Supercharger Question.

[contourspd98]

With a centrifugal type I can run higher boost and get bigger torque but has anyone any idea what psi roughly i'd have to run to get up to 300bhp.

Well you can figure it this way... For every p.s.i. that you put into an engine you will get a 7% hp increase... For example, 10psi=70% increase... Thats at least what Gale Banks said...

[striker2]

Well you can figure it this way... For every p.s.i. that you put into an engine you will get a 7% hp increase... For example, 10psi=70% increase... Thats at least what Gale Banks said...

Thats not accurate because gains are not based on psi but rather airflow (either CFM or lbs/min). also consider that i basically doubled the stock HP on 10PSI from a T3 turbo

[ButtonPuncher]

Exactly.

Stock Zetec with stock head, cams, and intake manifold = 20psi for 300HP

Zetec with FRPP head, turbo cams, cam gears and FRPP intake = 12psi for 300HP

More psi doesn't mean more power necessarily.

Having a better flowing motor also magnifies the power. The FRPP Zetec at 20psi would be putting down 400HP.

Just look at the SVT Zetec guys on the Focus forums. They are hitting 300-350WHP.

BP

[contourspd98]

Thats not accurate because gains are not based on psi but rather airflow (either CFM or lbs/min). also consider that i basically doubled the stock HP on 10PSI from a T3 turbo

Unless he said that 1psi is equal to 7% more air... That might have been... I cant remember for sure what he said.

[striker2]

Unless he said that 1psi is equal to 7% more air... That might have been... I cant remember for sure what he said.

doesnt matter, PSI is irrelevant to how much power a car will make. different compressors move different amounts of air at different pressures.

you can have a T3 turbo that moves 25lbs of air/minute at 10psi and you can have a T4 turbo that moves say 30+ lbs of air/minute at 10PSI. the T4 will produce more power at the same boost pressure.


note: those numbers are just guesses, they may or may not be accurate.

[jamesmason1]

the top mount jrsc they discontinued, right???? I've gone to their site and all they are advertising is the rotrex deal, here's a pic...

[Kresnik]

I have a pre '98 AWD Ford Mondeo Estate which i'm in the process of modifying. I'm looking at modifying the engine and want to go for a supercharger however I don't like to go on the normal route. Bit of an awkward sod me!!

The T'box in the AWD I have been informed can take anywhere between 250-300bhp so I want to squeeze as much torque as i can out of the little 4pot. Ideally i'd like to get a stroker kit if such a thing is made or possible. Also I know I could buy a Jackson Racing kit but that's limited to at best 8psi and if i'm correct uses the stock Inlet Manifold. The stock manifold is a very limiting factor as can be seen when you add throttle bodies which, even on a naturally aspirated engine can unleash over 20bhp. I was looking at using a Centrifugal Supercharger such as one supplied by Vortech, throttle bodies + all the necessary electrical kit that goes with it and fitting an Intercooler, the likes of a Saab 9000 as with minimal mods it'll fit comfortably.

Tell me though, can anyone tell me what are the pro's + cons of using centrifugal blowers over roots and other types of blowers? With a centrifugal type I can run higher boost and get bigger torque but has anyone any idea what psi roughly i'd have to run to get up to 300bhp. She will obviously get headwork + cams, custom induction kit etc to up the power naturally first. I'm looking for as instant power as I can get to get the big Estate moving quick, especially with AWD?

All answers welcomed.

A couple of basic things here.

Zetec engines rev reasonably high. High revving engines that are RELIABLE (i.e hondas) have a short stroke. Increasing bore slightly is okay, but only a hair. A blown engine will maintain a higher temperature than a naturally aspirated engine. With that in mind, you don't want cylinderwalls to expand beyond tolerances and cause some real problems. Not to mention that there will be less mass between the chambers to absorb harmonics.

Centrifugal blowers are the worst forms of FI to use on any automotive engine. Period. Centrifugal blowers take time to build boost, and as such, do not generate any substantial (if any) low end gains (i.e torque), modest mid-end gains, and a reasonable top end for about 10% of your power-band.

A centrifugal blower is only 'sort of acceptable' on OHV engines such as 302 or 350. Those have two-valve heads and cannot breath for - which is whey they create a lot of torque and require massive work to get them to breath on-par with an otherwise stock 4 valve OHC head. The engine will naturally create good low-end torque, and breath half-assidly (new word!) at mid range - the centrifugal blower will add some range and give it top-end that it didn't have before, so it would end-up feeling more like the engine got opened up to breath well enough to claim much of its volumetric efficiency.

We don't have poor breathing cam-in-block OHV engines, so we should strongly consider this when wishing to modify them.

A roots-type blower, on the other hand, will give you much desired low-end torque the instant that you hit the gas pedal. Positive displacement air pumps are nice like that. They aren't as thermo efficient as a centrifugal or turbo charger, because the compress the air in your entire in-take system, starting from the intake valves back to the helix of the blower. For lower boost levels (Typically 6-9psi) roots-types are just fine for most engines. If you really want more boost and power, then a properly matched turbo is going to out-shine a blower in most instances.

4-valve heads, as a rule, don't benefit greatly from 'head work'. The factory design is already greatly superior to most 2-valves OHV engine, even after major surgery. Forced induction thrives off of cams with little or no over-lap. Thus, a typical 'economy cam' that is found in most cars is actually going to be the /best/ cam for creating most idea rates with VE and thermal efficiency.

[Kresnik]

doesnt matter, PSI is irrelevant to how much power a car will make. different compressors move different amounts of air at different pressures.

you can have a T3 turbo that moves 25lbs of air/minute at 10psi and you can have a T4 turbo that moves say 30+ lbs of air/minute at 10PSI. the T4 will produce more power at the same boost pressure.


note: those numbers are just guesses, they may or may not be accurate.

The end temperature of the air charge is also a critical factor, as it determines how much oxygen as in there. The cloder, the more densely packed the oxygen will be, the more power can be had. Simple physics.

[striker2]

The end temperature of the air charge is also a critical factor, as it determines how much oxygen as in there. The cloder, the more densely packed the oxygen will be, the more power can be had. Simple physics.

for simplicitys sake i was assuming that the end air temps are going to be the same. it was more to show that boost pressure is really irrelevant to determining HP without a compressor map.

[Kresnik]

for simplicitys sake i was assuming that the end air temps are going to be the same. it was more to show that boost pressure is really irrelevant to determining HP without a compressor map.

Well, for the sake of due and proper of understanding, I had to add this. The temperature IS the direct catalyst for the difference in numbers. When (i.e, RPM range) the air pressure raises or falls is relevant to over-all performance, but not-so-much the numbers that people are interested in.

Compressor maps are great tools for understanding and interpreting threshold, power-band, and thermo-deficiencies in the system. A dyno will determine the HP.

I'm not trying to be a dick at all, don't read me wrong. I just would like to clarify and substantiate things from the correct engineering perspective.. that's all.