Detonation

[x2ryder]

I have a 5mm stroker with 85.5 bore running 195 psi. I was running a MSD enhancer and a b pipe with 93 octane fuel and a bit of octane booster and everythnig was fine. Last weekend I switched to a type 9 pipe and a Advent T 3 ignition and a oem flywheel. It ran awsome. This week I added water injection and a TBM flywheel. Well almost right away it burned off the front cylinders spark plug electrode. Also it started free reving. I can see where it started to burn a hole in the piston. The rear looked fine maybe a bit lean. Well I lost 15psi in the front cylinder. The curve I am running starts out at 30 degrees and retards to 15 degrees. Should I be mixing a couple of gallons of 110 fuel with the 93 octane? Any help always appreciated.

 

[crammit442]

I have a 5mm stroker with 85.5 bore running 195 psi. I was running a MSD enhancer and a b pipe with 93 octane fuel and a bit of octane booster and everythnig was fine. Last weekend I switched to a type 9 pipe and a Advent T 3 ignition and a oem flywheel. It ran awsome. This week I added water injection and a TBM flywheel. Well almost right away it burned off the front cylinders spark plug electrode. I can see where it started to burn a hole in the piston. The rear looked fine maybe a bit lean. Well I lost 15psi in the front cylinder. The curve I am running starts out at 30 degrees and retards to 15 degrees. Should I be mixing a couple of gallons of 110 fuel with the 93 octane? Any help always appreciated.

Yes. At least a couple of gallons. The dry pipe turns a lot of R's and does a lot of cylinder stuffing.

 

[x2ryder]

What is cylinder stuffing? Also what would cause the sudden free rev? Thanks crammit442 youre always very helpful.

 

[crammit442]

What is cylinder stuffing? Also what would cause the sudden free rev? Thanks crammit442 youre always very helpful.

The pipe(any pipe, not just the dry pipe) aids in filling the cylinder with fuel/air. The pipe helps suck air in and then helps further by stuffing any mixture that has escaped through the exhaust ports back in. As a rule, dry pipes do a better job of this than most wet pipes. This can effectively give give you higher compression similar to supercharging a motor. Octane requirements will normally go up a bit.

 

[x2ryder]

Last week I only ran about 2-3 gallons of fuel through it. Do you suppose it started last week? The flywheel is the newer TBM wheel that works with the Advent.

 

[#ZERO]

What size carbs are you using with your type-9 dry pipe?

Also what size jets, needle & seat, spring color & gram, pop-off pressure and screw settings?

If you're running 15 degrees timing at 7000+ rpm where do you think the timing is at around 5000 rpm?

 

[Crab]

Did you recheck timing after installing the TBM by chance?

 

[Watty]

The Advent curves hold too much advance too late.

195psi compression, too much ignition advance, and low octane fuel will kill your engine every time.

My best guess (assuming you tuned the carbs correctly) would be too much timing after 4k. Anything over 25 degrees adance over 4k is not needed, especially if you are running buoys. A bit (10%) of methanol will help with an agressive curve, but you'll still have to keep an eye on engine temps.

 

[x2ryder]

#0 according to my sheet here from Advent I have 30 at 5000 rpm still and at 7000 I have 16.4. I am running gen 3 48mm Novi's with 140 pilot 120 main 2.5 needle and seat 115 spring 20 psi pop off. lo out 1.5 and high out 2.

 

[Big Kahuna]

ADA's website use to say "35cc domes 81mm 92 octane, if you are running a dry pipe you need 100 octane" not an exact quote, but that is the gist, they tell you to up your octane with the dry pipe.

 

[x2ryder]

I am going to go with 3 gallons of 110 and 2 gallons of 93. That will take it to 103.2. With 195 psi I will need 98.5 octane.

 

[crammit442]

I am going to go with 3 gallons of 110 and 2 gallons of 93. That will take it to 103.2. With 195 psi I will need 98.5 octane.

That will be correct for the Research octane #, but you're not anywhere near that in Motor #. The research number is NOT what you're after. You're looking for Motor octane #. You can figure the Motor number of 93 pump gas at somewhere around 89 or 90. The Motor number for 110 will be somewhere between 105 and 107 depending on fuel brand. For starters I'd shoot for a Motor number around 100 and watch for any signs of deto. Most motors will run on 100 Motor octane safely. Just watch long WOT runs for a while.

 

[Watty]

Indeed.

Another thing, I think you are too lean on top, start with something like a 140 high, and tune with the tach to see what the engine is doing on WOT runs (start with little ones)

 

[x2ryder]

I have a call into Tim at Novi. I don't have a 140 but I do have a 130 main.

 

[#ZERO]

If you're at two turns on your high speed screws I'd say it's running a little lean on the top end.

I would lower the pop-off pressure with a 95 or 80 gram spring and maybe back the total ignition advance to around 28 degrees or set and new curve to retard the timing faster.