11.6:1 CR and 93 octane experiment results

[Guest norm[T12SDSUD]]

Just wanted to update y'all on my 11.6:1 CR with 93 octane experiment I started last fall...............it didn't work! LOL

 

Once the outside temps got up to 85 degrees the piston ringlands went to shattering from severe detonation.

 

I raced a week ago and still kicked Mustang booty though! Even with THREE broken pistons and racing on regular old street tires she still managed an 8.83 @ 80mph in the 1/8 mile with oil blowing all over the windsheild thru the K&N breather filter on the valve cover.

 

The back three pistons broke so it loooks like a slightly lean mixture on the rear SU with no room for error did em in.

 

Yesterday I got some used replacement pistons and rods from an engine laying out in the junkyard that thankfully had no water damage.

 

I am going to go back to the two head gasket setup I ran for 2 1/2 years at 10.7:1 CR and hopefully with new slicks and some yet to be discovered new speed tricks I can try and attempt again to lower my best run of 8.20 in the 1/8 mile down to a 7.99 with the old 2.9L stroker junkyard dog!

 

LAter,norm

[Guest Anonymous]

That's crazy, Norm!

Good to hear from ya again..

I would never be so bold as to try 93 with 11.6:1!

that's a pretty insane story, landing 8.83 with 3 broken bad pistons.

Its kind of funny, nature seems to work itself out: if your trying to use too much compression, too little fuel (or retard), something blows up, loss of total seal, and compression works itself back down again

I guess it wasn't meant to be

Mucho respect, 12's SU Norm (the name says it all).

-980mak

[Guest Anonymous]

seems like you could get a new and use that compression and not risk blowing a head gasket with so much compression and tall gaskets just a question should also give you better times too much cam hurts I know but so does switching pistons and rings. good luck

[Guest Anonymous]

cam

[DAW]

I guess it's too late now, but are you using octane booster too? I autocross with a F54 flat top/N42 which always wants to ping on 93 octane so I'd been using 108+ brand booster which helps some. Over the winter I've discovered one that works really well: Outlaw brand. I've got an old Datsun 720 King Cab with an L20B, 10.2:1, headers, and twin 240Z SUs. It wanted to ping, even with SM needles. I followed the tuning method in the book "How to Build & Power Tune SU Carburettors" by Des Hammill, where you identify the lean-ping rpm/needle position and turn down the needle on a drillpress, pinching it with fine sandpaper at the specific needle/jet level where it was lean. The improvement in performance and decrease in ping were like night and day vs before this tuning. Back to the octane booster. The truck no longer pings unless I get a marginal tank of gas. This happened recently while on my way to pick up a full load of bricks and it was pinging even unloaded. I filled the truck with bricks and put in one vial of Outlaw, and I drove it the 65 miles home at highway speeds and rarely had a ping (and got 20mpg). Huge improvement.

My L20B has a closed-chamber head, my L28 has an open-chamber (N42) head. If the Z still pings using Outlaw booster, then I'm going to try the P90 big shave/shim/longer valves approach ala Bobby (search for P79). DAW

[Guest super280z]

Norm,

 

im sure you've thought of this, but why dont you just run a much bigger camshaft to bleed off you're cyllinder pressure and retain you're 11.6:1 CR? im sure you could pull it off with enough valve lift. like i said, im sure you have you're reasons but i just thought i'd toss it out for discussion.

[Guest norm[T12SDSUD]]

I really don't want to go up much more in cam duration.

 

The loss of low end torque was significant when going from the 262/272 to the 272/282 cam.

I think the 282/292 cam would just take too much torque away to make it an enjoyable street car.

 

Later,norm

[Mike C]

I don't blame you for not wanting to give up any more low end. A bigger cam will only bleed off cylinder pressure at lower engine speeds. As speed increases, so does cylinder pressure. That's why power goes up, because cylinder pressure went up. Obviously a direct correlation between the two. If you have too much compression there are two options. 1. reduce static compression. 2. run more $ fuel.

[Guest Anonymous]

Speaking of compression, I got a F54 flattop on a N42 combo and I'm looking at somewhere around 10.1 : 1 compression. I'm in California and the highest octane we could get at the pump is 91. What do you guys think, I'm I going to be OK?