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iamalittlepepper
Post subject: M70 DOHC conversion update  PostPosted: Oct 24, 2006 - 10:04 AM
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Hello!

Just to report back on my progress on making new heads for the M70. My objective is to update the M70 using as much components from the M50.. so I am hoping to not to have to get new custom valves etc.

So I got a M50TU head. First observation is the M50 head is a lot bigger and heavier than the M20 series heads. It is mostly wider.

I've made a mould of one of the M70 block.. so I will be using that for modelling of the head.

GC
 
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AdrianBurtonOffline
Post subject: RE: M70 DOHC conversion update  PostPosted: Oct 24, 2006 - 01:49 PM
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I am glad to hear that you are continuing down that path, please keep us informed, from all that I have read there are a LOT of people looking for this.

I know you may not be that far, but how long do you think it might take to make this work????
How much better are those heads than the M20's?

And on a side note, has anyone seen any drawing of the head that the McLaren uses????

a

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iamalittlepepper
Post subject: Re: RE: M70 DOHC conversion update  PostPosted: Oct 24, 2006 - 11:36 PM
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You can see the McLaren's engine and drivetrain in all its glory by getting the book called Driving Ambition by Neye, Murray and Dennis. Page 100-101. I would say the head design is more simliar to the M50TU than M20. Especially electrical wise they use individual BMW coil packs etc.

Honestly I got the book bceause I am curious on their tranny design.. however after reading about it.. it is a VERY short gearbox basically it is a longitude box mounted sideways. I finally decided if I do it right I would cast a custom casing and stuff the BMW ZF gearbox and worm drive a BMW differential underneath the tranny and up front. The advantage of that is I can upgrade to M's yummy differentials if I want to.


AdrianBurton wrote:
I am glad to hear that you are continuing down that path, please keep us informed, from all that I have read there are a LOT of people looking for this.

I know you may not be that far, but how long do you think it might take to make this work????
How much better are those heads than the M20's?

And on a side note, has anyone seen any drawing of the head that the McLaren uses????

a
 
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iamalittlepepper
Post subject: Re: RE: M70 DOHC conversion update  PostPosted: Oct 24, 2006 - 11:43 PM
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I made a plastic model and want to finalise and test fit before I go for the sand casting. The biggest problem I see is I am not sure how strong the cam drive chain and pully needs to be.. right now I have it so on an adaptor so old M70 hardware would work, but then the gear looks mighty weak.. so I am afraid they will break off.

My engine is on a weird contraption I made which a AC motor drives crank. Because I want to use the BMW coil packs I have to redo the Megasquirt too.

As for engine enchancement #s I am not sure.. there is improvement in intake also the compression ration is higher. The more I read, it seems DOHC is taken mostly for emission purposes. ie Turbo will be more superior, assuming the intake is the same.

AdrianBurton wrote:


I know you may not be that far, but how long do you think it might take to make this work????
How much better are those heads than the M20's?

a
 
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AdrianBurtonOffline
Post subject: RE: Re: RE: M70 DOHC conversion update  PostPosted: Oct 25, 2006 - 12:37 PM
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So the next question is cams, what are you planning for them? I also noticed that you said the CR is going up, how much?

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iamalittlepepper
Post subject: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Oct 26, 2006 - 04:22 AM
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Haha I am still thinking about using stock cams.

as for CR.. I am sticking in the 10.5 range... but changing it is not too hard.. just have to use change the mould a bit.

The bigger question I have for myself is whether to make a billet head or a sandcast head. The problem I have is the small run of heads, the cost of billet ing vs casting is nearly the same.

AdrianBurton wrote:
So the next question is cams, what are you planning for them? I also noticed that you said the CR is going up, how much?
 
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AdrianBurtonOffline
Post subject: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Oct 26, 2006 - 12:05 PM
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I would like to see a slightly lower CR this way it would give more options ie. forced induction but if they flow well enough that might not even be a concern.

So how much would these heads go for? I believe that there is a larger market out there looking for these heads

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iamalittlepepper
Post subject: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Oct 27, 2006 - 11:00 PM
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Hi Adrian.. the problem is you have to change more than the head.. You have to also modify change the chain configuration. Since the intake angles is more smoother, the price fo that you need a new intake.. the exhaust need to be changed.. the stock cooling pipes have to change too. Because I want to use stock M50 ingnitor on plug configuration, then you need a new firing system.. though it seems the stock M50 wiring should fit.

The chain configuration is something that is bugging me.. becuase right now the timing is still done by the primary chain the splits off to 2 smaller gears (one for each cam).. however after reading a few books about the history of V12.. Jaguar engineers back off from that because of reliability concerns.

If lowering CR is the primary concern. I would suggest just taking the head off and make new copper gasket.
 
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cribbjOffline
Post subject: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Oct 28, 2006 - 02:53 PM
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Just to throw an idea on the table - the Toyota/Lexus DOHC V8's have their intake cams driven by the normal timing belt, but the exhaust cams are driven from the intake cams by scissors gear arrangements.

The scissors gears are located about midway down the cams, and due to the split "scissors" arrangement, they're both low noise, and have zero backlash. Really a nice solution. I don't know that they'd be strong enough to drive cams for six cylinders instead of four, but it's another idea to consider?

Best,

John
 
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AdrianBurtonOffline
Post subject: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Jan 16, 2007 - 07:49 PM
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GC,

What is your build status? I would love to have a set of those heads, I really dont want forced induction.

What trans are you using?

a

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cribbjOffline
Post subject:   PostPosted: Jan 20, 2007 - 08:17 AM
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Pepper, I was speaking with a UK fabricator (Bogg Brothers Ltd) yesterday about doing ITB setups on the M70 and he pointed me to his website where he had an example of a partially completed custom intake on an M70.

When I initially looked at his photos, something just didn't look right, then it hit me; those are DOHC heads on that motor!:



Anyone here know who's motor/project this is? I don't think this is a PhotoShop "come on", as Stephen Bogg told me he personally worked on this motor and made these inlet tubes and he confirmed both heads were on the motor and bolted down. So I've asked him to "please" put me in touch with the owner and I'll report back when/if I learn anything.

John
 
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iamalittlepepper
Post subject: Re: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Jan 20, 2007 - 04:17 PM
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The build status is I am working on the cam shafts. I have been experimenting with carbon fiber cams. I have also been tweaking sand casting procedures.

CribbJ I think that's a N73?

AdrianBurton wrote:
GC,

What is your build status? I would love to have a set of those heads, I really dont want forced induction.

What trans are you using?

a
 
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cribbjOffline
Post subject: RE: Re: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Jan 20, 2007 - 06:09 PM
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Maybe, but Stephen Bogg claimed it was an M70, and the owner had just had a number of custom bits made & machined for it to fit the DOHC heads. He said the next stop for the motor after his place was back to the engine builder for the final fitting of the cams.

Do those heads look anything like your M50TU head?
 
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iamalittlepepper
Post subject: Re: RE: Re: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Jan 21, 2007 - 05:40 AM
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Joined: Aug 19, 2004
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I have made comparisons to a M50TU head that just happens to be sitting on my desk.. the screw patterns referenced from the coil pack closest to us seems to match..

However I think in the picture we are looking from the clutch forward.. I would say the left side head has a custom front plate installed (hence you see the plate that is smooth).. I would suspect they also deleted the water pump connector.

I would say the head on the left is the replica since you can see the external bits much much larger than the one on the right.

cribbj wrote:
Maybe, but Stephen Bogg claimed it was an M70, and the owner had just had a number of custom bits made & machined for it to fit the DOHC heads. He said the next stop for the motor after his place was back to the engine builder for the final fitting of the cams.

Do those heads look anything like your M50TU head?
 
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iamalittlepepper
Post subject: Re: RE: Re: RE: Re: RE: M70 DOHC conversion update  PostPosted: Jan 22, 2007 - 01:48 AM
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I am hoping to fit a late model BMW ZF manual box on top of a BMW diff in a custom gearbox.

The way I see it is I need a longer shaft.. but the advantage is I can fit in any Quaife/BMW/etc diff stock.

AdrianBurton wrote:
GC,

What is your build status? I would love to have a set of those heads, I really dont want forced induction.

What trans are you using?

a
 
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