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MG MGB GT V8 Factory Originals Technical - Head choices

I've been looking through the different books and posts and I am not sure what cylinder heads can be swapped engine to engine.I am just starting a 3.5 rebuild and was wondering if 4.0 heads with the smaller 27 CC combustion chambers could be used on the 3.5. I was thinking that with the steel gaskets I could raise CR if desired and/or I could go composite and not lose any CR. Any head advice or swap advice for that matter and what can or can't be interchanged between engines would be appreciated. I'm trying to get MGB V-8 "smart" and am reading everything I can so I can build a 78 MGB chrome bumper conversion. Thanks..Dave
DWM Makos

Dave,

Yes you can swap the 4.0 or 4.6 Heads (they are the same) on to a 3.5 block the only main differences are the 28cc combustion chambers and that they have 4 bolts per cylinder instead of 5 for the original heads, this is not a problem as the recommendation for the extra bolt is not to torque it up to the same spec as the others and just tighten them enough to stop them falling out!

What engine are you starting with and what was the original compression ratio, it's stamped on the block by the dipstick tube. If it's a SD1 high compression it will be 9.35/1 and a 20thou skim of the original heads will get that up to about 9.8/1 which is high enough for road use. Theres no big advantage swapping to the later heads thay have the same valve sizes as the SD1 and the small combustion chamber may shroud the valve more than the SD1 heads.

If the car is intended for road use I would recommend doing some simple and basic work to the SD1 heads (see Peter Burgess web site for his Econotune Heads)
which will yield an additional 30BHP and plus a mild cam and poss Edelbrock 500 Carb and performer manifold with RV8 exhast headers, will get you in the 210BHP area. I have exactly this spec and the car is very quick and drivable in heavy traffic.

If you have other uses in mind, let us know so we can advise.

Kevin.



Kevin Jackson

I think the North American Spec SD1,TR8 and Range Rover 3.5 liter engines were only 8.13:1 c/r. I used the stock North American SD1 block and cylinder heads, 10.25 c/r Buick pistons and composite gaskets to end up w/about 9.5-10 c/r.
Steve Mc

Kevin/Steve,
Thanks for the replies..The engine is a complete 3.5 that I removed
from a USA spec. 1988 Range Rover, not sure of the compression ratio. I plan
on reusing the pistons provided the original bore is within tolerance. I
bought a slightly "hotter" cam and new lifters and will install new main/cam
bearings(?). I'm hoping not to need a lot of maching as the motor
"supposedly" (according to the odometer) had 88,000 miles. I bought the 500
cfm Edelbrock and original buick intake manifold and will be installing the
RV8 exhaust manifolds. I found/bought a set of 4.0 heads on E-bay ($52) last
week that have been skimmed and pressure tested and thought they might help,
especially if the 3.5 is the low CR which I'm guessing it probably is...It
is going to be a road use car with a T-5 trans & HTOB & stock rear but I was
looking to "warm" the engine up a bit and 200+ BHP is exactly what I was
shooting for. I am preparing for a long New England winter :) and hope to
get the body squared-away as it has slight rust here/there. What did you use
for motor mounts ...Did you buy or make them ? From pictures I've seen they
didn't appear to be very sophisticated.. I'll look for the CR and
appreciated any "enlightenment" you can provide..Much Thanks..Dave

DWM Makos

Dave,

I used the Standard V8 mounts to put the engine in the stock position, as your car is a 78 it's virtually a bolt in and there are several suppliers of parts on your side of the pond. If you want to put the engine in stock location you will need an SD1 front cover and P6 front pulley and water pump or some Buick 215 parts can be used to achieve the same result.

Do a search for D&D fabrications and have a look at the British V8 newsletter a few posts down, which will give you both inspration and information by those who have done it.

Good luck and have fun.

Kevin.



Kevin Jackson


This has some brackets that look very much like mine
(form follows function)
http://www.britishv8.org/Articles/Rover-Hot-Wire-EFI.htm
As you can see, not hard to make. The 'angle' is the same as the angle on the body brackets. Where you drill the "mount to the motor" holes is up to you. I put the motor and gear box in the car (supported on trolly jacks etc, then marked where to drill the holes.
Or you can save some effort and just buy them off Glenn. About $60 the pair I think. His (and mine) set the motor both lower and farther back than usual.
You do need to replace your rubber mounts with the V8 variety. They look exactly the same as the ones you currently have, but are made of a high temperature rubber (so they claim)



Clive wheatly (he's on the net) sells the 'orrigional' MGB V8 brackets.
Some one told me recently that the brackets on the rover P6's and 5's (mid 70's Rovers) are the same as the MGB V8's, which I haven't checked out but it does make sense.
The alternator bracket is the same, and that's where i got mine from.



Peter Sherman

That should read early '70's rovers.
Peter Sherman

This thread was discussed between 08/10/2007 and 10/10/2007

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