38 replies to this topic

[naughtyboydan]

Hello i am planing on building a 1380 superchared engine i was woundering what decompretion cc i would need if i wanted to run about 11psi boost. I am new to the super's. I have worked on turbo engins but not super's my friend has a turbo and i want a super would be good fun.
My plan is to run it with
-omegs pistons
-276 cam
-stage 4 / 5 head
-duplex twin timeing chaine
-1.5 roller rockers
-standered gearbox
-3.1 final drive
I know i will need a fule pump and other little bits but i need help with all the compretion ratios for my project to work. I might sound like a bit of a deadhead in this game but i want to lurn and build.
All help will be apreseated and look forword to your coments.
Thanks danny.

[Sam Walters]

You will need to replace the diff in the gearbox to a minispares crosspin diff. You will destroy it elsewise. While youre there you could recondition the standard box and put in a central oil pickup as this is fairly easy at that point.

If youre going to go to the effort of a supercharger ensure its blow through. Slark are just developing a kit. Personally I would run a gt17 turbo. But you seem to have your reason.....

Dont bother about the 1.5 ratio rockers.

Get a head from the likes of Benross or Turbo Phil rather then any other supplier. These guys specialise in forced induction heads. A head ported for N/A could be very diffrent to what you really need.

Im not a fan of the 276 in any application. Try the vp8c in this case.

you will need mapable ignition. The tried and tested method is megajolt. This junks your distributor and coil setup for a much more modern and reliable coil pack setup.

Also if you do go blow through ensure you buy a decent intercooler. Dont be fooled by these shiney new cheap ones in ebay. they are mostly *******! An inter cooler from a 2WD or 4WD cosworth would be much better. Of course if you dont mind it not being so pretty.

Compression ratio is dependent on the pistons you use, how far down the bore and head CC.........

I might add if youre going forced induction going 1380 over 1293 doesnt offer much advantage. Infact id say its a disadvantage as its harder to get the compression ratio down and you have to do it in a more comprimised way.

More on that later....for now I advise you have a good look through this website before you do anything else. Its turbo related, but its really quite relevent.

http://www.turbo-mini.com/index2.html

[Wil_h]

You need to be looking at between 8 and 8.5:1 CR if suck through.

I agree with the thought that a 1380 is unnecessary for a turbo, but if you're using a crappy M45 then the more cc the better, as the charger will be more efficient.

Personally I like the 276, and it seems a sensible choice for an SC setup.

[naughtyboydan]

Thanks for the help it is mutch appreciated.
I have a few more question, can i run the super with a dizzy dont fance paying £400 for a megajolt or do you have to advance the timing a bit more ?
That website you posted was a good bit of reading and help thanks.

[Wil_h]

You need to retart the ignition on boost, just like the turbo you will have built. A mapped ignition is the best option really as it will improve driveability as well as keeping advance retarded on boost.

Next best is a metro turbo dizzy, after that a fixed dizzy, fixed at around 25 degrees.

[naughtyboydan]

I have contactless pionts system at the minit so that is no good then can you map the megajolt system your self or do you have some 1 do it for you plus i have omega forged pistons alread they have what i mesur a 5cc dish on them but i have a little problem the pistons sit 3 mill from the top of the cylinder block the conrods are ballenced i am haveing a problem working out the how mutch cc i am loseing and why they sit that low pleas help.

[Wil_h]

Struggling to understand what you are asking, that's one hell of a sentance!

Yes you can map it yourself on a laptop. There are plenty of people who'll let you have their map as a base.

What do you mean by losing cc?

[new_zealand _minis]

you can get a really good app on itunes . called mini head .. the best way to work out ratio ....

[naughtyboydan]

Sorry i dont read to good normaley get my gf to typ and read it all. Basickley the pistons sit 3 mill form flush withe the top of the cylinder block so i cant work out how mutch cc i will be loseing compression wise hope tins makes sence.

[naughtyboydan]

Will put some piks up 2 moz so you can see what i mean

[Turbo Phil]

If the pistons sit down the bore at TDC you won't be losing any volume/cc you will be gaining it, This will give you a lower compression than an equivalent piston coming flush with the block face.
As you'll require a fairly low compression ratio for you proposed build, this could be an advantage. Though it's generally considered better to have the piston come flush & find the required volume in the dish.

[naughtyboydan]

This is the piston at TDS

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•  20120720_175932.jpg   57.38K   53 downloads

[Wil_h]

Pi x r^2 x depth (i.e. top of piston to top of block in cm
or
3.142 x 7.35^2 x depth
or
3.142 x 3.675^2 x depth

Looking that the phot I'd guess at a 3mm depth, so

11.5 x 0.3 = 3.4cc

Simples - but you need to actually measure the deck to piston distance.

[naughtyboydan]

ok thanks will give it a go

[ANON]

no.3 piston looks like it's been dropped??

don't like the dot punch marks on them either