14 replies to this topic

[Albino_Hedgehog]

Hello,

Been offered first refusal on a supercharger kit that has never been fitted to a Mini.

It arrives with the manifold, pulleys, belt etc.

I'm thinking if I do take it then it will go on my recently rebuilt mild 1098 engine.

However can I fit the charger without having a MegaJolt system? Am I ok to stick with my old skill dizzy, and also enjoy the benefits of the charger?

Cheers for any info!

[Dannyboolahlah]

Yeah they run fine with a dizzy.
I have mine on a 998 using the standard dizzy.

[HUBBA.HUBBA]

You need a vacuum advance dizzy

[Albino_Hedgehog]

Okies then thanks very much!!


Next question...


My 1098 Engine has recently been rebuilt and has not yet been fitted to the car.

The engine spec is as follows:

295 head w/skim of .60 thou

Standard pistons as fitted to MG 1100



Will I need to carry out any more modification to my engine, or will I be able add this supercharger straight up, and be away with some correct tuning adjustments?

Have read that I could need to fit a decompression plate between the head?

Edited by Albino_Hedgehog, 03 November 2019 - 06:14 PM.

[HUBBA.HUBBA]

You're best off having deep dishes pistons to get the CR low enough. Or worst case scenario decompression plate.

[DeadSquare]

If you had had the combustion chambers reprofiled, you might have got away without any further modification, but not with flat tops and .060" skimmed off a standard 295 head.

 

You need at least a 4mm decompression plate, and as you describe your 1098 as "mild", maybe even 6mm.

 

Go for it, it is a nice combination.

[dyshipfakta]

Get the compression ratio wrong with a non intercooled blower and your pistons will end up looking like cheese. I’m quite surprised the 998 dizzy doesn’t have too much advance either to be fair.

[G'Racy]

What amount of torque you could expect from a supercharged 1098 compared to say the 998 and 1275 ???

[HUBBA.HUBBA]

Rough guide is times the existing hp by 1.4, so 100bhp would be 140bhp

[mini13]

The 1.4 multiplier is used in a lot of racing regs for forced induction, there were some brothers hilclimbing a turbod 998 in a 1400cc hillclimb class rather successfully.

[HUBBA.HUBBA]

The 1.4 multiplier is used in a lot of racing regs for forced induction, there were some brothers hilclimbing a turbod 998 in a 1400cc hillclimb class rather successfully.

Yep. That's I got the 1.4 multiplier from, hillclimbing.

Edited by HUBBA.HUBBA, 10 November 2019 - 10:16 AM.

[G'Racy]

More asking about the torque rather than bhp, still a factor of 1.4 ???

[DeadSquare]

The 1.4 figure came about, because in the days before tapping in 3.1416 into a calculator, when working out the theoretical CC of the engine with pencil and paper, it was easier to use 22/7 for pi because 7 is half 14.

At one time, Formula 1 was either 3 litre or 1.5 litre supercharged, and in recent years I have seen turbocharged cars using 1.7.

"Not a lot of people know this" , back in the early 1960s, to run a supercharged A series engine in the 1,500 class, it needed to be no larger than 1,071cc.

Edited by DeadSquare, 11 November 2019 - 04:39 PM.

[MacFreuden]

What kind of compression ratio is optimum for using a supercharger like this one? Is there a formula to work it out?

And would using better fuels like the supers you get from garages which have an octane level of around the high 90s enable you to have a higher CR like with NA engines ?

Edited by MacFreuden, 18 December 2019 - 05:13 AM.

[mini13]

Well,

 

Generally people go with a rule of thumb type approach, which is a CR of 7.5-8 should be ok for most setups/ fuels...

 

Working it out properly is pretty tricky, as everything effects eveything else, and also theres not a hard and fast rule either, but basically, one way to approach it is pick fuel, from this evaluate how much dynamic compression can be run, pick a cam for the powerband I want to run, then work out the chamber volume needed to get the desired dynamic compression.

Trouble is how much dynamic CR can be run depends on charger efficiency, engine temp, charge temp, chamber design, boost, head flow, atmospheric temp, colour of your nans pants etc etc... 

 

personally I would always run a CR lower than needed to allow a safety net for dodgy fuel, hot days etc