roller camshaft opinions please.

[Terry F.]

Re: The whole point of a roller cam

Thanks again for the information. I will keep everyone posted on progress. I will pull the engine in a month or so. I would like it back in before the snow flys. Did I say snow?? Terry

[Clem Z.]

to get all cyl equal in CR

requires a lot of work with stock components because the manufacturing tolerances are so great. the easiest way is to CC each cyl at TDC and then go to work in the combustion chambers of the heads to change each one to match the cyl CCs to get the CR equal. the correct way is to deck the block,index grind the crank so all throws are equal,bush the pin end of the rods to equal length and use good quaility pistons. of course the head chambers must also be equalized in volume. big expensine job and not worth it on a stock engine.

[Terry F.]

Re: to get all cyl equal in CR

When removing material from a cylinder head combustio chamber, I assume you would sort of generally start to polish the surface down a bit. I think I will cc the combustion chambers just to see how close things are and to sort of have the experience. I will also cc the combustion chamber with the heads on just to see what that looks like for comparison. I will then measure how high each piston is coming up on each side. Might be a waste of time but maybe learn something also. Thanks, Terry

[Duke W.]

Re: to get all cyl equal in CR

Achieving equal compression ratio is only important if there is a limit that you cannot exceed, like NHRA racing and you want all cylinders at the maximum to extract the last available horspower, and like Clem said, it's a very labor intensive process.

For a street engine you need to manage your CR to a range that will work with available fuels, and if you can achieve a nominal plus or minus 0.1 within that range then all is well.

As far as calculating actual compression ratio, piston manufacturers specify "volume" that you can use in a CR calculator. Just be careful of the algebraic sign. For example, Speed Pro lists the domed 327 SHP piston volume as a postive number, 5.3cc, but since since they actually REDUCE combustion chamber volume, they are entered into some CR calculators as a negative number.

In contract, KB lists domes as a NEGATIVE number relative to an an absolute flat crown piston, so most flat pistons with valve notches have volumes that are listed as positive numbers, so you don't have to change the sign in the calculator.

For SHP engines that were originally equipped with forged pistons, I recommend the Speed Pro OE replacements. For engine that originally had cast pistons, like yours, I recommend the KB hypereutectics.

In the case of 327s KB offers two pistons, one with a 7cc notch and one with a mild dome and notch with a net volume of negative 0.5. And given the ready availability of shim gaskets in .015" and .018" (which is OE) and composition gaskets at .028" and .038" one can achieve any reasonable target range. As long as the deck and heads are level, shim gaskets can be used. Compostion gaskets will take up of about .003" warp and still seal.

Duke

[Terry F.]

Re: to get all cyl equal in CR

Nice info. I will figure compression ration two ways and compare them. I suspect it might be like compareing apples to oranges. I am just curious. So my 39 horse came with cast aluminum pistons?? I will use the hypereutectic pistons with moly rings. I suspect I should buy the rings fromt he piston manufacture?? Terry

[Duke W.]

Re: to get all cyl equal in CR

You can buy rings from piston mfgs, or they provide ring set recommendations. Make sure you get a standard tension set and follow the pistons mfgs. ring gap recommendations.

Duke

[Terry F.]

Re: to get all cyl equal in CR

No problem there. I am lucky that the guy that will assemble my engine races 427's and seems to have a fondness for them. He is very particular about them and I have been satisfied with other engines he has done for me. Easy to work with also. My engine has the original cast iron crank in it. Does it need any special treatment. Should I polish the journals or anything??? Terry

[Duke W.]

Re: to get all cyl equal in CR

As long as your guy understands the different requirements of a street engine versus a racing engines. Too many "race engine builders" want to put "racing engines" in street cars, which will not make for a very pleasant driving engine.

If he applies race engine building attention to detail to a street engine - like achieving a particular compression ratio and understanding that torque bandwidth, idle quality, and driveability are more important than "top end power", then it should work out okay.

It's up to the owner to do his homework and determine some basic performance specifications, like torque bandwidth, idle quality and driveability etc. If you say "I want 450 HP" you're probably going to end up with an unpleasant beast.

As far as the cranktrain is concerned, I always recommend Magnaflux inspection of the crank and rods. The crank should also be checked for straightness. NEVER GRIND a crank underside unless it is ABSOLUTELY NECESSARY. If the crank passes Mag and is stright, journal polishing is a good idea.

If the rods pass Mag., install new high quality rod bolts and nuts, which will require resizing. The rod bolts should be removed prior to Mag inspection. Secure the rods to the caps with small machine srews and nuts whose heads just barely overlap the surface. This allows the Mag inspection to include the critical fillet surrounding the bolt and nuts seats. Keep the rods this way for shotpeening (also a good idea) as it will allow the shot to reach this critical area. Then install new bolts and resize the rods.

Duke

[Terry F.]

Re: to get all cyl equal in CR

He is a very reasonable guy. He does factory rebuilds all day long. I just want a factory rebuild for the most part. I would like to improve the torque bandwidth on my 390hp but I believe the factory band width is pretty good. If you have a suggestion on how to improve the bandwidth I would appreciate it. I am not interesting in making it turn much more that 5000 RPM's for extended periods of time but if I happen to get there for a few brief moments of pleasure, that would be nice.

If I have to grid the crank, should I just replace it with a steel crank??

Terry

[Duke W.]

Re: to get all cyl equal in CR

The OE cam is what makes the bottom end of the 80 percent torque bandwidth, which is why it should not be replaced with an aftermarket cam. You can extend the upper boundary of the 80 percent torque bandwidth by working the heads as has been discussed here many, many, many, many times and is well documented in books for over 30 years, however, if you don't feel comfortable revving the engine over 5000 RPM, head work will yield little as the benefits start at about 3500-4000 and extend in increasing amounts to the valvetrain limiting speed, which is about 6000 for an L-36.

The only way to make a naturally aspirated engine "make more power" is to improve high rev volumetric efficiency and rev it higher. An aftermaket cam with OE machined heads may do this only marginally or not at all while killing the bottom end and destroying the idle quality. Massaging the heads will do job in conjunction with the OE cam without hurting the bottom end torque or idle quality, so you can almost have your cake and eat it, too.

If a cast crank NEEDS grinding, then grind it. Grinding a cast crank doesn't have a big impact on strength or durability, however, grinding SHP forged steel cranks removes the surface Tufftride hardening, which will reduce durability, though on a street engine, the crank is not likely to break unless it's run very hard. The rebuild philosoply should be "remove metal ONLY if absolutely necessary.

Unfortunately, "production" machine shops align bore and deck blocks, grind cranks, and machine head surfaces whether they need it or not, and a lot of people have lost their block numbers due to this practice, and they pay for unecessary work. You have to find a machine shop that does custom work. First they have to understand what you have and your objectives. Then you and the machinist need to reach an accord on what needs to be done, and only the minimum in terms of machining should be done, but this requires a lot of measurements, which is labor intensive, and if you can't do them yourself, you'll have to pay the machinist to do them for you.

Duke