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8port or twin cam? 1360cc
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Author:  Leroy-Riding [ Fri May 23, 2014 10:56 am ]
Post subject:  8port or twin cam? 1360cc
hi guys, I know I keep asking lots of questions and am new to the forum, so I guess another question canr hurt?

while I am looking to get the build plan all set out for my mini's rebuild I will more likely than not be using my 1360cc engine.

I am designing a custom fuel injections setup with electronic ignition also and cannot decide if I should go with an 8port single cam head or try and find a decently priced twin cam kit.

who has used either and can give me some feedback?

it will likely get forced induction of some sort in the future also.

I cannot remeber the exact specs on my engine off the top of my head, all i know is it shatters gearboxes (-_-) so a 5 speed straight cut is on the list also. I will try and find the invoice of the engine rebuild and post it up so you can see what the engine currently is, ill also grab the engine number so somone can tell me waht my engine started life out as! (I purchased it as a 1360cc engine out of an old guys race clubman that he decided to go with a suzuki g13B setup instead)

the benifit of my rebuild is it will be rather long term (its been 5 years so far and all I have are piles of parts!) so if parts are expensive I am not too concerned as I do not mind waiting to save for them.

thanks
Leroy
Author:  simon k [ Fri May 23, 2014 2:57 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Leroy-Riding wrote:
I cannot remeber the exact specs on my engine off the top of my head, all i know is it shatters gearboxes (-_-) so a 5 speed straight cut is on the list also.


"they" say that 5 speed gearboxes are weak - the 5th gear doesn't have enough support so any decent amount of torque in 5th and it breaks. Apparently - I think the minisport ones even state that they're not to be used on anything with more than 90fwhp, which rules out anything more than a standard 1275
Author:  Leroy-Riding [ Fri May 23, 2014 2:59 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
simon k wrote:
Leroy-Riding wrote:
I cannot remeber the exact specs on my engine off the top of my head, all i know is it shatters gearboxes (-_-) so a 5 speed straight cut is on the list also.


"they" say that 5 speed gearboxes are weak - the 5th gear doesn't have enough support so any decent amount of torque in 5th and it breaks. Apparently - I think the minisport ones even state that they're not to be used on anything with more than 90fwhp, which rules out anything more than a standard 1275


damn :( I just dont really fancy doing 4000rpm up the highway like I curently do. . . its painfull on the ears for one.

Leroy.
Author:  simon k [ Fri May 23, 2014 3:07 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Leroy-Riding wrote:
simon k wrote:
Leroy-Riding wrote:
I cannot remeber the exact specs on my engine off the top of my head, all i know is it shatters gearboxes (-_-) so a 5 speed straight cut is on the list also.


"they" say that 5 speed gearboxes are weak - the 5th gear doesn't have enough support so any decent amount of torque in 5th and it breaks. Apparently - I think the minisport ones even state that they're not to be used on anything with more than 90fwhp, which rules out anything more than a standard 1275


damn :( I just dont really fancy doing 4000rpm up the highway like I curently do. . . its painfull on the ears for one.

Leroy.


I just put a 3.1 diff in my car, still has more grunt than I can handle, but it is a fair bit quieter on the highway. I found myself leaving it in 3rd in 60 zones too which kept surprising me
Author:  Leroy-Riding [ Fri May 23, 2014 3:16 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
[quote="simon kI just put a 3.1 diff in my car, still has more grunt than I can handle, but it is a fair bit quieter on the highway. I found myself leaving it in 3rd in 60 zones too which kept surprising me[/quote]

what sort of highway rpm are you doing?

Leroy.
Author:  Kennomini [ Fri May 23, 2014 6:21 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
A well built standard gearbox should handle 100bhp no worries, their isn't any real reason you'd need anything else.
Also a SC box will be noisy so not ideal for a daily driver (or even a weekend driver), more suited to a track car.
I agree with Simon, the 5 speed boxes do have a "weak" 5th gear. Aparently it's only the 5th gear that is weak, it can't handle big torque which means it's for highway cruising not accelerating, if you're cruising along and come to a hill simply change back into 4th and power up it.
Also a 3.1 diff ratio diff is good for highway driving. 110km is around 3600rpm.

I am slowly building a BMW twinky engine (Matt the mini man's kit). 8 valve twin cam head (can get 16 valve heads if you want to spend the extra money), 1360cc, EFI, elc ign, n/a. It will have a std 4 speed gearbox and either a 3.1 or a 3.2 diff. I'm hoping it'll have a bit more than 100bhp.
Author:  drmini in aust [ Sat May 24, 2014 7:51 am ]
Post subject:  Re: 8port or twin cam? 1360cc
simon k wrote:
Leroy-Riding wrote:
I cannot remeber the exact specs on my engine off the top of my head, all i know is it shatters gearboxes (-_-) so a 5 speed straight cut is on the list also.


"they" say that 5 speed gearboxes are weak - the 5th gear doesn't have enough support so any decent amount of torque in 5th and it breaks. Apparently - I think the minisport ones even state that they're not to be used on anything with more than 90fwhp, which rules out anything more than a standard 1275

I think they actually said no more than 90 ft/lb of torque, not fwhp...
Most decently rebuilt 1275s with a few mods have that, or more these days. My 1412 had 113ft/lb...
Author:  s-c1293 [ Sat May 24, 2014 7:47 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Don't waste your money on a 5 speed. Spend it rebuilding your 4 speed with quality parts and fit a 3.1 diff as already suggested.
I did this over 6 years ago when I fitted my supercharger, never had a problem with it and love that it sits on 3200rpm at 100kph with 10" wheels.
Author:  MiniVLT [ Sat May 24, 2014 8:24 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Sorry for the slight deviation here....

I had a 2.95 diff with 10" 165/70-10 and it sat on the highway at ~3300rpm at 100kph.
What's your secret s-c1293 to a 3.1 diff only doing 3200rpm at 100kph?
Did you change the drop gear ratios?

Cheers Shane
Author:  s-c1293 [ Sat May 24, 2014 9:28 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Not sure Shane.
As far as I know I only have standard ratio drop gears, but I have never counted the teeth and worked out ratios.
My gearbox is a standard Cooper 'S' ratio box and I fitted a 3.1 ratio diff set.
Tyres are 165/70-10 Yokohama A032's.
The speedo has been recalibrated to suit the diff (reads 62mph with gps reading 100kph) and the tacho reads the same as Megajolt displays on my Laptop.
I will double check tomorrow on the run out to Pakenham for our Hay practice Motorkhana.
Author:  gtogreen1969 [ Sat May 24, 2014 10:55 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
I had a 2.9 diff in my Clubman and used a Marina speedo. Worked out pretty close without having to get a calibration.
Author:  s-c1293 [ Sun May 25, 2014 7:49 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
As it turns out I don't know how to read my tacho! My engine is at 3400rpm at 100kph with a 3.1 diff.
Thanks Shane for bringing this to my attention.
Author:  Morris 1100 [ Sun May 25, 2014 8:03 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
I just worked out a few with gearcalc. All based on 10" wheels with 165/70 tyres
Revs at 100 kph...
2.76 = 3019
2.95 = 3227
3.1 = 3391
3.211 = 3512
3.44 = 3763
3.647 = 3989
3.76 = 4113
3.938 = 4308
4.133 = 4521
4.26 = 4660
4.33 = 4736
Author:  Leroy-Riding [ Mon May 26, 2014 11:43 am ]
Post subject:  Re: 8port or twin cam? 1360cc
Morris 1100 wrote:
I just worked out a few with gearcalc. All based on 10" wheels with 165/70 tyres
Revs at 100 kph...
2.76 = 3019
2.95 = 3227
3.1 = 3391
3.211 = 3512
3.44 = 3763
3.647 = 3989
3.76 = 4113
3.938 = 4308
4.133 = 4521
4.26 = 4660
4.33 = 4736


so based on this, where would i find a 2.76 or 2.95 diff?

Thanks
Leroy
Author:  Kennomini [ Mon May 26, 2014 1:00 pm ]
Post subject:  Re: 8port or twin cam? 1360cc
Leroy-Riding wrote:
Morris 1100 wrote:
I just worked out a few with gearcalc. All based on 10" wheels with 165/70 tyres
Revs at 100 kph...
2.76 = 3019
2.95 = 3227
3.1 = 3391
3.211 = 3512
3.44 = 3763
3.647 = 3989
3.76 = 4113
3.938 = 4308
4.133 = 4521
4.26 = 4660
4.33 = 4736


so based on this, where would i find a 2.76 or 2.95 diff?

Thanks
Leroy

Just so you're aware those ratios will kill and "off the line" performance, you'll probable be cruising around town in 2nd or 3rd gear. Your 0-60km/h time will be slow.
On the plus side you'll be cruising on the highway in the engines power band so overtaking should be easy.

Most people like the 3.44 ratio for zipping around town, it's a very common ratio but it dose suck on long highway trips. I use to have a 3.44 in my 998 and it was great around town and I've also had a 3.44 in a 1275 and I didn't like it, you're constantly changing gears around town, the ratio doesn't match the power of the engine. But with the 3.1 and a 1275 it's great, you can generally select a gear and just ride it depending on the speed of the traffic.
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