276bhp@7400rpm 3.0l v6 engine). It ran fine on 91 octance but, I made sure all the engine components were perfectly balanced so not to subject the motor to added unbalanced stress. I was still reluctant to go 10:1 even after all the balancing. Never go higher than 10:1 on a street engine . 91 octane gasoline at certain places may not be 91 all the time. Too risky if you really want to take advantage of your new compression. You can always lag down the timing like someone else said but, less is more as correctly stated earlier.

Good luck!

I don't think you can really compare a carbed water cooled motor to an air cooled EFI one.
I think the thermal stability of a water cooled motor is going to let you run more compression (safely) for example.
-Chris