The V8 Owners Forum -

Ive got hold of some 4.6 rangerover heads in really clean condition for my 3.9 and was wandering if mgb hives block huggers flanges are big enough i.e, are the flanges the same internal size as the head ports?

Not sure about sizes but if you can help it you wan to stay away from the block huggers... Worth a lot of power!

what sort of power figure do they restrict at? its just space is tight.

On an otherwise standard engine, proper headers are worth 5 to 8% extra against standard manifolds, about 6 to 9% against badly made block huggers. Tune it a bit and you quickly get to 10 to 15% loss against proper matched headers get to an otherwise all out engine and probably 20 to 25% against a well set up set of headers may be more. There are different grades of block hugger but the best ones are only as good as standard 4:2:1 RR type mcast manifolds matched to the exhaust ports.
Mike

My engine is really only a mild 3.9, 9.35c/r, standard 4.6 heads, mild cam and offy/edelbrock and weber 500. I suppose i was looking for the 200bhp mark, do you think with mgb block huggers i would see this

Can't you put 2 X 2.5" holes in the inner wings on each side and run standard RR cast manifolds and RR style split down pipes and Y piece? you would see 200 to 210 ish then as opposed to 190 to 200 on block huggers.
Mike

just read this thread, i did this conversion a few years ago and can say that i tried every manifold set going sd1, p6 etc and i could only just get the mgv8 huggers to fit! other than that it would be a case of a set of custom headers! if you need any advice (if i can help) just let me know

Escort!!
If space is well tight, the blockhuggers will do a reasonable job.
But!!!!
Make sure you open up the exhaust diameter to the max straight after the down pipes. I know what you mean with tight space.
Best option would be to go to a 3" / 3.5" single system after the downpipes join.

I ran blockhuggers on my old 3500 in the MGB. These were a tad better than the stock cast manifolds and exhaust system. Then one day at the track I decided to remove the exhaust system and just leave the two down pipes open. This made a BIG difference. On open headers, the engine revved to max rpm much faster. So I chucked out the stock MGB V8 exhaust and made it a twin 2" system.
This was a big upgrade.

Since then I've chopped the engine to 4.6 and now run twin 3" headers.

As far as horespower potential is concerned. These manifolds will flow enough to make at least 260hp at the fly on a low CR 3500. I use nitrous on my engines. So I build the engines to use nitrous. My first nitrous engine was a 3500 8:1 CR lump whch was the factory engine for my MGB V8. I was using block huggers and a full 2" single exahust for my first dyno run a few years back.

Stock V8 was 134hp at the fly.
She made 187bhp at the fly with a full balance and new cam off gas. Then I stuck a 50hp shot of gas on and she made 257hp at the fly on blockhuggers with a single 2" exhaust system.

So I guess if you tune the nuts off the stock 3.9 without nitrous, the blockhuggers should be able to get you over the 200 hp mark.

I now have RV8 style manifolds on the 4.6 and she makes around 400hp with 200 of gas. If you can shoehorn the RV8 style manifolds into the engine bay, this would be worthwhile for future upgrade as you can chop the collectors back to 3" each side like I have!!

Thanks for the replys fellas, I think ive decided on what headers im going to use and it looks like they will be Headman headers. Ill just have to chop more bulkhead out! Its a small price to pay