HC?

[shpub]

simpo two said:

I'm still of the opinion that all 500s have the higher compression engine and that the 340/320 debate is an ECU thing - but then I'm quoting SH, and even he's not sure now!

No He's just looked it all up....

GRIFF 500 addendum to Grif 4.3 handbook. 10:1 compression ratio 500 engine
Griff 500 1995 handbook 10:1 compression ratio (HC engine)
Griff 500 1996 Handbook 10:1 compression ratio
Griff 500 1998 10:1 compression ratio no HC
Chimaera 1995 handbook 10:1 compression ratio HC version
Chimaera 1998 handbook 10:1 compression ratio

Definitely going for the cam definition. If you want an HC version, spend the £5 it cost for a 500HC plenum badge.

[HarryW]

Understood some of the very first 500's actualy ran with a cr of 11.5:1 .
Wouldn't beleive it myself but have seen one on a roling road trying to get its manners and pinking above 20deg of ignition advance sorted out , way too much for a road car using pump petrol IMHO.

Harry

[shpub]

Usually caused by the wrong head gaskets being fitted by someone after the car has left the factory to be honest. Highest CR I've seen was 13.5 to one. Wrong pistons without a suitable cutout in the top fitted. Wasn't a Griff though!

[HarryW]

The sceptic in me says that maybe some of these very early 5ltr engines with the high compression ratio, really did make the claimed power, albeit with octane booster etc. These were released to the press to get the performance figures, or was that the one with a slightly larger than 5ltr engine .
Either way I think 10.5:1 is as high a ratio as road engine on boggo petrol would comfortably go IMHO. When had mine rebuilt 'my requested' cr was one of the options, stuck just south of 10:1 for comfort

Harry

[mongoose]

shpub said:

If you want an HC version, spend the £5 it cost for a 500HC plenum badge.

and dont forget the 'special' lumpy ecu,oh and the hc spec page for the handbook. on a more serious note,whats the highest compression you can sensibly run on 98 octane fuel then?is it 10:1? i see rimmers sell 10.5:1 pistons for the rv8,albeit not in 5L bore size.what factors add up to set the limit for compression steve?

[shpub]

The 520 is running at 11.5 to 1. It needs a fully mapped ignition/injection to get the curve right and will overfuel if necessary to prevent detonation/pinking. This also means having twin fuel pumps to maintain a consistent pressure so that the mixture doesn't lean out which effectively means that cats are a bit of a no no... Then there is the need for cold air to help prevent pinking.

Even so, one piston was starting to go with detonation when the engine got rebuilt and and the eight 55mm throttle bodies added a few weeks ago. Part of the problem was that the injectors were borderline on fuel delivery. Been replaced with firehoses.

All in all... nothing that a wad of money can't overcome.

To be honest 10:1 is about right for a road car.

>> Edited by shpub on Sunday 18th January 10:59

[shpub]

HarryW said:

The sceptic in me says that maybe some of these very early 5ltr engines with the high compression ratio, really did make the claimed power, albeit with octane booster etc. These were released to the press to get the performance figures, or was that the one with a slightly larger than 5ltr engine . Either way I think 10.5:1 is as high a ratio as road engine on boggo petrol would comfortably go IMHO. When had mine rebuilt 'my requested' cr was one of the options, stuck just south of 10:1 for comfort Harry

Increasing the CR on its own would not give a big increase so I suspect that any of these hot engines were modded in other ways....

I think staying with the 10;1 is probably the right thing to do.

[DustyC]

shpub said:

On a Griff it is probably worth only a 5 minute argument and not the full half hour...

I think you better change that to half a week!