Discussion
I have a 1275cc mini at the moment and I am looking at building a performance engine for it, a few people have advised going for the smaller campacity 998cc block for a few reasons:
1.) Shorter throw crank allowing the engine to rev up to 6500 (as apposed to 5600 for the 1275cc).
2.) More reliable in a high state of tune (again because of the shorter throw crank)
3.) Better fuel econemy.
4.) That my 1275cc head and carb on a 998cc are common performance upgrades in there current state of tune and hence building a performance 998cc motor would be atleast £500 cheaper than a performance 1275cc one.
This all seems to make a lot of sense to me and I figure that although I will lose alot of torque, that a 998cc block with a balanced bottom end, a kent 276 cam and my head should give about 70bhp and be much more revvy (and hence fun) than my current motor.
Are my well advised freind speaking aload of balls and am I being silly or is this a very cheap way of getting a much stronger higher revving motor that will better suit my go kart style of driving?
1.) Shorter throw crank allowing the engine to rev up to 6500 (as apposed to 5600 for the 1275cc).
2.) More reliable in a high state of tune (again because of the shorter throw crank)
3.) Better fuel econemy.
4.) That my 1275cc head and carb on a 998cc are common performance upgrades in there current state of tune and hence building a performance 998cc motor would be atleast £500 cheaper than a performance 1275cc one.
This all seems to make a lot of sense to me and I figure that although I will lose alot of torque, that a 998cc block with a balanced bottom end, a kent 276 cam and my head should give about 70bhp and be much more revvy (and hence fun) than my current motor.
Are my well advised freind speaking aload of balls and am I being silly or is this a very cheap way of getting a much stronger higher revving motor that will better suit my go kart style of driving?
Unless you have specific restriction on capacity for e.g. a race series, then go for the 1275, or even better a 1380 if you can afford the engineering work and parts required. The cylinder heads on the large bore units is a far superior design to the small bore castings (apart from the infamous 12G295 casting), and the extra capacity means you can use a wilder cam without sacrificing as much low RPM torque.
Where did you hear that 1275's could only safely rev to 5600RPM? A bog standard MG Metro unit is red lined at around 6500RPM, and the manual for the Metro Turbo states that 7000RPM is allowable for brief periods during acceleration (although they were allegedly fitted with EN40B cranks). With the right components 8000 RPM would probably be achievable, although reliability for road use may not be very favourable.
Where did you hear that 1275's could only safely rev to 5600RPM? A bog standard MG Metro unit is red lined at around 6500RPM, and the manual for the Metro Turbo states that 7000RPM is allowable for brief periods during acceleration (although they were allegedly fitted with EN40B cranks). With the right components 8000 RPM would probably be achievable, although reliability for road use may not be very favourable.
In the overall scheme of things bigger capacity is always better. It won't cost any less to properly modify a 998 than a 1275, all the machining operations cost the same, the parts cost much the same, assembly takes the same time, so no advantage really !! The 1275 is a longer stroke, not as long as the 1098, but using this as the design criteria then you want an 850.......
As already mentioned that rev limit is pure fantasy, the rev limiter on my 1380 is set at 7000 and Mini Miglia racers red line at 8500. Stick with your 1275 and build on that, a decent head and a 276/SW5 mated with a decent stage 1 kit will be about right.
As already mentioned that rev limit is pure fantasy, the rev limiter on my 1380 is set at 7000 and Mini Miglia racers red line at 8500. Stick with your 1275 and build on that, a decent head and a 276/SW5 mated with a decent stage 1 kit will be about right.
Paul V said:
You’ll have more fun with a 1275cc engine with a modified head, apparently my standard 1275 with flowed head and 285 cam will rev to 6500 easily and will go more but its dangerous to rev a standard flywheel much higher than that.
Time to look for a lightened flywheel
Er, I've revved my bog standard 80k mile MG Metro lump to 6500 several times, and it's not blown up yet
Titanium might be a little OTT I'm going to try and get those brakes this week sometime, I’ll bring them to VW if you like?
I know that you shouldn’t over rev the standard flywheel, not sure what they are safe too but think about it, doing 7000 rpm and basically sits between you legs, not nice if it goes bang
I'm going to try and get those brakes this week sometime, I’ll bring them to VW if you like? I know that you shouldn’t over rev the standard flywheel, not sure what they are safe too but think about it, doing 7000 rpm and basically sits between you legs, not nice if it goes bang
Stick with the 1275 unit, you will get more bhp for pounds spent at the end of the day. If everything is lightened and balanced properly you will easily rev to 7000+. My 1380 was quite happy going past 7500 but that's with a steel flywheel. Keep an eye on the second hand parts ads, you'll be surprised what you can pick up.
If you go 998 you've got to have a 12G295 head casting, or else pocket the block to take the 12G940 head. 12G295's are hard to find now.
You can get over 70 bhp with a 998 and a 12G295, but it will be very cammy and the torque is poor also.
Having fond memories of my first Cooper, a 1964 998 I built a rally 998 for historics a few years ago. It had 73 bhp at 5800, but the tractability was very poor. We changed it to a 970 'S' lump which gave 84 bhp at 6600. Although it kept us in the under 1000 cc class, it was a nasty, revvy, gutless lump so we sold the car (it's in Mini Magazine this month on a rally driven by Brian Watson, its curernt owner).
You can't beat a nice 1275 with a few goodies fitted. With a 286 cam, a mildly gas-flowed head, lcb, 1.75" SU on a Metro manifold, 1.5 rockers, etc, you should see 85+ bhp and still have a very drivable car. You don't need a steel flywheel until you want to go well over 7000 rpm, especially if you use a wide starter ring. We used 8000 on the 970 with a lightened cast flywheel and wide starter ring. It was a fully balanced unit, however.
You can get over 70 bhp with a 998 and a 12G295, but it will be very cammy and the torque is poor also.
Having fond memories of my first Cooper, a 1964 998 I built a rally 998 for historics a few years ago. It had 73 bhp at 5800, but the tractability was very poor. We changed it to a 970 'S' lump which gave 84 bhp at 6600. Although it kept us in the under 1000 cc class, it was a nasty, revvy, gutless lump so we sold the car (it's in Mini Magazine this month on a rally driven by Brian Watson, its curernt owner).
You can't beat a nice 1275 with a few goodies fitted. With a 286 cam, a mildly gas-flowed head, lcb, 1.75" SU on a Metro manifold, 1.5 rockers, etc, you should see 85+ bhp and still have a very drivable car. You don't need a steel flywheel until you want to go well over 7000 rpm, especially if you use a wide starter ring. We used 8000 on the 970 with a lightened cast flywheel and wide starter ring. It was a fully balanced unit, however.
sausagepilot said:
Cheers guys, obviously my mate has no clue what he's talking about, I'm off to the pub to beat him up now!
What do you all reckon on the swifttune sw5 cam, they sell it as a kit with duplex chain and roller rockers, a good way to start?
Very highly praised in the mags...
sausagepilot said:
I
1.) Shorter throw crank allowing the engine to rev up to 6500 (as apposed to 5600 for the 1275cc).
2.) More reliable in a high state of tune (again because of the shorter throw crank)
3.) Better fuel econemy.
4.) That my 1275cc head and carb on a 998cc are common performance upgrades in there current state of tune and hence building a performance 998cc motor would be atleast £500 cheaper than a performance 1275cc one.
I have a very highly tuned 1 litre. True I foud it a bit smoother to drive, but it does get tiresome having to rev the nuts off it to get anywhere quickly.
1). If you Nitride the crank it will be ok, also get the whole lightened and balanced, or you'll never get to 6500 in 4th. Then be prepared for lots of screaming. Ask minmax as I took him out in my 1 litre the other day.
2). Lies. The piston rings on the 1 litre are not advised to be used over 5500rpm for long periods. Mine blew up after about 25000 miles. Lots of blue smoke. As long as you don't get the engine bored out too much reliability should be fine.
3). No. Car has to scream up hills, more revs hence lots more fuel used. The economy is better in my TVR on a run.
4). Lies again. The work required to fit a 1275 head to a 1 litre is much more involved than fitting it to a 1.3. The oil ways and some water ways need to be plugged and rebored, then the bores have to be pocketed, then the head matched to get the right compression ratio. More expensive as none of this needs to be done for a 1275. My engine cost around £1500 less the new head, which was £500. So not cheaper. I would have put a 1275 in if my parents had allowed it. (They controlled the insurance at the time I did it) and if I didn't already have a 1293 Cooper S.
But on the plus side the car sounds great, runs great and is fun to drive. Not very practical, but always surprises people when they ask what's in it, especially after you dust their moderately tuned 1293 on the track.
I think I'll try an SW5 in the next 1275 engine I build for my own use. It will be interesting to compare it with the 286 I have always loved when it's on the rollers with everything else unchanged. Got a few more events before my 1293 is due for another re-build though (at least I hope so!).
I think I'll try an SW5 in the next 1275 engine I build for my own use. It will be interesting to compare it with the 286 I have always loved when it's on the rollers with everything else unchanged. Got a few more events before my 1293 is due for another re-build though (at least I hope so!).
Hi Wildfire, I don't know if the SW5 is a scatter pattern. I'll look closely at the cam timing figures before I fit one. I run a standard 286 and havwe never tried the scatter version, so any info you can give me on the performance of the 286 scatter will be much appreciated.
That's what makes this forum so great as we get to exchange information, ideas and results without having to try everything ourselves and can, hopefully, learn by the others mistakes. Goodness knows I've made enough errors after 42 years with Minis and I'm still learning.
That's what makes this forum so great as we get to exchange information, ideas and results without having to try everything ourselves and can, hopefully, learn by the others mistakes. Goodness knows I've made enough errors after 42 years with Minis and I'm still learning.
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