What compression ratio?

dnb · Post by **dnb** » Sat Apr 14, 2007 9:57 pm

I have a choice with my 5 litre TVR engine.

Do I fit the composite or tin head gaskets.
One will give (the standard) 10:1 compression and the other will give just under to 11:1 compression.

The cam is as wild as you can go in a road engine and still maintain something that approaches road manners.

I have cutouts in the pistons, but I don't know yet if these are deep enough for the 11:1 option. (I will work this out tomorrow)

I will mainly run the engine on 95 RON fuel, as that's about all I can get on the Island. If required, booster is an option, but I'd prefer not to.

So, does 11:1 move the detonation threshold too low to make any power at 5 to 6k RPM?

Post by **katanaman** » Sat Apr 14, 2007 10:04 pm

you might get away with the 11:1 and the wild cam but its a gamble. What ignition are you running clockwork or ecu?

dnb · Post by **dnb** » Sat Apr 14, 2007 10:27 pm

Definitely ECU. I think I was the first Rover V8 with a V3 VEMS.
It's got knock detection capability, but this isn't really the answer.

Post by **katanaman** » Sat Apr 14, 2007 10:30 pm

yes Tony told me after I posted. No the Knock detection isn't the answer the better ignition control is though. Trouble is you might have to back it off to the point that you make no more or less power.

Post by **Coops** » Sat Apr 14, 2007 10:36 pm

dnb wrote:Definitely ECU. I think I was the first Rover V8 with a V3 VEMS.
It's got knock detection capability, but this isn't really the answer.

nah i think it was richard the first RV8 with vems v3 in new zealand

dnb · Post by **dnb** » Sat Apr 14, 2007 11:13 pm

Not sure if I would class his as an install - he reused too much of the Rover loom

I started in 2004, but didn't do much more than drawings & sums until 2005/2006.

dnb · Post by **dnb** » Sat Apr 14, 2007 11:15 pm

katanaman wrote:yes Tony told me after I posted. No the Knock detection isn't the answer the better ignition control is though. Trouble is you might have to back it off to the point that you make no more or less power.

Exactly the point.

I donbt it though - I was running a LOT of timing in the mid range and a fair amout at WOT with the standard TVR cam and 10:1 compression. (Still det limited though)

ali · Post by **ali** » Sun Apr 15, 2007 8:42 am

compression ratio is deterimined by how the cam so wilder the higher the ratio

ali · Post by **ali** » Sun Apr 15, 2007 8:46 am

ignore that last post, I Haven't woken up yet! What I meant to say is....... the more wild the cam the higher the compression ratio you should have.

ppyvabw · Post by **ppyvabw** » Sun Apr 15, 2007 10:55 am

dnb, you can get an additive called tetraboost. It isn't one of these rubbish things you can buy in garages, it's tetra-ethyl lead, the thing that leaded petrol has that unleaded hasn't. You can make up to 5 star fuel. I think it adds about 11p to a litre for 4 star. Dont know if this will help if you go to 11:1.

dnb · Post by **dnb** » Sun Apr 15, 2007 11:06 am

I thought the lead additive would kill the oxygen sensors, so this isn't ideal for this car as my ECU relies heavily on these sensors.

I have used Nitrous Forumla (based on toluene) in the past which works quite well for not killing modern sensors.

TBH I don't really want the bother of boosters if I can get away with it.

HairbearTE · Post by **HairbearTE** » Sun Apr 15, 2007 12:36 pm

dnb what are your cam specs?

ian.stewart · Post by **ian.stewart** » Sun Apr 15, 2007 1:30 pm

I am running 11.5+-1 on the street, I mostly use ultramax, but the engine will cope with 97ron fuel

dnb · Post by **dnb** » Sun Apr 15, 2007 6:33 pm

HairbearTE wrote:dnb what are your cam specs?

A V8 Developements H404. I don't have the numbers to hand.