Maximum deck cut for 250 block
- Thread starter dmsmith63
- Start date
I went .100 on mine , no problems , but remember , Custom pushrods will be needed
80Stang
Well-known member
You may be past the possibility already (if you have pistons) but using the 255-V8 pistons in a 250 block takes up 0.085" of that distance, as the compression distance in that piston is that much higher. It also is a flat top piston with tiny valve reliefs so there is some gain to CR there, compared to the stock 200/250 7cc pistons for example.
In your case no milling of block would be needed but the CR would be a little higher than 9.5, about 9.9 depending on real values in your case.
It is always a good idea to leave as much metal to the block as possible.
In your case no milling of block would be needed but the CR would be a little higher than 9.5, about 9.9 depending on real values in your case.
It is always a good idea to leave as much metal to the block as possible.
None. Never cut an I6 log head block unless it needs a cut to meet a 12 ra finish. Cylinder head bolt holes of an iron propogate cracks when the finish is cut.
Best option is to use some 6.00" 2.5 HSC Taurus/Tempo rods(1986-1995), or 1998- date 6.06" Ford Intec or Barra rods from the Aussie 3984 cc sohc and dohc sixes. The rods and little and big end diameters of each are the same as any 1960-1983 I6 small block Ford six. Stock 250 cid block with its 9.469" deck then yields a 17 thou positive deck with a stock 1.531 tall HSC piston. Most HSC and 255 pistons are 1.5 tall in 30 thou oversize, yieding a -17 thou deck, pretty much ideal. 8cc is the dish for the 255 piston, I think. For pistons, good Silverlite or KB items can be had in other dish cc's. Over here, we use time honoured cast Aussie 250 pistons from ACL / Repco/ Mahle which can be had in 5.5 to 15, 19, 22.6 and 27.9 cc sizes to suit your ideal compression.
If 6.06" rods are used, you can use Land Rover 4.6 or, better yet, Chev 305 forged pistons. The Rover pistons will require a bore out to suit the piston sizes, while the stock Gen I piston for the Chev piston will rquire a 56 thou over bore, which may be too much for some blocks. (You'll need to deck a Kith Black/ Ross/TRW 12.7cc forged 229 V6/305 V8 dish top down from 1.536" to 1.454", which will happen with ease as its one of the best forgings around). Others have looked into Yamaha XR600 or Chrylser LH V6 or certain Toyota V6 pistons, which will need a little bit of work with your machinist.
For me, I'd only ever look at the 6" rod and your 8 cc 255 pistons, and go to a larger chamber head with 60 ccs or so. 9.5:1 would be a good figure for an alloy head, probably okay with an iron head too.
Best option is to use some 6.00" 2.5 HSC Taurus/Tempo rods(1986-1995), or 1998- date 6.06" Ford Intec or Barra rods from the Aussie 3984 cc sohc and dohc sixes. The rods and little and big end diameters of each are the same as any 1960-1983 I6 small block Ford six. Stock 250 cid block with its 9.469" deck then yields a 17 thou positive deck with a stock 1.531 tall HSC piston. Most HSC and 255 pistons are 1.5 tall in 30 thou oversize, yieding a -17 thou deck, pretty much ideal. 8cc is the dish for the 255 piston, I think. For pistons, good Silverlite or KB items can be had in other dish cc's. Over here, we use time honoured cast Aussie 250 pistons from ACL / Repco/ Mahle which can be had in 5.5 to 15, 19, 22.6 and 27.9 cc sizes to suit your ideal compression.
If 6.06" rods are used, you can use Land Rover 4.6 or, better yet, Chev 305 forged pistons. The Rover pistons will require a bore out to suit the piston sizes, while the stock Gen I piston for the Chev piston will rquire a 56 thou over bore, which may be too much for some blocks. (You'll need to deck a Kith Black/ Ross/TRW 12.7cc forged 229 V6/305 V8 dish top down from 1.536" to 1.454", which will happen with ease as its one of the best forgings around). Others have looked into Yamaha XR600 or Chrylser LH V6 or certain Toyota V6 pistons, which will need a little bit of work with your machinist.
For me, I'd only ever look at the 6" rod and your 8 cc 255 pistons, and go to a larger chamber head with 60 ccs or so. 9.5:1 would be a good figure for an alloy head, probably okay with an iron head too.
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