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Moss Supercharger


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Make sure all the rotating parts are up to the extra strain on them, i.e. bottom end of the engine and all the UJ`s along with the cooling system. Check your compressions to ensure that it hasnt been raised too much by head skimming.

Stuart.

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Hello, welcome.

Compression ratio as Stuart says is very important - make certain it is within that specified by Moss.

Engine should be in good, sound condition. Must not have a high overlap cam - standard is great.

The one criticism I have of the kit is the air intake - its in the hottest underbonnet area- and Moss themselves suggest changing to a cold air intake.

I expect the instructions with the kit will stipulate the use of high ocrane fuel, 97RON or better.

 

I am unsure if the kit fits right hand drive cars - proximity of steering column and brake servo.

 

Peter

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The best upgrades start with handling and braking performance before "bolting on go faster/tuning" modifications. IMHO A well sorted car is much more pleasureable to drive rather than wrestling with more power and poor set up.

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A supercharged engine makes more power and torque at substantially lower rpm. Mine feels as if a couple of extra cylinders have been grafted on. It will easily pull a gear higher than normal. The engine smoothes out - thanks to the better mixture distribution and fuel vaporisation- the transformation from PI was remarkable. So a blower can be kinder to an engine than one that needs higher rpm and cam overlap to get to the same hp.

The down side is that detonation must be avoided. The Moss kit is rather conservative with max. boost so pistons should be safe, as long as the engine has the comp ration Moss recommend, the fuel they recommend and spark timing they recommend. ( the sales bumpf are not clear on these)

 

But it still helps to learn about supercharging essentials as more boost is always a temptation, and that M62 blower could get to 10-12psi quite easily with revised drive ratio! But then the compression must be lowered, and that hurts fuel economy.

Alan Allard "Turbocharging and Supercharging" is a good start. Out of print but often on Amazon.

 

I run 9-10psi on 250k bottom end that has not been reground, but is within spec - I just fitted new shells and thrusts. No balancing beyond factory. New pistons to go with the rebore. Standard camshaft is ideal. But suspension has been modified considerably, helping handling and braking.

 

 

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  • 1 month later...

Thanks for all of your advice, I've given the engine a thorough going over and all appears to be well.

 

Moss seems to talk about ensuring that the ignition system is upto scratch so rather than trusting an Old-Tech Dissy, would you advise going for something alittle more exotic like the 123ignition system? If so, what sort of retard/advance should I look at? I ask as they now offer a tunable option where the ignition can be mapped?

 

Any thoughts?

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Thanks for all of your advice, I've given the engine a thorough going over and all appears to be well.

 

Moss seems to talk about ensuring that the ignition system is upto scratch so rather than trusting an Old-Tech Dissy, would you advise going for something alittle more exotic like the 123ignition system? If so, what sort of retard/advance should I look at? I ask as they now offer a tunable option where the ignition can be mapped?

 

Any thoughts?

 

If your cylinder head has 9.5:1 compression and the Moss kit puts out max 6psi at 5000rpm then you will be OK with the standard curve*, providing you use 97RON petrol or better. Compressed mixture is said to take rather more spark to light it, but I use a standard coil and points OK. The 123 would offer the possibility of boost retard but Moss would have stipulated that if there was any risk of detonation.

 

 

A simple pair of tin ears is probably a good idea,

http://www.contactmagazine.com/Issue54/EngineBasics.html

 

Fit a wideband exhaust AFR sensor - better to have one of these than a new disy, going lean under boost is a piston killer.

And Allard's book. * Why? - Allard gives a rough rule of thumb that 3.7psi boost equals one ratio on the compression. Detonation risk is highest at ca 3000rpm where boost will be about 3.5-4 psi. So the effective compression there would be about 10.5, within the capability of the standard unshaved TR head. At higher rpm the risk drops off. A cold air intake can help reduce detonation risk too - better to fit a cold air supply to that air filter or reposition it.

 

Peter

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Many thanks Peter,

I've sent you a PM.

What about the merits of water injection? Do you think that it's worth looking at?

Its only used with extreme boosts where other ways of killing detonation have not succeeded.

No PM arrived yet...

Peter

Edited by Peter Cobbold
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The '250 came with a 8.5:1 c/r and narrow port spacing on the inlets. Head thickness originally 3.46".

 

Someone in Canada ( Morty on the 6-Pack forum ) has a s/c on his '250 with 9.5:1 c/r; the conversion was done after he'd modded the engine for normal aspiration ( guess he wasn't satisfied, but then he didn't go the Weber route ^_^ either ). I believe he's made some sort of water or alcohol injection rig to deal with detonation but haven't heard any raves about it - not a good sign :unsure: . There are some others with s/c on the same forum; might be worth plumbing it for all it's worth.

 

For what it's worth, I'm still waiting to hear a s/c success story like the ones Weber DCOE conversions have reliability-wise :huh: .

Edited by Tom Fremont
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The '250 came with a 8.5:1 c/r and narrow port spacing on the inlets. Head thickness originally 3.46".

 

Someone in Canada ( Morty on the 6-Pack forum ) has a s/c on his '250 with 9.5:1 c/r; the conversion was done after he'd modded the engine for normal aspiration ( guess he wasn't satisfied, but then he didn't go the Weber route ^_^ either ). I believe he's made some sort of water or alcohol injection rig to deal with detonation but haven't heard any raves about it - not a good sign :unsure: . There are some others with s/c on the same forum; might be worth plumbing it for all it's worth.

 

For what it's worth, I'm still waiting to hear a s/c success story like the ones Weber DCOE conversions have reliability-wise :huh: .

Interesting, 8.5:1 is what I use, with 9psi boost.

With 9.5:1 head 6psi will be safe, but its very easy to turn the blower faster ( if its an Eaton M62) to get more boost- that might be why he resorted to water injection. But boost retard should be used first, better still lower the boost until detonation is at bay rather than water injection.

Reliability wont be an issue with blowers if the rules are followed. Trouble is, its all too easy to change a pulley to get more boost.

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I'm more concerned with the solid damper than anything else.

Well that and it's a wet system.

Ymmv and all that...

 

The blower allows rpm to be kept substantially lower, for the same power. It will pull a gear taller than normal. The belt drives will provide some torsional 'cush'. Judging from the state of many original c/s dampers - including the ones I have - I wonder if they are doing the job the were designed to do, and as for aftermarket items....

What is the rpm range where torsional vibrations become a concern?

 

Running a wet blower is fine as far as the Eaton M62 goes. Wet is not feasible with screw-type compressors as the rotor-rotor clearances are too tight, but the Eaton is Roots type despite appearances. The 'wet' advantage comes in smashing the fuel droplets from the carb into a fine vapour resulting in a very equal mixture distribution and a very smooth running engine. An intercooler cant be used but they reduce the air density ratio below about 6psi boost, so there's no disadvantage for road driving.

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I don't know the failure mode of superchargers but I couldn't bear the thought of my engine eating its bits in the event :wacko: !

 

The original ROOTS factory is less than 100 miles from me in Connersville, Indiana. They were once a good customer of mine for their centrifugal blowers.

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Blowers disintegrating is a relic of pre-war and early post-war designs. For several decades until Ford/Eaton came along all we had were Roots type blowers designed for diesel engines. The Wade RO34 I run was built for a 1950s 2-stroke Commer diesel* and Allard gives dire warnings not to rev it over 4000rpm. So I dont! The ex-diesel 'Jimmys' widely used on USA drag racers were pushed waaaaaaay beyond their design limit- they are not a good advert for blowers, but are hardly representative of street machines.

The Eaton blowers are a totally new modern design fitted to Mercs, Jags etc. I might change to one, but only to get less heat not because the old Wade might expire. A decent set-up giving 8psi boost can give 50% more power reliably. Doing that with atmospheric induction means more rpm and a cammy engine. The blower gives more torque across the rev range, there's no waiting to come 'on cam'. I'd choose boost over revs any day.

 

 

* in action: the blower's finned casing is just behind the rad alongside the fan

 

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