I broke my forged piston ring lands after a one time WOT at a 3psi boost bump. Partially it's my fault, it was tuned for 14psi with good quality straight gasoline, and I fixed a leaky BOV flange and it went to 17psi, but only for a few seconds. But I've seen a number of other people losing motors lately for no apparent reason.

Since gas got expensive, I've been shopping for the cheapest Premium around, and typically the cheaper blends have ethanol in it. I'm sure I'm not the only one shopping by price these days.

Bear with me for a sec here, but Octane is RON+MON, RON is low load ping resistance, and MON is high load ping resistance. Ethanol has a higher RON rating which increases low load ping resistance, but if RON is higher, MON must be lower to get to the same sum Octane rating (91 octane here in CA). The new 91 octane ethanol blend must therefore detonate more at high load (where guys like us drive). Ethanol also leans out the fuel, the PCM eventually learns (through O2 readings?), how much more fuel to flow. I vaguely remember reading that the PCM learning is not immediate, it takes a little while. So, that make me think that after running on straight gas, then driving hard right after filling with an ethanol blend may not be a great thing for the motor. The PCM probably hasn't learned the blend yet, and will probably run lean for a while. Now my 2005 Avalanche is a flexible fuel vehicle, which means it can adjust itself to flow enough fuel to burn the E85 blend. My supercharged vette may not have enough margin of error to withstand even a 10% leaner mixture (like going from 12.5:1A/F to 14:1A/F and with low octane during WOT).

So, does this sound right? Will an ethanol blend damage out high - stress high -horsepower motors?

 

On my F2R blower car, it hates 10% ethenol 94 octain. It will ping if i put it in. If i use unblended 93 fuel it works perfect. Also, i get 50 more miles per tank on the non blended.....

 

Do you keep a wideband in your car? You might want to try that or even keep a laptop to monitor what is actually going on. It sounds like you know whats going on, and you will find that it might help to keep you eye on your motor alittle more. The computer will reset everything everytime you fill up the tank. From this is how the computer knows to kick into what timing table. This also gives the computer a basis to learn off of.

A few questions for you.

Do you have cats?

What type of dyno did you use to tune on?

what A/F did you shoot for?

What type of timing are you running on the top end where boost is highest?

What were your ring gaps set at?

This info would help some more to figure out what went wrong besides the fact that your motor was restricting an additional 3 psi.

rick

 

The adaptive fuel trims are always monitoring the fuel as long as the temp is over 176 " or what is specified in the bin file" The reseting the gas with a fill up is not valid.

The Spark adaptive learn system is constantly working just like the fuel. In the operating system you can change some bits to make it use a set blend of high/low octain, ect..

The computer looks for a pattern that looks like a knock and if it sees the knock signal, it will pull a percentage from the high octane table and move that percent closer to the low. So, if the car sees 2 degrees of knock, it may only use 60% of the difference of the high and low octain, so, if the high table is 28, and the low is 16 in that same cell, the value it would be putting out as final timing would be around 20. HOWEVER, if the computer sees that it is no longer getting the knock in that area, it will slowly "depending on rate set in the bin" move itself back to 100% high octain in that cell.

 

Yes, 2 3/4" Random cats.
Dynojet
12.5:1 A/F, pretty even in the dyno chart below.
24deg
They were Diamond file-fit rings, and I used a flat gauge to measure the gap for each cylinder they were filed for. I ended up filing each ring a bit more than I tried for, either the gauge didn't fit or it slid in and wiggled. After break-in the compression test showed 145psi across the board.
The motor was tuned for 14psi, I didn't expect that fixing an o-ring leak would get it up to 17psi, I don't think was even near redline.

 

Good info. I was under the impression that most of the relearn change was made under fill up to reset. But thanks for the added info.

Rick

 

I meant what was your gap size on the rings that you filed down? Thats whats important.

12.5 is real lean if you are measuring after the cats. You realy need to keep a wideband before the cats in the headers to know what your true A/F is when you tune. Plus, if you use a dynojet for tuning on that A/F, then you go leaner on the street. These are things to think about. An additional 3 psi is worth breaking stuff.

rick

 

I don't recall, but I remember calling Diamond and asking what the gap should be for FI, and it was a bit larger than the spec sheet.

 

Adds to the evidence that ethanol could be bad for modded motors.

 

The announcer (Bob Fry) at the NHRA event last week said the volume of fuel needed is increased when you add more alcohal to a gasser...

So I get from this that the higher priced alcohal blended gas will decrease mileage even though it costs MORE!

In NY this blended stuff in mandated 12 months per year. It used to be only in winter. Both my cars hate this stuff.

I am convinced that my last two SES problems were alcohal-blended gas related....

PS- Every time I go to NHRA, I wish that Bob Fry would hang up the mike. He is like the Energizer bunny, however...