Rocker arm ratio?

[mk1storm]

Hi, I'm new to this forum so hello to you all.

Over Christmas I stripped my RV8 down ready for inspection and rebuild. The engine came out of an old range rover but the engine number tells me it's an SD1 block, so I thought it was a 3.5l lump. That was until I measured the bore (93.5mm) and the journal sizes on the crank (the big end journal is a lot smaller than normal, yet it is a rover crankshaft) so with some reading up and searches on here I'm pretty sure it's an early JE Engineering 3.9+ conversion. I've not measured the throw yet but the bore increase alone makes it 3.9l.

Anyway, I'm now looking to work out what camshaft it has. I've got a table of cams with their various valve lift values, but I need to be able to translate this into lobe height. So what I'm missing is the 'gain' or ratio of the rocker arms. It's something like 2:1 but can't be sure.

Does anyone have this information?

Cheers,
Gary.

[sidecar]

Hi, I'm new to this forum so hello to you all.

Over Christmas I stripped my RV8 down ready for inspection and rebuild. The engine came out of an old range rover but the engine number tells me it's an SD1 block, so I thought it was a 3.5l lump. That was until I measured the bore (93.5mm) and the journal sizes on the crank (the big end journal is a lot smaller than normal, yet it is a rover crankshaft) so with some reading up and searches on here I'm pretty sure it's an early JE Engineering 3.9+ conversion. I've not measured the throw yet but the bore increase alone makes it 3.9l.

Anyway, I'm now looking to work out what camshaft it has. I've got a table of cams with their various valve lift values, but I need to be able to translate this into lobe height. So what I'm missing is the 'gain' or ratio of the rocker arms. It's something like 2:1 but can't be sure.

Does anyone have this information?

Cheers,
Gary.

Normal rockers are 1.6:1

[ian.stewart]

Now you have got me curious, I think my engine is a 3.9 built by JE, I will have to check the stamped numbers on my block, it has extra numbers on it, but it does not have normal engine numbers, all I have on the pad is comp ratio,
It could also be a TVR 3.9 or even a 4,2
Another thing, I would think it would have forged pistons as well, Probably Omegas

[katanaman]

My engine is a bored out 3.5 JE engine but its a later one with the proper 3.9 sized bore. It has normal sized mains and big ends as well and it has Omegas pistons. This day and age the block is nothing special but the heads are quite nice.

[mk1storm]

Yeah pistons are Omega's but they're still cast items.

I assume because I've got smaller big end journals (to get the larger stoke) that the conrods aren't standard rover items too but not identified that they actually are.

Cheers for the rocker arm info. Cam lobe height is 6.3mm so that would give me valve lift of around 10.1mm.... Seems a bit more than a standard cam but not exacly a high lift item....

I just hope I can still get 93.5mm piston rings and also the smaller big-end bearings. What's happened with JE Engineering now? I remember something about them going through some sort of split?

[katanaman]

There is a post about the pistons somewhere so have a search for it. I don't think the person found any at the time. You should be able to bore it out to standard though if you have to do anything.