few questions about cam and valves (2.7 mishaps)

[liam012]

ok so i i started my 2.7 conversion with stripping my 731 casing 320i head and cleaning up me 2.7 525e block.
pistons and bores in top nick so was happy bout that - main bearings and big end bearings need changing as they have started to discolour and are mildy scored - not to upset -
get to work on stripping the 320i head to find several things chunks mising of 2 lifting lobes and awful scoring on the round lobes - valve seals gone and too much play in valve guides - not good so -

1) i have accsess to a 325i cam in good nick will this substitute ok? will it give more less the same lift?
2) do the valve guides come out down through the combustion chamber or up into the cam amd rocker section of the head
3)where can u get uprated valve guides or is profiling urself best bet?

cheers
liam

[Jhonno]

325i cam wont fit without machining the head

[liam012]

thats bad news
thanks tho - i was gonna get one.

[Templ8e30]

325i cam wont fit without machining the head

Sorry but that's Bollocks, that is the accepted way of making a simple 2.7.

My 2.7 has a 525e head fitted with a 325i cam the only mods being 3 extra holes for feeding oil to the cam bearings that are not used by the 525e cam. I have a spare head just in case which is a 320i (731) head fitted with a 325i cam and no machining was required whatsoever.

If you look into uprated cams the same parts are listed as fitting 320i/323/325i as well.

Cheers,

Iain T

[Jhonno]

i didnt know what sort of machining was needed hence what was needed to be done was not specified, i was just under the impression that the 325i cam had larger diameter or something..

so just drilling extra oil holes is required, cool

[Brianmoooore]

So a 325 cam will fit straight into a 731 head then? This is different than i was told on a previous thread, but I wasn't convinced then.
Do I assume that the standard 325 cam in a 731 head on a 2.7 block will produce more power than the 320 cam in the same set up?
Anyone know lift, duration and overlap for the two cams?
Also how does the eta head (modded for 320 or 325 cam) compare with the 731?

[Turbo-Brown]

The valve guides come out into the rocker chest if that's any help

If it were me though, I'd take it to a machine shop as they'll be able to heat the head to fit new guides, ream them out and then re-cut the seats.

EDIT> Not sure what you mean by uprated guides? Think the standard ones are able to take 200K, and even then the exhaust guides seem to be the ones that suffer.

[Templ8e30]

So a 325 cam will fit straight into a 731 head then? This is different than i was told on a previous thread, but I wasn't convinced then.
Do I assume that the standard 325 cam in a 731 head on a 2.7 block will produce more power than the 320 cam in the same set up?
Anyone know lift, duration and overlap for the two cams?
Also how does the eta head (modded for 320 or 325 cam) compare with the 731?

Hi Brian, a 325i cam just slots in to the 731 head. The cam bearing dimensions are identical for 325i/323i/320i. The 320i cam has about 250 degrees duration whereas the 325i cam is about 258 and has about 1mm more lift at the valve.

Fitted to a 2.7 the 325i cam does indeed make more power than a 320i cam.

The eta head (similar to the e21 320 head and shares the same '200' casting) has the same size valves and combustion chambers as the 320i head but has smaller ports and the cam uses 4 out of the 7 cam bearings, the 3 unused bearing housings don't have the oil feed drilled into the head from the rocker shaft. the eta cam is extremely mild and has a lot less lift.

My eta head had the valves and seats machined to give a 3 angle seat, this improves airflow considerably. This is why I'm getting such good power from a standard cam (209bhp). I spent lots of hours with a die grinder hogging out the ports to slightly larger than 325i spec, then smoothed them up and polished the exhaust ports.

The polished exhaust ports stop carbon build-up from reducing the port size and also makes the head run cooler. The inlet ports need to have a rougher finish to aid swirl which helps torque and responsiveness.

My next idea is to have 325i valves installed in my spare 320i head and give the seats/valves/ports the same treatment as the eta head.

Cheers,

Iain T

[Brianmoooore]

Hi Brian, a 325i cam just slots in to the 731 head. The cam bearing dimensions are identical for 325i/323i/320i. The 320i cam has about 250 degrees duration whereas the 325i cam is about 258 and has about 1mm more lift at the valve.

Fitted to a 2.7 the 325i cam does indeed make more power than a 320i cam.

The eta head (similar to the e21 320 head and shares the same '200' casting) has the same size valves and combustion chambers as the 320i head but has smaller ports and the cam uses 4 out of the 7 cam bearings, the 3 unused bearing housings don't have the oil feed drilled into the head from the rocker shaft. the eta cam is extremely mild and has a lot less lift.

My eta head had the valves and seats machined to give a 3 angle seat, this improves airflow considerably. This is why I'm getting such good power from a standard cam (209bhp). I spent lots of hours with a die grinder hogging out the ports to slightly larger than 325i spec, then smoothed them up and polished the exhaust ports.

The polished exhaust ports stop carbon build-up from reducing the port size and also makes the head run cooler. The inlet ports need to have a rougher finish to aid swirl which helps torque and responsiveness.

My next idea is to have 325i valves installed in my spare 320i head and give the seats/valves/ports the same treatment as the eta head.

Cheers,

Iain T

Thanks, that's the definitive answer I was looking for.
How do 325 valves compare for size with 731 ones, and any issues fitting them to the 731 and just opening up the valve throats, or would this be pointless without opening up the ports as well?
I'm trying to do a 2.7 build on the cheap. I've got a complete good 525eta bottom end, a 731 320i head, and a totaly clapped 325i engine with recently rebuilt cracked head on it to select bits from.

[Templ8e30]

Thanks, that's the definitive answer I was looking for.
How do 325 valves compare for size with 731 ones, and any issues fitting them to the 731 and just opening up the valve throats, or would this be pointless without opening up the ports as well?
I'm trying to do a 2.7 build on the cheap. I've got a complete good 525eta bottom end, a 731 320i head, and a totaly clapped 325i engine with recently rebuilt cracked head on it to select bits from.

The 320i valves are 40mm inlet/34mm exhaust and the 325i has 42mm inlet/36mm exhaust. Obviously new larger valve seats need to be fitted, the throat has plenty of meat to reshape to the new seat and the port can be opened up to 325i sizes and a few mm beyond if you wish.

I experimented with a knackered head and found that the ports have a lot of metal on them and take a lot of grinding out before breaking into the water jacket.

Sounds like a good combo you have there eta bottom end/320i head/325i valves/325i cam/325i inlet and injectors and also the 325i AFM

Cheers,

Iain T

[Simon13]

325i cam does not work in a 731 head!

[Brianmoooore]

325i cam does not work in a 731 head!

Back to square one! What exactly is the problem then?

[Simon13]

it won't idle well Brian. Plus the 323 cam is unique to that engine too. I don't think any of the cams are interchangeable(sp) as 320/323/325.

The easiest and fastest way for u Brian is just bolt the complete 731 head on to your complete eta bottom end. All it will need then is a ecu re map. job done! and of course fit a 325i throttle body. You do this in a weekend a man of your abilities!

If your really going for more performance then it's 325 pistons and head and that route with machining work, like i am doing!

[Templ8e30]

it won't idle well Brian. Plus the 323 cam is unique to that engine too. I don't think any of the cams are interchangeable(sp) as 320/323/325.

The easiest and fastest way for u Brian is just bolt the complete 731 head on to your complete eta bottom end. All it will need then is a ecu re map. job done! and of course fit a 325i throttle body. You do this in a weekend a man of your abilities!

If your really going for more performance then it's 325 pistons and head and that route with machining work, like i am doing!

What a load of old cock ! Have you actually built this type of 2.7 ? I have and it does work.

A 325i cam in a 731 head whilst fitted to a 320i engine won't idle well but when fitted to an eta 2.7 block it works very nicely indeed

What exactly do you think is different about the 731 head ? the entire camshaft/rocker/rocker shaft area is identical to all other M20 heads regarding dimensions and design. The only differences are valve head sizes, port shapes and combustion chambers.

The only difference between the 320i/325i cams is the duration and lift of the lobes, the bearing dimensions are identical. There is nowt special about the 325i cam.

Who exactly started all this 'it won't work' bullshit ?

Iain T

[Brianmoooore]

Let's keep this civil please! It's an important point which has been discussed before on the forum and no definative answer has been given.
I think we've established now that the 325 cam physically fits in the 320 head.
The question is whether it performs properly.
It seems reasonable to me to expect the 325cam in a 731 head on a 2 litre block to give different results to the same on a 2.7 block, but I'm looking for facts, not guesses.

[Templ8e30]

Let's keep this civil please! It's an important point which has been discussed before on the forum and no definative answer has been given.
I think we've established now that the 325 cam physically fits in the 320 head.
The question is whether it performs properly.
It seems reasonable to me to expect the 325cam in a 731 head on a 2 litre block to give different results to the same on a 2.7 block, but I'm looking for facts, not guesses.

That's exactly what I'm on about, it's no guess I HAVE actually built a 2.7 with an eta bottom end/731 head and a 325i cam and it DOES perform brilliantly. The parts were all standard un modified bits, no porting or fancy valves etc.

Sorry if i came over a bit defensive but it really f@cks me off when people who've never even attempted to do a modification make claims based on word of mouth and guesses rather than practice.

Cheers,

Iain T

[chu346]

Did you not use the 200 (Eta) head?

Have you had it dynoed yet?

[Templ8e30]

Did you not use the 200 (Eta) head?

Have you had it dynoed yet?

Yes I used a modified 200 eta head on my 2.7 but I have built another ultra budget 2.7 for a workmate using a 731 head. Although it's not as powerful as mine it's still a nice grunty motor and makes 185 bhp.

Cheers,

Iain T

[chu346]

I used a 200 head like you, but haven't had any work done to the head yet. I know that the ports really need opening out.
No at the mo tho