Exh. camshaft for Volumex

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david bienvenu
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Exh. camshaft for Volumex

Post by david bienvenu » Mon Oct 17, 2016 7:42 am

I have stripped a Lancia VX engine, to rebuild , and will be fitting it in to a Fiat 131.
Being a 131 it has given me a couple of problems.
1st problem is exh.camshaft, was going to run OE ex. cam, but can't because of no room for distirbutor against fire wall,
so for me that means top mounted dist.
Question, does anyone have experience of running 1608 BC ex. cam (66-26 timing I believe). Slightly worried the cam. may open too early and close too late. I do have other cams with drive gear,3 have base circle ground which I prefer not to use. I do have a ex. cam from 2lt 131, but this is in use and makes engine change over a bit messy.
Some specs.I am aiming for are:-

2 lt engine
STD VX cyl. head, with ports matched up (leaving room to gain confidence later)
Inlet cam is GC 3A
Forged CP pistons 84.6 mm aiming for 7.5 :1 cpr
Std VX gearing

2nd problem
I don't think there is enough room for DCOE carb. unfortunately.
I have an Abarth downdraft carb. manifold, does any one know if this will work nicely with a 40-42 mm DCNF carb.
The car will be used as road car, with a bit of fun.And should I connect the water heating in the manifold to cut icing.
Hopefully I have given enough info. for some more experienced people to advice.

Regards
David Bienvenu
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Spider 1969
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Re: Exh. camshaft for Volumex

Post by Spider 1969 » Mon Oct 17, 2016 8:05 pm

Hi David,

Not a subject matter expert but as far as I'm aware a pressure charged engine uses short duration and low lift exhaust cam. (VX exhaust timing is 37/3 with a lift of 8.6mm) so tread carefully.

Interesting project of fitting this engine in a 131 and I would appreciate updates and pictures of your build in the readers cars section.

Regards,

Charles
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Guy Croft
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Re: Exh. camshaft for Volumex

Post by Guy Croft » Wed Oct 19, 2016 5:24 pm

Hi David

sorry for slow response been a bit #under the weather# last few days.

As Charles says the ex cam does need to be less radical than the inlet. Rule of thumb is a bit indeterminate but 1mm less full lift seems about with the 8v TC because it has such a high flow characteristic on the exhaust, if you stick to a valve-ration of 43.5mm inlet - 36mm ex (or of course 42/36 more so). Porting mods GC style enhance the ex flow more still.

On a supercharged unit you MUST run a low back-pressure header and tailpipe/silencer setup. Unlike a turbo setup which quite naturally does need high back-pressure betw engine and turbine to operate the turbo - if you use a restrictive exhaust on a supercharged unit you won't get good power and will likely knock the piston rings to pieces and never be able to fuel it right, far less accelerate the engine - in extreme even off-load. The acid test is simple: if the exhaust note doesn't sound harsh and explosive when on-cam (3500rpm +) like they used to call 'tearing calico' - it's over-baffled or there are restrictive bends or pipe sizes and primary lengths causing problems. As I have often said - a big bore 4-1 header with 3ft primary pipes is my pref choice.

Regarding cams. Inlet - you can use anything you want. Exhaust - less peak lift than the inlet cam. As for timing and duration etc? You should take advantage of the cylinder pressure - far higher than an atmo engine, meaning that you can open the ex cam way later than any atmo unit and get the most out of the power stroke and at the same time minimise the work the piston has to do on the ex 'up-stroke'.

Charles mentioned the VX ex cam timing. The figures he cited are not wrong but are based on the Fiat system of quoting at a clearance not used for setting cam-bucket clearances - a figure of 0.8mm springs to mind. So to an extent irrelevant - except to say that if you do the math on a cam with timing of open 37 deg opens BBDC close closing 3 deg ATDC you get ex cam full lift at 107 deg, some 3 deg later than most of the atmo units. In the case of the 16v Integrale which had some 15psi gauge boost you get 105 deg.

See the picture? You open the ex cam way later than for an atmo unit and thus get more power - free!

Can you put an atmo cam in and just dial it in to open later? Yes, but of course owing to the duration of atmo cams it will close later as well and have measurably more lift at TDC (in the overlap phase) than usual. Anything wrong with that? Yes and no!

This subject is very poorly understood by most and esp by a certain firm who claim to be experts on cams (they aren't) with a company name based on a well-known small furry household pet with four legs and sharp teeth. Not a company I have any time for to be honest. A firm eg who sell atmo design cams as ex cams for turbo units (because they can get away with it) and just tell the buyers to time them in at weird settings to reduce the lift at TDC, which is of course a really critical thing with high-back-pressure. The first time I saw this I really fell off my chair and told the client too. I'm an agent for Kent and Piper and they would NEVER do that. Not good. Really not good.

If you use an atmo cam and open it later so as to achieve FL at anything betw 107 and 105 deg (or even less..) you will extend the overlap by the crank degrees you retarded the cam. Result? Blow-down. As it's called. Massive cylinder purging by the incoming charge, very pure mixture left in the cylinder when the ex cam closes. More power than with less overlap? Potentially yes. Clean charge burns quicker. Downside? Works better the faster you - exactly as with an atmo unit with competition cams - and wasted gasoline blown down the exhaust system.

Can you use a std VX ex cam with the GC 3A cam? Categorically YES. I had first hand results on this near 14 years ago when German client Dieter Enkler tried it. Dieter was a qualified and approved motor vehicle engine, which is a thing in Germany, he was no fool. He reported that his Lancia VX with a GC 45 DCOE conversion was faster than his 8v Integrale up to 110mph.

What is the limit for the VX ex cam? The answer is rather more involved, special design maybe needed really, not just a re-timed atmo cam.

Perhaps you can have a read of this and we can continue another day. As I said, I have been rather unwell for a few days and should like to sign off at this juncture and hope that what I have said - and Charles too - is useful at this time. As for the carb I can help with a solution as usual but I would request some photos, as rules for GC Q&A do dictate.

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Guy Croft, owner

david bienvenu
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Re: Exh. camshaft for Volumex

Post by david bienvenu » Thu Oct 20, 2016 7:25 am

Thank you Gentlemen, hope your running at full throttle soon Guy. I shall read and re read your responses in days coming up.
And I'll look at my options to see what will work well. There are more expensive options I know, but finding a suitable cam , I hope, will be easier.
I'll get back to the forum when I've had time for some photo's, and seen what else is available.
Thank you again.

Regards
David Bienvenu
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david bienvenu
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Re: Exh. camshaft for Volumex

Post by david bienvenu » Sat Oct 29, 2016 7:42 am

Hi members.
I got some time to take some photo's for the story. Very sorry Guy if I've got the attachments wrong, haven't done the photo thing before.
The pistons are CP forged, I'm hoping get around the 7.5-1 comp. with them.
The downdraught carb. manifold is the one I'm thinking of using a 40 dcnf with,(fellow member Eric may recognise it and have some suggestions), but I'm not sure if the carb. orientation is correct for RWD.
The Ex. cams are, front to camera is Right to left ,1608 bc 66/26, STD VX , a very bad n/a cam that did actually work well in n/a race motor, but poorly made.
A locally produced built up cam Wade 137 Grind, .410" lift of 70/30 but only runs with valve clearance of .009" but very well made.
A locally produced built up cam Wade 132 Grind, .410" lift of 80/50 but only runs with valve clearance of .009" but very well made.This cam was excellent in a n/a race engine .

The Ex. cams are, rear to camera is left to right , 1608 bc 66/26, STD VX , a very bad n/a cam that did actually work well in n/a race motor, but poorly made.
A locally produced built up cam Wade 137 Grind, .410" lift of 70/30 but only runs with valve clearance of .009" but very well made.
A locally produced built up cam Wade 132 Grind, .410" lift of 80/50 but only runs with valve clearance of .009" but very well made.This cam was excellent in a n/a race engine .

Obviously the Wade 132 is out.But I need an ex. cam with gear drive. So I'm still looking.

Regards
David Bienvenu
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david bienvenu
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Re: Exh. camshaft for Volumex

Post by david bienvenu » Sat Oct 29, 2016 7:52 am

Sorry , having trouble posting photo's , say's it doesn't like my file names, or is there more to it. pic's are on my computer not public server??
Sorry a bit slow on this.

Regards
David Bienvenu
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david bienvenu
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Re: Exh. camshaft for Volumex

Post by david bienvenu » Sat Oct 29, 2016 10:13 pm

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