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Advice On Engine & Gearbox Build Spec


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#1 MK1russ

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Posted 06 July 2018 - 11:21 AM

I'm in the process of starting my first engine & gearbox build for my mini and would like some advice and a second opinion on the spec i've decided on.

 

It's going into a 1969 early mk3 mini, so i'm doing a period build with parts that you could of got around the time (with the expection of internal parts) as I want it to look right. The whole engine and gearbox and all parts will be rebuilt/refurbished.

 

The Mini is manily used on A & B roads and country lanes, so i'm mostly doing 50+ mph and cruising along, so I don't want it revving too high. I won't be revving the engine much over 6k rpm, I'm after a nice torquey engine rather than a high revving screamer but something that'll still be fun on the country lanes. I'm also after something that'll pull resonably well up the hills around here too.

 

The majority of the parts I already have and there's a few parts that I have a choice on and/or i'm not sure which to go for, so i'll list both with question marks.

 

The spec I have though out is as follows:

 

Engine

 

1275 11-stud pre A+ block with A+ crank and con rods

 

Stage 3 spec 12G940 11-stud cylinder head

 

Pressed steel rockers (big bore wide pad version)

 

HS6 1 3/4” SU on Howley inlet manifold OR twin HS4 SU's on minispares inlet manifold?

 

Minispares EVO1 camshaft?

 

Rebuilt Lucas 45d dizzy with advance curve altered & electronic igntion kit

 

RC40 single box exhaust

 

Cooper freeflow manifold or LCB?

 

Gearbox

 

22G1128 4 synchro remote gearbox

 

S/GT close ratio 1st motion shaft & laygear OR early A+ type 1st motion shaft & laygear with pre A+ tooth profile along with 18mm nose bearing mainshaft?

 

3.21 or 3.44 diff?

 

Cross pin diff or rebuild standard diff with competition moly diff pin?

 

 

 



#2 nicklouse

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Posted 06 July 2018 - 11:49 AM

carb I would fit an HIF44 way better than what you have listed. ok not available then but I would still do it.

 

cam yes that works.

single or twin side exit. knowing some of the roads tHere I would go single as it will give a little more clearance.

LCB medium size.

3.44 FD and a cross pin diff.



#3 ukcooper

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Posted 06 July 2018 - 03:55 PM

HIF44= 1275 great carb

#4 MK1russ

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Posted 06 July 2018 - 05:29 PM

Ok, i might be conviced to swap the hs6 for a hif44 carb. I'll sell the twin hs4 setup i have then to fund the build further, they do look nice though...



#5 dotmatrix

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Posted 06 July 2018 - 07:35 PM

Fit the hs6 dashpot and piston to the hif44

#6 MK1russ

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Posted 06 July 2018 - 08:08 PM

I did think that but I'd loose the better ball bearing type dashpot.

I'm decided on the engine spec now, I'll fit all the parts to a newly built bottom end. I'm just unsure on the gearbox now, are the S/GT ratio's really a lot better?

#7 Retroman

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Posted 06 July 2018 - 08:14 PM

One of the advantages of the HIF44 is the dashpot / piston the stem runs on bearings.....this gives it a better response

 

So changing to the HS6 dashpot would be a backwards step

 

Good spec for your use and yes the close ratio box is better, makes it easier and better to drive, especially on the twisty roads

 

It means the engine revs don't change as much and if you had a cammy motor it doesn't fall out of the useful rev range



#8 MK1russ

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Posted 06 July 2018 - 08:22 PM

OK I'll keep the S/GT ratio's then. Would they work well with the 3.21 diff? I know the 3.44 diff has been recommended but I think the extra drop in revs might be better for cruising.

#9 Retroman

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Posted 06 July 2018 - 08:34 PM

If you are going to use it to 6k which it will comfortably do I would go 3.76 not 3.1, I live in a similar area to you and will never fit a 3.1

 

3.44 is a good all-round ratio

 

People are obsessed with the higher ratio diffs which the mini was never designed for...

 

1275 Cooper S options started at 3.44 went to 4.1

 

http://www.retromini...d=19&chapter=20



#10 Moke Spider

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Posted 06 July 2018 - 08:38 PM

What's the stage 3 head consist of?

 

While I agree that a HIF44 would be better (almost academically so), the HS6 will give it that period look you are after, though, if it were me, and for a period look, I'd probably run with twin HS2's given your spec and usage.



#11 nicklouse

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Posted 06 July 2018 - 08:40 PM

OK I'll keep the S/GT ratio's then. Would they work well with the 3.21 diff? I know the 3.44 diff has been recommended but I think the extra drop in revs might be better for cruising.

i would not,

 

why. ok back in the late 80s early 90s what you have speced is basically what i ran. with some small differences. i had a 286 cam and it was a 1380 on points. and i ran many carbs. singles HS4, twins, DCDs, DCOEs HIFs. the most recent build i did for a friend was a 1380 with Evo 001 cam HIF44 and had a 3.2 FD and cross pin diff. 

 

Now back then i lived in Yorkshire. the Holmfirth area. so what has that got to do with the price of Fish. well my parents moved to Ledbury 5-6 years ago. 

 

nope i would not want a 3.2FD



#12 Moke Spider

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Posted 06 July 2018 - 08:48 PM

I find the S / GT ratios 'better' than stock but they have just that ever so slightly wider than desirable 'gap' between 2nd and 3rd. This is improved if you run with a 3.76 FD or as Retroman suggested, a 3.7.

 

If you hunt around, they did make a few Laygear for the last of the GT's that take the 3 step layshaft. Hard to find, but, IMO, worth chasing up.



#13 Retroman

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Posted 06 July 2018 - 09:41 PM

Another under-rated suggestion which would keep it exactly in period... a single HS4 1 1/2" vizarded

 

More flow and gas speed than a pair of standard 1950's tech HS2's

 

Cheaper insurance, easier and cheaper to set up and looks dead standard.



#14 Moke Spider

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Posted 06 July 2018 - 09:50 PM

I was only having a similar discussion with a friend this morning;-

 


People are obsessed with the higher ratio diffs which the mini was never designed for...

 

 

I must be missing something as I just don't get that (the 'want' to fit ever taller FDs).

 

If someone can fill me in, I'm all ears.



#15 Retroman

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Posted 06 July 2018 - 09:59 PM

Ditto spider....should be a new thread ?






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