Tuning the 850 engine?

[Chalkie]

Hey guys

since my 1000 blown up I got given a 850 engine but 35 bhp isn't quite enough in my eyes

since i ride a quad with 55 odd and all my mates have 1275 minis

anyone got any ideas

thanks Stephen

[contour51]

Hey guys

since my 1000 blown up I got given a 850 engine but 35 bhp isn't quite enough in my eyes

since i ride a quad with 55 odd and all my mates have 1275 minis

anyone got any ideas

thanks Stephen

IMO
There are soooo many "tweaks" and different opinions/ideas.I suggest get 'Tuning 'A' series engines ' by David Vizard or 'Mini Tuning ' by Clive Trickey and read up.Then you can do do what your budget runs to.
G.

[e-type]

I had a nice 850 engine 15 years ago.

spec. was:

head 2mm off to raise comp. ratio
stronger springs from std 1275.
alloy inlet with gas flowed 1.5" S.U. and tweeked needle
LCB with RC40
homemade alloy flywheel (same weight as ultra light steel flywheel)

won some auto testing events with that one even against 1275cc minis

maybe it only had 45 bhp, but it was realy quick in 1 and 2nd gear

Follow my 850 speedwell project for some more tuning tricks

Thomas

[Chalkie]

I had a nice 850 engine 15 years ago.

spec. was:

head 2mm off to raise comp. ratio
stronger springs from std 1275.
alloy inlet with gas flowed 1.5" S.U. and tweeked needle
LCB with RC40
homemade alloy flywheel (same weight as ultra light steel flywheel)

won some auto testing events with that one even against 1275cc minis

maybe it only had 45 bhp, but it was realy quick in 1 and 2nd gear

Follow my 850 speedwell project for some more tuning tricks

Thomas

Got a link please

I love small bore engines always more fun!

I'm going to build an engine up for my next mini a 1310 16v but for this one i want a quick small bore

and i have Vizards book i haven't read it yet

[Tim]

If you really want a quick small bore, why not start with a 998 or 1098? The 998s should still be very common over there (they're not that hard to get here) and they have a stronger crank, proper bearings on the camshaft etc. There's no substitute for cubic inches.

Its perfectly possible to build a warmed 850, I'm actually building a lightly modified one myself, but that's entirely for the sake of originality. I'd be going for an 1100 if I was trying to get more power on a budget.

Tim

[Chalkie]

I have a 998 engine but needs an over bore what I can't afford at the moment

Just wanted the 850 to be a little bit quicker

My old boss said his mate use to have a "Hot Rod" 850 it use to sit and rev at 1500rpm idling use proper scream along the street


also my 850 have cam bearings

[Tim]

Its entirely your call. All I'm suggesting is that you do your sums before you start. By the time you do a cam swap, some work on the head, a set of extractors and a bigger carb, your free engine won't be looking so cheap.

Tim

[Chalkie]

is a 998 cam better than a 850? cause i have one

I have hs4 gas flowed carb sat in the shed

and i can polish all the ports

think that will do to be fair then ill build one when i have more money

[Tim]

is a 998 cam better than a 850? cause i have one

Actually, I don't know enough to say, but would guess 'not much', I'd have to look up Vizard to see what he reckons. From memory there are incompatibilities with oil pump drives or something.

I have hs4 gas flowed carb sat in the shed

Probably a good start, you'll want to be sure not to over carb it. That will depend on how much work has been done on gas flowing it. and What you do with the head and inlet manifold Do you have a matching inlet manifold for it? The 850 one suits an HS2 and is a bit small. A later 998 one to suit an HS4 is needed.

and i can polish all the ports

On its own, that probably won't help enough to be worthwhile. You really need to reshape the combustion chambers to open them up. The 850 head is the worst for 'shrouding' of the valves, and they have the smallest valves. you could put a lot of work into an 850 head for not a lot of reward. If you can track down a 12G202 cylinder head that was used on the 1100, it would be a better starting point for modifications, unless you can find a 12G295 or 206 head and get the compression ratio up.

think that will do to be fair then ill build one when i have more money

Yeah, they are all on the right track, but be prepared to find that you haven't gained a huge amount. I've kind of reached the limit if my experience with 850s now though, so I'll shut up. Hopefully someone who has done it before can fill you in on what will give you the biggest gains most cheaply. Also the yellow Vizard bible is a great background reference when you are starting out, and so cheap now. http://www.amazon.co.uk/Tuning-A-Series ... pd_sim_b_1

Tim

[Chalkie]

Okay thanks for all that information

you know what Ill change the gear box to rod change as my cars rod change

and leave it!

thanks so much

Stephen