Crossflow Maximum Bore Size and Liners

Cox Custom Mechanical

Well-known member
Supporter 2022
One question I get asked often is, what is the maximum bore size you can go with a crossflow.

So to demonstrate I have taken a damaged 84DA block, popped it in the mill and started cutting.
IMG_3444.jpg
As you can see I have hit a corrosion at approximately 3.90. This block was in fairly good shape for its age(except for some un related damage).

Depending on what your desired bore thickness is you could have potential ran a 3.740 bore on this engine. Clearly corrosion is a killer and 9 times out of 10 the limiting factor on these engines these days. Please also note this is just one bore and only about 1.500 deep. If I was going to bore the whole block the results may vary. I've don't this purely for a visual exercise to demonstrate why those old blocks are not always a +.060 etc.



Now this brings me to the second part of the exercise, which is what is the absolute maximum bore size for a Crossflow (and any other ford small block 6)

IMG_3445.jpg
As you can see here the bore has been taken out to 4.070 (which was the limit of this boring setup on my small milling machine). Keeping in mind the bore spacing of a Ford small 6 is 4.080 you can run a 3.840 bore in a dry block with .120 thick liners for a drag only application.

Not one to sit around and do what everyone else does, I am in the process of having some wet liners made. The goal bore size is 4.000, is it possible? Time will tell. In attempting a 4.000 bore there will be some major considerations and engineering challenges which is the exciting part.

Wish me luck.

Andrew Cox
Cox Custom Mechanical
 
4.00 would not think so, that only leaves 0.040 for the gasket to sit on, doubtfull. IMO you would be better off keeping to something more modest and simply adding manifold pressure. When your boosted displacement does not become a limit to BMEP and thus torque. People like Errol Quartermaine run 187ci barras with tonnes of boost to run in the 7s in a BA sedan! I run a boosted 3.3litre crossflow with stock parts, its about 200kw 500nm on 15psi and civilised. As you have stated, finding blocks without a heap of corrosion is a problem, core shift is another. I had one block go through at .040, then I was lucky and found two blocks with mint stock bores. Western Australia is terrible for corrosion, they use ground water for the scheme water, its corrosive!
Just my two cents worth.
 
4.00 would not think so, that only leaves 0.040 for the gasket to sit on, doubtfull. IMO you would be better off keeping to something more modest and simply adding manifold pressure. When your boosted displacement does not become a limit to BMEP and thus torque. People like Errol Quartermaine run 187ci barras with tonnes of boost to run in the 7s in a BA sedan! I run a boosted 3.3litre crossflow with stock parts, its about 200kw 500nm on 15psi and civilised. As you have stated, finding blocks without a heap of corrosion is a problem, core shift is another. I had one block go through at .040, then I was lucky and found two blocks with mint stock bores. Western Australia is terrible for corrosion, they use ground water for the scheme water, its corrosive!
Just my two cents worth.
Hey Aussie

It would leave .080 between bores which is not really a huge concern at the moment, if you take a look Japanese or Euro engines they run incredibly close between bores, granted not 2mm but worst case I go slightly smaller on the bore, biggest concern is splitting the liner where its only .040 between bores.

I have a few good blocks sitting around that I could go .080 with room to spare which are either 84's-86's. I'm with you on the water, I lived in Alice for quiet a few years and you should see the calcium that would come out of some blocks, you had acid bath them and hope there was something left to play with.

This isn't something I'm doing to win or to keep up with the boosted bunch, truth is while I respect what forced induction is capeable of its not my thing, unless its a roots blower. This is just an engineering exercise.
 
I remember back in the 351 C Pro Stock Engine builds people like Dyno Don was fitting thick Sleeves and getting finished bores of 4.250. Those Sleeves were being Furnished Welded into the blocks, it worked well and soon after people were doing that to 352 and 390 FE Blocks to make them into 427’s.
 
Hey Aussie

It would leave .080 between bores which is not really a huge concern at the moment, if you take a look Japanese or Euro engines they run incredibly close between bores, granted not 2mm but worst case I go slightly smaller on the bore, biggest concern is splitting the liner where its only .040 between bores.

I have a few good blocks sitting around that I could go .080 with room to spare which are either 84's-86's. I'm with you on the water, I lived in Alice for quiet a few years and you should see the calcium that would come out of some blocks, you had acid bath them and hope there was something left to play with.

This isn't something I'm doing to win or to keep up with the boosted bunch, truth is while I respect what forced induction is capeable of its not my thing, unless its a roots blower. This is just an engineering exercise.
Ive got a Sprintex twin screw compressor on mine and I run LPG, IMO its great, now Ive gone boosted I wouldnt bother with anything else for a road car. Keep up the experiemental work. I still have a hankering to do a cut off log head, but I dont have access to a mill, and i cant afford for someone else to do it. I had thought of using a slitting saw in the mill, then facing it off to give a flat surface to bolt to.
 
I remember back in the 351 C Pro Stock Engine builds people like Dyno Don was fitting thick Sleeves and getting finished bores of 4.250. Those Sleeves were being Furnished Welded into the blocks, it worked well and soon after people were doing that to 352 and 390 FE Blocks to make them into 427’s.
There has been reports of all sorts of furnace brazed jobs, welded up cleveland heads for the 300ci six (Sissel?) etc. Lot of effort to go too, I doubt they would last for very long.
 
Ive got a Sprintex twin screw compressor on mine and I run LPG, IMO its great, now Ive gone boosted I wouldnt bother with anything else for a road car. Keep up the experiemental work. I still have a hankering to do a cut off log head, but I dont have access to a mill, and i cant afford for someone else to do it. I had thought of using a slitting saw in the mill, then facing it off to give a flat surface to bolt to.
I've done a few of them. Milling off the log is the easy part, it's welding on runners that can be tedious. With with straight runners you could outflow a Aluminium 2v.

For the vintage speedcar/midget I'm thinking of doing a cut off log head for it, but as its only 161ci, and it needs to be about 13:1 getting the combustion chamber small enough is the challenge.
 
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