348 compresion

[Lonnie taylor]

I'm building 348 with 454 crank. Using new aluminum heads. I want it to run on pump gas so I need compression under 10 to 1. My block has 1 big notch in top of cyl. Icon makes a piston at 10.8. Show cars says they don't figure the notch into the compression ratio advertised. So how many different blocks are there? Need to know how to identify. Any help would be appreciated.

 

[Tom Kochtanek]

The single notch 348 block is most likely a passenger block with one "eyebrow" which drops compression about half a point or so. Lete us know the casting # and we can confirm. Easy to get her to run on pump gas, just select the correct piston, and Icon is a good choice for a forged piston for such a build.
TomK

 

[Tom Kochtanek]

There are basically four types of 348 blocks, the early 1957-8 castings, the double notch truck blocks up to 1962, the single notch passenger blocks from 1958-62 and the single notch truck blocks from about 1962-65.
They all can be built as you intend, but the better choices for performance seem to be the truck blocks from 62-65 as they have improved webbing and better main caps (ArmaSteel).

 

[Tom Kochtanek]

How to identify? On the back flange you'll see a casting number on one side and a casting "date" on the other. The suffix code is on a pad in front of the passenger side cylinder head. Use the sources in this site to verify what those codes mean, or post them here and we can inform you .

 

[Don Jacks]

We've got at at least one guy here whose street car is running 12-1 on pump fuel with IRON heads on it so it can be done,but I don't recommend it.Using alloy heads,a really decent ratio would be close to 11-1.There are many W engines on this site that run perfectly on pump fuel at 10.25-10.5 using iron heads.The W engine was designed with a high degree of detonation resistance built in as long as they are built with things like quench area and fuel and timing curves adhered to.

 

[Lonnie taylor]

My casting number looks like 3798962. 61 block??? So I can get the 10.8 compression pistons subtract half point and be around the 10 to 1 area? Play with gaskets to achieve what I want.

 

[MRHP]

My question is, all 348 blocks have at least one exhaust notch, so why would a piston company compute compression not accounting for at least one notch! I think I would call the piston manufacturer for some clarification. A 409 block can be had without a notch, but not a 348.

 

[Lonnie taylor]

Exactly my point.

 

[Tom Kochtanek]

That "962" block is likely a "service replacement" part from GM. Does it have a "Julian" date (numeric from 1 to 365 for day of year) on the other side of the rear of the block? Or a date code that includes the last two digits of the year? And take a look at the mains, if they say "ArmaSteel" that will tell us something.

 

[tenxal]

The 962 blocks I've seen were all '62-'65 truck blocks. Should have an 'X' cast on the block, as well. Single notches are all I've seen on those blocks. Not saying there aren't some doubles, though.

 

[Don Jacks]

All the Icons that I've seen for the 348 blocks are figured based on the one notch blocks,409's a different animal.If your block has the X on the front of it,it will have the armisteel caps.There were some very early 962 blocks that did not have those features.There aren't many choices for the head gaskets on these engines like there is for a small block.Head gasket thickness should be used for helping with quench,not compression ratios.A 10-1 with a .065 plus quench will rattle,an 11-1 with .034 won't.

 

[tenxal]

Head gasket thickness should be used for helping with quench,not compression ratios.A 10-1 with a .065 plus quench will rattle,an 11-1 with .034 won't.

Amen!

Why people use quench amounts w-e-l-l in excess of what it takes to prevent physical contact between the piston and the head baffles the (bleep) out of me.........

 

[1964SuperStocker]

Thanks for helping Ronnie out guys. We have been talking back and forth by phone and I forced him to come to the dark side and throw some questions up on here.
I will mention that I personally spoke to the ICON piston guys and was told that no one there really knows what formula LAMAR WALDEN did to consider the design of the pistons. Rest assured the single notch would have been considered in the 10.8 compression ratio because LAMAR was no fool and also keep in mind that those pistons (in one of my own engines) are ONLY made for the 348 stroker motors.. They were not considered for anything but a 4 inch stroke with the 6.135 rods in a 348 because of how common the 4 inch stroke conversion is.

Now I'm not saying that Ronnie was given bad information from Showcars about the notch being considered but keep in mind that there is no such thing as a 348 block WITHOUT a notch (that I am aware of). That can only mean that one notch gets you 10.8:1 (most likely with 690's or Eddy heads) and 2 notches would get you less. I did ask which head that CR was created with and the ICON guys didn't know that either. But again its likely Eddy heads or something similar like 690's. LAMAR probably didn't make his considerations for 10.8:1 based upon 379 heads and 2 notches.

 

[Don Jacks]

There's another use for these pistons.They work out to roughly 10.25 by using them in a 348 ,409 crank,6.385 rod in a 380 inch build.

 

[1964SuperStocker]

Wonderful! That's what I love about you guys! Information is power and the more we share about what we know the better. I might have to use the 409 crank I have gathering dust and build a 380ci.

 

[Don Jacks]

Another option for a 380 ,especially if you want 11-1[more than that if you use Bob Walla heads] is to use the Icon piston for the stock stroke 348,rated at 10.5-1 ,the stock length 409 rod,and the 409 crank.