Supercharging

[geordie]

Damn your a smart one with this stuff, i saw one of the m90's go on ebay for 650 i think it was...in excellent cond, i will be keeping my eyes out for them now, you ever built a SC onto an RB25DE???

I would need to stroke my engine to put the GTR pistons in wouldnt I?? What would be a very rough price of the total cos of this if i was to get the pistons for 200??

[Warpspeed]

RB25 and RB26 blocks are identical dimensions, crank rods and pistons all interchange (drop straight in) I know this for a fact. The RB26 has I think about 1.3mm extra stroke, so the RB25 and RB26 crank and rods are very slightly different.

As far as I know, the RB26 pistons are a straight fit into an RB25 block with RB25 crank and RB25 rods, so all you would need would be the pistons, and a new set of rings to do it. A fair bit of work, but not a lot of cost. (maybe $600 or something for pistons, a quick hone, rings, and gaskets).

That would drop your compression down from 10:1 to 8.5:1

I have a set of R34 GTR pistons here (that cost me $200, he he). If you can find an RB25DE piston somewhere, the only thing that is likely to be different is the pin height. We can compare measurements, just to be absolutely certain.

[geordie]

So you believe this miller cycle would be an easier route to take to ge the compresion down?? You said the torque would be lost but with the SC coming into play very quickly this would/shouldnt be very noticeable right??

[geordie]

I been reading up about the millers cycle that sounds like a very tricky process, but you would need some pretty expensive management to deal with the wouldnt you?? Like it sounds like it really changes the characteristics of the engine??, Would an Engine mangemnt such ast the microtech mt8 be able to deal with this??

[Warpspeed]

Nothing tricky about the management at all, any tunable aftermarket management will work fine.

All the Miller cycle does is reduce the effective stroke length of the compression cycle by closing the inlet valve later. This late inlet closing also gives better high RPM breathing as well.

Suppose you do a computer simulation of two engines say an RB25 with 10:1 compression ratio, and 8psi boost fitted with a Miller inlet cam, and an RB25 with 8.5:1 compression ratio, 8psi boost, and stock inlet cam.

The Miller engine has a bit less less low down torque at say 2,000RPM, but will still be far gruntier than a stock normally aspirated RB25DE down low.

Midrange and top end power are absolutely identical in both engines. The Miller engine will have slightly better part throttle cruise fuel economy, so really there is not a lot of difference in the final result either way.

Fitting a different inlet cam is all you need to do, and you can always take it out again just as easily. Fitting low comp pistons means you have to remove and completely strip and rebuild the engine, but cost wise, both are going to end up very similar.

Funnily enough, you can use similar cams in both engines. In the Miller engine you put the longer duration cam in the inlet and use a stock exhaust cam.

With the low compression pistons, you use a stock inlet cam, and a longer duration exhaust cam. The identical pair of cams works out optimum for both engines. If you plan to get a longer duration cam ground to try either approach, make sure it has the drive tang to operate the optical sensor on the exhaust cam.

In other words make sure you have two exhaust cams so they will each fit on either side of the engine.

[geordie]

Just out of a matter of interest, if i was to go with the millers cycle, the m90 SC, and the microtech mt8, what would a rough estimate of rear wheel killowatts be?? roughly......

[Warpspeed]

Difficult to say, but here are my figures from my computer simulation.

Stock RB25DE 10:1 compression, valve timing (non VVT) 15/54 54/15, these are both 248 cams as used on early non VVT engines.

Torque at 3,000 RPM 171 ft/lb

Max torque 181 ft/lb flat between 3,500 and 4,000 RPM

Max power 173 BHP at 6,000 RPM (129Kw)

Rear wheel kilowatts (82%) 106 Kw

I know this is a bit low, but that is how it came out. There are things I cannot enter such as intake runner length and exact exhaust details and so on.

RB25DE miller modified engine, 10 psi boost, roots blower with average intercooler (80% efficiency). Compression ratio 10:1, inlet valve timing 20/72 (272 duration). Exhaust valve timing 54/15 (248 duration).

Torque at 3,000 RPM 299 ft/lb

Max torque 315 ft/lb flat between 4,000 and 4,500 RPM

Max power 354 BHP at 7,000 RPM (264Kw)

Power at rear wheels (82%) 216Kw

RB25 modified with RB26 pistons, 10 psi boost with roots blower and average intercooler (80% efficiency). Compression ratio 8.5:1, inlet valve timing 15/54 (248 duration). Exhaust valve timing 72/20 (272 duration).

Torque at 3,000 RPM 314 ft/lb

Max torque 316 ft/lb flat between 3,500 and 4,500 RPM

Max power 348 BHP at 7,500 RPM (260Kw)

Power at rear wheels 213Kw

So either way it is going to double your power.

[geordie]

Yeah i am not considering the toyota puffer any more any how, if i am going to spend the time and cash on such a project, why not doit to get some decent gains rather than a 'gain'.

I know what you mean about turbos and getting massive top end power etc, to bad they have to wait till high rpm to get the power and it all comes in a big hit, not very streetable if its big power, where as a slab of torque and a little lower on the power levels, is still going to create some serious fun, and the main problem will be getting traction.

[Warpspeed]

You are right there Geordie. The big horsepower turbo car can turn impressive numbers on the dyno, and be mighty quick down the quarter as well, as long as you seriously thrash it.

It makes for a powerful and exciting car, no argument there.

But on the street, you might not want to thrash it all the time. So while the guy with the big turbo drops down a gear and 1.....2.....3....then....WOOOOoooossssshhhhh, and he is off.

Meanwhile you are about two car lengths in front. The turbo might be quicker to 0-250Kmh, but who cares.

You will be quicker to 0-100Kmh, and you will not need to do the big high RPM clutch dump to get there either.

There are two reasons for this. First you do not need to shock load the tyres at launch, in fact you do not really need to launch at all. So you will have better traction. The turbo HAS to launch in order to get boost up before it bogs down completely, but furiously spinning wheels do not grip.

Second reason, the engine is accelerating in first gear, and the turbo also has to accelerate to catch up. The lower the first gear ratio, and the larger the rotating mass of the turbo the worse this is, the turbo car can never reach anything like rated torque and power in the lower gears. It sure will in top gear though.

With a crank driven blower the blower accelerates as fast as the engine in first gear. So although steady state rated dyno horsepower might be a bit less than with a turbo, its all there in every gear. Instantly.

So you can easily end up with less power, a slower et, and a quicker car on the street. None of the drag racers understand any of this.

[eryc]

warpspeed g'day do you know where in aust you can buy a whipple super charger from. and what size to get

thanks eryc

[Warpspeed]

Sprintex over in WA used to advertise Whipple in some of the car magazines. I stopped buying magazines a long time ago, so do not know if they are still available from them.

Your best bet would be to contact Whipple USA and ask them who their Australian agents are.

http://www.whipplesuperchargers.com

As to which one, you need to buy Corky Bells book "Supercharged" and do your own calculations. A lot depends on the desired power goal, so there will be more than one possible size you could use.

They all cost about the same, so that is not really a factor. It is more a case of getting the very best results for your intended application.

[eryc]

thanks for info

have been to their site

have sent e-mail still waiting for reply

thanks again

eryc

[eryc]

i still have not had a reply from whipple

also could not find a web site for sprintex

guess i have to find a WA phone book

eryc

[Warpspeed]

I sent a e-mail to Whipple a while back, asking about alternative pulley sizes, and I received a reply pretty promptly.

But I have given up on Spritex.

Keep trying Eryc, the smell of money might smoke them out.

[eryc]

"You can buy the unit form us. "

this was my only reply from whipple spelling included

also got this from capa

Hi Eryc,

this will need to be a custom install.. We can supply you with the required components for you to create a system on the car to suit.. (check out the Eaton M-90 or Vortech units on our website) www.capa.com.au

Regards,

Scott.

now all i have to do is buy the book "supercharged" to work out what i want.

eryc

[Warpspeed]

Sounds good eryc.

Reading between the lines, it sounds like Whipple have become a bit cheesed off with Sprintex as well, hmmm.

Interestingly, all these blowers end up costing about the same these days after factoring in the Oz/US exchange rate. Larger or smaller sizes also cost the same, so dollars are not really going to be a factor in the selection process.

Personally I would still prefer the twin screw blower over a roots or centrifugal on an RB engine. But the centrifugals would be more ideal on a push-rod V8 though.

[eryc]

so you suggest i should still stick with the whipple but just buy from the states

buy the suppercharger in the states

possible get the rest of the parts i need here

do you think

thanks eryc

[eryc]

just for talk sake have you heard about electric turbos

powered by dc motor

i think they are only for 1.6litres and under and produce about only 3 psi

eryc

[Warpspeed]

I would give the electric turbo a big miss. There was a thread on Performance Forums not so long back on this topic, and the sales guy from the company selling those things was torn to shreds.

As I recall that particular device was advertised to produce up to 800CFM and up to 3psi boost and it was powered by a 12v electric motor which reqired 20 amps.

Now if you grab Corky bells book "supercharged" and turn to page 203, there is a formula for calculating supercharger drive power:

Drive horsepower = psi boost x airflow CFM, divided by 229

Now if your electric supercharger can generate 3psi at 800cfm, that would require 3 x 800 / 229 = 10.48 horsepower

That is the thermodynamic energy required to compress the air at 100% compressor efficiency.

If the compressor wheel is 70% efficient, you need 14.97 BHP actual shaft drive power to turn the wheel.

If the electric motor is 80% efficient, it comes to 18.7 horsepower worth of electric power, or 13.96Kw.

Now the electric motor on the thing is only 12v at 20A or 0.24Kw.

There is not a snowballs chance in hell that an 0.24Kw motor is going to drive a supercharger that requires 13.96 Kw to operate at full rated boost and flow.

So it might blow UP TO 800CFM with zero back pressure, and it might produce UP TO 3psi with zero airflow.

Some poor bastard is going to put one on his engine and see maybe 0.2 psi boost or something. Not a good investment.

To properly design an electric supercharger like that, which will deliver 800 CFM at 3 psi would require 12 volts at 1,163 amps. And that is why it is never going to work. And it is also why any decent supercharger is driven by a big nasty very serious looking belt drive system straight off the crank.

[eryc]

yeah i just bought it up as a point to talk about

i had no intention of getting one

as a sparky i could not see how they could get a 12 volt motor to drive the thing

if it was just a hair dryer maybe

eryc