B30 OHC

[Pigeon]

Marquis_Rex said:

Ok, I'm a bit pressed for time as I'm about to go out and fit roller high ratio rocker arms on my challenger.

I've been following that, sounds like quite a saga...

Marquis_Rex said:

My appologies, for some reason I thoght the B30 was a V6.
In which case I'm sure it should be alot easier in terms of the cam drive- just carrying over pretty uch, especially if the blcok deck height and position of the idler pulleys can be duplicated etc etc. How is it tensioned?
Belt drives are also easier to mess with than chains.

It is tensioned by a spring-loaded movable pulley on the "slack" side; you fit the belt, allow the spring to pull the pulley into the belt, and then tighten a nut to hold the pulley in that position.

As well as driving the camshaft in the head it also drives the original "camshaft" from the OHV incarnation of the engine, which is still there to drive the distributor and oil pump. The OHV engine has a gear drive to this shaft, with a fibre gear on the camshaft for quietness; these have something of a reputation for coming loose after a couple of hundred thousand miles and it is recommended to replace them with the steel gears from the marine version of the engine, although plenty of engines don't have the problem.

This arrangement is a possible source of niggling but awkward problems; if I left the original drive in place it would require a large overhang on the end of the camshaft so the belt would clear the drive casing which would be inelegant to say the least. It would be much nicer to do the complete conversion, but since the original gear drive is of course lubricated it would require fitting an oil seal to the end of the shaft and repositioning the front oil seal on the crankshaft, which might be awkward.

Marquis_Rex said:

From what you say the design is direct acting with all the valves inline- so not a cross flow head?

Yes, direct acting with all valves in line. Not a crossflow head in the manner of something like the Jaguar XK where there is more or less a straight line path from inlet port to exhaust port with both valves open, but it does have the inlet and exhaust ports on opposite sides of the head, whereas the OHV engine has them all on the same side. The less cramped arrangement of the ports in the casting has allowed them to make the ports in the OHC head a larger diameter, and I think also the exhaust port in particular approaches the valve at a much more appropriate angle.

Marquis_Rex said:

Do you hope to weld up the two cylinders from the OHC 4 cylinder head to the other 4? now you've inspired ME to do something to my BMW project but thats another story!

Do tell...

I was thinking more in terms of 3 + 3 cylinders rather than 2 + 4, but yes, that's the general idea I would really want to get two heads on the bench in front of me before making the final decision so I could see which option would make it easier to make the cuts and to fit the two bits together.

Marquis_Rex said:

I think what BBq and wildoliver say, makes rational sense in a kind of function approach, but this project doesnt sound like its a rational thing- more to do with passion and the 'journey' being more important than the end result.
I've done similar things also- I wanted to do a 4 valve straight six for my BMW E21 3 series, but NOT by simply dropping in the modern fully mnapped 328i engine- as I wanted it with dizzy drive and how BMW would have made it if they produced it and I used to get alot of flack for that. I also wanted to use a purely mechanical plunger pump fueling system rather than K jet or some mapped affair and I got alot of flack for that also- just stick to your guns and do what makes you happy/fulfilled

Sounds exactly the same sort of thing I can dig that. It's sort of recreating an alternative bit of history that didn't actually happen, but might have done.

Marquis_Rex said:

I think 200 Bhp is ambitious from a 3 litre non cross flow Volvo engine: Its not impossible, as you can go for a more agressive cam and shift the power torque compromise toward top end power- but it doesnt sound like this is what you want to do. 200 BHp from a 3 litre is the kind of numbers BMW would get from their excellent flowing-fast burning shallow 2 valve hemis with good torque around the late seventies. if you reduced intake and exhaust losses- you could possibly approach this figure without an agressive cam- if you were willing to compromise on exhuast boom and intake noise (which would probably sound great anyway).
There are examples of high BHP/litre engines with this combution chamber/port arrangement: The original 1.6 litre 1588 cc VW golf GTi, but that used an agressive cam and was peaky with peak torque at 5100 rpm and peak power abouve 6000 rpm.

Yes, the picture I have of the combustion chamber shape of that engine is very similar to the Volvo one, but the Volvo head doesn't have such a cramped port layout and probably flows better.

Looking at the power figures for the OHC fours in K-Jet form as used in the 240 series, the 2127cc variant has a compression ratio of 9.3:1 and gives 123bhp @ 5500rpm, the 2316cc variant has 10:1 compression and gives 140bhp at the same revs. So if I bore the B30 block to accept the pistons from the 2127cc four - which it can easily take - and use the same 9.3:1 compression ratio, a simple x1.5 gives an initial estimate for power output at 184.5bhp.

Making the somewhat less justifiable assumption that that part of the power increase between 2127cc and 2316cc fours which is not proportionate to the capacity increase is due to the increase in compression ratio, the estimate for the OHC six rises to 194bhp if I go to 10:1 compression.

It may be a bit questionable to express these estimates to 3 significant figures but I think "something under 200bhp" is a reasonable way to put it... and given the nature of the project, they are not targets, they are just an idea of the sort of area I'm likely to end up in.

Marquis_Rex said:

The difference in projects such as these and my BMW stuff I've done for years is that you really have to be innovative and a pioneer in your own right. There's very little availiable. I used to hate the Ford guys- they had everything- special pistons were availiable for the Essex and Cologn engines, cam profiles, especial cam profiles etc etc. I had to get stuff custom made for my BMW all the time, and I had to populate my own knowledge as people didnt really know stuff about them. It wasnt too bad, as I work in engine R and D, with access to flow benches etc etc.
You'll have to be equally innovative. Now I'm playing with American stuff- its all easy-almost too easy. Everything is availiable off the shelf. roller lifters, rockers with needle bearings, disc brakes, rack and pinion steering set ups etc etc.

good luck

The situation for special parts for Volvo engines is actually pretty good - for the fours, both OHV and OHC. What you can't readily get is much by way of parts specific to the I6. Pistons, rods, valves, what-have-you, no problem... camshafts, crankshafts and heads, not a lot there.

A significant difficulty is keeping track of minor changes to unlisted but significant dimensions during the production histories of the various engines. There are various combinations of parts which one would think ought to be possible but turn out not to be because of some unexpected minor difference. In particular the transition from OHV to OHC, while being in mechanical terms nothing more than boring it out and sticking another head on, with all major dimensions remaining the same, did involve a lot of detail changes to the block casting - pushrod tunnels removed, different waterway pattern in the deck, bolt holes for ancillaries in different places...

A big part of the project will be sorting out the details to minimise the number of special parts and special operations required. The more of it I can do myself the better...

Marquis_Rex said:

The 90 degree V6 sounds like its uneven firing to get the crank/piston balance. So it probably fires 150-90-150-90. The other way to get a 90 degree V6 balanced is do what Mercedes and Audi do now and offset the crank pins. Its unlikely a modern engine would ever do the uneven firing thing. In the 19070s it was common however, with Masserati and this Volvo, I think Buick chopped a V8 and did the same thing.

Yes, the engine was originally intended to be a V8 but they got cold feet in the 1973 fuel crisis and chopped two pots off. The original version had uneven firing but in the 80s they revised it with offset crankpins to give even firing intervals.

It's an engine which seems to polarise opinion a bit, it seems to me that people who (like me) have come across it in Volvos aren't usually so keen on it whereas those who know it from its more glamorous French sporting applications view it with more favour I get the feeling that Volvo themselves weren't too keen on it and sort of tried to push it to one side when the 700 series came out; only one of the 760 models actually had the V6, for the performance variant of the 760 they used the OHC four with a turbo on it to give more power than the V6.

Marquis_Rex said:

I would be interested to hear what that uneven firing sounds like. I know the uneven firing of a conventional V8 leads to its beautiful burble- and introduced some interesting harmonics. I can also believe, no, I know this kind of uneven firing will lead to powerloss- due to charge robbing/interference issues-could even lead to a rough idle. I always thought it would be characterful. So bored of anodyne corporate refined motors

In a Volvo it's heavily silenced and it doesn't sound like much really. It doesn't feel very smooth from inside a 260 though...

For me this is perhaps an instance when it's not always a good thing to know too much... I can only really appreciate an uneven exhaust note when it's coming from something with separate inlet and exhaust tracts for each cylinder, like a Moto Guzzi. When the unevenly-firing cylinders are sharing tracts what I hear is the sound of charge robbing and interference... my prime thought is always "those cylinders are not all operating under equal conditions". I can be a bit obsessive about balancing things sometimes and it spoils the sound for me.

Marquis_Rex said:

Interesting that you say it eats camshafts, I heard the 90 degree Buick V6 has chain drive issues, due to un equal loading on the chain drive.

It basically has marginal lubrication to the top end and the oilways tend to block up and starve it. Then to add insult to injury, when you come to do the repair the various covers interlock in an infuriatingly backwards sequence so you end up having to take off a chain of nominally unrelated parts before you can get at anything...