924Board.org

[Martijnus]

At the moment, car runs great with a 1mm decked block, custom runners and 40mm itb's, MSII, LPG blabla.
Only thing I need is a new upgraded MS unit, I'll order that tonight (to be able to switch between petrol and lpg).

It's no fun when the car's good to go, I need a new challenge.

The goals are:
- Run on petrol and LPG
- Run economically and efficient
- More power (not really important, but I guess it's a side effect on my plans)

The plans are:

- Build a turbo engine, with 8.5:1 CR by means of 931 pistons (cgt) and a 931 head.
- Use 38mm throttlebodies instead of 40mm
- Build a new intake manifold/plenum/runners out of fiberglass/polyester to match the tb's (so I don't have to space them)
- Get a small turbo
- IC etc etc
- Build the whole engine indoors to be able to swap the whole engine when the time's there.


I've got two 931 heads and I'll try to get the pistons from mahle and see what the financial setback will be.
The engine I've got lying around is the first oversize, I'm planning to go back to the stock bore by means of sleeving the engine.
No problems here, I'm able to do all of that (if the spacing of the cylinders allows sleeves but I guess it's no problem)

Because I've spent hours on my stainless runners, the choice was to go for aluminium, but because I don't want to space my throttlebodies (several reasons, see below), I thought fiberglass could be an option.
It appears it can be done, it's rigid enough, but it has to withstand fuel and heat. Fuel appears to be no problem, but the resin doesn't take the heat if I understand it correctly.
Another reason for using this material is that I want to work with it... just that. I know wood, I know metal, I don't know fiberglass and I want to learn how it is to work that stuff.

Advantage is that I can make a clay model of the runners, creating a round 38mm runner at one end and an oval shape on the head flange. getting the best flow. 38mm should be more than enough, the 931 ports are actually a bit smaller (37,5mm high iirc, 35+ wide) so it won't be a restriction.

Turbo isn't decided yet, but there's lots of choice. Probably a subaru impreza turbo is easy to get and comparable on engine size.

I want a small turbo which puts out MAX 200hp. Raceboy's experience is that after that the clutch and transmission (last i'm not sure about) will protest and 200 hp is more than enough for my purpose (which is building a new engine...not hp gain)

Using a small turbo would mean that it spools early (which I'll try to optimize when I rebuild the head and try to improve flow)

Management will be MSII with extra code, whole car is adapted for that so the only thing I'll have to change is a boost controller or something like that...


So that's what's in my head....any comments or ideas?
Especially that intake system from fiberglass has a lot of doubts over here, but I was told my fuel rail from plumbing material was crap too, and that thing's just great
I'm not afraid of trying new things, the current engine has wayyyy too big throttlebodies and crappy runners and it still runs fairly good.
That's one of the things I'd like to improve.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[ideola]

Hmmm...why not use carbon fiber for the intake? I know it's more expensive than fiberglass, but I think CF should be more fuel & heat safe? I know it is used a lot on high end super cars and racers for intake plenums, but not sure if it requires any sort of special coating or treatment.
_________________
erstwhile owner of just about every 924 variant ever made

[morghen]

AFAIK it requires a different and special type of reisin, a bit more expensive but not by a whole lot..
_________________
Supercharger and EFI kits
https://www.the924.com

[Martijnus]

[Martijnus]

I forgot to mention why I don't want to space the tb's.

The GSXr tb's all have secondary butterfly valves between the actual butterfly valves and the air filters. The reason for these valves is like the workings of the CV carburators, if you open throttle too much, air velocity will drop so much that the engine runs bad or even stalls.

In CV carbs, the butterfly valve controls the desired air flow, and by opening it a higher vacuum is created, which opens a secondary regulator (in the form of a slide) which gradually allows air to pass into the engine. RPM rises, even more vacuum, slide opens the venturi even more...

Works like a buffer.
The secondary butterflies work the same, but are electronically controlled.
The current tb's (gsxr1000) were controlled by a stepper motor. The other gsxr600 has some sort of servo.
The stepper motor is nice and more precisely controllable... but requires more complicated hardware and software changes in MS.
The servo type works a bit more easy, and therefore has less accuracy.

Servo in rest (no current) -> sec. butterflies are 50% opened (remember the butterflies can turn ~90degrees, so 50% open is about 45deg).
Servo gets a positive current -> sec. butterflies are 100% closed
Servo gets a negative current -> sec. butterflies are 100% open.

Now this can be controlled with a simple set of relays, using MS's spare programmable outputs, reversing polarity.

The conditions for the programmable outputs can be set to rpm and/or tps etc etc.

I figured out I need to use at least 2 programmable outputs.
The first programmable output should be active from 1500 rpm until max rpm. That way, there's a positive current on the servo which closes the valves until output 1 becomes active @ 1500 rpm, grounding both sides of the servo, setting the valves in 'idle' position which is half opened.

Progammable output 2 should be active from 2500 rpm until max rpm. When 2500 rpm is reached, the other side gets a positive current (both sides are grounded before this 2500rpm mark) which changes the polarity, fully opening the valves.



I could arrange another possibility of wiring, but that's not really necessary.

So that's doable. The question raises: how to set the conditions?
The rpms I chose are intuition and partly random.

I know at idle the valves should be closed, and on full throttle (or when turbo delivers boost above 0psi?) they should be fully opened.

I'm a man of theory and I like to figure out how to determine those conditions. The advantage is that there are just 3 possible actions, instead of the (modern) stepper motor, which allows way more in-between actions/positions. The servo setup is easier because of the limited actions.

Any ideas? Maybe MAP could be used instead of rpm or both rpm and map as a condition....
Spit your vision and theory please!
The function of the valves is to maintain air velocity at all times, getting a better filling of the cylinders at low rpm. I hope that's clear.

edit: I don't know if it's possible in the software of MS, but if I drive exactly on the conditions (let's say exactly 1500 rpm) the rpm will could vary between 1499 and 1501, completely flipping the relays out.. there should be some off condition, so on= above 1500 rpm, off = below 1450rpm.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Martijnus]

Again, there are some ideas which I like to try.

VNT turbos have a variable geometry, which means that the guide vanes on the exhaust side (intake side of the turbo) are variable. This means the flow and thereby the air speed can be altered.



Looks like a great way to improve efficiency. If MS can support 'dual boost control' I can control the intake boost, as wel as the characteristics of the turbo itself (hmm maybe that's possible with only one boostcontroller combined with a generic output).

Not sure about additional costs. I've seen rebuilt units which are really crap because of the complicated design. That's throwing money away.


The next thing is something I thought of completely by myself, but I already found out it has been done before. Still my idea

The crankcase ventilation is often connected to the intake manifold for several reasons: the crank fumes are bad for the environment and if you burn them in the engine that pollution is reduced. I don't care about that.
Another reason is that it creates a slight underpressure in the crankcase.
This is interesting, and i've thought of several advantages:
- pressure differential above and below the piston is bigger, directly creating more movement energy (or whatever). efficiency of the engine goes up, it's like raising your compression ratio (well....in a way).
- less air in the crankcase means less air resistance for the moving parts. Less drag, more net power.
- boiling points are lowered. Not sure if that's an advantage...but it should be the opposite of the cooling system which works under pressure to raise boiling points.
This means water and other stuff evaporates better from the oil. Downside could be that the oil itself evaporates or something.

All of the above is ofcourse within limits. A complete vacuum isn't desireable I guess, and during the compression stroke a vacuum in the crankcase sucks up energy again (also with the exhaust stroke).

Anyway. A slight underpressure should be what you want. At the moment my crankcase breather just has a ricerstyle filter on it, breathing in my engine bay. Just a slight overpressure (or atmospheric pressure at lowest) in there....and again, part of the fumes will be sucked into the engine again.

Connecting the crankcase ventilation to the intake should provide a nice underpressure (even with boost that should be possible)...but then you'll get crappy fumes in your engine. Yuck.

I woke up semi stoned this morning and realised during my philosophy lecture that if I connect that crankcase breather to my exhaust (possibly using a venturi to raise air velocity) I could suck air out of my crankcase.

I'm really really really sure that nothing will be blown back, but worst case I could mount a one way valve.
In practice I'll probably won't get really much underpressure in the crankcase, but at least it's not in my engine bay and every psi of underpressure is an advantage.

I also found HERE that creating an underpressure in the crankcase will help the piston rings seal better. I don't know how much of that is true, but it would be another advantage.

Any thoughts? It's real easy to setup for a few bucks and with this much advantages I'll be happy to try it.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[!tom]

That's one of the several motivations for going to a dry-sump system.
_________________
78 924 NA
5-lug

[simsport]

How about using a crankase vacuum pump? its a bit simpler and lighter than a full blown dry sump system......dont know what the typical hp gains are though.

cheers
simon
_________________
Blown is always best!

[ideola]

This topic has come up before.

http://www.gzmotorsports.com/vacuum-pumps.html

A complete dry sump will cost in the range of $2000. A complete vacuum pump setup from GZ Motorsports will cost in the range of $900.
_________________
erstwhile owner of just about every 924 variant ever made

[morghen]

i'm pondering a VNT too
_________________
Supercharger and EFI kits
https://www.the924.com

[Martijnus]

to reply on all of the above (except you morghen )...

I really really really want dry sump. But it's too expensive.

I'm not paying 2k or 1k just to get a big vacuum if I can do it for 10bucks. There will be less vacuum than with a real pump (which sucks up power also) but it's better than what I have now

morghen, you got any info about how the VNT's are controlled? I've read something about vacuum (just like the WG on a std turbo) or ecu controlled (which uses a vacuum solenoid iirc)
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Rocco R16V]

[Martijnus]

mentioned the plans at work today. They figured I would pull smoke as a mofo if I connected the oil vapours to my hot exhaust. A positive side of connecting it to the intake is that it would cool/lube my valves and top piston ring a bit.

On the other side... the vapours will be burned and probably leave carbon deposits.

not sure about the whole thing. If only I could seperate the oil vapours from the 'air' and water vapours....

Connecting it to the sucking side of the turbo could be an option to create a bigger vacuum. That way I'm sure I don't need a check valve, have some extra lubrication with additional downsides like carbon deposits and all kinds of other crap in my intake.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[ideola]

So why not just run a conventional air oil separator as on the 931???? Use a device like what Rocco posted, add a homemade or aftermarket air-oil separator, drain the oil residue back to the oil pan, and vent the vapours to the airbox. That's how it's setup on the 931. Works well.
_________________
erstwhile owner of just about every 924 variant ever made

[Martijnus]

Today I received my new MS2 unit

I also found out I'm able to get new pistons. They're expensive... but I've decided this project has to be done for self satisfaction.

I know there are much more cheaper alternatives to go way faster, but I just want to build another engine. That's the whole goal... try to see if I learned something from my last build.

I don't want to regret it in 20 years that I didn't do it.

To be able to finance it I'll have to sell some other projects and parts, like my hovercraft project and a lot of porsche/honda parts I've got lying around in my garage.
I need that space to build my turbo engine.

I'm not sure if I'll go oversize or stock bore. The difference will be that I'll have to sleeve my engine to maintain the 86.5mm bore.... I like stock bore, and I really like sleeved engines... there are some advantages with sleeves.

The CR will be 8.0:1, maybe 0.1 more because of the machining of engine and head.

I'll rebuild the head to be sure it'll withstand the LPG.
Because I'll limit it to 200hp I wont be upgrading the con rods... maybe just the bolts if I can obtain them.

Bigger problems will be the undersized bearings... I've got a spare crankshaft but I'll machine it to 0.25mm undersize... both the main bearings as the big ends.... problem is obtaining appropriate bearings. I remember porsche only offers stock size for the main bearings.

I'll have to check that out.
Most of the project will be done inside my garage, so the engine will be built as far as possible in the next year or so... when the time's there, I'll quickly swap engines and modify the under-hood stuff (like radiator, intercooler, plumbing for both exhaust and intake). That way I'm able to still use the car most of the time.

Another thing I'm considering is the coolant flow upgrade....
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment