M30B35 on petrol / LPG. CR increase - discuss please......

[gareth]

I've currently got the head off my standard M30B35 anchor and was thinking of skimming the head to increase the CR a bit while i'm at it - mainly to take advantage of the increased octane rating of LPG.

at present i have a 9:1 CR (afaik) and using rough maths a 1mm skim will give me 9.8:1 which seems more like it.

implications i can see are:
1. valve to piston clearance - i guess as it's a standard cam there will be little issue here.
2. cam timing - again quick maths says it'll retard timing by less than 1°. theoretically costing me bottom end grunt in favour of more top end. not all bad?
3. expecting the plastic cam chain tensioner to take up the extra slack in the chain when it's probably old and brittle (not a lot of wear on it though)
4. possibility of pinking while running on petrol?
5. ideally it would need remapping to get the full benefit of the change? i have an ignition advance module for the LPG if it's needed. not played with that yet

I'm not looking to change the cam, fit emerald management of anything expensive. just a freshen up and to make the situation better for running on gas if i can. If a few more ponies can be extracted while i'm there, then it's worth doing.

mechanically the engine is in fine fettle, 110k ish miles, no pitting on the valves, no corrosion on the head, no oil/carbon sludge buildup, no cam wear to speak of, honing marks still very clear in the bores, valve stem seals all still perfect etc etc etc.

[DRIFTBOY]

Hi Gareth!

Glad to see you still fettling the 335!

I can't answer all of those questions but I have a couple of bits to chip in.

Firstly, valves to head.
These engines run very close even as standard, could you check it first by putting the head on without a gasket and turning it over?

Get the head skimmed with the top timing cover bolted on, it'll make life much easier later, I found out the hard way (cracked top timing cover)!

Timing the camshaft can be made very easy with just a little filing of the camshaft sprocket; (these are not photos of my engine by the way).





Good luck mate!

[gareth]

now that's the kind of DIY tuning botchery i like!

one thing you might know... timing marks: i have a mark on the OD of the front pully / vibration damper but can't see anything convincing and obvious at the cam end. any ideas? the haynes manual is less than helpful in this respect. so far i've not turned the crank or cam (i think - would be nice to know!)

[DRIFTBOY]

Yes, the Haynes manual is useless for that, and I had trouble with it too!

I should be able to send you a scan of a diagram I have a bit later, it's easier than me trying to explain it!

[zaust]

For the cam timing, Make sure cylinder 6 lobes are one coming on and one coming off and your there.

[DRIFTBOY]

You're not wrong Marc, but with that method - and especially after a head skim I still find it all too easy to get the timing a tooth out either way.
I've heard others make the same mistake too.

Maybe we are just silly!

[gareth]

i for one am confident in my silliness and am sure i can cock it up!!!

a scan of your diagram would be much appreciated

[DanThe]

Lump of plasticine on the piston during a 'test build' is the best way to get the exact valve-piston clearance

[gareth]

true. i guess the old HG would be ok to use for this? i don't want to trash a new one while squashing replicas of morph

[zaust]

I have alway's done it this way. with the lobes one coming on and one coming off, when you put the front pully back on the locator hole will be at the bottom, And if you look at the front top face of the head (rocker gasket face) nearest the pully there is what looks like a jetty in the middle pointing back towards the cam. The front pully bolt closest to it must line up with this and job's a good'un or tdc.

[DRIFTBOY]

I see, I might try that method on the next engine build!

[zaust]

If you get stuck phone me whilst your doing it and i can talk you through it mate.

[DRIFTBOY]

Thanks for the offer, but I'm a pennyless loser at the moment so the new motor won't be built for a loooong time!

[zaust]

Same for us all fella. Let me know when, only happy to help.

[casper8r]

3. expecting the plastic cam chain tensioner to take up the extra slack in the chain when it's probably old and brittle (not a lot of wear on it though)
4. possibility of pinking while running on petrol?

Sorry, I'm very much a noob when it comes to tinkering with engines, but maybe this helps:

3. Would that be difficult/expensive to replace for more peace of mind?

4. I would have thought you can get around this issue by filling up with Super Unleaded which has higher octane ratio - the price difference is negligible since you'll be using LPG most of the time.

[gareth]

cheers for the scan you sent me martin, agrees with what i thought. with number 1 at TDC there is a mark on the outside of the vibration damper that lines up with a pinter on the front casing. the top end looks straightforward enough too. one thing mine has also is a small (3mm?) drilled hole in the nose of the cam itself, this points straight at the crank when correctly timed.

that and the follower test (cheers zaust) gives me enough places to check to be totally sure it's not a tooth out.

[gareth]

3. expecting the plastic cam chain tensioner to take up the extra slack in the chain when it's probably old and brittle (not a lot of wear on it though)
4. possibility of pinking while running on petrol?

Sorry, I'm very much a noob when it comes to tinkering with engines, but maybe this helps:

3. Would that be difficult/expensive to replace for more peace of mind?

4. I would have thought you can get around this issue by filling up with Super Unleaded which has higher octane ratio - the price difference is negligible since you'll be using LPG most of the time.

3. on a M30, it's an utter barsteward and involves a 3/4" breaker bar to get the front pully off to get the lower timing cover off etc etc. to be avoided if at all possible!

4. super unleaded would be an easy fix if i do have problems.

[DRIFTBOY]

No probs mate.

Something to look out for though is; after a head skim the notches and marks don't quite line up, mine was out by about half a tooth either way, hence next time I'll do the d.i.y. vernier gear!

[gareth]

that's fair enough, the cam should be positioned anticlockwise in relation to the crank.

how much did you have skimmed?

[DRIFTBOY]

To be honest I don't know how much was taken off.

I know it wasn't a lot, just enough to get the head flat.

[gareth]

ahaa, probably about 0.2mm then. not enough to save me worrying about valve to piston clearance without a dummy build...

[DRIFTBOY]

I'm afraid not, no!

[e30_singh]

Gareth i am at the same stage as you and I also considered raising compression ratio. But theres a guy on Revlimited who says that the M30 is running near enough to its max compression anyway.

if you mill too much material off you may have adverse consequences. The two biggest issues, as I said, would be valve to piston interference which can be countered with having reliefs cut into the pistons if necessary, and cam timing, which can be countered with an adjustable sprocket that are available from BMP Design and a couple of other places. On a budget this might net you a bit of power, but for the trouble, I'd be more inclined to get a different set of pistons and do it that way.

Look at the manual, they don't recommend milling much.

The down sides to milling the head over spec are that you might have valve to piston interference, and by reducing the height of the head you will change the cam timing enough to need an adjustable cam gear. Other than those two problems I can't really see a downside to it...

I'm not sure how much you can actually remove but I doubt it would equate to a huge gain in compression. I'd look into custom pistons if you are looking for 11:1 or higher.

So after this comment from someone who has already tried it, I decided to give it a miss...

In my opinion on the research I have done the best way to get the most power from a M30 is to turbo it.

[Rav335uk]

Or supercharge it

[ImysE30]

400 bhp apparently by supercharging it

[Rav335uk]

Not on stock internals though

[ImysE30]

Probably not, quote taken from Blingsta

[gareth]

cheers for the comments. forced induction is out of the question, this is my daily drive and though it would be fun, i'm not looking for that level of performance and the related build / running costs. if i wanted to spend that much money, it would be on a pure track car.

I've been busy this evening and have performed a dummy build at the totally standard state it is in at present and found i have 3.5mm of valve to piston clearance on both inlet and exhaust valves so removing 1mm from the head won't cause clearance issues. the head also measures up at standard height so hasn't been touched before. the 1° change to the cam timing shouldn't cause significant problems with running, in fact it should alter the characteristics in a positive way. The increase from 9:1 compression up to 9.8:1 isn't extreme and as it runs on LPG (much higher octane) 95% of the time.

If you look at the advice in the manual, it doesn't make any mention of recommending FI either!!! it will be outside of factory spec - for a low compression lazy engine. this is exactly what i'm hoping to change

[320Touring]

cheers for the comments. forced induction is out of the question, this is my daily drive and though it would be fun, i'm not looking for that level of performance and the related build / running costs. if i wanted to spend that much money, it would be on a pure track car.

I've been busy this evening and have performed a dummy build at the totally standard state it is in at present and found i have 3.5mm of valve to piston clearance on both inlet and exhaust valves so removing 1mm from the head won't cause clearance issues. the head also measures up at standard height so hasn't been touched before. the 1° change to the cam timing shouldn't cause significant problems with running, in fact it should alter the characteristics in a positive way. The increase from 9:1 compression up to 9.8:1 isn't extreme and as it runs on LPG (much higher octane) 95% of the time.

If you look at the advice in the manual, it doesn't make any mention of recommending FI either!!! it will be outside of factory spec - for a low compression lazy engine. this is exactly what i'm hoping to change

done and running for the roam?

[gareth]

it had bloody better be, or i'll be in a 1.8 mk3 chavalier

what's the ideal CR for running on a fine single malt?

[320Touring]

it had bloody better be, or i'll be in a 1.8 mk3 chavalier

what's the ideal CR for running on a fine single malt?

depends..

on a high output 440 cu lump like me.. its 3bottles to a splash of water..

get a weedywarburton on the other hand, and you'll need 3 of water to 1/2 of whisky

[Andy335Touring]

E28 535's were around 9.8-10.0:1 so you shouldn't have pinking issues, not sure if you're going to get much gains with a .8 increase though TBH ?

I increased the C/R 1.5apx on mine and the gains wasn't that noticable. I also tried getting it mapped on E85 fuel but only gained about 6-7bhp/lbft.

[gareth]

ahaa, that's good to know. I'm not really looking for huge gains, just a lean on anything tht will help running on LPG a bit mainly. I've had too many highly tuned and unreliable cars in my time, it's nice to have a lazy way of getting the pwer without stressing anything too much!

might as well have an update while i'm here... I've pulled the head apart - totally ignoring the haynes jokebook in the process i found that if i slackened off the eccentrics and removed the jet propelled rocker retaining pingy clips then positioning the cam so the exhaust valves for cylinders 4-6 are all slack meant i could just fit an allen key into the end of the rocker shaft and turn / pull at the same time. hey presto, the shaft slid straight out. repeat for 1-3 exhaust then the same for the inlet side. job done in 10 mins

the engine seems to be in very good fettle everywhere i've looked. no cam wear (lucky as one of the spraybar banjo's had just started to work loose . valves are all really good and tight in the guides, no significant pitting on the seats or valves. just really suprising condition for a 21 year old engine i expected so much worse!

the plan now is to clean up the ports a little while it's apart - nothing major, just remove machining imperfections around the seat / throat interfaces. then a 1mm skim, helecoild the damaged plug thread, lap in valves and rebuild with all new gaskets and valve stem seals (all perfect still incidentally but i got new ones in the gasket kit)

[petrol_1]

For info
i run a ETA 2.7 E30 thats on LPG , on petrol it used to pink when heavy loaded , ie up step hills etc , but it has never pinked on LPG, so it appears the std 10:8 :1 cr is ok with lpg
i am building a 2.8 and hope to skim the block to get the cr up over 11:5:1 to get the max out of the LPG JUST LOOKING INTO PISTON VALVE CLEARENCES !!!!!!!!! as that will be the deciding factor ,
if you need any info pm a number to discuss

[gareth]

That's good to hear, cheers! Sounds like an interesting build you have there