ettore bugatti
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| posted on 14/12/06 at 07:09 PM |
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Big bored smallbore (A-series)
Hello,
Is it possible (and already been done) to bore the 998 to 70,6mm o r even 73,5mm with the big bore cylinder bore spacing (and using Cooper S con
rods)?
I would love to have a short stoke 1293cc
Richard
[Edited on 14/12/06 by ettore bugatti]
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udo
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| posted on 14/12/06 at 09:31 PM |
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big boring an small bore A series
I don't think this can be done
With the standard 998 block the biggest you can go to and still get pistons for is +0.060" which gives you 1046cc with the standard rods (76.2mm
stroke)
Not sure about interchanging the rods as I think some where along the way the size of the journal changed
Cheers
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hillbillyracer
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| posted on 14/12/06 at 10:26 PM |
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Most things that can be done with the A series has been by now. I dont think that this is possible, there are 2 basic types of block, the small block
& big block (makes em sound much bigger when you put it like that ). Small blocks are:
803cc A30etc?,
848cc Mini850
948cc Minor1000
997cc Cooper
998cc Mini1000
1098cc Mini1100
Big blocks are 970cc Cooper S
1071cc Cooper S
1275cc Cooper S plus everything that was a 1300.
I dont think the small blocks have the meat in them for big over bores.
The big blocks are what is usually used for a tuned engine, the standard ones all sharing the same bore & differing strokes. This makes the 970 a
real short stroke screamer but they aint easy to find & expensive when you do.
I'd build a 1380 which is a standard 1275 stroke & as big as you can overbore without having to offset the bores I think.
Get Vizard's book "Tuning BL's A series engine" & it'l tell you far more than you could think possible to do to an
engine.
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ettore bugatti
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| posted on 14/12/06 at 10:37 PM |
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Cooper S rods fits the smallbore crank
Vizard doesn't mentioned it at all. Only grinding a new billet crankshaft.
When BMC introduced the Cooper S (the big bore block) did they made a new casting or did they just bore the excisting block out?
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Stu16v
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| posted on 14/12/06 at 11:07 PM |
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The 'S' block castings, whilst related to the 'big blocks' were unique to the Cooper range, having an exposed tappet chest.
Hillbillyracer is essentailly right, however, it needs to be remembered that there are transverse and inline blocks as well, to complicate things
further.
It really isnt worth the time/hassle/expense of trying to squeeze every last cc out of a 1000cc A series, when you can drop a 1275 in, and have
reliable(ish) power. If you have some money to burn, as has already been said, create a 1380 (73.5mm bore from a 1275). But get the bores offset bored
as if it is going to 74mm (1400), which will give you one last refresh if needed before junking the block...
[Edited on 14/12/06 by Stu16v]
Dont just build it.....make it!
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hillbillyracer
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| posted on 14/12/06 at 11:11 PM |
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It's a different casting. And there are a lot of different big block castings, they have more & less metal in all sorts of places making
some better or worse depending on what you want to use it for. Some have tappet covers & some dont & the A+ that came out about 1980 has a lot
more bracing to stiffen the block. Some have the oil filter mounting cast into the block & others have it on an alloy mounting.
You really need to talk to some one who has built a few & knows them inside out ( I know that there's a helluva lot that I dont know!)
One thing thats for sure is you can build an A series to produce more power than an engine of its type has any right to.
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Syd Bridge
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| posted on 15/12/06 at 09:06 AM |
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You can offset grind the 1275 crank to drop the stroke, then use the S rods. This will get you what you are looking for in a 1275 block. Some of the
MG Metro and Turbo blocks had a bit more metal in them as well. Rare though.
We did it here for a grasstracker. It produces a screamer of an engine with very high revving capability. Just make sure you get a set of steel rods
and arp rod bolts.
Cheers,
Syd. 
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Nick Skidmore
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| posted on 15/12/06 at 10:17 AM |
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I think the largest capacity small bore you can do is using Hillman Imp pistons in an 1098, makes about 1240cc.
I guess an 850 crank would get that back down to 1000cc ish?
I had a short stoke 1300 which was a 73.5mm bore with 76mm billet crank.
I can get virgin ie unmachined EN40B forgings that have enough meat on them for any stroke from short to long (1600cc) and will do both FWD and RWD.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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DIY Si
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| posted on 15/12/06 at 06:01 PM |
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I have something similar to what you're looking for in my mini. It's go the same bore as a 1380 (73.5mm), but the crank has been offset
ground to accept Cooper S rods to give 1338 cc. With less of an overbore this can bring the size back down to roughly 1300. Incidentally, my engine
has a red line of 8,500 and with it's current cam and near race head produces 150 bhp and 98 lb ft, with one of the flattest torque curves
I've seen (wobbles by +/- 3lb ft between 3,500 and 6,800!) It's not the most drivable engine as the cam comes in at 2,750, but this could
be changed to allow more power lower down. It is a huge laugh though.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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