[scapaldo]

I would agree with you in thinking the wall clearance was too small. The loss of power and extra piston slap on a motor at .006" is well worth the tradeoff of safety in a high hp motor IMO.

You should definately look into your ring gaps also. If your rings close up at high power levels piston scuffing or serious damage can occur. Second gap should be a bit larger then the first. The pressure needs an easy exit, if the pressure gets trapped between the two rings the top ring will lift and wont do its job.

Next time you assemble the motor also check that the pins arent sticking. Just make sure the rod moves smoothly back and forth. If it is have your machinist ream it till it doesnt stick anymore. Ive been told that you could break the piston if it sticks during driving.

Im building a 2.4 right now with the wall clearances at .006" and the 1st ring at .021 and the second at .024. Its way on the loose side but its not going to be driven on the street and I plan on spraying it quite a bit so I dont care

 

[scapaldo]

Its likely going to be impossible to correctly measure that clearances now. With that amount of scuffing on the pistons the bores are definately trashed.

Another thing to look at is the fact that hes running a 2.4 with worse rod ratios. Ths means more rocking/sideloading on the piston on the bore. Then your looking at more cylinder wear, and the need to be on the looser side for clearances. This would definately be magnified as he pushed the motor to higher levels.

Ive been reading alot before assembling my current motor. And the general consensus is that theres no real reason not to run things on the looser side if you plan on making alot of power.
http://speedtalk.com/forum/index.php
http://speedtalk.com/forum/viewtopic.php?t=921&highlight=piston+clearances

 

[scapaldo]

I know the ratios are ok but they still have to be taken into account when clearancing the motor. Ill let you know what happens with my ross 2.4 in a couple weeks when I get it back in the car

 

[scapaldo]

I actually did a ross 2.3 before ,which as you know has the same rod ratio angle as a 2.4, and had it clearanced to .004 like you mentioned. When I pulled it apart after a year or so it did have major scuffing on the pistons and bores. But there was never any slap or excess blowby. Makes me think I couldve gone as far as .0045 or .005 without problems

 

[scapaldo]

I don't understand what the big deal is. Just run a big clearance and call it a day. You are not gaining enough by trying to run as tight as you can.

My logs and plugs were clean, even after the motor blew up. There was no data anywhere to indicate something bad was going to happen. Mind you my fuel mixture was 25% methanol.

I agree completely, the motor is bieng built to race, no reason to try to get it as tight as possible. All thats gonna do is give you a cieling of horspower, heat, detonation, whatever.. before it fails.

i'm going to be testing out the clearances suggested by wiseco with a t70 and 90 shot this year hopefully. also i would imagine with a thermal barrier coating on the pistons would help with eliminating thermal expansion the heat wouldnt be traveling through the piston as much.

Coatings will help alot from what I hear. Not only for heat but also in case theres a situation where the piston would get scuffed on the wall, its said to give you more protection from damage.

 

[scapaldo]

Im building a 2.4 right now with the wall clearances at .006" and the 1st ring at .021 and the second at .024. Its way on the loose side but its not going to be driven on the street and I plan on spraying it quite a bit so I dont care

Quick update..

Got the motor fired up a few days ago and got a chance to take it for a quick break in pull. When starting it the very first time I heard very mild piston slap when it was cold. Of course there was a bit of blow by but thats expected on a fresh motor. By the time it was warmed up there was no slap at all.

I took it out for the first hard pull, and according to a friend who was watching, there was a puff of smoke when I got into the throttle in 1st.

On the second pull the smoke was all but gone. Parked it and let it cool down, fired it back up and I heard no piston slap at all. and there was only a very small amount of smoke when cold.

Ill follow up in a couple days when I can mess with it again but my impression is that .006" is fine for a race motor. If it were a street car I would go .005"-.0055".

BTW: The 2.4 spools the 14b like nuts off the line with a stock converter.

 

[scapaldo]

Got to take the car out a few more times and got some more input on the .006" clearence. There is in fact a bit of slap while the car is warming up, nothing Im worried about though. I just dont rev it too much while its cold so I think it should be alright. Once its fully warmed its silent. Like I said before I wont be driving the car on the street so Im confident that it will be fine. Blowby is nonexistent from what I can tell. Ill run another compression test some time to see where Im at there.