848 cylinder head

[docka]

A friend of mine has a 2A628 cylinder head which he has had skimmed and ported and flowed himself. It retains the standard valves but has bronze rocker shaft spacers. He said it provided a good boost in power and economy when fitted to his 848cc minivan back in the day (before an altercation with an oak tree). However, that was with a Vizard-style modified carb. The head looks a neat job and has been sitting well wrapped in his loft for 30 years.

My question is; might this be a good buy or would I be better off getting a standard 12g202 or similar to go on my stock 848cc woody?
I also have a set of twin 1.25" SUs to go with it plus the Maniflow Freeflow exhaust.
Thanks

[timmy201]

A skimmed 2A628 would give you a higher compression ratio than a standard 202 head. That could be one reason for the increase in power.

[mk1]

Its very difficult to give a definitive answer on this without seeing the head in question.

If it was me I'd probably use the modified 850 head, just to keep the car closer to original. I would however, NOT be using twin HS2's. they are way too big for a slightly modified 850. Better to use either a single HS4 or twin H1's if you can get a good set.

[docka]

Thanks.
I like the fact that the head was home modded and has a story to it so I'll probably buy it and try it with the standard 1.25" existing carb.
I do have two sets of twin carbs both needing a rebuild but I haven't the faintest idea what model they are, must do some more research or stick a thread up on here

[1071 S]

Its very difficult to give a definitive answer on this without seeing the head in question.

If it was me I'd probably use the modified 850 head, just to keep the car closer to original. I would however, NOT be using twin HS2's. they are way too big for a slightly modified 850. Better to use either a single HS4 or twin H1's if you can get a good set.

I've often wondered about this. AIUI each carb works independantly so a particular cylinder only sees one carb no matter how many are fitted. Twins (allegedly) work better because of the manifold layout ??

Waaayyyy back my Uncle (a professional engine tuner) modded my 850 by working the head (with the benefit of hindsight , we probably overdid the valves sizes) and fitting twin HS1s and a home made manifold/exhaust (not a lot of tuning bits available back then over the counter ...(in the Colonies).

Even though the twins were on the shelf I could never really decide if the the single HS2 might have been a better bet.

Cheers, Ian

[mk1]

Very far point Ian, & you are of course absolutely correct.

When I said "too big" I really meant "over the top".

The advantage with twin H1's is the increased charge speed (the speed the mixture passes through the carb) which gives better low down torque, this is exactly what you want with an 850 as you are never going to make it a reliable fire breathing monster

[cheleker]

A personally imported car could have come in as a Minor. Otherwise, Morris 850 is correct.

!!Good answer. Now how did I get it in the wrong thread?!

[abri]

I'm planning to do a similar modification on my 850 and have a question about the manifold. My twin H1 set is on a manifold with throats about the same size as the carbs (tiny). Where the manifold meets the head, would it be of any benefit to open up the manifold to meet the size of the head port? My initial idea was to put the H1s on a Cooper manifold until I saw the stud patterns are completely different. What's the suggested best practice for making the best flow path for the mix through a set of H1s to a 202 or standard 850 head then?

Mark, what needles would you recommend for these carbs on a skimmed down 202 head on an otherwise standard 850?

Thanks

[abs]

Port velocity is what you need so I wouldn`t enlarge the manifold at all.
A good 3 branch exhaust manifold will help lower the pumping losses and the step from the exhaust port to the ex. manifold actually helps to reduce reverse flow on overlap. The standard cast exhaust manifold removed from the inlet is far better than you might give it credit for on an 850.
I personally used to grind out the valve guide boss and fit short iron guides to the exhaust ports. that with a bit of de-shrouding with a CR of 9.75:1 with standard size valves made the little 850`s a lot perkier.
A good skim actually gains you a little valve lift and changing the manifolds removes the hot spot gaining torque and allowing a little more advance before pre-ignition and thats really helpful with the bad fuel these days.
Small bores are ace

[andy1071]

abs -you are correct about port velocity, but it has to be the correct velocity...

A step on the inlet manifold works the same as on the exhaust
(though of course the other way around -head bigger than manifold).
-If you can, the best option is to offset the manifold slightly, so the upper edge is more in-line, and the step is on the bottom edge (the bottom of the manifold has lower gas speed, so it reverses direction easier/sooner). -Same as exhaust, again.

-not too big a mis-match though, otherwise the gas speed will drop, and the fuel will tend to fall out of suspension.

[abri]

Thanks for the advice.

My exhaust manifold is a 3-1 Cooper item which I think will probably do the trick. I was just concerned about the tiny little manifold throats vs the bigger head ports. The offset mounting to make the top more in-line is and interesting idea. I would never have thought of that. I will investigate where the biggest match/mismatch is at the moment.

My idea was to run about 9:1 compression (as opposed to the standard 8.3). I'm on the cautious side of skimming the head too much and also the effect of a high compression on an otherwise great little motor.

Next question is needles...and springs!

[docka]

Yes, thanks for the info. I'm going to invest in the head I think but first need to check my manifolds fit it.
I assume I won't be able to convert to unleaded as the valve seats are part of the casting?

[abri]

Yes, thanks for the info. I'm going to invest in the head I think but first need to check my manifolds fit it.
I assume I won't be able to convert to unleaded as the valve seats are part of the casting?

My apologies for hijacking your thread

[docka]

No worries, it's all relevant