~nomad~

iTrader: (4)

Thought I would post a techy one for once

When tuning a engine for power / torque and keeping it n/a, what is the best route regarding C/R?
I am told raising it will raise the power, the engine in question is a 2ltr blacktop, but lead me wondering what the rule is in general. Would be running twin carbs, not sure weather 40s or 45s are the way forward, seem to remember the pintos respond better to 40s? Obviously a different engine thou, single cam etc.

Discuss!

CBenno

Fast ford have been doing a feature on these sort of things for the past few months it might be worth a look on there web page.

CBenno

They also have a feature on tuning zetecs next month with a 575bhp zetec focus

jammerrs

higher and 45's all the way

~nomad~

iTrader: (4)

Thats gonna be a turbo thou, so not really what I am interested in tbh, but cheers.

~nomad~

iTrader: (4)

Whats the science behind that though?

Rick

The science behind bigger carbs is that bigger chokes are less restrictive and so flow more. A carb works by placing a restriction in the intake in order to create a region of low pressure for the fuel to be drawn out into. Fuel injection does away with the restriction, and so increases power all things being equal.

Rick

~nomad~

iTrader: (4)

So what are the good points of smaller carbs? better drivability? And whats the benefits of higher C/R?

Oranoco

What about bike carbs? Dan will have the set from his XR2 for grabs soon as we're putting that ST170 engine in on ITB's. Just a thought. BTW my mate Clint wants a spin in the popping Plus

Rick

Yes, smaller carbs give better low rpm drivability and better economy.

Higher CR gives you more power providing you have high enough octane fuel.

Rick

Markb_s1

as above, definitely 45s on a 2.0 zetec unnless you're really going to town on the internals.

i have a mate who runs a 1600xflow on 50s but that's a full race dry sumped screaming thing.
(at least he did.. he's now swapped to jenveys)

~nomad~

iTrader: (4)

defo want to run carbs mate, we have our reasons lol.

Popping plus should be legal in a month or so, happy to scare Clint in it lol

~nomad~

iTrader: (4)

do you mean rather than anything bigger, or rather than smaller?

Markb_s1

rather than smaller mate.
twin 45dcoes were perfect on my old 2.0 zetec with standard internals. (well, as perfect as carbs can get!)
they would have been ok for a little more power too.

~nomad~

iTrader: (4)

cool, what sort of power was that making?

Markb_s1

iirc it was 172 bhp (unsure of torque) from a standard 2.0 zetec with twin 45 dcoe carbs.
I think it made 171 the next run a couple of months later. These were both when the engine etc belonged to the previous owner who I have 100% confidence in.
Both runs were at track and road in essex, who apparently have very accurate rollers used by the likes of Mosler.
Was running MBE ECU for the ignition i think. (been a while now as i've long since sold the lump, ECU etc).

only other mods were stuff like an oil cooler & catch tank, raceline water rail, dunnell sump and adding a breather to the rear of the cam cover which was all a result of it being run in a rwd car.

Markb_s1

PS - that was running a lanel filter behind the grille from which the air was then ducted to an airbox on the carbs. found a pic of the original installation..

~nomad~

iTrader: (4)

that engine looks so right in that bay! cheers!

Markb_s1

it does look pretty sweet, but alas it wasn't to be in my case!

jammerrs

a higher compression ratio means that it compress's the air and fuel more making a bigger bang when its ignited

this is why average turbo cars run lower c/r because the air is already pressuriesd so compressing it more means it more likely to explode before the spark plug ignites which as you can imagine is not good for the engine at all

(all in very basic and generalising terms)