Moderator Curtis Jacobson Portland Oregon (4576 posts) Registered: 10/12/2007 02:16AM Main British Car: 71 MGBGT, Buick 215 |
maximum overbore for Rover
Steve e-mailed me this question:
Quote: Please give Steve your thoughts! |
mgb260 Jim Nichols Sequim,WA (2461 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: maximum overbore for Rover
Steve, Buick 300 crank will work but 340 is the same stroke as 350. The newer Rover block is 3.7 bore .036 is the most I've heard to use standard 305 Chevy bore(3.736)pistons.
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MGBV8 Carl Floyd Kingsport, TN (4511 posts) Registered: 10/23/2007 11:32PM Main British Car: 1979 MGB Buick 215 |
Re: maximum overbore for Rover
I believe the max recommended is .030 overbore. The 3.736 has been done. Can be iffy. Block should be sonic tested. With new liners 3.800 has been done.
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BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6468 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: maximum overbore for Rover
The 340/350 crank is going to be a tight fit. I really don't know if there is enough room for it or not but I do have doubts. The stroke is 3.850" which is over an inch longer than the 2.800" stroke of the BOPR meaning you need better than 1/2" of clearance all around. The 3.736" Rover overbore is just .014" shy of the 340's 3.750" bore so possibly standard 340 pistons could work in terms of the diameter, though with your stroker you are probably going to end up with slipper style pistons and the wrist pin moved right up under the ring package. Happily there is a lot of room there to work with but custom pistons are a definite necessity.
The 215/3.5 has a rod/stroke ratio of 2.02, and with the 350 crank and stock length rods that will drop to 1.47, see this reference for more info on what that means: [www.superstreetonline.com] One result is higher side loading on the cylinder walls so keeping a thicker wall would be a good idea. Your deck is real close to 1-3/16" shorter than the 350 (1.227") and you can get almost that much out of the piston pin-to oil ring spacing (Measure a piston). This would seem to indicate you would not have room for any longer rods. Than you still have to allow for the extra 1/2" of crank throw. This might require both custom pistons and custom rods. If you use thin rings, pack them tight and close to the top of the pistons and use a bridged oil ring so the pin can go under it and a decreased diameter wrist pin, say maybe 3/4" diameter, you might be able to get by with stock length rods. Be aware though that with that kind of a rod ratio builders recommend you use the strongest rods you can buy. Jim |
Re: maximum overbore for Rover
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BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6468 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: maximum overbore for Rover
Ah yes, I remember that now.
So again the question, how much is 80 lbs worth to you? The 300 block gives you an awful lot for what it costs in weight. Jim |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: maximum overbore for Rover
FWIW, at a 3.736" bore on oem sleeves, they will be more likely to migrate away from the deck. Why?, thin, weak, not integral cast like 215's, no nip/step at bottom of bore to stop migration, and no flange at top. Other than all of these reasons, why not ? "If" they are all in correct location, you "might" consider pinning them, parallel to wrist pins, near bottom of bore, using "slipper skirt" pistons . Make sure pinning is below ring travel. Your results may vary. Good Luck, roverman.
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roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: maximum overbore for Rover
To "Steve", You may want to perform a bang-per-$, cost sheet on different components of your build. Depending on how far-out,$-wise on those 300 heads, you "might" get better bang/durability, with bare TA heads. They also take stud mounted sbc roller rockers, saving $'s over sbb style. Perhaps a "moderate" HR cam would suffice ? If so, you could consider "short body" oem HR lifters. Good Luck, roverman.
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RDMG Dave R Northern Virginia (138 posts) Registered: 04/07/2016 08:29PM Main British Car: 1979 MGB 4.6L Rover V8 |
Re: maximum overbore for Rover
This is an old thread, but to capture some knowledge referring back to the original question, I have a quote for a large bore to the Rover block from May 2016 from Darton East, Inc. in Winchester, VA:
"$1250 for installation of the sleeves, which includes a step deck surface for better head gasket sealing." The sleeves in question were the Turner Engineering Sleeves from the UK, available in 94mm (3.70 in) and 96mm (3.78 in) ID sizes. I believe the actual OD bore needed to install either version of the liners is 3.90 in or more, but I'm not sure. The 96mm liners are notably thinner than the 94mm liner, so I assume the OD of each type is the same, and Westwood Liners in the UK offers a similar tophat liner product with a stock 94mm (3.701 in) ID and a 3.900 in OD, which apparently can be bored out to the larger 96mm (3.78 in) size. The cost of the sleeves is additional to the labor cost quoted above. Turner's stock-size 94mm ID sleeves are +/- $68 each, 96mm ID sleeves are $90 each ($720 per set). In an odd twist, Darton, a US company, manufactures the sleeves exclusively for Turner, a UK company, but a US customer has to buy the sleeves from Turner and have them shipped to the US, for Darton to install them. DHL shipping of sleeves from UK to USA is about $48. All in, the price to install large-bore tophat liners/sleeves in a Rover block is about $2100, plus the cost of shipping the block to/from the installer. Since the OP was planning a pretty extreme build, I assume flanged liners with a stepped-deck gasket surface would be a wise move. ARP head studs at $200 a set too. So, if the slightly overweight, and ferrous, but also magnetic personality of the 300 block is not for you, you're looking at $2300 for Rover tophat liners and studs, plus the bottom-end machining costs to fit a larger crank. Dave |
mgb260 Jim Nichols Sequim,WA (2461 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: maximum overbore for Rover
Look at L.A. Sleeve custom option. EDIT: They have one specifically for the Rover now. Don't know the price.
Edited 1 time(s). Last edit at 06/11/2016 12:49PM by mgb260. |
BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6468 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: maximum overbore for Rover
Food for thought: The 3.780" bore will result in a sleeve thickness of only 1/16 of an inch (.060"). The bore centers are 4.240" leaving a maximum of .170" around the liners IF the cylinders were siamesed, which I am sure they are not. That may sound like enough, but if 1/8" is left for coolant between the cylinders you are down to only .103" of aluminum. Then there is core shift. So by all means sonic check your block before you go down this road. What you find may not make you happy.
Jim |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: maximum overbore for Rover
So Steve, How did this oversquare build go ? Thin/weak cylinder walls coupled with a 3.85" stroke,(hi lateral thrust on the cylinder walls)., is a risky scenario. 62' Buick Skylark, use of the car ? roverman.
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