compresion ratio

[wicksee]

Just worked out my compression ratio at 7:1 is it going to pull away

[Roosie]

my 3dr is 7:1 with GT35 bit laffargic until you get going.
if i would change it i would go high comp

[Wesley P.]

So I'm not the only in this day and age running a 7.1 engine... Mine wasn't by choice and I would have rather standard but it has to do for now. Still getting opinions on turbo choices, so far been told a T34/.48, or a GT2860rs, but I have also been looking at the GT3071r. My main requirement is good street response and somewhere around 350-400bhp.

[Cossie col]

There are so many different opinions now, some say 7.2 so ultra safe (less heat) some say standard compression rate improved driving of boost 8.1 but heat can be a problem unless maped correctly so bit of a minefield, so many different views

[cossiedavid]

mines 7.2.1 and the last four iv built have been to , just trying to convince cossie col to do the same but he ant having none of it

[Cossie col]

mines 7.2.1 and the last four iv built have been to , just trying to convince cossie col to do the same but he ant having none of it

Know what your saying mate as ultra safe and ain't going to melt it's just want more response of boost as steves evo just gets me on the roads round our waymore torque down low is what I needoh and driving lesons before you say it lol

[tommi]

Standard small turbo boosted to 280-300bhp is a great driver's car low down power great for the street.

[Sunnysidebb]

Anyone that posts too strong an argument against 7:1 or 7.1:1 has only read other posts and has no experience of a Low compression motor. It was the done thing years ago. Do you think we all just crawled about, dont think so. Don't listen to anyone who has not got experience of a low comp motor. Ask them what experience they have or tell them to shut up as bad info is worse than no info IMO. For clarification I dont mean anyone on here.
With a Low comp engine you use the gear box, thats what its there for. It is possible to tune out a lot of lag off boost. Its all in the tune.
Frank

[Paul RS]

As Frank says - lag = cog a lower gear That what i do on mine anyway which is a unknown comp ratio

[L8 ECU]

............it's just want more response of boost as steves evo just gets me on the roads round our way:cry........

Col, you MUST talk to Mark Shead about a twin-scrol turbo and matching manifold. Twin scroll will make a huge difference........much more difference than a 7.2:1 comp engine being compared to a 8.0:1.

As you have seen, EVO's spool up real quick - and they have twin scroll turbo/manifold as STANDARD.

[wicksee]

any ideas on what boost to run or what i can get away with at 7:1 ratio and what i should be running to run it in its going to be on standard management with blue injectors

[Wesley P.]

I was told that some of the response lost from lower compression can be recovered with additional ignition timing in the map, also the turbo choice should not be dependent on the compression ratio... although you can run more boost as a result of the lower compression. Kinda of a contradiction...

You will need a chip to run the lower compression regardless of injector or turbo choice, the differences in the maps from high to low is too dramatic, even to run it in.

[Sunnysidebb]

any ideas on what boost to run or what i can get away with at 7:1 ratio and what i should be running to run it in its going to be on standard management with blue injectors

power is not just about boost. Its in the tune. But with a 7.0:1 CR you have a bit of a safety margin. I had a 7.1 wrc head gasket, short studs, ported, Mountune cams, t35 hybrid, 2wd manifold and a Collins stage 4 chip . I ran 32 psi with no problems for over 7 years.

Remember its in the Tune. ie ignition timing and lambda and if you run it Knock control limits. So try and get away from the standard programme, its not going to be a very nice car to drive with standard. you need a low CR map/ Chip. Its the only way to enjoy a low CR engine.
frank

[Wesley P.]

My situation has an added concern; since I'm in the states it's impossible to have my setup live mapped so I must rely on a tuner there to write a map for me based on the info I provide, for this reason I'm trying to stick to similar setup someone else has already done and proven over there.

[cossiedavid]

sure harvey gibbs would do you a chip or even danny at ep you will need to give them the exact info on your engine