Thread: Why such low compression?

Something in the back of m mind tells me it was to do with the head design. I think some TVR's were running up to 10.5:1. There was something somewhere about some E85 Heads that enabled you to up the compression considerably.

My 4.6 Rangie is running 9.55:1 on GEMS EMS but i only use 98RON Fuel.

longevity and the vehicles always maintained the ability to be used anywhere with 3rd rate fuels (well up till the later 3.9s anyway)

if you want to keep them in pulp you can push 12:1+ out of them, same as the japs

the minimum mine could be is 9.7,,
and I asked for a good slice off the heads as well to try and get me to 10-1

Back in the early 70's the Rover 3500S manual sedan had 10.5:1CR and went like the clappers. Later on emission control tightened and I suspect nitrous oxide emissions would have been way too high. With the advent of better engine management (Thor) the last few engines could get away with higher compressions. Then the end of the RV8 came and multivalve engines now rule the roost. I doubt if any of the tweaked LRV8's running around would pass a stringent emissions test.

As far as i know it is head design.I once had a classic rr 3.5 efi rebuilt and had 9.1 compression pistons,as high as you could go on standard unleaded.Europe had 3.5,3.9 and 4.2 high compression engines but they had to run on premium.Dont forget these are basically very old designs.

My '98 D1 has a 9.35:1 high compression 3.9 in it, which is the original motor.

It seems that it is a rarity, as bee utey says he's never seen one. Not sure how it ended up with a HC, maybe just because of it being one of the last off the line.....?

Originally Posted by bee utey

Later on emission control tightened and I suspect nitrous oxide emissions would have been way too high.

I'm guessing ADR27a did this to a lot of petrol powered cars in the late seventies/early eighties.
I remember Holden CR's were pretty low across the board.

NOx is what killed off the TD42T in the Patrol here too.
The intercooled version gave the old banger a few years reprieve (no more grunt stock, just cooler combustion temps = better NOx numbers) but as the Department for Heritage and the Environment here tightened diesel emission regs Nisssan couldn't do anymore with the old IDI engine.

my previous 83 "in vogue" RR had 9.35s from the factory and was more economical compared to the 8.13 engine i replaced it with, my fathers early sd1 had 10.5s from the factory and went like the shower of **** and was very economical to