Charlie,

        Different areas of strength. A normally aspirated motor won't see the cylinder pressures that a blown motor can generate. BUT it will usually need more RPM to achieve the hp numbers, So the bottom ends and reciprocating parts will take beating. Remember from you high school physics that the amount of force goes up with the square of the velocity. Rods, pistons, and the bottom of the block (main bearing webs) as well as the crank must be much stronger and lighter reciprocating pieces are a major benefit. Blown motors, where the mixture is forced into the cylinders don't have to spin as hard to see big HP numbers. But boy do they make torque, On ther dyno at ESI my F code made over 425 ft lbs at 3200 or so rpm. The torque curve starts to drop after 4000 /4500 because with stock valves I run out of cylinder head at that point. I've made changes to the motor since the dyno runs that have extended the range, but it's still a low rpm motor. But, the walls on my motor are fairly thick and stiff, because we wanted to be sure we didn't lose ring seal and pressurize the crankcase, no horsepower there.

     Ted or Wally or Dave on the other hand, don't make the torque numbers I do, But they all bury me on the Horsepower end from 4 grand up. Make sense? 

Frank/Rebop

Bristol, In ( by Elkhart) 

I've always heard that a boosted motor needs to be durable. Why does a boosted motor need so much more durability than a NA motor?

I have always understood that a motor producing 500hp will have a certain combustion pressure regardless of the induction system. Based on my understanding the NA motor would have to be just as durable as the boosted motor. To take it further, it seems to me that the NA motor would have the highest potential for failure because the power would peak at a higher rpm so there is less time between combustion cycles for things to, for lack of a better word, relax.

So what is the deal with boost?


Lawrenceville, GA

Chuck.  As John and Frank brought up, stick with the thicker wall scenario versus going "as big as possible" in the blown application.  Cylinder wall flex ends up being a player when adding a supercharger to the mix.  Although adding some block fill can alleviate some of the flex, just keeping the cylinders walls thicker is the best insurance.  When initially sonic checking Randy's C2 block it was good for being bored 0.110" over if being normally aspirated but because of the blown nature, I just cut that value in half and kept the finished bore size to 3.800".  Here's the sonic check results of Randy's block after final boring.

These are all the minimum values when sweeping the sonic check probe the length of the cylinder wall.

After sonic checking a variety of Y block castings, there is no set rule for one block casting number being better than another.  I've now seen 272's that would bore out to 312 plus while others are iffy at 0.060" over.  The C2 blocks seem to be the most predictable but core shift is still an issue thus forcing offset boring if going for the larger bore sizes.  Sonic checking is a prerequisite if wanting to be sure of what you have.

Lorena, Texas (South of Waco)

Chuck.

         I would doubt that adding cubic inches would make horsepower as fast as adding boost. Here's the deal, lets assume that your 312 is 100% efficient at max hp. It would make 312 ft lbs at that point. (theoretical, won't happen unless you're Wally or Ted Eaton). If you could add a blower that blew 7.35 lbs and consumed zero hp to do it, you would now have an engine that acted like a 312 x 1.5 or 468 cubic inches. Kick that to 9 lbs and it's now a 502. This all assumes the heads can carry that much air, the blower doesn't take any horsepower away and the heat of compression in the blower doesn't thin the air out (it does). But you get the point, you can't make a 312 that big with boring and stroking. Best to make the walls stiff, the rings seal, and the heads flow all they can. Then run a cam with limited overlap so the blower stuffs the cylinder, and does not blow half of the charge out the exhaust pipes. Retard the timing, run 106 octane, and keep the carb a little rich, Make sure you have fuel pressure and Moon Shadow will destroy tires and the '56 rear end.  

Frank/Rebop

Bristol, In ( by Elkhart) 

Jan, I've been scrounging late 50's blocks. One of my ECZ-C 312 blocks has the tilted cylinder (it's already at .060 over), but the other looks good (standard bore. Go figure). I still have to pull the freeze plugs on a B9 block to see what it looks like, and I have a line on an EDB-E truck block that I should follow up on. I also have a 1956 EDB-A engine, but it's almost ready to install and I'm loath to pull the fresh freeze plugs out.



I think the other choice would be the ECZ-A 292.



I looked at the price of sonic testers today. $800? I might spring for one, a birthday present to myself

Best regards,



Paul Menten

Meridian, Idaho

Thank you.  I did find that info on Mummerts site.  I might have to back up and regroup on my plans. 

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

Re: C2AE block, the one I looked at had tilted cylinders, visible through the freeze plug under the starter. I've heard that it sonic tests thinner than 50's blocks, too. I think that was on Mummert's site.

Best regards,



Paul Menten

Meridian, Idaho

Someone mentioned a C2AE block.  Does having that block change the allowable bore?

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

So a near stock block 292 or even a 40 over 272 might be just as good with the blower? I've always been a bigger is better kind of guy when it comes to engines. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Cactus:

You are correct, I'm boring 292s .080 over.  With the stock stroke 312 crank, I get 317 cubic inches.

John

John - "The Hoosier Hurricane"