NEWTON

which comp ratio would be best to run big boost thanks

crazycage

about 9.1

Andy_R

iTrader: (3)

or 7.1

JamboRS

cant say,engine needs to be specced for what it requires,too much other things to consider,turbo,head,inlet exhaust all needs to be considered

crazycage

is yours 7.1 then mate ?? my new build is 8.8.1 ,what sort of power you going for? i want 330-360 .

juffer

i'd say 7.4:1 thats what my engin builder said

AustenW

7.2:1

NEWTON

ive got rods and pistons from the states,that give 9-1 ratio with a 48cc zetec head,thought that might be a little high? i was thinking more the lower 8,,,,8-2:1example

rstdave

iTrader: (3)

Another open ended argument that's bin done a few times on here.....different people seem to use various c/r's and get good results.....i'd take the advice of your tuner and who's gonna map the car....if they've got proven results go with what they suggest imo! Personally i'd go for nothin below 8:1....but that's just my opinion and that of the tuner i take advice from.

JamboRS

andys will be a tame 300@wheels,though i dont reckon it will stay there for long,power bug will kick in,dunno what the engines specced for,though i think its well higher than the 300 that andys will settle for

NEWTON

thats good advice ,nothing below 8-1,i dont want the car to drive like a pig off boost,ill be using the car a a fast road car and for a few track days

sas

I am running 9.1 to 1 in my Zetec turbo.

S.

NEWTON

why so high? what boost do you run on that comp? thanks

smitsturbo

7.3;1 is what mine will have...im told

sas

I am maybe getting carried away as I only have got upto 21psi and the thing is the fastest car I have ever driven. You have to run V-power fuel.

Last year my Zetec Turbo was 8.5:1 and in combination with its big turbo had a fair bit of lag, but now at 9.1:1 I have no lag and the car is very nice to drive.

Simon.

NEWTON

thanks sas,is your engine an st170 zetec?iam thinkin of a six speed box allso,you have any prices on the shafts and mounts to be made up?thanks again

Maki

The question would be what sort of a car you want to have?
Drivable car should have no les than 8.7:1 but if you want mad boost with big turbo, go as low as you can... the lower the CR the higher the boosts safe limit. You'll have the lag, but you'll have power that you will not handle when the turbo kickes in By the way with to low CR it is hard to start the engine. Thats' my opinion... 8.2:1 for me always as I like the power kick whick you don't feel so much with high CR cars and low boost. That's what they do to NA hondas ... high CR, low boost... 250 BHP and it pools all the time, but not as fun as our fords with that boost kick

NEWTON

thanks mate,i like to feel the boost kick in hard more fun like that

Andy_R

iTrader: (3)

I dont know where the misconception that low compression = lag comes from, its simply not the case at all. An engine built and spec'd correctly matched with a decent turbo and with propper mapping, will not result in a laggy drive.
I've driven more than just a few Turbocharged cars where the complression ratio's are well into the low 7's (and below) which were all far from laggy.

Maki

Good example is 1.6 CVH xr3i and 1.6 RS Turbo... Of the boost NA 1.6 is more responsive and thats got to do mostly with the CR

P.S. people should start knowing, that thing which we like to call "lag" should be called "spool up time".... in real theory "lag" is the time between shifts and not the time before turbo kicks in from the start that is called "spool up time"

Andy_R

iTrader: (3)

Im sure if modern day engine managment were added to the RS Turbo then the outcome would be somewhat different.

Maki

The same thing's could be done to those NA 1.6 engines, so... it's just the comparition

NEWTON

thaks everyone

JesseT

Also, I can't think where the misconception of "big turbo need low CR" comes from as it's just the opposite. It's the restrictive exhaust housing that creates much of the detonation problems for high CR engines.
There are loads of turboed 16V engines running CR from 9-10 with 2bar boost and silly power with turbos like Holset HX50 fitted.

Maki

I know none maybe WRC focus, but we don't have that king of money I guess... I street life there is simple rule. low CR - high boost, high CR - low boost.... and for high CR/low boos't car you don't need huge turbo, but I dont know why are they using them, maybe for show off "look at me I have BIG turbo" or maybe for that reoson you've mentioned, restrictive housings... I can't say. In my region all the big boost and power cars have so low CR's that for starting they need additional injectors and so on...

rstdave

iTrader: (3)

Think there's more cars runnin big power/high comp than u think.....there are some jap cars, evo's definately that i know of running c/r in the 9's and over 700bhp so it's possible. Low comp is tried and tested obviously but more people are managing to get the power with higher c/r's now. As for high comp and big turbo's...that's the whole point, means you can get power without havin to run mega boost, don't know what the obseesion with massive boost is, if u can get the power running lower boost it's gotta be better...lower temps and strain on everythin etc. The low comp versus high comp is always goin to be argued either way but high comp/ big power can definately work if specced correctly!

Maki

We talked about it ... simply no fun with no boost kick fuck jap crap

Red16

lag is the time it takes to make positive boost pressure... whereas boost threshold is the time it takes to get from just masking positive boost pressure to actually making full boost.

Maki

We read different books

Big Will_

I haven't cc'd mine yet but theoretically mine should be low to mid 8's and i'm aiming for 450-500bhp

JamboRS

i thought lag was the time from positive boost pressure to full boost,boost threshold is the time it takes for the turbo to spin up,as in off boost comin onto positive boost

no?

wul young

totally agree andy,mines is 7.5.1,spect to run 28psi,and 1 thing is for sure,my car has no lag whatsoever,thats with t34,andy and several other people who have been in my car will verify this,as said proper management, mapping,ignition advance etc play a vital roll between lagy and not.

rstdave

iTrader: (3)

Guess it depends what u want out of your car......if fun's havin a car that's laggy as a peach off boost then lightin em up everywhere when it finally makes boost then fair enough! If it's a quick point to point car then linear power's what you want really....as for jap crap, agree it's not what i'm into either but there's no arguing their methods make for some fuckin quick motors!!

Maki

Then you should stay NA... plenty of cars with big power enough to spin wheels on dry, so why going turbo way at all in FWD car?

rstdave

iTrader: (3)

Should i now lol......what because i don't want some lag monster with a massive boost spike that just lights up the tyres??!! Don't know what the fascination with spinning the wheels is...plenty of big power turbo fwd cars that put in some very impressive times without doing so....and funnily enough they're the ones that manage to avoid having massive boost/torque spikes!! I've got an rst so obviously have nothin against turbo and fwd...think you're totally missing the point....that they can be made to go quickly without just lightin up the tyres!