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View Full Version : SC Overdrive: 10% vs. 15% vs. 20%



DrFishbone
07-13-2011, 07:28 PM
I ended up with a complete set of aluminum supercharger and jackshaft OD pulleys: 5%SC, 5%JS, 10%SC, & 10%JS. Up until this point, I have only used the 5%JS & 5%SC pulleys, but want to bump the overdrive up to 15% to see what the ACT's look like with my setup, and if that goes well, try 20% total overdrive. (By the way - this is a Magnuson S-port, with about 15-16psi max boost on my engine w/10% OD).

My initial thoughts are that if my IC is doing it's job well, the 15% may let me keep the timing curve I have, or possibly even add some (I've not found how much advance my car can take just yet, but in general, ACT's stay right around 100F at WOT, max RPM). But, the 20% may make the temps too high. I remember reading a great thread by Fraser awhile back where he did some testing on this very topic, but can't see to find (or remember :o) the exact parameters of his setup....anyhow, I'm going to to some testing on my own. :)

Anyone care to speculate what the results will be? I will have an 1/8mi track to play on while trying to find the best balance between pressure and temps - hopefully sometime in the next week or two...only bad thing is the weather...it's been hovering around 95F recently. :rolleyes::( I guess that basically means that I'll be able to get a little better results when racing weather is back - huh? ;)

fturner
07-13-2011, 10:21 PM
You might get away with 15%, but forget about 20% on that blower. The limiting factor is not the IC or anything like that, its the inlet to the blower that is restricting you from going to 20%.... hence the reason for the big inlet change with the MPX setup. The standard rectangular inlet cannot flow enough air to support 20%, and is actually starting to be outflowed even with 15%.

I ran a DIC with a well ported 94 blower at 15% and my ACT's would get to around 130-140 on the 1/4 mile so timing was getting pulled.

You'll also have to pull timing if you are going to 15% OD, not add timing. The IC won't cool the charge that much to safely add timing on pump gas. You want to do that, you have to either run a couple gallons of race gas or the better alternative is to run alky injection.

Fraser

DrFishbone
07-14-2011, 12:07 AM
You'll also have to pull timing if you are going to 15% OD, not add timing. The IC won't cool the charge that much to safely add timing on pump gas. You want to do that, you have to either run a couple gallons of race gas or the better alternative is to run alky injection.

I thought that might end up being the case. Did you use an MP inlet in your testing, Fraser? I can't remember if you had a ported 94/95 inlet or the MP. (where is that thread anyway? :))

fturner
07-14-2011, 08:35 AM
I thought that might end up being the case. Did you use an MP inlet in your testing, Fraser? I can't remember if you had a ported 94/95 inlet or the MP. (where is that thread anyway? :))

I had both, and did comparisons of both. The stock inlet plenum is pretty close to be outflowed at 10% OD.

Fraser

DrFishbone
07-14-2011, 12:03 PM
I had both, and did comparisons of both. The stock inlet plenum is pretty close to be outflowed at 10% OD.

Fraser

That must've been why I was thinking 15% was as far as I could take it with the S-port and MP inlet... I had forgotten about the inlet and was thinking that the OD amount was solely heat-limited. :rolleyes:

Well, in that case, I may not bother with 20% for now. Maybe if an MPX comes along at a good deal. Although it may be pushing the limits of the inlet, we'll see what the 15% does vs the 10%. :)

I'm hoping if I can squeeze a little more out of my setup, and improve a little on the launching, I might be able to get a 13.0X or maybe a 12.9X at the shootout this year. That's would be pretty good for a heavy 5-speed with an s-port blower. :cool: