Technical Hemi help

Hello all looking for some help selecting the proper pistons for a 57 392 I would like to run pump gas naturally aspirated is 10-1 the highest or could I go higher ? this is for my 37 Plymouth coup thanks for the help

 

I think you are a little high on the CR if you are running iron heads, but I am no Hemi expert.

 

Thanks khead . I thought that was the factory cr but after a little reading I believe it was 9-1 . I thought I read some where you could run higher cr with the Hemi because the head design ? But I am running factory heads at this point . Really looking for some past experience from a Hemi builder maybe thanks again guys.

 

Don't have my books at hand, but I believe the 392 was either 9:75 or 10:1..

 

Search---Hemi tech,lots of info.

 

'57 was 9.25 & 58 was 10. The hemi can run the same octane as a wedge with 1 point lower compression. So a 9.25 should run on what a wedge @ 8.25 would & 10 is same as 9. 10:1 on rebuilds is common, but with a lower number you could probably go with regular. Haven't seen any real world measurements on the 392, but the C/Rs listed for earlier hemis have measured out up to a full point on the optimistic side. could probably go a point higher with alloy heads.

 

I am running a true 10-1 compression with custom pistons from Ross with no problem in my 354 hemi with a Isky cam

 

i run pump gas on a 57 392 without any problems for 3 years now.

 

Thanks guys ! I really appreciate all the reply's . Just don't want to buy the wrong eq. Trying to get all the lower end so I can have it balanced. Going with stock length K1 H beam rods also. It seems cheaper to buy new than to rebuild the old with arp and so on. Just want to build it once . Not a drag car just a cruising car with a little lead in my foot from time to time

 

You have found the Hemi Tech Index? http://www.jalopyjournal.com/forum/showthread.php?t=118764&highlight=hemi+tech+index

 

I know it's the dreaded "E" word, but has anyone set one up to run on E-85??

 

I truly cannot recall the last EarlyHemi we sent out that was not 10:1. NO issues with pump gas. However, your cam profile may or may not be helpful. Valve opening/closing and overlap can affect cylinder pressure. What are you planning to use?

E85? No reports from anyone I know so who wants to be first?

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Hey 73RR What cams worked for you? I'm also building 331 10:1 dual quad, mech lifters.
I was thinkig of that Isky from hotheads B777@108 (.480 lift, 240 Dur .050, 108 ls) Suposed to work good from 2500 to 6000 rpm.

 

Hemis can handle 10:1 or a bit more with out any trouble at all.

 

I don't like or use any of those tight lsa jobs, too many trade offs to suit me. Your results will vary.
If you want to run solid lifters I have a couple of nice solid regrinds available. Send a PM if interested.

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Thanks a lot for the replies . Really my 1st hemi so all new to me . Have know idea what cam to go with was hopping to ask around here for some suggestions as well . Plan is 700 r4 thinking dual quads or a fuel injection old style hill born ? Would like a nice amount of hp out of it. But not going to drag it daily . Was hopping the roller lifters & cam would suit me ok ? Never ran a solid lifter type cam really do not know much about them pros - cons ? Help on this would be reeeeeeeeeaaaal helpful thanks guys

 

A solid lifter cam is what an engine is meant to have. There are no cons other than a little noise. Pros? Less headaches, higher RPM capability, better low end power for a given profile. That said, with all the lifter issues going on, a roller might be a good idea.

 

My 354 is bored 0.060”, allowing me to use cast 392 10:1, resulting in ~10.3:1 with 354 heads.

This is my first Hemi, but multiple sources said it would be a good hotrod combo. Cam is a Schneider 280 hydraulic grind: 224*@0.050/0.435” lift/108*LSA. Intake is a Hot Heads single 4 bbl.

It's going into a '28 Ford Tudor backed by a 700R4 & 9" rearend.

Hope this helps.

 

Scott, Solid lifters were used in the original 300 motors and industrial motors. They used the adjustable rockers which are very expensive if you don't have them. Valve covers used with them had raised bumps to allow for the adjusters, also hard to find and big bucks. a roller cam and lifters are pretty pricey for the hemis. I'm sure if you have been looking you've found that out. Hope your project goes well. I'm putting the one i'm building in a 34 chev 5 window coupe.

 

No one on here has ever reported finding adj rocker arms under the dimpled Ind valve covers.

 

Found the Hemi Tech Index yet? http://www.jalopyjournal.com/forum/showthread.php?t=118764&highlight=hemi+tech+index

 

I didn't Know that. I wonder why they had the bumps then?

 

We speculated on that a while back. no one knows. Probably planned on an option for a solid cam but didn't get any orders/interest so they cancelled the option after creating the tooling for them, but we don't know.

 

Call Nick Arias 3 , they will have exactly what you need in stock. As for a cam go easy , Isky has a good selection of hydralic cams that make great power and perfect off idle

I was at Arias today and NA3 was off sick, should be back on Tues, he is the guy to give you the right scoop

http://www.ariaspistons.com/

 

I run the Isky hydr. 280. 238 duration at .050 with 108 lobe separation, runs good on the street with multiple carbs,2800 torque converter and 3.50 gears.

 

Is this an actual measured c/r or is it just a guess?

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A guess.

 

Don't know if you are aware of this but.... IF your pistons were marked 10:1 in a 392 you actually have about 9:1 because of reduced swept volume. You would have needed 11:1 392 pistons to get 10:1 in a 354.

 

This subject has been covered in various discussions since the 392 hit the showroom.
The reason for the actual lowering of the c/r is simply that the 354 has less swept volume than the 392 so you are, in effect, cramming less stuff into a similar sized chamber.
If a 354 and a 392 have similar c/r, and similar cc heads, and the 392, obviously, has more volume to stuff into the chamber, then the volume of the dome must be smaller to account for the swept volume of the cylinder.

Some day when I run out of projects I'll assemble some parts and make some actual measurements...unless someone else volunteers...
If you have a calculator and some math aptitude it can also be done on paper.

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Here is my .02 on this. The kicker to this scenario is the piston design. As Gary stated, if ALL things were equal (dome volume and head cc), the outcome would be different. In this case, the pistons are nearly identical.


If you take a 354 car piston (9:1)and put it along side a 57 392 piston (9.25:1), slide a pin between the two, the domes are the same height. (The valve notches are smaller in the 392 piston, giving it slightly more dome volume.)

Now bore your 354 and install those 392 pistons. Compression of the 354 will go up due to the increased bore size taking in more air to be compressed. Now figure in the smaller chamber of the 354 head, and compression increases more. Use 58 392 pistons for another increase.

Run the numbers through a compression calculator, and they will show this. All things being the same (piston dome height, head cc), a 4.0 inch bore 354 will have an increase in compression of approximately .3 over a 3.94 bore.

354 piston on left. 392 on right.

http://performancetrends.com/Definitions/Cylinder-Volume.htm