Paxton bracket...

[68mustang]

Ok so I picked up the whole Paxton sn89 kit for a foxbody for 200 bucks in working condition.... But my goal for the car I'm building is 11.50.... I don't think the sn89 will cut it... I see guys barely breaking 12's with sn89's seems wrong.... So my question is it's a stock pulley kit... I'm gonna run it and see what I can get out of it... But what is my best bet to upgrade tue blower to that uses the same bracket and wil fit without Any problems.... (vr4 would probally get me into the 11's but they don't make the kits). So which one should I look for?

[Michael]

An SN89 with a high-output impeller will produce between 6-6.5psi boost with about 750-800cfm flow. Depending on how heavy your car is, what engine the blower is bolted to, gearing, etc... 11.5 may be a far reach, but not necessarily impossible. There are a lot of factors which need to be addressed/answered before discounting an SN as being incapable of getting you into the mid-11s.

The VR4 kit would put you exactly where you want to be (and probably beyond), and would allow you to reuse all your existing hardware (brackets, pulleys, etc...) but as you said, they are difficult to find. I'm assuming you've contacted the usual sources: Paradise Wheels, Solanksi Performance, CUNDN Racing, etc... to see if they can help with respect to a VR4. I know Paradise Wheels was running a group buy for a short-run of VR4 kits a little while ago, but I don't know what ever happened with it. It might be worth calling and getting your name on the list, especially if you're planning on keeping the SN89.

However, outside of a VR4 I don't think there are many options for directly reusing the SN's brackets/hardware with another blower. You might be able to use one of the gear-drive NOVI units - and a properly pulleyed NOVI 2000 will more than likely get you into the E.T. range you're looking for - but I'm not 100% sure.

But if you're convinced your performance goals aren't going to be met using the SN89, it might just be easier to sell the entire kit - brackets, blower, pulleys, etc... - and purchase a NOVI 2000 with the appropriate brackets/pulleys for your application. The NOVI 2000 has an excellent service record and can produce some incredible horsepower numbers.

[68mustang]

Car is a 79 mustang... Weighs about 2800lbs... Has a s rod right now... With a t5 on the shelf incase it blows... Rear is a 8.8 with 3.55 right now... Might change to 4.10...motor is basic 69 351 heads, performer rpm intake, edelbrock performer rpm cam( sucky but free) has shorties no cats... And as far as I know stock sn89... Runnin it on slicks...

[68mustang]

Motor is a 302 forgot to put that

[Michael]

Just working with a very simple E.T. and HP formula, I've calculated that in order to run an 11.5 second quarter mile in a 2800lbs. car, you'll need an engine that can generate approximately 365HP. I don't know about you, but that doesn't seem out of the question for a properly built, well tuned, supercharged 302.

Here's how I worked it out (I found the formula in HP Books' Auto Math Handbook):

HP = Weight / (E.T. / 5.825)³

Knowing that your car weighs 2800lbs., and that you'd like to run a 11.5 second quarter mile, we plug those numbers into this formula and we get:

HP = 2800 / (11.50 / 5.825)³

HP = 363.875 ~ 364hp (let's call it 365hp for simplicity's sake).

I realize this formula is simplistic, and doesn't take into account factors such as transmission and final drive ratios, tire diameter, driveline loss, etc... but based on what's presented in the Auto Math Handbook, it seems to be pretty good for setting up a 'baseline' to shoot for.

So unless I've done the math wrong (which has been known to happen), this doesn't seem like an unattainable horsepower figure for a healthy, supercharged 302 to achieve.

[68mustang]

Sounds like it is very attainable... Thanks alot for your time.... I might try and drop another 200lbs off the car to help...

[Michael]

No problem.

BTW, I found the same basic formula but instead of using 5.825 as a constant, it uses 6.290. I have no idea how either of these constants were derived, however I reran the calculation using the 2800lbs. weight of your vehicle and the desired 11.50sec E.T., and the "new" horsepower number I get is 458hp (let's round up and call it 460hp). Admittedly, that's close to a 100hp difference between the two numbers, but even 460hp isn't unattainable from a healthy, blown 302. And lets face it, using the higher second number as a benchmark will only make it that much easier to get to your target E.T.

Oh, and it's also important to note that the vehicle weight used in either formula includes the driver and all fluids.

[68mustang]

Hmm so a stock sn89 puts out what 5-6lbs? I think I can get about 325-350 or so... Just getting into the 11's would work for me... Maybe add a 75shot on top of the blower if it's running good on the blower...

[Michael]

A stock SN89 realistically puts out between 5lbs. - 5.5lbs. of boost, assuming you're only spinning it up to it's intended RPM (which is 39,000 rpm if memory serves me correctly).

Similarly, an SN89 equipped with a high output (HO) impeller puts out between 6lbs. - 6.5lbs of boost spinning at the intended 39,000 rpm.

More boost is possible (some people on this site have seen spikes of 8lbs. of boost from HO impeller equipped SNs) if you spin the blower beyond the 39,000 rpm design limit, but be aware that it'll also be developing a lot more heat by doing so, almost to the point of negating whatever increase in boost is being produced. And that's to say nothing of the exponential rise in wear of internal parts, requiring frequent tear-downs and rebuilds.

Using NOS along with the blower is also an option. Several people do it; search the site to see if you can find any further information about doing so. But typically, NOS is used primarily as a means of dropping the inlet air temperature from the blower, so another option in this vein is to consider water/methanol injection.