The V8 Owners Forum -

bonnet bulges have gone. I'm using a fibreglass MGC replica bonnet.

Inner wings have pretty much all been removed, with strengthening bars instead. No pics of exhaust yet - but they're huge side exit monsters!

Just acquired a bunch of spanky parts for my next engine build; Group A conrods, Cosworth forged pistons, Group A adjustable rockers and some custom rocker covers

Ollie

Which Cosworth pistons are they as I couldn't find anything suitable when I last looked,

What bore size, small end/gudgeon pin size and compression height?

Would love to know, and how much are they?

Kevin.

Hi Kevin,

The pistons that I have are 3.5l bore, with standard 3.5 grudgeon pins as they are currently on some standard rods. I only have 7 of them though so I'm gonna get in touch with cosworth and see if I can get an 8th one to match, but for the price I paid it would have been stupid not to they we're practically free. The part number is PA0470/1 and I believe they are about 8:1 comp ratio. I've got another set of high comp ones that came with the group a rods I have just got, part number PA0753/1, which I have for sale in the classifieds as they're to high a comp ratio for me and the guy wanted to sell them as a set with the rods.

The low comp ones have standard grudgeon pins, but the high comp ones have floating pins with cir-clips. I already have a newly balanced crank, so I'm just a piston short of the rotating assembly, planning on building a super strong 3.5l and whacking a hell of a lot more boost through than the 5-6psi I'm running in the 3.9 I have at the moment. Have a small matter of a block to buy tho first!

Thanks Ollie, I thought they were for the 3.9 large bore block as when I was looking for a full flat piston top for my new engine I could not find any without having them specialy made which would have been cost prohibitive.

The nearest I could get was a set of Keith Black Hypereutectic cast pistons with 5cc cutouts which I got from Summit in the states for only £180.00 ! They also do a dished piston which would give a lower compression ratio with a bore size of 94.89mm so you need to have the block bored and honed and you need a set of Chevy con rods at £250.00 to match the larger gudgeon pin.

Hopefully my new 4.35 engine is going into the car in the next few days.

Kevin.

I got mixed up, the floating pins dont have cir-clips in them

Floating pins shoulds have circlips or they they will move and contact the bores. The small ends should also be bushed.

Kevin.

Well I'm well confused now. Looking at the low comp pistons, they have standard rods and use circlips - the pistons even have a little grove in them for the clips.

The high comp ones don't have circlips or any groove for them, and using the group A rods, the grudgeons do move a bit but seem well secure?

All the rods are bushed, yeah.

I believe you then need teflon buttons at either end of the pin

The teflon stuff will not score the bore if / when the pin moves

Ian

Just spoke to a bloke at Cosworth, not looking good for finding a replacement piston . . .

If you are using standard rods which have interference fit pin, then no circlips should be used.

If the rod is bushed for a floating pin, then circlips or buttons must be used.

Ok some updated pics;

Trigger wheel and VR sensor


Nearside turbo;


Home made battery box, mounted to original MGB battery access plate;


Engine bay mock up, without intercooler/turbo pipes (not ordered them yet!);


Inside boot (old photo);

Tight squeeze !!!!....but stronger crank sensor bracket required. That will vibrate.

you're telling me mate! I've changed the position of a few thinsg at the front since the lat photos, namely the oil breather and oil filter. And that's not including the 6 pieces of pipework and custom plenum!

Bracket was made from 3mm alu, I've got some 4mm mild steel that should be ok then, will use the alu bracket as a template. Took me over an hour to make that and get it in position right! Typical

god i gota get my arse in gear and do something about turboing my ole gal.

nice install mate,