compresion ratio
Turbo Mini Forums

hi all i have an avonbar turbo engine with 1380 offset bore what compression would i be looking for to use a opcon supercharger
(ie mini speed kit) to its best advantage

i also need to know the size of the head chambers this would entail etc so i can finally get my engine put together

cheers for any info

ps is an intercooler a good idea and if so where the hell does it go?

Welcome !
The compression depends on how much boost your gonna run it at really, the lower the CR the more boost you can run. I dont know what these chargers run at , so its hard to say whats best for it. Have you asked Minispeed ?
The head chambers will be dependant on whatever CR you decide on . ( After you have calculated the cc's in the piston, and head gasket etc.) See if this helps.

http://www.maverickracing.co.uk/compratio.exe


Chris

Edited by 8PortChris on 12th Jan, 2005.

minispeed recommended 8.5:1 is that the right way round and does it sound about right?

Edited by sandfly on 13th Jan, 2005.

www.afracing.com/cr.xls

AlexF

8.5:1 sounds a good figure, do you know what boost the charger will be running at yet??
As for the intercooler, i would have thought it would be worth fitting one, more reliability and a little more power, but not too sure on supercharger requirments for intercoolers. Anyone else recommend it???

Forgot to mention, the intercooler will go between the superchargers output side and carb, so the forced air coming out of the supercharger passes through the intercooler to err, cool it. Then into the engine, you will have to make up pipe work to plump it all in.

Edited by T3Tone on 13th Jan, 2005.

-MINI CLUBMAN 1380 TURBO-

will be running about 15psi as standard i think
the intercooler cannot go there unfortunaly as the supercharger is a draw through type which acctually pulls through the air fuel mix and fires it into the cylinder could the intercooler be mounted before the carb to cool the air coming in

so having the air sucked thorugh rather than blown through?

No ,the air gets warm as its compressed, that why you have an intercooler....after the charger/turbo.

Chris

You cant run IC with suck through... the fuel puddles in the IC core!

WHat supercharger are you running to get 15psi?

alex

AlexF

it is the opcon charger from the mini speed kit according to mini speed 15psi is the standard for this will have to check it out more thouroghly when it arrives

according to opcon the charger is 80%/90% efficent and causes very little heat (just to state this is what they claim)

so how do i cool my air if the intercooler cannot go after the charger?
can the intercooler go at the before the carb to cool the initial air or is this not worth it the air goes through the carb then the charger then into the engine

Edited by sandfly on 14th Jan, 2005.

the air gets hot when its compressed so it needs to be after the charger.
you could try water/alcohol injection after the charger. i think that might cool the intake charge. someone with more knowledge than me could confirm that though

might have to go with a breath of nitrous
any opinions as this in small amounts is ment to cool the charge?

nitrous or methanol injection


alex

AlexF

15psi from the Opcon???

Not so sure about that to be honest! I'd do my own research on that.

You'll find very few poeple on here have any dealings with minispeed (other than to buy stuff at prices others can't seem to match).
If I were you, I'd do your own research.
Log onto http://www.minimania.com/msgthreads.cfm and ask about the Opcon kit there. As i understand, it was designed in Australia, then rights were initially given to minispares/minimania, but Minispeed also got in there and undercut minispares to the point they no longer sell it.
There are a few on there who do have it however...

Be wary of minispeed though (i've said it twice now - anyone else?)

Edited by turbodave16v on 14th Jan, 2005.

as yet the only prob i have had with mini speed is the time to get parts past that everything has been fine but i suppose the proof will be in the rolling road


just to add this is the site that orginally tickled my interest,

http://www.theminiworld.com/compresor.htm

i am just off to work out the pulley ratios to get about 10 psi initially bye bye scoobies

Edited by sandfly on 14th Jan, 2005.

hmm beating scoobies at 10 psi in a mini..,,

good luck!

as for minispeed.... don't they are unreliable liers!

No, they can't do me for liable as its the truth!

alex

AlexF

I would hope to have more than 144bhp, if i was running 14psi.
I might not, but i'm expecting more than that, from 8 psi.

Chris

i am just getting the kit and various bits and bobs that they do cheapest from mini speed the engine and head is a prepped avonbar gear box jkd which have been lying in a garage for 5 years since some twocking git nicked my last mini

was going down the turbo route but for some odd reason the supercharger won and yes i did win the lottery

ho hmm that is basically why i am asking about comp ratios etc to make sure that when put together in aint gonna go bang

so back to the plot does this sound right for 8.5 : 1ish

15cc dished forged powermax pistons, 28cc in the head on a 1380
where the pistons travel to to flush with the top deck of the block

oh god so confused

Sounds pretty good to me m8.

I run a 1380 and my piston dish area + head chamber area = 44cc and give me about 8.3-1 with a standard payen head gasket.

I make yours 8.49-1

-MINI CLUBMAN 1380 TURBO-

Twin Screw blowers top out at about 84% adiabatic efficiency, they are up there with turbos, according to the rotor design (high low boost) you get different compression ratios. they are either geared to pass loads with less internal compression or more. As the compression happens within the charger, it follows that the heat must be conducted away from the charger. Therefore the charger gets HOT.
They can blow up to 35 PSI without too many problems, allthough your blower would get very hot and this would limit the dT so you would need an intercooler. Of course, that assumes your belt can take the 70 or so Hp required to drive it.

The Opcon is a beautiful blower, can you put down as much about the spec as you can find. I'm really interested.

I would look at using a decompression plate instead of silly pistons. For the boost you are realistically going to run with a 1380cc. What was maximum recommended by avonbar? I think 15PSI is pushing it. As you will be running a cool charge (coolish) it will handle a higher ratio before it bites and you will get more out of it. It's going to put a serious amount of stress on those components....

Bugger off, I'm getting there.

here are a couple of links

http://www.hi-flow.com/HPSuperchargers.htm
this is the aussies who originally developed the kit for the mini with the opcon charger

http://www.opconab.com/index.asp?langID=2&cID=14&spage=1
the manufactuers page lots of tec spec

past that there is the mini mania website that used to have a couple of threads

i choose the opcon for reliablity and as you say unlike the bini supercharger it does not heat the charge overly and is more efficent as they say you pays your money you take your choice

ps i am not slaging off vmax conversion it look well put together and from staurts rep i am sure will be fantastic i just dont like the bini chargers characteristics
oh and when i bought mine staurt had not released his kit
yes it has taken a year so far in about 4 years it should be about right

I would always go blow through on principle.

If bini blowers were not ?100, I would hanker after an Autorotor/opcon?etc. Rig it up blow through. Mazda Millenias have a 1L pass screw blower, but it requires machining and looks about twice as big as the A series. The Bini blower can produce more than enough welly for unreliability, if I keep busting it, I will look at other cars.

Bugger off, I'm getting there.

Is 80-90% efficient so causes very little heat !! so have minispeed managed to cause some temperal rift in space time so that the laws of thermodynamics have altered in some way !!! lol.

The opcon is a good bit of kit and has a Uk distributor, i have his number somewhere.

Twin screw superchargers are true compressors unlike your old roots vein or shorrocks type of blower. You will find twin screw compressors in modern whisper quiet compressors that supply about 8-10 bar. They are efficent as well.

Dont see there is any reason you could not have a blow through system on these either. You would have to sort out slightly different boost pressure control though else you may blow your butterfly in ya carb down its throat when you close the throttle.

One thing i dont like is the loss oil system these things have. These end up introducing oil into your inlet system so it ends up being burnt. Oil isn't good in there as it affectively lowers your octane.

I think what Stuart at vmax has done is great. If you get chance try looking in your local BMW dealers skip. I know of a few that simply dump the old blower and head when they fit the new kit.

Dont think a supercharger can match a turbo if you look at the overall system efficency as the turbo uses waste energy (ok not 100 free energy), but the blower uses some real HP to spin it over. How many competitive race cars have you seen in recent years using a supercharger ?????? I'm sat here thinking, but icant think of 1 at the mo.

The system will generally be heavier as well.

No turbo here... :)

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Granted, but it's not exactly high tech. Or a race car for that matter. Not very reliable either !

Besides i would have thought turbo lag would rule them out here anyhow as they would be up the quarter before the thing came on song.

Was thinking more of circuit racing, ralling, etc.

Good discussion here!!!

Stuart - The lad won the lottery! Would you still use a 'decompression plate' if you had plenty of ??? ???