16 replies to this topic

[whee]

While there have been quite a few threads on this and I have browsed them, none answer my question exactly.

 

I have an 850 Moke that I drive at altitude that results in the loss of about 7 bhp. That makes it quite underpowered. I'd like to try and get it back to the original spec *without* changing the look of a very original car. I'll do bolt-ons if I must.

 

Thoughts on best way to achieve this goal?

 

998 Cooper cylinder head? Exhaust is probably a choke point - I'd like to keep as original looking as possible, but I can always put the original back on. I have plenty of storage place.

 

Thanks!

Edited by whee, 08 August 2019 - 02:55 PM.

[cal844]

I wonder if it would be beneficial to fit a small bore RC40 along with a small amount of head work, I know you'll be best to open up the ports slightly then deshroud the valves

[whistler]

Stage 1 kit is about the best improvement for the money but have the needle changed in relation to your normal altitude.

[Rorf]

Put a 1275 in

[whee]

I wonder if it would be beneficial to fit a small bore RC40 along with a small amount of head work, I know you'll be best to open up the ports slightly then deshroud the valves

 

It certainly would, but the more I look at the bigger exhaust the less I like the look of it. One 

 

Stage 1 kit is about the best improvement for the money but have the needle changed in relation to your normal altitude.

 

Oddly enough, I've tried different needles on my various minis, and always gone back to the original at altitude (6,400 ft). Also, I don't believe the standard Stage 1 kit fits the Moke - needs longer exhaust so that adds to the cost.

 

Put a 1275 in

That would achieve the power purpose, but not the originality :) 

[unburntfuelinthemorning]

A 998 Cooper casting will work if you can get a good one but they normally need a lot of skimming to get a decent compression ratio as the 998 Cooper used raised pistons and yours are likely dished. 

 

Nearly as good as the Cooper head are modified small bore heads from lesser models. 

 

Use the highest octane fuel you can easily get and use the highest compression ratio you can for the fuel.

 

Separate the inlet and exhaust manifolds to get rid of the hot spot - you'll need another set of manifolds - cut the exhaust off of one and the inlet off of the other.

 

Replace any restrictive exhaust mufflers with straight though versions.  No need to increase the pipe diameter.

 

Throw in a K&N replacement element air filter and try to get the vehicle tuned on a rolling road to get the correct needle in the carb and also the distributor recurved.

 

Doing these things will get you the power you require and a little more without the vehicle looking any different.

[timmy850]

An 1100 engine with stock manifold and carb makes 50hp and looks near identical to an 850..

[ACDodd]

Make the 850 22.7% bigger to compensate. Fit a 998 crank and bore the block 0.125" oversize and fit 998 +0.060" pistons. Or if you don't want to go that big a bore, fit the 1098crank and STD pistons and stretch that little 850 to 1098cc. That's only a +0.065" nominal overbore for a 29.5% increase in capacity. This will more than make up for the altitude loss.



Ac

Edited by ACDodd, 09 August 2019 - 12:14 AM.

[unburntfuelinthemorning]

So it depends whether you want to change the engine or not. 

 

The easiest option is to drop a 998 or 1098 engine in to replace the 850 as timmy850 says.

[whee]

A 998 Cooper casting will work if you can get a good one but they normally need a lot of skimming to get a decent compression ratio as the 998 Cooper used raised pistons and yours are likely dished. 

 

Nearly as good as the Cooper head are modified small bore heads from lesser models. 

 

Use the highest octane fuel you can easily get and use the highest compression ratio you can for the fuel.

 

Separate the inlet and exhaust manifolds to get rid of the hot spot - you'll need another set of manifolds - cut the exhaust off of one and the inlet off of the other.

 

Replace any restrictive exhaust mufflers with straight though versions.  No need to increase the pipe diameter.

 

Throw in a K&N replacement element air filter and try to get the vehicle tuned on a rolling road to get the correct needle in the carb and also the distributor recurved.

 

Doing these things will get you the power you require and a little more without the vehicle looking any different.

 

Hadn't thought of using a straight through system. That could be a good option. The rest looks very doable too. Will likely get on this during the winter. Thanks!

 

An 1100 engine with stock manifold and carb makes 50hp and looks near identical to an 850..

 

Near, but not quite alas!

 

Make the 850 22.7% bigger to compensate. Fit a 998 crank and bore the block 0.125" oversize and fit 998 +0.060" pistons. Or if you don't want to go that big a bore, fit the 1098crank and STD pistons and stretch that little 850 to 1098cc. That's only a +0.065" nominal overbore for a 29.5% increase in capacity. This will more than make up for the altitude loss.



Ac

 

Thanks. If ever I need to do a rebuild this would work. 

 

So it depends whether you want to change the engine or not. 

 

The easiest option is to drop a 998 or 1098 engine in to replace the 850 as timmy850 says.

 

Yes, I know the easiest would be to do a different engine. I'm just being difficult wanting to keep the 850 I know :)

[tmsmini]

I have an old Tuning Your Mini book from the late 60s/early 70s that talks about adding super chargers to 850 engines. I doubt if the parts are available these days and the added stress would lead to an earlier rebuild...

Terry

[unburntfuelinthemorning]

 

Hadn't thought of using a straight through system.

On standard systems with two mufflers the rear one is normally very restrictive but the front one is often a straight-through type.  Replacing the rear one with another front one will help.

[DeadSquare]

I have an old Tuning Your Mini book from the late 60s/early 70s that talks about adding super chargers to 850 engines. I doubt if the parts are available these days and the added stress would lead to an earlier rebuild...

Terry

 

 

A 1098 has about 30% more capacity than an 848, but uses slightly smaller main bearings.  Adding a supercharger, to an 850 adds about 30% more power, so not much difference in the stress.

 

I took the already 2nd hand Shorrock off the Morris Minor, bolted it on to my Mini and drove away.

 

Actually, it wasn't quite that simple.  I had mounted the Shorrock above the rocker cover under the capacious Minor bonnet, and driven it via a second pulley welded onto the water-pump/fan pulley.  The home brew mounting made tensioning the belt very easy, and more important at the time, quickly removable when I went home, in case somebody lifted the bonnet.

 

I had to make a new manifold, which I did out of iron water pipe fittings. Fitting and tensioning the belt was by loosely fitting the manifold to the front port and pulling the manifold down on to the rear port with a very long stud.

 

Shorrock are silly prices, like £1,000 these days, ones from old Mercs are about £150

[Minigman]

Innocenti 850s c.1971 had a 12G295 head and made a reported 50bhp. (My inno knowledge isn’t great but I did investigate this when I almost bought one last year). Improve the inlet and exhaust manifolds possibly with a HS4 one modified to take the HS2 vertical studs (4mm wider bore) and cheap to obtain. Vizard the HS2 (see Retro Minis)and you’ll be making plenty more power on a standard 850.

Edited by Minigman, 11 August 2019 - 05:51 PM.

[Minigman]

https://www.carandcl...uk/car/C1122287

There’s an 850 here with 12G295 head but with HS4 carb (50bhp), although there are mixed reports on spec. Just shows that 850s can be improved quite a bit over 34bhp without looking too obvious.