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MG MGB GT V8 Factory Originals Technical - Rover V8 Output

I have a restored 1970 gloss black 911 Porsche waiting for an alum V8. I was looking at the 1963 Buick 215, but Rover has the better block and crank setup.

I think the 4.2 & 4.6 with the 1964 heads will be a good start, I am planning on buying a complete valve train from one source, hopefully that will solve any of those problems. Crane looks it has the best valve train combo I have seen so far.

The Porsche will have an interesting look, I am putting a set of fully polished 16' Fuchs alloys on it, but the centers be powdercoated a clear gunmetal grey. 215/45ZR16

I am trying to get approx 250hp/tq under 5,500. I spent the extra $ and have a 930 4 speed trans so the gearing is ok (the old 5 speed gears are too steep).

1st Question: Anyone know how much horse power? and torque?

The 4.2 or 4.6 with an Edelbrock 600 cfm, Performer intake, mild port and polish. About 10:1 comp. GM High Energy Ignition (HEI), A Crane cam with something like 218 intake/226 ext >>@.050<<, and .455/.465 lift. And a header 2 5/8 or 2 1/2. ????

2nd Ques: If I did go with a 3.9, how much less horse power and torque could I expect?

3rd Question: How come I cannot locate any Euro cam dealer/parts sellers that rate their cams @.050?

If they don't state the '@.050' the duration very inaccurate. I is common for the US HiPo dealers to have the @.050 cam specs so you know what you are buying! The difference from advertised and @.050 can be huge.


1. Dont use the old heads, they are far inferior to the later ones in valve size and porting design.
2. TRW do valve train components - or at leat they did about 15 years ago when I built my first V8GT.
3. I recommend the 3.9. It revs better than the bigger engines and you dont need them.
My 3.9 V8 GT was showing 215 hp at the wheels on a reputable rolling road with only a couple of thousand miles under the belt. It has a 600 double pumper Holley, Lumenition ignition, Piper 270 style cam, very well modified head (which is where the power really comes from) 9.75:1 and tubulay manifolds.
I think the exhaust sytem is 2 1/2 inc od. 215 at the wheels is easily 250 at the flywheel.
4.My 3.5 raodster gives 210 hp at the flywheel at 5300 rpm and about 225- 230 lbft at around 4300 rpm -
just for comparison.
5. Talk to Piper cams - their 270 grind will suit you. Crane have a similar one as do RPI engineering in the UK.
Good Luck
bob p

Thanks and I'm looking for more responses! More motor combinations with HP & TQ readings.

98 4.6L carb engine w/ "stage 3" RPI heads, home made full length headers(25 inch 1 3/4 primaries, 2 1/8 exhaust) , Carter Competition AFB(same as Edelbrock) -about 650 cfm, lightened flywheel, balanced,ugly cold air induction,elec. ignition, 295 deg. piper cam?(don't remember specs), raised compression ratio...that's all I can remember off the top of my head. I believe RPI represents their stage 3 engines at about 265 Hp and just over 300 ft-lb. I believe mine should make just shy of 300 hp maybe 315 ft-lb toqrue.

If you need a CNC adaptor and flywheel to mate to the Porche box, Goforth Engineering has them on the shelf for about $380US. He is located in El Dorado Hills. He also has very rare prototype Bucik engines, OHC cammer engines... 300 heads... FYI. If you need his number e-mail me off list.
Curtis Hunter

My first buy looks like a good set of heads, some have said the alum heads off of the steel blocked 1964 Buick flow better, some say the 3.9 flow better, Joaquin, Texas chose to open up his 4.6 heads....

With a good port and polish of the intake and exhuast runners (ports)....Which heads flow the best? Has anyone seen flow tests?????

The Porsche provides plenty of room so I am of course LOOKING FOR a good used set of stainless steel full length headers 1 5/8 primaries.

I am also LOOKING FOR a good used Edelbrock Performer intake and a new or almost new Edelbrock 600.


There is far more to this than a few line her can answer, however the basics are that the 3.9 is the sweetest unit as it retains the 71mm stroke of the crank. All larger standard engine suse the same bore size of 94mm but with longer throw cranks.

There is another issue to consider and this is the actual design capacity of the heads in respect to the displacement of the engine. This means that you will have far more work to do to stand still the larger the displacement. Torque will rise in proportion to the rise in displacement but the peak power will not rise bay anything like the same proportion. In addition the effective rev range will reduce so where you have a stock 3.9 peaking at about 4800 with a Range Rover profile camshaft the same engine taken to 4.6 will peak about 4 to 500 rpm lower.

The effect of the greater displacement in the Rover engine is for a stump pulling engine which is ideal for the Range Rover type of vehicle but not for the sharp and crisp responses associated with a sports car.

The reason I said you have to do more work to stand still is because the power peak drops proportionate to the rise in capacity. So a very good porting job on a 3.9 will create a real storming engine with very significant increases in power and torque from idel upwards. The same heads on a 4.6 will give more low down power but the mid to upper rev improvments will be far less so the character of the engine will be somewhat starined when compared to the 3.9 which will actively want to respond and beg to be driven.

In terms of the head choice I have no experience with the US made units, but I have done some extensive development with Peter Burgess using the pre and post SD1 series of Rover castings. I have the results on my own 3.6 (slight overbore) V8 which on a standard cam standard size valves and Federal injection made 190bhp at the wheels at 4900 rpm with over 220lbs ft of torque from around 1400 to 5700 rpm(approx) The heads actaull flowing 36% more air than the standard pre SD1 heads and from memory 22% more than the SD1 type. Even the Vitesse with mods that were specifically aimed at high end flow improvements were some 12% behind.

These tests were done in the mid 1980's. Since then things haven't stood still and other specs have been developed. One TR7V8 which featured a 3.9 with standard single throttle injection system was delivering a rock steady 265bhp at the hweels the first season it was out and the car would take 5th gear full throttle from 1000rpm (Crane 248 cam). It went on to win the Cox and Bucles TR National championship three years in succession and ended up with well over 320 bhp at the wheels, but with a little loss of low speed tractability.

I recall driving this car on a test track (an old V Bomber runway) and being able to pootle along as per a normal road car, then floor the throttle and find within a mile and a bit the engine was on the limiter at 6750rpm in 5th gear at a true speed of just over 165mph. This car suffered from restricted tyre choice and size (Series regulations) but achieved a 0 to 60 time in a repeated time of just over 4 secs and then reached 100mph is 8. Wheelspin at just under a ton when changing gear is interesting.

I have digressed somewhat but the base line is that once over 3.9 litre it is torque which is the big gain, peak power is not that different for like spec engines. The bigger engines are less smooth and have a more lethargic character and their power bands peak much earlier. Hotter cams and other tuning mods don't then compensate for this as the ultimate breathign capacity of the heads becomes the restricting factor. (Unless you use forced induction!)

Roger Parker

Anyone interested in a 4bbl intake manifold from a '63 Oldsmobile 215 (part no. 581830x stamped on top)? I have one from a previous life as an MGB owner, yet sold the car years ago.

Email me at


Had my newly rebuilt (december '99) engine dyno'd yesterday. It produced 217HP at the wheels@4600rpm and 275ftlb of torque at about 2500rpm (the trace started lower, it produces about this number from 2000-3500rpm).

The engine is a Leyland P76 V8 bored out to 5 liters using range rover 3.9 pistons and new liners.

The heads have standard sized valves (same as pre-SD1 Rover) with a 30 degree backcut on the valves and some mild bowl blending.

There is a fast road cam fitted along with a single plane inlet manifold. SD1 exhaust manifolds are used with a single 2.5" system.

The engine runs on dedicated LPG (propane).

Simon Sparrow

Good power and the effect of the cam is seen in the peak power rpm being raised to 4600. On a softer standard cam this would be probably 300 or so rpm lower.

Roger Parker

This question is for Joaquin, texas
In you comments from April 10th you mention "electronic ignition"
Could you provide me with more information on what parts you used or how this was hooked up.
I also have a 4.6 with a flex plate and have not figured out how I will hook that up to the manual gearbox.

I was a little vague in my description.I have a flyweel with standard BW 5 speed and front timing timing cover from my 215. I have a Mallory Unilite electronic ignition. It uses a shutter wheel and an optically operated control module that directly operates the coil. You should use a ballast coil, as the module is powered by ignition side of coil. Shutter wheel is very accurate(but cheap plastic) and I don't get the points bounce problem I had, allowing higher revs. Price about $130-150 US, if I remember correctly. If you have fuel injection or don't have a distributor( or a place for it to go) plan on using a direct ignition system. I believe you can use the stock crank sensor to signal an aftermarket ignition control device (MSD for example), if not you'll need an aftermarket crank sensor. There are various models and makes available and can usually accomidate various input signals, (points, pick-up coil, crank sensor signals, control modules etc., ) and can also control rev limiting, and timing, and other related. They can, however, get expensive.

Hi Guy,
my English is not as good as my German (I am a German guy) but I hope you will understand my information.
Last year I bought at RPI Engineering in Great Britain a 4.6 Rover engine with the following specifications:
285 cam, Weber 500 cfm, Stage 3 heads, more compression, lightened flywheel, Offenhauser Manifold and K&N for enough breath for engine. This engine have a little bit more than 400 Nm torque and 280 bhp.
This engine is in a MG B GT 1967. The MG is running like pressed air.
I never give up this 4.6 engine.
With a 4.6 engine you have more options to get more power than with an 3.9 engine.
Homepage from RPI with some informations:

Regards from Germany
Juergen Guther

Thanks Joaquin for your response.
Your right I have a 4.6 fuel injection engine without a place for the distributor. I am also missing the wiring harness and sensors. Looks like my next stop will be the MSD catalogue to see what can be adapted.

It appears I will be buying a 1999 4.6. Long block without the front cover, and ignition components. What are my options? With the 4.6 accept buick front covers AND the dist drive parts?

Andre, Yes.
Joaquin Lopez

This thread was discussed between 07/04/2000 and 27/04/2000

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