Max overbore Daimler V8

Sonus
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Joined: Wed Apr 13, 2016 2:19 pm

Max overbore Daimler V8

Post by Sonus » Thu Oct 12, 2017 1:04 pm

Does anyone know what the Daimler V8 engine block over bore limitations are?

When do the cylinder walls become too thin?

Barry Thorne notes on his webpage that his 'engine was bored out to +156 thou'.

Is this max or could it be taken even further?

Piston availability is not a problem as new pistons will be made.

Ian Slade
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Location: Akrotiri Cyprus

Re: Max overbore Daimler V8

Post by Ian Slade » Thu Oct 12, 2017 2:54 pm

Generally there is no maximum over bore, the limitations are the proximity to the next cylinder, the amount of cooling you can achieve and the reliability loss the larger the over bore due to cooling or weakening the block, it can be a cheap way of gaining power without resorting to special rods and expensive head modifications. The safest way is to overbore then insert steel liners, I would suggest obtaining a damaged block, then overbore gradually to see when it is no longer feasible then make a sensible decision as to what suits your purpose. Many years ago when the mini was first introduced a friend of mine over bored an 850 to 1300cc long before BMC thought about big engined minis, he achieved this by boring into the centre cylinders so a the wall was penetrated, he then took the steel liners and filed flats to ensure there was reasonable wall thickness with maximum bore, yes it worked and was cheap but at 8500 rpm the crank tended to fail :D
Owner since the 70's, Genghis is slightly to my left.

daimlersteve
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Re: Max overbore Daimler V8

Post by daimlersteve » Fri Oct 13, 2017 8:39 am

Get a saloon block, thicker walls for a 2.8 ( +150 )

ddstewie
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Re: Max overbore Daimler V8

Post by ddstewie » Fri Oct 13, 2017 9:54 am

The engine in my car has been bored out .150" .The pistons were custom made by Ross Racing Pistons in California. I sent a standard SP piston up as a sample and supplied all the specs that I hoped to achieve. The pistons are forged and internally milled to achieve a weight as close as practical to the original as possible. The dome volume is 23.5 cc which is less than the std piston. Compression ratio 9.5 to 1.The quality looks good and the engine balancing was achieved easily. The hard part is to find a block that has enough material thickness in the cylinders to bore out. SP blocks appear to be a bit thin on it, but the saloon blocks that Steve and I have had ultra sounded are ok. After machining you need to have about .180" wall thickness remaining on the thrust side. The engine has done 5000 miles with no issues. The latest "Dart Talk " ("E" publication öf the Daimler SP250 Club of New Zealand ) has photos and a factual article on the engine specs and mods . Keith Humphreys compiles a great magazine every second month . It would be well worth while joining the club just to be able to have the benefit of accessing the treasure trove of information , excellent photos and articles that emanate from down under. If you own a Daimler SP250 , subscribe to " Dart Talk " you will love it !!!

ddstewie
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Re: Max overbore Daimler V8

Post by ddstewie » Fri Oct 13, 2017 10:49 pm

Go to "Dart Talk" issue 420,The Official Magazine of the Daimler SP250 Club Of NZ for all info/photos.
Membership contact - kenlee@orcon.net.nz :D
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tjt77
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Re: Max overbore Daimler V8

Post by tjt77 » Sat Oct 14, 2017 12:14 am

Consensus seems to be that .125" is safe on the saloon blocks.. there is plenty of space between the bore centre, so it should be possible to go larger provided one liners the block to give a minimum wall thickness of +/- .125" . machine shops in my area are able to sonically test cylinder blocks for wall thickness, but even this seems to be a little 'hit and miss' as a small area of thin casting imperfection CAN be missed ..
due to all manner of issues (primarily with cylinder heads .. my usual machinist broke his tool when attempting to replace some valve seats) Iv'e decided to scrap the idea of building 3 good engines and am settling with just one... one of my car will get the projected majestic major engine (one of which is supposedly bored to 5.0.. I have yet to take it apart.. was rebuilt in Germany in 1980s and never ran..there is a short article on this engine online @hemmings motor news site)
the other car will get Ford 5.0 and 5 speed gearbox.. (less than 1/2 the cost of rebuilding the turner V8..plus I get around 280 BHP and well established reliability)
given the small dispacement of the 2 1/2 V8 and the weakness of the bottom end ..added to the time and cost of making it into an engine with acceptable power output that will hold up.. common sense forced me to take another route..

ddstewie
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Re: Max overbore Daimler V8

Post by ddstewie » Sat Oct 14, 2017 9:52 pm

The bottom end isn't weak if you utilize best work practices and attention to detail when rebuilding these engines. The problems rear their ugly heads when back yard rebuilds are carried out, with the best of intentions of course, and good on them for having a go !!! I have pulled many of these engines apart and have been horrified at some of the "butchery" and poor workmanship displayed, no wonder they failed !!!. The problems that these engines develop are not a product of the design at all , but a reflection of inadequate or lack of maintenance and low quality rebuilds. Best work practices should always include fastidious cleaning (particular attention to the block), inspection, crack checking, assembly clearances and most importantly have the engine balanced by a reputable engineer. We are blessed in NZ as we have an engine balancer who is an absolute perfectionist in Bob Mead. Another item to always consider, if you spend heaps of time and money on an engine rebuild , always open your wallet a bit more and spend some money on the radiator and a high quality anti freeze. I would suggest Recoring or replacing the radiator . We are all aware that impurities in the cooling system are one of the primary causes of head corrosion and failure. I learnt this the hard way , as many have. A radiator flush is not always what you pay for.If your radiator is ancient and you are rebuilding your engine, get rid of it. :D

Lets talk Horsepower - Please talk to Steve Carr about Horsepower !!!
200 from the 2.5 ( I have been in this car, it is very impressive :D )
280+ from his 2.8 ( Steve has gone beyond here with his research ,design and development .It will be impressive :D :D :D )
Looking forward to his article in "Dart Talk"
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Sonus
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Re: Max overbore Daimler V8

Post by Sonus » Mon Oct 16, 2017 1:12 pm

Thanks all for your input.

I spoke to Russ Carpenter a while back and he mentioned cross bolting the main bearing caps. Anyone seen this done?

ddstewie
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Joined: Thu Feb 18, 2016 8:13 am

Re: Max overbore Daimler V8

Post by ddstewie » Tue Oct 17, 2017 10:19 pm

Enough horsepower :!: :!: :!:
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John-B
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Re: Max overbore Daimler V8

Post by John-B » Wed Oct 18, 2017 9:33 am

Wheelspin ?? Sack of potatoes in the boot ?? ;)

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