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 Posted: Sep 14, 2012 12:11AM
Total posts: 884
Last post: Oct 19, 2014
Member since:Aug 5, 2000

No one has mentioned stronger valve springs;  stock springs would be the first thing limiting RPM, esp if you're using bigger valves.  Light rockers, and retainers next, along with better rod bolts.

California manufacturer of VTEC/Mini performance conversion kits
 Posted: Sep 12, 2012 04:04PM
Total posts: 1318
Last post: Oct 29, 2014
Member since:Mar 10, 1999

my old race car has a 1275, so all my 1275 stuff becomes race car spares.  If I were building a stock-looking spinner for the street, I would try to find a 12G2827 crank from South Africa and base my engine around that, should be easy to make a 1071 (or bigger) go-fast motor. 

What I am building now does not need to look stock, its a 998 block and crank with BMW K100 head.  If I can make it work, it will have the K100RS 16V head and pistons (67mm) on modified 998 rods.

 Posted: Sep 12, 2012 05:45AM
Total posts: 2431
Last post: Oct 30, 2014
Member since:Oct 8, 2011
US

Isn't that the way it goes, decide to get involved in a build thread and it fades away. OK, back to it. If you have 93 octane for the foreseeable future ( does that look like a word? ) you can plan on running from 9.5 up to 10.2 CR. The idea is to set your block up for zero deck clearance. All pistons coming to the deck flush. This should reduce detonation. You will still need to be very careful with your fueling and dizzy advance curve. I'm not a big fan of the very expensive numbered dizzy. I'd suggest you contact Jeff at Advanced Distributors once you have all your figures on the engine build and have Jeff build you a dizzy.

Someone was talking block prep yesterday. On true race engines I have a steel four bolt center cap installed and line bored as well as ARP hardware. The block is also driled and tapped for the extra head studs. Cyl. boring and honing is done with a deck plate in place.  I also have a set of long drills and fixtures that allow me to drill all oil passages out 1/16 larger than stock. Then if the passage does not line up with the hole in the bearing shell I move the hole in block around a little. Run a tap into all threaded holes and install cam bearings properly to control oil flow to the cam.

There is so much happening with cams now it's hard to say what to use. I have always like the ST 643 cam for a street/ autocrosser. With a good intake/exhaust system and 1.3 rockers it should pull well from 1800 though your target 7500. Have Swift / Calver or someone who still ports heads do one to your specs. Calver is less likely to go over board on intake port size.

As for engine size I like to go up .020 at a time. I currently have a 1360 Cooper S that I have worn out at each over size in the years I have run it since 1971.

Now you mention trannys, you can select something from around $1500 to more like $7800. If you are going with SC drops spend the extra and get a taper bearing idler gear. As mentioned before a center oil pickup is a must and a windage tray would be nice if you have an extra $100 more less. Buy the best synchros and shift forks you can find. Careful shifting will help them last, abuse them and they can be done in a day. It would be the same with 4 synchro SC/CR. You have not said what type track time you are looking at. We like to use a 3.9 or a 3.7 for most east coast tracks. For a serious autocrosser 4.10 / 4.26 or 4.35 will serve you better.

Steve (CTR) 

 Posted: Sep 12, 2012 01:12AM
Total posts: 8050
Last post: Oct 28, 2014
Member since:Mar 24, 1999
GB

I'm not convinced that two of the goals are mutually compatible - sub 100 bhp and 7500rpm.
The maths tells us that revs make power, so unless you put an anemic cam in or run a terrible head you ought to beat 100 bhp easily with a big 1275.

If you want to have loads of revs for the aural pleasure, then either destroking the 1275 to 970 or a big overbore on a smallbore block would probably suffice.
A 68mm bore on a 998 (+.135") gives 1107 and the blocks are next best to disposable so much cheaper.

Metric is for people who can't do fractions...

 Posted: Sep 11, 2012 04:29PM
Total posts: 11295
Last post: Oct 30, 2014
Member since:Jan 22, 2003
CA

Weird...all the messages gone.

Drive to the track....but what kind of track...autocross, circuit?  Autocross would need a different cam than a high speed circuit

 

"Everybody should own a MINI at some point, or you are incomplete as a human being" - James May

"WET COOPER" (Terry Snell of Penticton BC ) - Could you send the money for the unpaid parts and court fees.
Ordered so by a Judge

 

 

 

 Posted: Sep 11, 2012 04:03PM
Total posts: 307
Last post: Oct 28, 2014
Member since:Nov 2, 2011

crap - lost all the good comments.

here's a little more on what i intend to do - and answers to CTR's questions (the ones i can remember in any case)

so - i think the higher octane gas available here is 94 but has some ethanol % in it.
MPG doesnt matter
intend to drive to the track and back, not building a city car.
3.5k tops

the goal is to have a sub 100 hp engine to be able to keep stock gearbox (+ straight cut roller type drop gears and xpin diff), but move the power band higher in the rev range and have a top end that can handle the revs.

to start with, i have a 1275 s block (AEG312) bore is around 71.40mm (+020?), 940 head slightly ported but with stock valves (has 12G1805 along with a big "K" stamped next to the thermostat housing). 12G1505A crank, AEG521 1B rods... need to get everything crack tested before i start. not sure what size pistons to go with.


 Posted: Sep 11, 2012 05:05AM
 
Total posts: 307
Last post: Oct 28, 2014
Member since:Nov 2, 2011
Starting to think about rebuilding the 1275 S shortblock i have sitting in the workshop, would like something that has peak HP between 5000 and 7500rpm. i know this is possible with an A Series, just wondering whats the recipe? obviously the valves