Burned P/C TRACK CAR

[r lane]

A fresh 3.0, twin plug, crank fire, 12.0 to 1.0, 110 fuel, MFI engine, my best engine that I had just freshened up. Felt very strong for the first few laps and then began to deterioate. By the time I pulled into the pits she was missfiring. 3 cylinders involved, #s 1,3 and 4. #1 being the one most effected. The injectors all spray well and I had the pump on my test bench right before installing it. My ignition is Electromotive XDi and timed at 22,7 and 1 degree giving me 30 total. Running this system for 4-5 years with no issues. I noticed that the headbolts had loosened a bit, but I have experienced that on other rebuilds right after the initial outing. I have to think something has gone south in the ignition box. Any thoughts. Thanks,

[stownsen914]

Ugh, sorry to see this.

How loose where the cyl head nuts? Just lost a little torque, or spinning loose?

[Henry Schmidt]

I'm guessing you're looking at detonation.
Detonation causes abnormally high cylinder pressures and heat which would explain loose head studs.
Ignition malfunction is a pretty good guess.
I'm wondering why you're running cylinders with a CE rings instead of flat tops or Ni-resist rings with that much compression?
What cams are you running? Did you calculate dynamic compression?

[stownsen914]

There is a stand-alone knock sensing system you can use on analog cars. It triggers a flashing light that you can put on your dash. Made by a company called Link. Doesn't pull timing or anything, but it lets you know to back out of it if detonation is happening. I'm putting one on my 911 vintage racer to go with the rebuilt engine.

[r lane]

Thanks for all the response. Head nuts had lost 2-5 foot pounds. Henry, those were the cylinders I had at the time. I have a set of 3.2 KS which I will send out for Nikasiling but have run these cylinders for 4-5 years with no issues. Elgin cam 306/288 100 centerline which is not as hot as the 314/296. Did not calculate dynamic compression. Again, is same motor that I have been running for a while with one exception. Went from 3.2 heads to a set of 78 SC heads reconfigured by Xtreme heads. Bill said an additional 30 HP and I said I don't know if I want an additional 30 as I think in its previous form was probably making 325-330. Maybe the CE cylinders can't handle it. A way to monitor detonation I probably need. I am 80 and ran out of projects 7-8 years ago and turned to this addiction and it has been expanding with much fun and related problems but I knew that would happen. Bob

[JoeMag]

Don't the pistons and heads get a sandblasted look from detonation? The head looks pretty smooth still, but pic is not so good. How about top of piston's?

[r lane]

Originally Posted by JoeMag

Don't the pistons and heads get a sandblasted look from detonation? The head looks pretty smooth still, but pic is not so good. How about top of piston's?

I know little to nothing about the science of detonation. Other than you have explosions rather than a controlled burn which can rapidly raise the cylinder head temp and cause things to start coming apart. Running too lean or too advanced in the ignition. The piston and rings don't seem to have been compromised surprisingly and the surface is smooth. Have just machined .010'' from the damaged head and appears another .002 will be required. Will need to add a shim and cut .002'' from the other two heads. Right now I am trying to decide if the CE style cylinders cannot take the stress. I have a set ready to go. Thanks, Bob

[MoreGAS]

Bummer R
Looks and sounds like it was detonating. You changed the heads but didn't recalculate compression it seems(CC the new heads and piston)?

Do the math , if the head reconditioner took off .010 or .020" , you may have lost several CC's of head volume, that will make quite a difference in compression. Also your math on the ignition timing: 22.7 plus 1 is 30 , can you clarify? As a rule of thumb, when we twin plug an engine like this , we generally need 5-6 degrees less ignition advance, vs a single plug to get to max tqe, pk hp. . So generally speaking, a race engine like that single plug may achieve max tqe and Hp at roughly 30-31 degrees, so 25 degrees of advance twin plug we commonly see. This is where Porsche Motorsport would set the factory RSR 3.8 sprint & original 3.8 Std engines we have seen, run and tuned . Of course there are exceptions and not all engines built the same run identically, but your advance of 30-31 would be way way too much advance.
You can check those damaged, and your other pistons and check the top ring land gap between top ring and the piston land with a feeler gauge and see if all pounded out, .004" is the limit tested with a new ring., but with your existing rings you'll get an idea of condition. New, this should be at or just under .002". You rod bearings also are likely pounded out with the detonation.
You also can send your pump out to whomever you use the service and calibrate it and check each cylinder flow is correct and even. On the last OG 3.0 RSR engine we rebuilt Gus at Pacific gave us our new injectors back(we supplied new streeter injectors) with each cylinder position noted to be more even.
Ideally, you need to be checking lambdas each side on a new engine(we log these ALL the time if EFI) , and use some form of high quality audio knock detection when optimizing your ignition timing at initial set up. I know it isn't always convenient but finding a Dyno and savvy operator with necessary equipment will save a bunch of time and money in the end. If you cannot do this be very conservative and stick within known realms.

Kevin
GAS Motorsport

[Henry Schmidt]

If all things are equal, the only way to make more horse power by head configuration (IE: porting or combustion camber reduction) is to improve cylinder filling (volumetric efficiency or compression).
Increased volumetric efficiency will increase dynamic compression.

[r lane]

Originally Posted by MoreGAS

Bummer R
Looks and sounds like it was detonating. You changed the heads but didn't recalculate compression it seems(CC the new heads and piston)?

Do the math , if the head reconditioner took off .010 or .020" , you may have lost several CC's of head volume, that will make quite a difference in compression. Also your math on the ignition timing: 22.7 plus 1 is 30 , can you clarify? As a rule of thumb, when we twin plug an engine like this , we generally need 5-6 degrees less ignition advance, vs a single plug to get to max tqe, pk hp. . So generally speaking, a race engine like that single plug may achieve max tqe and Hp at roughly 30-31 degrees, so 25 degrees of advance twin plug we commonly see. This is where Porsche Motorsport would set the factory RSR 3.8 sprint & original 3.8 Std engines we have seen, run and tuned . Of course there are exceptions and not all engines built the same run identically, but your advance of 30-31 would be way way too much advance.
You can check those damaged, and your other pistons and check the top ring land gap between top ring and the piston land with a feeler gauge and see if all pounded out, .004" is the limit tested with a new ring., but with your existing rings you'll get an idea of condition. New, this should be at or just under .002". You rod bearings also are likely pounded out with the detonation.
You also can send your pump out to whomever you use the service and calibrate it and check each cylinder flow is correct and even. On the last OG 3.0 RSR engine we rebuilt Gus at Pacific gave us our new injectors back(we supplied new streeter injectors) with each cylinder position noted to be more even.
Ideally, you need to be checking lambdas each side on a new engine(we log these ALL the time if EFI) , and use some form of high quality audio knock detection when optimizing your ignition timing at initial set up. I know it isn't always convenient but finding a Dyno and savvy operator with necessary equipment will save a bunch of time and money in the end. If you cannot do this be very conservative and stick within known realms.

Kevin
GAS Motorsport

As stated in my original post, the engine is twin plug and 12 to 1 compression. The XDi ignition timing is configured as initial, 3000 and 8000. 22* plus 7* plus 1* equalling 30*. AFR are high 11s-low 12s. This engine has been in action for 3-4 years and on this refresh it got a diff set of heads and pistons to match so the compression stayed the same. On paper, the heads should have added power, but enough to blow up the motor? Don't know and that is my conundrum, what caused it? I will rebuild it, drop the timing to 28*, keep the compression at 12-1, test with a timing light, probably get a knock and head temp sensor. Again thanks for all of the response. Bob

[rudedude]

Was the original engine set up on a dyno by chance?

[MoreGAS]

Bob
You need to actually calculate compression by getting volume numbers for your new piston and heads. We have returned likely 20% of the custom pistons we order because the manufacturer totally missed on some critical detail, either way too much compression, or way to little. Hard to explain why but they mess up too, like all of us.

If head folks report you are going to gain 30 HP, they think they have achieved a ton more air flow(I suspect way to rosey a prediction unless you old heads were absolute junk- totally possible w someone who has no idea what they are doing ported them however) and logically that means in keeping with a 12:1-x A/F ratio, you are going to need a corresponding bunch more fuel in those areas. On a dyno monitoring lambda(A/F) you would have seen this and adjusted accordingly.

Setting an arbitrary number like 28 degrees is a tiny step in the correct direction I believe, but these lumps are expensive, and to not dyno it and set it up properly, tune it for fuel and ignition, is very risky(as demonstrated) . You don't want any more ign advance than what makes peak power and Tqe, and really want to build some safety margin in above that by taking out a wee bit more advance in some areas for when things get really warm etc. We have that ability w Motec (any decent EFI system actually but shameless plug for me being a Motec dealer in North America for 12 yrs or so) and when head temps creep up we pull timing. You don't have that luxury w MFI. If you cannot dyno it at bare minimum get a high quality Lambda meter always displaying in the car (I can link you to one and you can thereby check fueling is in the "ball park" , dual lambda one on each side would be better not sure if avail. in a meter display) , set timing at 25 , and hopefully you get lucky. Realize, we NEVER do this and dyno , and tune every engine we build, customer's and our own, but trying to give you a chance here. These are way more fun to enjoy on track at RPM than work on, so hope I have convinced you .

Last thought, also verify w a timing light (easy to do on a dyno or briefly free revving to say 5500 RPM -oil warmed up already!) that at rpm and load at Peak Tqe , that ign advance is where you believe it is.

beST

Kevin
GAS Motorsport

[dannobee]

MFI? Do as Kevin says and get a standalone Lambda sensor (or better yet, 2) and a knock retard system. Then religiously observe the lambda and "adjust" the MFI as necessary. 25 degrees is a good place to start, 23 might be better. Leaving a tiny bit of hp on the table is better than torching a cylinder. And if you're too "busy" when driving, set up a camera to watch the lambdas under load. Too lean and too much advance will quickly destroy any engine. Oh, and what kind of fuel did you have in it? 12:1 is race gas only territory.

[PeteKz]

Innovate sells a 2-channel AFR meter. Check with the usual suppliers.

[r lane]

I am running an AFR meter and see high 11s to low 12s. 110 race fuel. The piston build sheet says the dome is 47.5 cc which should give me a little over 12 to 1. They I think were basing that on a 87.6 cc head. My heads are 86.6, I measured them. I calculated the dome as 48.9. By the time I removed material from the valve pockets and small relief for the plug tips, my dome was down to 47.34cc. Approx 12.09 to 1.0. So far as depending on the speculative additional HP numbers I wasn't. Not that it wasn't a potential improvement over what I had, but what I had was an unknown in terms of its flow numbers. Bob

[MAH77]

How old is the AFR meter sensor? The lead in race gas damages the sensor and it loses accuracy.

Originally Posted by r lane

I am running an AFR meter and see high 11s to low 12s. 110 race fuel. The piston build sheet says the dome is 47.5 cc which should give me a little over 12 to 1. They I think were basing that on a 87.6 cc head. My heads are 86.6, I measured them. I calculated the dome as 48.9. By the time I removed material from the valve pockets and small relief for the plug tips, my dome was down to 47.34cc. Approx 12.09 to 1.0. So far as depending on the speculative additional HP numbers I wasn't. Not that it wasn't a potential improvement over what I had, but what I had was an unknown in terms of its flow numbers. Bob

[r lane]

Originally Posted by MAH77

How old is the AFR meter sensor? The lead in race gas damages the sensor and it loses accuracy.

I think you can test the sensor with a volt meter. Would want to do it under load or install another one and compare. As long as they are cycling in a normal manner, I want to trust them. Have dealt with numerous failed ones that began to act erratically.
Cycling in a normal manner may not necessarily mean they are accurate though. MFI is not known for having lean issues unless you have a leaky check valve. Doubt if all would suddenly fail together. Fuel pump, filter and fuel console check valve have to be checked. The problem effected the whole motor, some cylinders more than another. Will put everything back together, confirm timing with a timing light. If that checks OK will still install my backup XDi unit. Of all the problems I thought I might have to deal with, this isn't one of them. Plan to have head temp and knock sensor installed by launch.

[stownsen914]

With leaded fuel, the failure mode might be different than what you would see on a car running unleaded. Not sure the electrical signal test is valid. With gradual lead buildup, the sensor slowly becomes less sensitive to inputs and may give false readings. I think Bosch says something like 50-100 hrs of use with leaded, assuming a properly tuned engine. Could be faster if running rich or lean, etc.

[TimT]

What Bosch says about leaded gas and 02 sensors

More about sensor degradation and failure

[Odin911]

It sounds like you've got a solid setup, but the issue with misfiring on cylinders 1, 3, and 4, especially with #1 being the most affected, could indeed point to an ignition issue. Given that the Electromotive XDi has been reliable for years, it's possible that the box may have developed a fault, especially after some heat cycles.