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MG MGB GT V8 Factory Originals Technical - Which camshaft?

Hi all,

I have recently been investigating the necessary replacement of the cam in my 1973 factory V8.

I received a quote from my local garage to replace the cam, lifters, timing chain, etc... and also service the carbs (factory standard). They have quoted for 16 hours labour to carry out the work.

I have also spoken to RPI Engineering, and they have recommended I fit a Piper RP4 or Piper 270/2 camshaft [ More info at http://www.rpiv8.com/engine-6a.htm ]

Does anyone have any experience of running with these components in an original MG engine?

RPI additionally suggested I pay attention to the oil pump, and modify the carb needles(?).

My aim is to lay the ground work for future improvement (handling, brakes, perhaps a 3.9 upgrade), without going so far as to need immediate attention be paid to brakes, handling, and other areas.

Should I be immediately replacing/modifying anything else with this aim in mind, and as a result of these changes?

Thanks in advance,
Guy
Guy Harper

no way it takes 16hrs to swap camshafts and rebuild the carbs..... Unless they remove and replace the camshaft bearings.

remove radiator, remove necessary front engine stuff, remove valve covers, loosen or remove rocker arms, remove pushrods noting where they go and which end goes down, remove intake, remove lifters, remove timing chain assembly, remove camshaft.
Maybe 4 or 5hrs work.
James D.

I think the James forgot that the factory service instructions say that the engine has to be lifted to get the cam out of the front of the engine. And if the garage has done the job before then they will know that you can never get the front cover out without breaking the sump gasket.

I would NOT fit an uprated cam to the engine if your going to change to a 3.9 later, save your money for later!. To improve the 3.5 sensibly I would raise the compression and improve the breathing before changing the cam IMHO.

Real Steel in Uxbridge used to do standard cam replacement kit - cam, lifters, timing chain, gaskets and seals - for the cost of a piper cam. Call 01895 440505 and see if they still do it. They have also had new SD1 type front covers which will give you an oil pump the same as the upgrade plate kits and a proper lip seal on the front pulley.

Check back through the list archives for more suggestions on power upgrades.

Dave
Dave Brooke

Dave, you mention raising compression as an option to a new cam. What are some ways of raising the compression? I have a 3.5 SD1 engine with fairly low miles on it. 8.13:1 from factory
Dana

Dave, I don't know, the stock cam leaves a lot on the table. I put in an Erson with .478" lift both in. & exh., setup 31/81/73/39, on a 4.2L Rover. That's a fairly wild profile for this motor. Bottom end unchanged, midrange and top end much, much more spirited. I agree with folks who say, don't do anything to compromise the bottom end on the Rover ... it's got such fat, torquey performance ... but you can go up quite a ways cam-wise before this becomes a factor. Running 9.75 comp. Put in the bigger Vitesse valves ... I know this is somewhat controversial. Also bigger springs. (BTW I have no special tools and I could have done the swap four times in 16 hours, and consumed many beers to boot!)

Dana, you can deck the block and/or the heads. But on a V engine there is a very distinct limit to how much you can take off before you run into problems with inlet manifold fit. I forget what the exact limit is. You can also put in different pistons ... probably the best way to do it.
Bob

If I wasn't so busy I'd do it for you at half the cost!

I would recommend the standard 3.9 cam with new lifters and a roller chain conversion in place of the factory standard chain. Real Steel are a good source for the parts.

Seriously, before doing anything talk to Clive Wheatley on 01902 330489, what he doesn't know about these engines isn't worth knowing.
chris

Thanks for replies so far.... a question:

Dave Brooke wrote:
>I would NOT fit an uprated cam to the engine if your going to change to a 3.9 later,
>save your money for later!.

I asked both my sources about whether uprating the cam at this stage would be negated by later modification - both said no, if I consider a 3.9 upgrade at some point, then the work for that concerns heads and pistons - no change to cam. So why not fit one now?

Cheers!
Guy Harper

Guy,

I was thinking of the cost difference between the standard cam and an uprated one - I think you would be better off saving the pennies. AFAIK the standard factory cam in 3.5 and 3.9 applications has a single profile whose timing has been moved backwards and forwards in 2 degree increments for different applications, Chris, Roger Parker and John Eales know far more about this!

Converting a 3.5 to 3.9 is possible - new cylinder lines and pistons, machining costs etc .

A new 3.9 short engine is comparable in cost (secondhand units will be cheaper) and has a number of design impovements to make it stronger and stiffer.

The difference between the factory V8 @ 138 bhp and the SD1 @ 155 bhp is more compression (8.13 against 9.35 in the SD1) and better cylinder heads, inlet and exhaust manifolds. Roger Parker's EFI equiped roadster achieved even better power outputs because it can breath well.

If you have invested in better heads before doing the capacity increase then just buy a short engine and transfer the heads. Transfering the cam from one engine to another is usually a false economy.

Before you buy a performance cam or 'flowed' heads ask the vendor to show you results of comparative dynonometer/rollingroad tests. Ask yourself how do I really drive? can you enjoy a car with peak power at 6000 rpm and no power below 3000, alright thats extreme but I hope you see what I mean.

Regards,

Dave
Dave Brooke

Dave,

It seems you are proposing that a 3.9 upgrade would be best done by replacing the engine? In which case, your point re: std cam makes more sense.

I'm not sure I want to go down this route though, so I was looking to achieve more from the original unit, but allowing for a possible 3.9 upgrade (to the original unit) if I have the resource in the future.

>Roger Parker's EFI equiped roadster achieved even better power outputs because it can breath well.

My car has tubular manifolds, and K&N filters - would more breathing mods be on the cards?

>Ask yourself how do I really drive? can you enjoy a car with peak power at 6000 rpm and no power
>below 3000

From speaking to RPI, they suggest that a Piper RP4 or 270/2 are the more 'usable' piper cams, both emphasising low end torque..... this is what I'm after.

Unfortunately, I don't have unlimited funds to throw at the car...... I seek a modest increase in power, without spending a fortune. The extra cost of a piper cam (
Guy

Guy,

Yes, personally I do advocate the engine swap root, but your circumstances/obvectives will be different to mine.

I don't know what people are currently quoting for converting a 3.5 to 3.9 by relinering it. Rimmer Brothers sell liners and pistons at 300, then there is the cost of removing the old liners and fitting the new ones - plus fitting the pistons to the conrods for which you need the appropriate press and jig. They don't currently list the 3.9 short engine and my web connection to RPI is very slow today.........1150+vat

It is possible that its economic to do if you reuse all the other components from the 3.5, but a new 3.9 will have the latest spec conrods and should be crossbolted - plus a new crank and bearings. AFAIK the crossbolting is not essential even on a race engine, but I haven't had any sump gasket problems with my 3.9 like I had with the 3.5 it replaced.

If you want a secondhand SD1 spec short engine mail me direct, I have a surplus one.

Which tubular manifolds do you have, RV8 or close to block? Do the ports on inlet and exhaust manifolds match the ports in the heads?

I could go on ( I told I often do... :-)

Unlimited funds would be great, the new MG-Rover V8 with 375 bhp or a BMW 4 litre V8 would go well.

Keep asking the questions! I'm sure there will be answers!

Dave
Dave Brooke

This thread was discussed between 19/04/2001 and 24/04/2001

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