Fuel choice for a supercharged VX

[VehiGAZ]

I've been putting premium gas in the VX since installing the S/C last summer. It runs just fine on it, of course, but the rise in the price of gas got me wondering about the sensibility of continuing to do this. Yes, I know that the price difference between 87 and 91 in a single fill-up is minimal - less than $4 - and not worth the risk of hurting the engine, but it still got me thinking...

If I understand it right, higher-octane fuels are used in high-compression engines tuned to the edge of combustion performance in order to avoid detonation and knock. The VX's engine in normal configuration is not in this camp, and is perfectly happy on 87. When supercharged, the S/C packs more air and fuel into the engine, extracting more power from the engine, but I don't think it changes the combustion rate, and I know it doesn't change the compression ratio, so I think that the engine would not benefit from high-test fuel.

Is my logic right? Or am I missing something?

If you have a supercharged VX, what grade have you been putting in it? Any issues or noticeable effects?

I filled up on 87 yesterday, and I will be watching the performance closely. I took it to redline a couple of times afterward, but I didn't notice any pinging, knocking, or nothing. I should get around to installing my ScanGage already so I can more empirically monitor the goings-on under the hood. But I'll leave it up to my ears and butt in the meantime...

[Jolly Roger VX'er]

I'm coming up on 40k miles of being supercharged (VX is about to have 80k) and like you always ran premium in it since that is what Alpine reccommends.

Tone told us early on that he used to run regular basically all week when doing basic commuting with the VX; and filling with premium before doing any rallycross or other "demanding" duties.

Since my cross-country trek in the VX (PA to Malibu, CA and back), I was "forced" to run lower octane during several fill-ups (mainly around Denver) and ran like 87 octane several times and actually noticed an improvement in mileage. Since then, I've been running 87 octane almost all the time with no ill-effects at all and seemingly better mpg. I've been avg. 17.5 mpg all around driving (city-highway). I've kicked her into passing-gear a few times here and there and noticed no ill-effects.

If you think you're going to run your VX hard for any length of time...I'd still run premium though just to be safe! That's my $.02

[Gussie2000]

Ok guys,i think your are the right guys to ask these questions....

Supercharging the VX is really worthy to do so ?

How much it cost you guys to have that job done. ?

How much horse power your VX gain after installing the S/C kit ?

Is much faster the VX S/C ?

Is the VX's acceleracion much better than before ?

Which is the best S/C brand out there ?

I asked those question 'cause i'm wondering about doing that too

I'll appretiate all inputs regarding this matter

[etlsport]

Ok guys,i think your are the right guys to ask these questions....

Supercharging the VX is really worthy to do so ?

How much it cost you guys to have that job done. ?

How much horse power your VX gain after installing the S/C kit ?

Is much faster the VX S/C ?

Is the VX's acceleracion much better than before ?

Which is the best S/C brand out there ?

I asked those question 'cause i'm wondering about doing that too

I'll appretiate all inputs regarding this matter

the supercharger new costed about 3200.. a shop would probably charge you another 500-1000 to install it.. they are no longer made, so finding one is hard.. so expect to pay more for the unit

typical horsepower gains are about 50-60 i beleive

there is only one company who made them.. eaton.. and they dont make them anymore

[johnnyapollo]

Ths supercharger itself is an Eaton MP62 (3rd or 4th generation). As stated, I don't believe it's available any longer as a production model.

The company that produced the manifold and kit that contained the Supercharger is/was Alpine. Retail was about $3500 at it's height - those of us who bought from Tone when the kit was first offered paid about $2400 as part of a group buy. This kit would work on any Isuzu 3.2 or 3.5 up to the direct-injected models found on the 2002 Axiom and some other Isuzu models. The kit is not without it's flaws (I removed mine last weekend to send off to be rebuilt) but it's the only game in town. There have been some other attempts at forced-air systems - MorganTech custom built a turbocharger for his Axiom, so there are some possibilities, but it's not something easily done without experience, resources, time and money. Hope that clarified.

-- John

[Gussie2000]

I guess an extra 50/60 horse power is acceptable in a SUV such as the VX.

Well i'll start my quest for any remaining brand-new supercharged kit.

By the way guys thanks for the input

[VehiGAZ]

typical horsepower gains are about 50-60 i beleive

Take it all with a grain of salt, but I think you will have a tough time using that extra power in NYC, Gussie.

The S/C itself only bumps peak power about 25-30 hp on it's own. You need to add a high-flow intake filter, a high-flow muffler, and larger-diameter exhaust system to get the other 25-30 hp out of the boosted engine. (Does anyone have a copy of that dyno graph that Tone used to have on his site? That shows exactly where the gains are with and without exhaust work. It MUST be on this site somewhere - searchie-searchie, Gussie!)

The power increase comes at the very top of the rev range - it has virtually no effect until you hit 4000 rpm, and doesn't really make a worthwhile difference until you get over 5000 rpm.

Alpine seems to still be selling the S/C kit here. Try here too.

The kits were seldom complete, by the way - they were typically missing the throttle cable bracket, a new slightly-longer cruise-control cable, and some other miscellaneous parts. If you have to have someone fab up a bracket, add another couple hundred dollars to the bill.

I bought my kit used for $1500 and paid a shop around $750 to install it for me. I got it for a pretty good deal, all things considered, but I probably wouldn't do it again for the same price, and definitely not for full retail. Here's why:

1) If you do all of the upgrades, the 50-60 hp gain will be there, but it's not so pronounced that it's worth the ~$4700 it will take to get there ($3500 S/C kit + $750 install + $350 exhaust + $100 intake).

2) Until someone comes up with a good high-flow muffler choice, your exhaust will be brutally loud when you're done. It's easy to say that you can live with that ahead of time, but harder to follow through with it afterward.

3) The power isn't as usable as you would think, since it's all at the high end of the rev band. (Although there seems to be a noticeable gain in torque just off idle when you open up the exhaust.)

4) The difference in acceleration 0-60 time isn't very much. I don't think anyone has any reliable before-and-after times to compare, but I can't believe it's more than a 0.5 sec quicker to 60, judging by my seat-of-the-pants-accelerometer.

You'd think that almost $5000 would totally transform a vehicle's performance, but it doesn't.

[Gussie2000]

Oh,well that's a good piece of info you provided me with.

I guess i should leave my engine along

I had the same thoughts about the NYC driving condition,the reason i had to think about the S/C is because i'll problally moving to maryland near future

However your input is all i need it to make a final decision. Thanks again

[Ldub]

I'm coming up on 40k miles of being supercharged (VX is about to have 80k) and like you always ran premium in it since that is what Alpine reccommends.

Tone told us early on that he used to run regular basically all week when doing basic commuting with the VX; and filling with premium before doing any rallycross or other "demanding" duties.

If you think you're going to run your VX hard for any length of time...I'd still run premium though just to be safe! That's my $.02

This is what I've been doing since the price of petrol has moved closer to $4.00 gal.
Regular for daily back & forth to work etc., premium or mid grade w/ 10% ethanol for a treat on weekends or for wheelin' trips etc.
I never see a CEL unless we're at a higher altitude, & IMO, regular is plenty good for interstate trips across the flatlands.

I've also experimented with "octane boosters" (Amsoil) with no effect on mpg or performance.