Rotrex supercharger compression question

[Jake Mcaulay 6]

Hi guys.

Currently got my head apart on the vr6 and fitting a mk4 head gasket and some schimmel 263 cams, a rotrex kit has come up and I'm very interested.

I've had a z engineering S/C before on a practically stock engine.

When using the rotrex c30 94 what is the ideal compression. While the head is apart I would like to get it correct.

The mk4 gasket will take to 10.5:1 apparently, and doubling up will take to 9.6:1.

Is this compression good enough for the rotrex?

Any help is appreciated.

Thanks

Jake

[D11PS 146]

Hi mate, you need to lower the compression with a spacer plate. 8:5:1 is what most people say you should run. You can run higher compression as I know people who have had 15+ psi on a 9:5:1. It al depends if your willing to take the risk

[Mk3highline 287]

As above but depends on how good your charge cooling is like

How big/efficient your intercooler/charge cooler is

What fuel you use

How good it's mapped

Water meth injection

The cams will iirc lower the dynamic compression too

Have you done a compression test or a leak down test?

[CALICO 130]

His head is off so cant do compression or leakdown

[Jake Mcaulay 6]

Thanks for your responses.

With regards to the spacer plates, where is best to purchase these?!

I don't want any risks to be honest. It's a stage 1 kit at the minute but I would like the engine prepped for more power as and when.

There is no charge cooling with the kit that I am getting.

Would this benefit greatly even at low psi??

The map will be done at stealth by vince.

The reason I have the head apart is because I had low compression on 3 cyclinders due to leaking valve and seals.

The seats and valves have been machined and piston rings too so compression should be good, oviously doing the HG at the same time.

I appreciate all your help

Jake

Edited September 8, 2015 by Jake Mcaulay

[Mk3highline 287]

Did the piston rings get gapped for forced induction ?

As forced induction like turbo or supercharged run a bit hotter so the rings need to have a slightly/fraction bigger gap to compensate for the slight extra expansion

Yes charge cooling of any sort will make power as the air is more dense when cooler

Eg; cars feel quicker on cold mornings than a hot summers day

Also the cooler air will reduce the chance of detonation etc

Also with the rotrex's you will only get full boost at the red line so how often will you be sat on the limiter lol

I will edit this as there is couple more things

Edited September 8, 2015 by Mk3highline

[c00k 435]

A charger cooler will also cause boost loss. Any longer pipework, charge cooler or intercooler will lower boost pressure. So this should be kept in mind also.

Look in to boost loss on google and you will find everything you need to know.

Why alot of people keep lower boost supercherger to minimal pipe work. And no cooler.

Edited September 8, 2015 by c00k

[Jake Mcaulay 6]

The rings haven't been done yet so I will talk to the guys doing it. I can imagine if it needs doing they will as they are shit hot!

I understand about the dense etc.

Some good info!

Any where to find these spacer plates?

Thanks

Jake

[Mk3highline 287]

A charger cooler will also cause boost loss. Any longer pipework, charge cooler or intercooler will lower boost pressure. So this should be kept in mind also.

Look in to boost loss on google and you will find everything you need to know.

Why alot of people keep lower boost supercherger to minimal pipe work. And no cooler.

I could be wrong but the charger will suck in a given amount of air to force in to the engine so regardless of the pressure drop after the cooler the same amount of oxygen will be forced in to the engine?? Just cooler ???

As you get the pressure drop as all the molecules have come closer together?

United motor sports do the de comp plate or see if the phirm have one in stock?

[Mk3highline 287]

Do you know the pully size your getting with the kit etc and what your aim is for end power result?

Do you want top end power or prefer more mid range poke?

[Jake Mcaulay 6]

I'm not sure of the size at the minute. I'm waiting to hear back from the seller, to be honest what is possible with them without major work and compromising realiability?! Around 300 would be a nice starting point.

Much needed for that?!

With regards to injectors what would people recommend??

Mid range would be nice, it's a weekend/ track car on occasions.

When I know the pulley size I shall get back to you.

Thanks again

Jake

[D11PS 146]

You should see best part of 300hp with the C30-94 if not more with 263 cams and other performance mods . Most people use Bosch Green tops 440cc but once again it's up to you. With regards to the charge cooler, I'd always recommend one as it will give you more consistent dyno figures as when the cars 'cooler' it will make more power in essence as it gets hotter the HP will subsequently drop. A PWR barrell charge cooler will fit. If your going down the intercooler route you will need to take into consideration if the extra pipework and the size of the I/C the Charge will have to fill hence the psi drop. Anywho that's my 2 pence worth.. hope it helps.

[Jake Mcaulay 6]

Really appreciate the feedback mate. Nice to actually understand what's being said!

With regards to injectors I've read that green tops are good. And again will allow for extra fueling if needed when the psi is upped.

Thanks again

Jake

[c00k 435]

I could be wrong but the charger will suck in a given amount of air to force in to the engine so regardless of the pressure drop after the cooler the same amount of oxygen will be forced in to the engine?? Just cooler ???

As you get the pressure drop as all the molecules have come closer together?

United motor sports do the de comp plate or see if the phirm have one in stock?

This is half right buddy, yes it does make the air more dense as it cools.

But longer pipework and any type of cooler cause drag.

The internal flow area is the major controlling factor. Tube length is the second biggest consideration, as a tube twice as long as another will have nearly twice the drag at the same air velocity. Tube entry and turbulator density play small roles and can be considered insignificant.

Boost loss is what is measured in the pressure loss and is the restriction presented to the smooth, easy air flow through the system. Essentially, the drag. It is measured by a pressure difference between the air charge entering the cooler to that exiting the cooler. This flow loss is due to the aerodynamic drag offered by the shape, the net area of the tubes, the length of the tubes, and the density and style of the turbulators.

One of the worst things they can be done to any forced induction system is an incorrectly set up cooler. Meaning the wrong type, wrong size or poor shape cooler has been used. And could see anything up to a 7-8psi loss.

Also many other things can cause boost and flow loss. Bigger cams, bigger more free flowing exhaust systems, this is because there is less back pressure.

This doesn't mean they shouldn't be used. It means that knowing this is a key part of building a forced induction engine and should taken in to consideration.

Edited September 8, 2015 by c00k

[c00k 435]

Also another way to cool the air, to stop pre-detonation, and higher intake temps....

Is water and methanol injection. This is one of the only ways to cool the air without any boost or flow loss. But this is not always idea for road, or daily driven cars, as it can never run out. So you have to top up petrol, and water and methanol all the time. This is why it's mainly used on track, drag or weekend cars.

Edited September 8, 2015 by c00k

[Mk3highline 287]

yup his right ^

I was told to keep the pipe work same diameter as the superchargers outlet up to the throttle body

[Jake Mcaulay 6]

Some interesting reading there guys, thank you!