Estimated speed for a 1275 A+ Engine

[jaguar68]

Hi Chaps,

can anyone tell me the expected speeds I can see from a 1275 A+ engine running through a Ford Type 9 'box?

The engine is modified from standard with a big valve 940 cylinder head, K&N pancake air filter, LCB exhaust, running through a Ford gearbox and (currently) a standard 1098 4022 rear diff.

I've been using a sat nav as a speedo since the old speedo is wildly erratic and the fastest it's registered is 82 mph,( overtaking on the M25)

The engine seems a little harsh too, sounding like a squadron of V1's currently, but some of the harshness may be due to the "harder" new engine mounts.

Cheers

John

[Alex'n'Ane]

Standard cam? And rocker ratio? I imagine that is somewhat limiting given the other parts.

[jaguar68]

yes, standard cam and rockers.

[bmcecosse]

Changing rockers is the biggest waste of time/money.......but yes - an MG Metro (or any 266) cam would be useful, and keep revs at 6000 or so. You don't say carb size - HIF 44 would be handy. It's possible the highest top speed will be in 4th gear on that box with the present spec ?

[MarkyB]

Back in pre sat-nav days I got my old 1275 van up to an indicated 95mph.
Nothing was very happy at that speed including me
Apart form the carb it was standard, 65mph was OK for a cruising speed.

[JOWETTJAVELIN]

At the very least 90 MPH, but top speed is academic - stick to whatever it sounds happiest cruising at and is safe for a Motorway.

[bmcecosse]

The National Limit is 70 mph....... so speed is irrelevant! A 1098 can easily handle 70 mph. Why fit a (hopefully) more powerful 1275, and then hamper it with an overdrive gearbox?

[grumpydad]

hi
think this is what you need

Gear 1 2 3 4 5 Final
Ratios: 3.650 1.970 1.373 1.000 0.850 4.200

RPM Limit: 5500
RPM @Peak Power: 2500
Tyre Size: 155/80 x 14
Tyre Diameter: 23.76 in
Tyre Circumference: 74.64 in


Gear Mph per 1000 RPM Mph @2500 RPM Mph @5500 RPM
--------------------------------------------------------
1 4.61 12 25
2 8.54 21 47
3 12.26 31 67
4 16.83 42 93
5 19.80 49 109
but if you go 3.9

Gear 1 2 3 4 5 Final
Ratios: 3.650 1.970 1.373 1.000 0.850 3.900

RPM Limit: 5500
RPM @Peak Power: 2500
Tyre Size: 155/80 x 14
Tyre Diameter: 23.76 in
Tyre Circumference: 74.64 in


Gear Mph per 1000 RPM Mph @2500 RPM Mph @5500 RPM
--------------------------------------------------------
1 4.97 12 27
2 9.20 23 51
3 13.20 33 73
4 18.12 45 100
5 21.32 53 117

before people tell you that a standard 1275 wont do it it will
we have a Austin A35 that dose
for us the top ratio is still to low
so the plan is to cut the tail shaft up on the type 9
and fit overdrive so 6 speed box
this should give a cruising speed of 75 mph
at 3000 the sweet spot max tourk

[jaguar68]

The gearbox was replaced with the engine due to the fact that I had one and the fitting kit in the garage for another project. The original minor gearbox was knackered and kept jumping out of fourth. Changing the cam in the 1275 A+ is a real pain in the bum, and not likely to be on the cards for a while unfortunately.

I know the national speed limit is 70, but it would be nice to know that the replacement 1275 is an improvement over the 1098 that was in the car before, although there was nothing wrong with the 1098 it seemed logical to upgrade whilst the gearbox was being replaced. I travel around the M25 occasionally and seeing as the average speed is 80+.....

Thanks Grumpy, that's the information I was looking for. However, I think its unlikely that I will be going any where near 90 as the vibration, let alone the noise is prohibitive

[IslipMinor]

Changing the cam in the 1275 A+ is a real pain in the bum

Depends on the cam type - if it is a 'star' type (did they fit these in A-Plus?) then engine out, or at least sump off. If it is the 'slot' type, then it is pretty straightforward. You need 8 of the small telescopic magnets to hold the cam followers up, and then it is the same job as an 803/948 or 1098.

Radiator and grille out, crankshaft pulley, timing cover, timing chain and sprockets, rocker cover and rocker shaft all off (undo ALL the head nuts and leave the head in place, lift up each follower with a magnet and secure up with a clothes peg, then gently slide the cam forwards, supporting it to avoid damaging the bearing surfaces in the block.

Replace the cam, line up the 'slot' and reassemble everything, re-torque the head studs, new anti-freeze etc. and check the head stud torque and valve clearances after the first heat cycle and again after 100 miles.

To answer the original question, our 1380 has 112bhp at the flywheel and I have seen 110mph on the speedo a few times (against the GPS it reads 1mph fast at ~100mph). That's about it though, a topless Minor doesn't exactly have slippery aerodynamics!

With the Type 9 gearbox, I would stick with the 4.22 diff, 5th is quite a long gear. The Toyota 5-spd we have, has a closer 5th, and we have a 3.9 because I wanted good cruising revs, but if I had a Type 9, I would very seriously think about going to a 4.22 diff. Our 5th gear is ~20.7 mph/1000 rpm.

[bmcecosse]

Why do you want to take the rocker shaft off??? If you loosen the head nuts - it's madness to not fit a new head gasket, especially on a 'performance' engine. Just slacken the adjusters and tweak the rockers to the side - releasing the push rods, which can then be pulled out - and replaced by the magnet sticks...... At least in the Minor - the sump is easily removed if a follower drops (not so easy in a Mini!!) . In any case - it is generally a good idea to fit NEW followers with a new camshaft - or at least, they should be examined for any crazing or unusual wear .........

[IslipMinor]

I had forgotten that I have 1.5:1 ratio roller rockers, which are aluminium and wider than the standard rockers, and do not allow the pushrods to come past them, especially numbers 1 and 8.

Does just slackening the adjuster allow 1 and 8 to be removed as well, as they cannot be moved sideways?

[bmcecosse]

If need be - the end rockers can be easily slid off the shaft - better than disturbing the head nuts!