ross flat top piston compression on my 1970 455

Unless you have to drive this car thousands of miles a year or have absolutely no access to it the only logical answer is run a mix of race gas in there. 110 and pump 75/25 will probably do the job. No changes necessary. Shift at 5700 with that cam and run good gas and it will live a long life. That is your cheapest option.

Back in the day when I tried to run 12:1 on the street it could get hairy if you didn't have good gas in the car or octane booster. After trying to drive 350 miles to Columbus and running out of booster the car decided to run-on badly when I tried to shut it off. And I mean BAD! In gear it didn't help(auto). Retarding timing with MSD box didn't help. Still running-on. It took some doing but finally stopped. Got some booster on the road before I tried shutting it off again. Good gas and no problem.

The best mechanical solution is to get new pistons in there with a correctly calculated dish to get you 10:1 compression. Thick head gaskets will only get you into the mid 11's and you'll still have to fuss with everything to keep it from pinging. If you are pinging while in neutral that is severe. Shut the engine off, back away from the car, and don't restart it until you get some good gas in it. That pinging is pounding the pistons, cylinder walls, and rod bearings.

 

Thanks to everybody and all this great advice. As soon as I buy 112 and try I will let you know what happens. I have two friends (Chevy guys) that I have to clobber at the track before working on my compression. Nothing against Chevy power its just that they think Chevys are the only engines that run fast.

 

It sounds like a great platform for a monster build and done right you will achieve your goal. Define your goal, design your build to it. BUICK torque will prevail over Chevy HP.

There have been many good short term fixes offered here......Looking long term and big picture, also opined herein, consider taking your build back down to basics and blue print the specs, because at this point, for the money, you should dial it in while it is apart before it comes apart out of control.

 

A set of the late model '75 or '76 open chamber heads would bring down the compression to around 10.7 to 11.5 depending on the other engine specs, would take it down even further with thicker head gaskets to possibly 10:1 with about .070" thick gaskets.

The late model 455 heads have a better short turn I have read, with a bit of backyard porting they should be the ticket until you can get a set of aluminum heads, heard they can be ported to flow as good as the earlier model heads they just don't offer a quench pad in the open chamber design.

The problem with the aluminum 455 Buick aftermarket heads is that they aren't flat top piston friendly unless race gas is planned for strip use mainly because a larger chamber isn't offered to run flat tops in a BBB with them. You will be in the same boat with thick gaskets with aluminum heads as well GL



Derek

 

If you went to open chamber heads and thick gaskets you probably wouldn't be much better off anyways, unless you got it closer to 10:1 or lower.
The quench is a big contributor to octane tolerance.

 

While we all seem to agree that the Ross Pistons are the root cause (as in the title of this thread), how about talking to Ross Racing Pistons to see how much material could be removed from the top. I spoke with them a few months back about a set of their pistons I have and was able to get every detail as to the various thicknesses of the piston. With that information I ended up sending the pistons to T/A Peformance and Mike was able to enlarge as well as deepen the valve pockets for me. If there is at least .150 final thickness (after machining) at all given points, the top of those pistons may be able to be dished...lowering the compression. Besides re-balancing the good thing is that is usually not very costly to have that done, other than the tear down and gaskets,fluids,etc.
But at the end of the day it's just one more idea to add to the list. I personally would opt for "Race Fuel",............ but that's just me.

Larry

 

:gp::gp:

Works well.
I've done this when there aren't off the shelf options.
Best of all, the quench can be maintained.
E85 would be a better choice still, if available.

 

If these are the "light weight" forged pistons for a BBB they are already only about .150" thick at the top, just like the light weight BBB flat tops I have. Trust me I already looked into this so I could use them with cast iron heads, was a no go. Only the lesser name pistons like Speed-Pro or perhaps KB BBB flat tops(if they even exist?) would be thick enough to convert to a dish IMO. GL


Derek

 

Obviously it would need to be checked to be considered.
Whoever clamps them down to mill them might have an opinion to that as well.
The valve notches can be seen from below (if it isn't solid there)
(Good point, Derek!)

 

Will methanol give me better results than 112racing fuel at the track. Remember I'm just going to do this once.

 

You would need a special carb to run on straight methanol just like you would to run E85 so it is not really a good once and done thing to do. On top of that depending on how good your fuel system is now it may need to be upgraded because you would need to burn over twice as much as gasoline. E-85 wouldn't need as much but would still need considerably more fuel delivered to the engine than gasoline.

 

I'm not going to run methanol straight I was going to mix it with 93 pump gas. Any suggestions will be appreciated.

 

You will need straight race fuel, of at least 110 octane to run that engine safely.

Mixing Methanol and pump gas will not work. Fuel system volume and carb modifications/calibration would be a nitemare, and more likely than not, you will lean the engine out and hurt it.

Don't overthink this.. run straight race fuel in it.

JW

 

Thank you very much Jim, will do exactly that.:TU:

 

Its 25-30% more E85 @ full throttle over Gas, not twice.

 

I run water-methanol injection on my motor and it works great not running super high compression but I can run regular gas on my motor timing cranked up without pinging.

 

I would experiment with changing the way the cam is degreed to lower the cranking compression. If that doesn’t work I would have Scotty brown custom grind a cam for your application.

Lowering the compression with thicker head gaskets may make the long worse due to lack quench.

 

Gary, sorry to intrude upon this post but I am wondering if you can PM me? I don't know how to do it since this website switched formats. I have a question about a vendor/engine builder who is no longer in biz, but whom you used. Or, you can call me at 803-645-9156. (I am the guy who sold you/shipped to you the slippery BFG drag radials that I think ended up on your wife's car).

Thanks!

Ranger
Aiken, SC

 

The 73 860's with unshrouded valves and bowl work flow 250ish on the intake. You must increase the minimum cross sectional radius at the shortside to increase flow. And blend the shortside way back. Then your looking at 280ish. Aluminum heads make the wanted the power easier to attain. I disagree with that statement earlier about a BBC. I built one w/73 truck heads. 489cid, 10/1 255/265/110 70s solid crane cam. 030"lash 623hp 5800rpm. Varied only 2hp through 6700rpm. 91 octane.
Ray