Pre - SD1 (P6)V8 efficeny mods - what to expect?

[J1MMY]

Hi again folks

Now the bug has taken hold, I'm wanting to modernise and pep up the old lump a little. Considering - Holley 390cfi 4 barrel w/edelbock or similar manifold, electric igniton conversion to throw spark at the extra air. But what about fuelling? Should I be looking at a higher flowing pump?

Also, I'd like to get round to fitting unleaded heads - where, how much, etc?

What sort of (if any) gains over std will I see - both paper figures and real world? Anything to tie in with the above that I haven't thought of?

[ChrisJC]

I've seen somewhere a list of BHP figures for the various RV8's in their guises over the years. That would be a good place to start.

I can't remember where I've seen it though!

Chris.

[jefferybond]

Hi again folks

Now the bug has taken hold, I'm wanting to modernise and pep up the old lump a little. Considering - Holley 390cfi 4 barrel w/edelbock or similar manifold, electric igniton conversion to throw spark at the extra air. But what about fuelling? Should I be looking at a higher flowing pump?

Personally, i'd choose an edelbrock performer carb (weber 500) over the holley 390, but then I'm biased because I have one! From what i've heard, the weber/edelbrock carb is easier to set up and less fuss.

Also, I'd like to get round to fitting unleaded heads - where, how much, etc?

I think SD1 heads and later are all compatible with unleaded, and they come up quite often on ebay.

Jeff

[mgbv8]

Your standard pre sd1 P6 lump will have come off the shelf with about 135bhp at the flywheel if I remember correctly.

I had a pre sd1 in my factory MGB V8. An 8.35:1 CR lump

I fitted a weber 1404 500cfm carb.
Comp head gaskets
A Typhoon cam
Rhoades lifters
Cloyes cam chain set
RV8 style free flow exhaust manifolds (block huggers were too restrictive)
Had the lump bored +20 thou
I used the original heads with unleaded for 3 years with no trouble
And I fitted an auto box from a Camaro in my MGB.

I Dyno'd it last year and saw 187 at the flywheel.

I stuck a 50 shot of gas on and saw 257 at the fly, which gave me 202bhp at the rear wheels.

[mgbv8]

I forgot to mention, I fitted an edelbrock 360 low profile inlet manifold to take the Weber.

[steve b]

I believe only later SD1 heads are truly unleaded fuel compatible vitesse, discos and upwards,best ask ray at v8 developments, he sorted me a pair out, not easy to get hold of.

And I thought p6 's came with a cr of 10.5

Mine gave 170 at wheels with K&N's modified needles,early SD1 heads,p6 block,p5 manifolds and 2.5hrs on a rolling road.

steve

[mgbv8]

Steve
I think you are right about the CR of the P6 engine. Mine is a factory MGB V8 engine which is a wimpy version.

[dicky]

I have an old very early P5 engine which I think has 10.5:1 CR.

I am after a set of unleaded larger valve heads also.

I will be using comp gaskets so that should bring the CR down to about 9.8:1 iirc which is more tolroble on low octane fuel.

Either that, or stick with stock CR on tin gaskets and use a longer duration cam which will lower the effective compresion anyway.

[mgbv8]

I've been using 1975 Pre SD1 heads in my MGB for 4 years now with no ill effects from using unleaded with no additives.
And they do get some ragging with Nitrous as well.

I've been looking for big valve heads, but they seem to be quite expensive to buy?