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MG MGB GT V8 Factory Originals Technical - Rover V8 inlet manifolds

Its becoming a bit of a habit. Every winter I get the spanners out and try and improve on what I have already.
Last year I fitted the 4.6 crank and rods with top hat liners and the previous year I fitted rear discs with twin master cylinders with bias control from the dash. The year before that I designed and made the adjustable rear anti roll bar. It goes on!

This year I have extensiveley ported the heads and am having the larger valves fitted with modified guides and dual springs etc.
The inlet manifold that I have been using is the JWR offenhouser which as well as being the lowest is also the most restrictive. You only have to look to see that it doesnt flow at all well.
I do a lot of track days, but also the car is fun on the road.
Now, Do I go for the Edelbrock performer manifold which seems to have good reviews, or go the next step with a Huffaker or The Wild cat spider manifold.
The Edelbrock is just under 200 and the wild cat is 280 but the Huffaker is no longer manufactured so second hand, they go for about 250. To complicate matters the Huffaker has no provision for a thermostat although stat housings are available.
I realise that the high rise single plain manifolds will loose a bit of low down torque but that is traded for more mid and top end.
The Performer is the best road manifold without doubt.
To overcome the bonnet/hood clearance problem, Im planning on cutting a hole in the fibreglass and let the filter protrude.
I really fancy the Wild Cat but would imagine they work best on high revving engines.
Any thoughts.

69 GT V8 4.6

Mark, I'm interested in having the heads ported and maybe flowed. I don't know much about these things yet but it seems to even my uneducated eyes that there is an awful lot spare metal around the manifolds. Does doing this really make a lot of difference to power?. Is it worth doing? Does porting the heads effect reliability at all. Also I was quoted the remarkable price of $1500 australian dollars for getting this done and this seemed a bit steep. I would have thought $500 would be more in the ball park, or am I dreaming?

I think in my case it will make a considerable difference.
On the rolling road the 4.0L engine made 197hp at the wheels and the 4.6 makes only 13hp more and thats with an uprated cam.
Im sure this is due to the standard heads inability to flow enough.
Luckily I was able to copy some stage 3 heads off a mates engine.
Porting and flowing is very time consuming, must have taken me 8hrs - 10hrs per head. I think I made a better job than the ones I coppied. To get maximum effect you will need bigger valves and bulleted and maybe shortened guides depending on which cam youve got.
The rolling road will reveal all, but not until next year.



I would go with the Huffaker, if you can find one. The Wildcat is most likely too much for the street. The Edelbrock may be a bit better than what you have now. I had a chance to do an eyeball comparison of the Edelbrock and a stock Buick 4bbl manifold. Looked like the same manifold with 1/2"-5/8" added to the top and the 4 holes carved out to two. I doubt that the Edelbrock is much better than the Buick. With a spacer, a Buick manifold could easily be turned into a Edelbrock. Even Edelbrock says 5500rpm & below. So, try the Huffaker. :)
Carl Floyd

You didn't say which heads you you had, ie 3.5/3.9 or 4.0/4.6 the later heads are more restrictive to flow and have smaller combustion chambers so there is more shrouding on the valves. If you used the earlier heads with standard 4.6 pistons your compression ratio may be far to low. Did you also relieve the valve spring seats because depending on the cam spec you could find that the lift will exceed the the amount of free movement of the valve spring with expensive resultsand also did you open up the valve throats as this yields one of the biggest improvements in flow. Just a thought for 250 or so you could probably pick up a hot wire EFI system off e-bay if you are patient and you could sell the carb and existing manifold to more than cover the cost of fitting the system.

Kevin Jackson
Kevin Jackson


Re the cost of a decent pair of heads, 1500 Aus Dollars is about right, Peter Burgess charges 595.00 for a pair of his econotune heads which on a 3.5 will yield about an extra 35BHP. Don't be put off by the name these are probably some of the best road heads around. When I did my heads we pretty much followed his spec but I don't suppose that mine will be as good,however with an Edelbrock/Weber 500 performer manifold, Real Steel Hurricane Cam, the mildly modded heads and RV8 exhaust, this spec has produced a pretty quick car for road use. The performer manifold definitely has better distribution and flow and really flies from 3000RPM and up and is still smooth and torquey from tickover and above.Haven't had it on a rolling road yet so there is probably a bit more to come and I would anticpate 200+ BHP.
Check out Peter Burgesses web site, if it is not showing at the top right of the page keep clicking the refresh button until it appears.

Kevin Jackson.
Kevin Jackson

Thanks Carl

I was using the 4.6 econotune heads by Peter Burgess.
The econotune has minimal work just behind the valve with standard valves and guides. Stage 3 heads are quite different.
Compression ratio is 10.5:1.
The machine work is being carried out by DJE near Coventry.
The seats will be recut to suit the larger valves. Spring seats machined to suit as well.
Prefer to stick with carb as its so easy to set up.
Would love to go for throttle bodies and mapable ECU but I fear the gains are not enough to justify the cost.



At the last British V8 meet there was a portable dyno. A friend's MGB with an Oldsmobile 215 was found to be putting 215HP to the rear wheels. The heads were well massaged, but he was still using the stock 4bbl intake manifold & block hugger headers.

I don't think the dyno was reading high, either. One of the Ford 302s was found to be making a good bit less HP than last year on the same dyno.
Carl Floyd

This thread was discussed between 01/12/2005 and 02/12/2005

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