BB hypereutectic piston source

[Joe L.]

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.

Michael-----



Keep this in mind: if you build an engine with a compression ratio that results in unacceptable pre-ignition/detonation that cannot be resolved through "tuning" (and, in many cases, you won't be able to resolve such a problem through "tuning"), your options will be limited to the following:

1) use expensive and inconvenient racing fuel:

2) use expensive, inconvenient, (and illegal) aviation fuel;

3) use expensive and inconvenient octane boosters in every tank of fuel;

4) tear the engine back down and replace the pistons.

The above is why engine builders who build STREET engines are very conservative with compression ratios and I strongly suspect why GM uses a compression ratio of 8.75:1 in all cast iron head big block engines.

[Duke W.]

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.

The OE BB gasket of that era is .028". The OE SB gasket of the same era is .018", and mid-'62 to '63 SHP/FI engines had double gaskets from Flint.

The gasket thickness may be measured with a feeler gage at the corners, but I don't think any head gasket thickesses are listed in the JGs. I don't recall ever seeing any judges measure it. I have measured them "for research purposes" at chapter judging events.

Duke

[Michael G.]

Re: BB hypereutectic piston source

I hear what your saying Joe and agree. However should my pistons need replacing, the hypereutectic pistons choices (which are slim) for my 427 are limited to 3 KB styles.....the least compression offered and is the KB 360 offering 9.7 c/r (using this as a guide only) with my 98.2 cc chamber heads. Sounds like your saying this is still marginally too high.....so in stating these facts what choices would I have here in lowering the compression to more tolerable limits?

[Duke W.]

Re: BB hypereutectic piston source

Is this engine as far as you know OE built?

Have you measured the head gasket thickness?

Does it detonate?

During the teardown process you take all the measurements to determine the current CR. If it doesn't detonate and you use an exact OE design camshaft, there is no need to "lower" the CR.

Duke

[Michael G.]

Re: BB hypereutectic piston source

Drove the car prior to disassembly. Engine operated with original normal tendencies (other than smoke some..)...did not detonate. Have purchased O/E style blue print cam shaft for use at rebuild.

Haven't measured anything as of yet....engine still together. Soon to start tear down.

[Patrick H.]

Re: BB hypereutectic piston source

Michael,

I think what we're getting at (and especially Duke) is that you're just guessing until you get in there and measure.

I have a suspicion that your heads will be more than 98.2cc, and I hope that you measure them and post the results. I know of another big block owner who found them ranging from 107-110cc when they were listed as 106.8cc (425 horse). 4cc difference make about 0.5 difference in static compression ratio. Once you open up the chambers to get to, say 102 or 103cc (should you find you need to in order to match the largest) then the choice of pistons may change.

Keep us posted.

Patrick

[Duke W.]

Re: BB hypereutectic piston source

Have purchased O/E style blue print cam shaft for use at rebuild.

Right now the only replacement camshaft assembly (cam and pin assy., GM 3883986) that I would trust to be an exact duplicate manufactured to GM drawing no. 3883944 (finished camshaft drawing no., which is also the ID number on the camshaft) is the Federal Mogul Sealed Power CS1093M or Dana Clevite 229-1953, but I'm not sure if these have the rear journal groove, which is required along with the "three hole" rear cam bearing on a '66 block.

You also need the second design dual valve spring, which AFAIK is only available from GMPP. Both of these issues have been discussed in great detail here.

The quality of the final product will be directly proportional to how well you plan and manage the project.

Duke

[Joe L.]

Re: BB hypereutectic piston source

I hear what your saying Joe and agree. However should my pistons need replacing, the hypereutectic pistons choices (which are slim) for my 427 are limited to 3 KB styles.....the least compression offered and is the KB 360 offering 9.7 c/r (using this as a guide only) with my 98.2 cc chamber heads. Sounds like your saying this is still marginally too high.....so in stating these facts what choices would I have here in lowering the compression to more tolerable limits?

Michael-----


I think the APPROXIMATE 9.7:1 achieved with the KB360 will be OK.

Here's the deal:

First of all, I agree with what others have said. You do need to get all the parameters MEASURED before you go out and buy pistons. Also, as I think you understand, the KB "simple" calculator results in only an APPROXIMATE compression ratio. However, considering that there are only 3 pistons available, an APPROXIMATE ratio pretty well narrows down the choices.

If your current engine is still as originally configured and you experience no pre-ignition or detonation problems, then you pretty much know that it will support pistons producing the original compression ratio without problems. However, as Duke noted, the ACTUAL original compression ratio was usually about 1/2 point lower than the advertised ratio. The advertised ratio for you engine was 10.25:1. So, you could expect that the actual ratio was APPROXIMATELY 9.75:1.

The pistons available from KB will produce these APPROXIMATE compression ratios in your application:

KB227-----11.8:1
KB176-----10.8:1
KB360------9.8:1

You sure don't want the KB227. The KB176 compression is too high and I believe that regardless of your engine's final MEASURED volumetric parameters, the KB176 will still result in final actual compression being too high. I don't think you'll get down to below 10:1 using the KB176.

So, that only leaves the KB360. With these, I think you'll end up in the 9.5-10:1 actual final compression. That's why I recommended it in the first place.

Actually, this is a little higher than I'd recommend, but:

1) if your existing engine operated satisfactorily without pre-ignition/detonation and likely at an ACTUAL compression ratio very near this range, you should be ok;

2) there is no hypereuctic piston which will produce a slightly lower compression ratio and I HIGHLY recommend the use of hypereutectic pistons.

[Patrick H.]

Re: BB hypereutectic piston source

Michael-----


I think the APPROXIMATE 9.7:1 achieved with the KB360 will be OK.

Here's the deal:

First of all, I agree with what others have said. You do need to get all the parameters MEASURED before you go out and buy pistons. Also, as I think you understand, the KB "simple" calculator results in only an APPROXIMATE compression ratio. However, considering that there are only 3 pistons available, an APPROXIMATE ratio pretty well narrows down the choices.

If your current engine is still as originally configured and you experience no pre-ignition or detonation problems, then you pretty much know that it will support pistons producing the original compression ratio without problems. However, as Duke noted, the ACTUAL original compression ratio was usually about 1/2 point lower than the advertised ratio. The advertised ratio for you engine was 10.25:1. So, you could expect that the actual ratio was APPROXIMATELY 9.75:1.

The pistons available from KB will produce these APPROXIMATE compression ratios in your application:

KB227-----11.8:1
KB176-----10.8:1
KB360------9.8:1

You sure don't want the KB227. The KB176 compression is too high and I believe that regardless of your engine's final MEASURED volumetric parameters, the KB176 will still result in final actual compression being too high. I don't think you'll get down to below 10:1 using the KB176.

So, that only leaves the KB360. With these, I think you'll end up in the 9.5-10:1 actual final compression. That's why I recommended it in the first place.

Actually, this is a little higher than I'd recommend, but:

1) if your existing engine operated satisfactorily without pre-ignition/detonation and likely at an ACTUAL compression ratio very near this range, you should be ok;

2) there is no hypereuctic piston which will produce a slightly lower compression ratio and I HIGHLY recommend the use of hypereutectic pistons.

Joe,

Just thinking here...
Do you know if the 176 could be machined down to make a piston part way between a 176 and a 360? I know that you can machine a forged piston; I have no idea if you can machine a cast (hypereutectic) piston.

OH, and given the numbers you cite above I suspect that he will end up with the 360. However, it still doesn't hurt to measure. BTW, Michael, be sure you measure deck height, etc when you pull the motor apart so that you will know what your baseline was.

Patrick

[Joe L.]

Re: BB hypereutectic piston source

Joe,

Just thinking here...
Do you know if the 176 could be machined down to make a piston part way between a 176 and a 360? I know that you can machine a forged piston; I have no idea if you can machine a cast (hypereutectic) piston.

OH, and given the numbers you cite above I suspect that he will end up with the 360. However, it still doesn't hurt to measure. BTW, Michael, be sure you measure deck height, etc when you pull the motor apart so that you will know what your baseline was.

Patrick

Patrick-----


It depends upon whether the dome is a solid dome or a hollow dome. I believe the domes on these pistons are solid, but I'm not 100% sure. It's pretty easy to tell, though, simply by looking on the underside of the piston.

If they are solid, they can be machined down. However, I'd be reluctant to do this. In any event, I think he's going to end up with near-perfect compression ratio with the KB360.

[Duke W.]

Re: BB hypereutectic piston source

Joe,


BTW, Michael, be sure you measure deck height, etc when you pull the motor apart so that you will know what your baseline was.

Patrick

Deck height, which is the distance from the crankshaft axis to the top of the block deck is not easy to measure without special fixtures.

However, deck clearance, which is the distance between the piston crown and block deck at TDC can be measured with simple tools such as a machinist's bar and feeler gages, and this dimension - deck clearance - is what it needed by the cgnet CR calculator.

Do not confuse deck height and deck clearance

Once deck clearance (for each cylinder) and head gasket thickness(measure it with a mic or caliper), are known, one can use available specs for piston volume and head chamber volume to compute the approximate CR range of the engine before teardown. The deck clearance data will also tell you if the decks are parallel to the crankshaft axis, how much deck clearance varies from nominal OE spec and whether one deck is significantly higher or lower that the other.

If the left deck is high, it can be machined down to equal the right, but don't touch the right deck unless you want to ruin the stamped ID numbers.

More than .005" difference in deck height can also be compensated with different gaskets (do some research to determine available head gasket thickness in the various brands like Felpro, McCord, Victor Reinz, and ROL).

Assuming the heads are massaged including chamber relieving, measure their volumes after the heads are complete and assembled, and along with the specified piston volume use the CR calculator to select suitable head gasket thickness(es) to get into the proper range, then grind the highest chambers a little to knock down the highest CRs and narrow the range as I previously mentioned.

On a production engine it is not uncommon to find average side to side deck clearance delta of .010", which is about 0.5 CR. On a precision engine restoration I recommend 0.1 maximum, which will allow you to push the average CR to a relatively high value without having a couple of cylinders detonation prone, even if the others are well below the detonation limit.

Duke

[Michael G.]

Re: BB hypereutectic piston source

No pistons nor any other measurable moving parts have been purchased until all is known. My fact find is centered around "getting my ducks in row" being sure I understand the processess and terminologies to make the best decision(s) possibly for this orginal BB engine/car.

[Michael G.]

Re: BB hypereutectic piston source

As mentioned original style cam I've purchased is the F/M Sealed Power CS1093M, however a groove will need to be added to last journal to bring into spec. Why the need for a double spring application rather than single?

Help me with your acronyms...AFAIK and GMPP ? Thanks.

[Joe L.]

Re: BB hypereutectic piston source

As mentioned original style cam I've purchased is the F/M Sealed Power CS1093M, however a groove will need to be added to last journal to bring into spec. Why the need for a double spring application rather than single?

Help me with your acronyms...AFAIK and GMPP ? Thanks.

Michael-----


The groove is absolutely critical and must be added. This will be no problem, at all, for any competent machine shop with a lathe. It's also critical that the proper rear cam bearing be used. This bearing was unique to 65-66 big blocks. It's long-since GM discontinued but available from Federal-Mogul and Durabond. I recommend Durabond cam bearings.

The double spring kit GM #3970627 is the replacement for all 65-72 big blocks. It is THE one to use. An engine set can be purchased under GM #12371061 at a considerable savings over purchasing 16 individual kits. The kits and 12371061 set contain retainers with integral seals. Keys ("keepers") are not included.

The 3970627 replaced the earlier design which was a spring and damper. Originals were VERY prone to breakage. The 3970627 is THE way to go. Period.

AFAIK= "As far as I know"

GMPP= "General Motors Performance Parts"

[Duke W.]

Re: BB hypereutectic piston source

Do some research in the archives for all the details. The early BB single spring/damper is prone to failure and was replaced circa '69/'70 by a dual spring setup with integral retainer and seal that as far as I know is still available from General Motors Performance Parts, whose catalog is a downloadable pdf (portable data format, which is widely used on the Web for documents, and the reader software is a free download from Adobe Systems).

Duke