15 replies to this topic

[Ray Bell]

My nephew Ben has been trying out his freshly arrived sonic tester to see what the wall thickness is in the block we picked up the other week to use as a guinea pig for the Dodge engine build.

For those not familiar with the project, it's under the heading of '225? Why when there's a 318 to be had?' and the particular engine is the 318ci Polyspherical Chrysler unit.

He tells me that on the thrust side of the cylinder walls he's getting readings of around .23" and that he's read that .18 is the thinnest anyone should go.

Does anyone have any further information on this? Perhaps some good links he can read up from?

One thing that occurred to me was that there might well be .010 or even .015" wear on that cylinder wall... or it might have been previously rebored, so it will be important to do some serious measuring. We know nothing about the block really, only that we picked it up in a buncle of bits and it was cheap. It's a '64 casting.

We are looking at taking the bore out as far as it's practicable to go, but the engine does have to be reliable.

[Engineguy]

Bill Jenkins, discussing standard cast iron small block Chevys (before special Bowtie blocks, etc.), says Chevy's nominal spec is 0.223 (thrust wall) with 0.125 the minimum for front and rear sides. He preferred a (thrust wall) minimum of 0.215 and ran 0.205 in individual bores without problems. Claims power loss when going from 4.035 bore to 4.065 bore, despite (slight) displacement increase and (again slight) valve unmasking... and attributed it to wall wiggle waggle and resultant ring seal issues. Note that he's talking about 700 HP engines here... he says that 0.180 thrust walls are OK for high performance street engines, which may be closer to your situation than his 700 HP Pro Stock engines.

[Ray Bell]

Yes indeed, small block Chevys putting out 700hp is well beyond our thoughts...

If we get 450hp we'll be happy, though a bit more would be welcome anyway. I guess problems escalate much nearer those top outputs.

As yet he hasn't measured the block for originality, something to be considered. If there's substantial wear or it's been bored previously, then he's got a lot of lattitude. This is his first experimentation with the sonic tester and I guess the novelty had him forget certain things. He even needed a prod to remember that the bore increase has to be halved to determine what's coming off the wall.

We've actually had problems finding blocks... three 313 blocks have readily come our way, yet only one 318. The only differences are the use of the cup-type welch plugs in the 318s and a different oil pump, which apparently means a different rear main bearing cap.

It's possible, however, that the 313s, cast in Canada from about 1958, could have a thicker wall... we'll soon know. That might mean modifying the oil pump setup, and Ben's very worried about using the flat dish type welch plugs. They can't be that bad, surely? They were used for many years!

[Catalina Park]

I would avoid the flat welch plugs, I have seen them blow out on the track. Can the welch plugs be replaced with screw in ones? I know of a few engines that use them.

[McGuire]

With the sonic tester I will take 8 readings per cylinder (12, 3, 6 and 9 o'clock, top and bottom) and lay them out on an 8-cylinder diagram. From that it's easy to visualize how the block was cast. Every engine and mfg'er has its traits -- on the SB Chevy #8 is usually thinnest. .180" should be fine for this application. Of course straight and round beats a few CID every time.

For these and all the other questions that may come up along the way, may I recommend The Step-by Step Guide to Engine Blueprinting, by my good friend Rick Voegelin. Best book ever on basic preparation and assembly of production engines.

[Ray Bell]

Originally posted by Catalina Park
I would avoid the flat welch plugs, I have seen them blow out on the track. Can the welch plugs be replaced with screw in ones? I know of a few engines that use them.

A moot point... we found that the block has some major differences and can't be used...

McGuire... Ben has read that book. He also wants to make torque plates for when he gets the block bored. I'm sure when he gets serious and has a couple of blocks from which to choose he'll try your suggested method.

[McGuire]

Using my sonic block map as a guide, I may choose to shim the boring rig to recenter the bores for maximum wall thickness. Of course, after inspection the first step with a used block is getting the main bearing bore dead true, and then aligning the decks to it.

[Ray Bell]

The 313 block I picked up was a dead loss...

Not only are the bores (very consistently) no thicker than those on the 318, the thing has a lot of extra weight in it from increased webbing cast in, and the bellhousing bolt pattern has some differences.

Fact is, though a lot of the patterns used were very different (to produce that webbing) on these Canadian castings, the bore casting was identical. No point in looking further at 313s.

They also have a different oil pump and rear main bearing cap, and the old style longer end on the crank with the 8-bolt flywheel fitment. At least we got a couple of heads out of it for experimentation...

[TDIMeister]

I wanted to pick up on this question but from the standpoint of what is currently state of the art in motorsport.

I have seen bore-to-bore wall thicknesses down of around 5 mm, so with 95 mm bore diameters, one would employ 100mm bore-to-bore centers. What is the practise in F1?


Cheers,
Dave

[TDIMeister]

Nobody? Pretty please?

Thanks in advance.

[J. Edlund]

Originally posted by TDIMeister
I wanted to pick up on this question but from the standpoint of what is currently state of the art in motorsport.

I have seen bore-to-bore wall thicknesses down of around 5 mm, so with 95 mm bore diameters, one would employ 100mm bore-to-bore centers. What is the practise in F1?


Cheers,
Dave

In F1 they are now limited to a 106.5 mm bore spacing. Maximum bore allowed is 98 mm, most engines are probably at 96-98 mm.

[Ray Bell]

Going back to the original question, I guess the length of the unsupported cylinder wall would be important too...

[TDIMeister]

Thank you, J. E.

[hydra]

Originally posted by J. Edlund


In F1 they are now limited to a 106.5 mm bore spacing. Maximum bore allowed is 98 mm, most engines are probably at 96-98 mm.

Are the bores siamesed? If not how much space is there between them for the water jacket? I remember Uncle McGuire saying that given a choice, siamesed bores are NOT the way to go for an all-out racing engine...

[Gustave]

I'm not the last word on the subject, but I did give some thought to it when I rebuilt my BMW S14 some years ago. Here are two articles I wrote that might give some food for thought:

http://e30m3performa...onic/sonic1.htm

and:

http://e30m3performa...amics/index.htm

I wish I'd thought of off-setting the bores to increase wall thickness on the thrust side. That is a good idea.

Gustave

[Ray Bell]

Problem with a V8 if you do that is that you run into a number of issues... one bank versus the other.

Ben's determined not to offset the bores. Even if it means a smaller bore in the end. Still checking blocks... slowly...