5% Off

800-946-2642
Shop by Car
 

 What is the redline on a 1275?

 Created by: Newkid
   Forum Width:     Forum Type: 

 Posted: Jun 12, 2017 08:38PM
 Edited:  Jun 12, 2017 08:46PM
Total posts: 867
Last post: Oct 19, 2017
Member since:Jul 15, 2008
US
Quote:
Originally Posted by Newkid

I'm hoping with the 3:21 gears it won't scream too badly but sounds like I will still need to expect it to be north of 4000rpm at 70mph. Sound matting will be on the agenda for sure.
After riding in a half dozen classic Minis (including my own), I've concluded that the Mini is a very noisy car. My engine and drivetrain are new and/or rebuilt, I have a final drive ratio of 3.3:1 and I've installed ½" Dynamat on the floor pan, firewall and up under the dash and have nice & thick Newton carpeting throughout. Still, by modern car standards it is NOISY. Granted, my exhaust is loud, but it's not so much the exhaust noise but the singing transmission and the rattles, buzzes and harmonic vibrations that make it a most unpleasant auditory experience—if you're not into that kind of thing. I rarely exceed 60 mph (except for on the track) and almost always use earplugs on the highway. Just part of the charm, I guess.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Jun 12, 2017 02:58PM
Total posts: 39
Last post: Jun 12, 2017
Member since:Mar 28, 2016
thanks tons. Great feedback.

given what you're both saying I'm not going to be too worried about over reving. I'm hoping with the 3:21 gears it won't scream too badly but sounds like I will still need to expect it to be north of 4000rpm at 70mph. Sound matting will be on the agenda for sure.

I think with most cars we get to know after driving for a while, you can hear and feel the comfort zone, and start to know when enough is enough.

TJ

 Posted: Jun 11, 2017 02:43AM
Total posts: 3522
Last post: Oct 21, 2017
Member since:Oct 8, 2011
US
One of the things I have loved about the A series since the beginning is it's ability to rev. My first mini in 1968 was a Morris 850 which I had bored for .060 Power Max pistons, balanced and line bored for three cam bearings. Running a Cooper S camshaft, Isky valve springs, push rods, 295 cyl. head, twin 1 1/4 SUs and a 4.10 gear. That engine was revved to 8500 at every autocross and driven back and forth to college on weekends. Traded the car and $300. for a 67 Cooper S. After a couple of years as a driver the S became a dedicated autocross/Solo 2 car. The engine in that car was balanced and blue printed with 643 cam, 11.3 CR, big valve 940 ported and polished cyl. head. The engine saw spurts to 9300 on a regular bases. When done with autocross, I converted the car to vintage racing. Removed the bottom end and stored the block as it was worn at .060. As a vintage racer I reduced revs to 8700. Here is the catch at that kibd ob rpm I was able to break three cranks in six years of vintage racing. The first came apart at 8400 rpm and broke the block half in two. The next two were found cracked during annual mag inspection of the cranks. I rebuilt a 948 Sprite engine for a Lotus 7 last year and the owner took a lap of  Talladega at 8000 rpm all the way around. If ask I would not have suggested him doing that. I suspect the only reason it is still running is it is a race quality engine with ST crank and new A+ press fit con rods. We will pull, mag crank and replace mains and rods if all is well. Yes they will turn but you must be willing to pay the price. 

PS the 1275 Cooper S block removed in the late 80s was placed back in service a couple of years back as a 1360 73mm in a street driver. With a O/A FD ratio of 2.56 it now travels at 70 mph at 3000 rpm and 96 mph at 4000. Wondering about oil pressure yesterday I recalled reading some place 10 lbs per 1000 rpm is required. Rolling along at 2500 rpm with 195 water the OP was at 50 psi. Bringing it up to 3000 the OP came up with the revs. 

If you really like rpm a 1071 or a 970 should be a fairly stiff crank and love the high numbers. I have cranks for both and a thick flange Cooper S block with all three main caps replaced with steel caps, a four bolt center. If I could find a set of 6 inch rods I'd be busy building a big RPM short stroke.  Steve (CTR)

 Posted: Jun 11, 2017 12:17AM
Total posts: 1181
Last post: Aug 8, 2017
Member since:Jan 28, 2005
Because the bottom end is fairly strong and the engine is small, it can live at 7,000 rpm with good preparation. (more with custom parts.) I don't know the factory redline for something like a 1275 Cooper S but I imagine it's something around 6000-6200 rpm, and other 1275's around 5500 rpm.

But, the trick would be to get it to rev to 7,000 rpm, since breathing is going to be the barrier with that. Better flowing head/induction/exhaust and fuelling to match will be needed, along with a camshaft to let it rev that high. But most of those mods will reduce torque on the low end and make the engine peakier. The stock redlines are probably less about the physical limit of the bottom end and more about the lack of breathing to get much higher than the "limit."

The smaller available valve area for a long-stroke engine is the main reason they can't rev like a short stroke, all other things being equal. But the smaller valve area increases gas velocity at lower rpms, which makes them more torquey down low.

Now what the stock A/A+ series engines are known for is being able to run at high revs all day long. i.e. on a long motorway trip, you can keep the thing at 5,000+ for hours and it won't hurt the motor. If you have to tackle some steep grades you can shift down and keep it pegged for a long time if you have to, as long as the motor stays cool.

It's just a matter of being OK with with noise and racket that comes from keeping it revved high. That's the main reason some people choose taller (lower numerically) gears, for more comfort. Plus improved fuel economy, as long as you're not lugging the engine.


DLY
 Posted: Jun 10, 2017 03:50PM
Total posts: 39
Last post: Jun 12, 2017
Member since:Mar 28, 2016
I suspect this is going to be controversial subject but since I genuinely want to know more about it, I'm throwing out the question;

What is considered the redline on a typical classic Mini motor, and specifically the 1275A+?

I know that the 1275 has a longer stroke than bore, and to my old way of thinking this means that the motor should have higher torque but lower revs than something else with a shorter stroke. But I have also heard that while it is still torquey, the Mini motor revs quite happily at high revs and have heard that they are comfortable up to 7G RPM. That is much higher than I would have expected.

I have yet to drive it, but we have just rebuilt our motor/trans (and put in 3:21 gears to get the revs down on the highway), but at this point it is only running on the stand - not in the car yet. In short bursts it sings sweetly at 5G but I'm curious to know what is considered safe.

Thanks in advance.

TJ