BB hypereutectic piston source

[Michael G.]

Good evening all. Am soon to start the rebuild of my 427 (1966) and looking at a potential block rebore with past engines using hypereutectic pistons with great success. As I will be lowering the compression (somewhat) to accomodate todays gas, haven't seen much offered (available) for the Chevrolet 427. I've looked at Keith Black web site with not many choices. Any suggestions? Thanks.

[Patrick H.]

Re: BB hypereutectic piston source

Two comments,

1. According to the Summit Racing website, only Keith Black makes hypereutectic pistons for your application. If those are really what you want I suspect that KB's are all you are going to find.

2. Please consider searching the Archives and especially reading some of Duke Williams' posts. I think you will find that many members are no longer building "detuned" or "lower compression" motors but rather are sticking with stock specifications. With a bit of preplanning and thinking you can keep all 425 of your original horsepower and also keep your engine from detonating or knocking.

Patrick

[Michael G.]

Re: BB hypereutectic piston source

Patrick,

More credit than I deserve.....only a 390 HP engine. I'm sure it'll still put a smile on my face when done.

[Patrick H.]

Re: BB hypereutectic piston source

Patrick,

More credit than I deserve.....only a 390 HP engine. I'm sure it'll still put a smile on my face when done.

OK.

Same idea, though.
And, a 390 horse will have no problems at all running on today's gas with stock specs. You just gave yourself even less reason to mess with it.

[Joe L.]

Re: BB hypereutectic piston source

Good evening all. Am soon to start the rebuild of my 427 (1966) and looking at a potential block rebore with past engines using hypereutectic pistons with great success. As I will be lowering the compression (somewhat) to accomodate todays gas, haven't seen much offered (available) for the Chevrolet 427. I've looked at Keith Black web site with not many choices. Any suggestions? Thanks.

Michael-----


427 pistons are not as easy to find as they used to be. The last use of a 427 in a passenger car was 1969 and they were only used for 4 model years. Plus, most folks building a big block these days are going to go 454 or larger. So, none of these realities make manufacturers too interested in offering much in the way of 427 pistons.

The only 2 major manufacturers of hypereutectic cast pistons are Federal Mogul and Keith Black/Silvolite. I don't think that Federal Mogul currently manufactures a 427 hypereutectic piston which would be appropriate for your application and intents. However, Keith Black offers 3 different hypereutectic pistons for 427's, each with different dome heights. You don't say what engine or cylinder heads you have, but I think that one of these 3 pistons should provide pretty much what you're looking for.

[Joe L.]

Re: BB hypereutectic piston source

Good evening all. Am soon to start the rebuild of my 427 (1966) and looking at a potential block rebore with past engines using hypereutectic pistons with great success. As I will be lowering the compression (somewhat) to accomodate todays gas, haven't seen much offered (available) for the Chevrolet 427. I've looked at Keith Black web site with not many choices. Any suggestions? Thanks.

Michael-----


OK, now I see that you've posted that you have a 390 hp. In that case, I'd use a KB 176 with 0.039" thick head gaskets for slightly higher than stock compression ratio or use a KB 360 with 0.039" thick head gaskets for slightly reduced compression ratio. My recommendation would be to go with the KB 360.

[Patrick H.]

Re: BB hypereutectic piston source

Michael-----


OK, now I see that you've posted that you have a 390 hp. In that case, I'd use a KB 176 with 0.039" thick head gaskets for slightly higher than stock compression ratio or use a KB 360 with 0.039" thick head gaskets for slightly reduced compression ratio. My recommendation would be to go with the KB 360.

Joe,

I note that the only difference between those two pistons is the height of the dome.

I think I'd be measuring and equalizing chamber volumes as well as checking deck height, and then order my pistons based on those numbers once I know the true compression ratio. That way you'll end up with the "best" results.

I also could not find any FM/Sealed Power hypereutectic pistons for his application.

Patrick

[Michael G.]

Re: BB hypereutectic piston source

Joe/Patrick,

You saw the same as my research yielded.....pistions choices for my 427/390 are slim to none.... Believe the KB 360 is a likely replacement canidate but other considerations such as gasket thickness, deck height and corrected chamber volume will come into play for the engine building process. Appears higher compressions and crummy gas have some shops/machinest operating conseratively.

[Joe L.]

Re: BB hypereutectic piston source

Joe/Patrick,

You saw the same as my research yielded.....pistions choices for my 427/390 are slime to none.... Believe the KB 360 is a likely replacement canidate but other considerations such as gasket thickness, deck height and corrected chamber volume will come into play for the engine building process. Appears higher compressions and crummy gas have some shops/machinest operating conseratively.

Michael-----


Keep this in mind: most current GM crate big blocks, and all of those with cast iron cylinder heads, are built with a compression ratio of 8.75:1 AND require 92 octane fuel.

Big blocks are big bore engines and, consequently, are more susceptible to detonation at a given static compression ratio than smaller bore engines.

[Michael G.]

Re: BB hypereutectic piston source

So I understand clearly Joe, please explain your comment BB being more susceptable than SB to detonation?

[Duke W.]

Re: BB hypereutectic piston source

Larger bores are more prone to detonation, and the practical bore limit of spark ignition engines is about 6", which is as large as reciprocating aircraft engine bores ever got. To get more power more cylinders had to be added, and some prototype 5000 HP aircraft engines in the WW II era had 36 cylinders. There is no limit to compression ignition cylinder bores, which is why big marine engines have bores on the order of 36".

Fortunately, the turbine engine ended the ever increasing complexity of reciprocating aircraft engines.

As far as big block CRs are concerned, since most original big blocks run without signficant detonation on most pump premiums, there is no need to "reduce" CR, but keep in mind that "as-built" CRs are typically up to one-half point lower than "advertised".

Duke

[Michael G.]

Re: BB hypereutectic piston source

Duke,

As stated and assuming the block needs boring am considering the KB 360 hypereutectic. Using their calculator shows to make around a 9.77 CR with my 702 heads with 98.2 cc rated chambers. Would also look at cc'ing the heads making all equal. Do you see this a viable choice and effective path? Thanks in advance.

[Duke W.]

Re: BB hypereutectic piston source

Don't rely on their calculator. Use the one I've referenced a zillion times (archives) and do all the teardown and buildup measurements to get your target range, which should not exceed 10:1.

Head chamber volume should be measured and the final step is to grind a little on the two or three highest CR cylinders to bring the delta across all to no more than 0.1.

Duke

[Gene M.]

Re: BB hypereutectic piston source

For flight judging I would use a correct head gasket thickness as judges will catch a .04" thickness as it is twice original gap .019" shim gasket head to deck distance.

[Patrick H.]

Re: BB hypereutectic piston source

Don't rely on their calculator. Use the one I've referenced a zillion times (archives) and do all the teardown and buildup measurements to get your target range, which should not exceed 10:1.

Head chamber volume should be measured and the final step is to grind a little on the two or three highest CR cylinders to bring the delta across all to no more than 0.1.

Duke

Agreed.

Do all your measurements first, then order your pistons based on your target compression ratio.

But I said that once before.