fiestaturbo.com

[FezzR]

Right then guys this is mainly aimed at the guys like Excursion Gaz7 and you other very knowledgeable guys,

Right then, I know about runner lengths, diameters, plenum, and throttle bodies, I couldn’t care less about carbs, hate them with a passion,

Basic engine theory suggests you want maximum air flow into the cylinders to get maximum performance. I know this not to be true though, so what do t you want? I know that you can end up loosing torque quite seriously if you flow a head too much on a turbo, I assume this is applies to N/A too?
Do you want to be able to flow just enough that the valves can deliver and no more?

There for making the valve flow more import than head / manifold.

Next bit is Compression ratios; does anyone know advantages disadvantages of raising compression?
I seem to remember that Rally (I know not N/A) run raised compression ratios, but most people lower the compression so that they can run more boost,

DISCUSS


Cheers Ian

[Uni]

whats good for a turbo is not necisarrily good for atmo...

i can state with reasonable authority that high compression=more air and fuel in a smaller space.

what does this mean? a bigger bang of course, as the increase in compression means that the air wants to get out faster, hence increasing torque. The ultimate example of this is the diesel engine, which in modern designs is made to run as high as 38:1 and in some cases higher

so, why lower the compression ratio in a blown engine if it gives you so much power, i hear you asking...

the reason comp ratios are lowered in blown engines is to prevent stress fracturing the block or destroying con rods, pistons, crank bearings and the crank balance. It also makes it easier to make sure the head stays on the engine rather than being put into orbit at the first sign of full boost. Low comp ratios also mean that the car is easier to tune, particularly in boosted situations as the detonation threshold is much greater and more defined.

remember that forced induction already compresses the air prior it reaching the engine, which means that raising comp ratios within the engine serves negligable purpose in power terms.

Raising compression on a hi-po atmo engine is essential as it provides greater urgency when detonated. Hence for the average atmo engine, a higher compression ratio serves one main purpose: more torque right across the rev range. This is due to all the factors mentioned above, but primarily the bigger bang ...

never, ever, ever, ever, ever decrease compression in an atmo engine. ever. you lose power and torque. you gain revs, but all the revs do is make more noise hahaha fart car

there are however, a number of downsides. by increasing compression, the car will need a serious tune. it may also require a bottom end balance after the initial run in period, and stronger head bolts in aging engines.

it will no longer be capable of running on regular 91 RON petrol either...

ohhh fiddlesticks





Uni/.

[xrsi]

Basic engine theory suggests you want maximum air flow into the cylinders to get maximum performance. I know this not to be true though, so what do t you want? I know that you can end up loosing torque quite seriously if you flow a head too much on a turbo, I assume this is applies to N/A too?

to tune a car bigger valves is a must, there is no point spending loads on trick mainfolds only to keep the same restrictive valves and not be able to draw the air(or push the air out) of the combustion chamber. The biggest valves you can get in the head the better! (this oftern means angled valves seats

couple this with effective porting and polishing and you will get a very well flowing and high reving engine! - bear in mind that the limit of an engine reving is the speed at which it can get a cylinder full of enough air to make an effective combustion process

Do you want to be able to flow just enough that the valves can deliver and no more?
There for making the valve flow more import than head / manifold.

As above, all the engine work should be considered together to get the best from the engine!

Next bit is Compression ratios; does anyone know advantages disadvantages of raising compression?
I seem to remember that Rally (I know not N/A) run raised compression ratios, but most people lower the compression so that they can run more boost,

Rally cars have alot more development going into them (think of it as sunny spending money on his car and then the average fiesta owner spending a bit, suny can in this case be considered as spending the amount that the average fiesta owner spends compaired to the works teams/engine builders developing thier cars and engines!)
The reason rally cars run high compression ratio is that they run lots of trick stuff to enable the head to ramain where it is and not lift, to stop the onset of detonation and also the fact that they are fitted with restrictors to limit the amount of power they can produce! A rally car is all about torque!!!!

as you wanted to know about N/A tuning tho.....

Raising a compression ratio on a N/A engine is the best thing you can do (aslong as you maintain a safe clearance volume in the head so that the valves and pistons never meet each other at TDC!)

you think, by raising the compression ratio you get the same bang in a more confined space, so get a greater force exerted on the piston top! this produces more power on the power stroke so spins the crank harder!

Do this in deisel engines and the increase is astonishing! on deisel engiens the addition of a turbo actually helpes fuel economy! as does raising the compression as they are compression engines not spark ignition engines as petrol are!
[b]
ive got bored of typing an answer now, so hopefully you have what you need!