sn 93 tpi set up---help

[timdpetty]

I just bought used sn 93, how easy should it spin? It spins very smooth but takes effort. I also need to know how to set up the computer and engine?

I have 1967 327 bored 30 over, with Patriot aluminum heads and a 92 tuned port with 24 lb injectors. I have a XFI cam 268 and 280 duration 224 and 231 @ 50.



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[Michael]

Welcome to SCH.

A properly functioning SN (like your SN93) normally takes considerable effort to turn - something like 45 in-lbs if you were to put a torque measure to it. If the charger has fluid in it, it will be a bit easier to turn, but it will still require effort.

However, what's most important is that it should spin very smoothly (no notching or 'catching' of any kind). If that's the case, then you're blower is probably in good shape internally.

As for your "how to set up the engine and computer" question, I'm afraid that's a bit vague. What do you mean by this? Is the engine not together yet and you're asking if the combination of parts you have will work well? Or are you curious as to how to scan and tune the ECM to get the engine running optimally once the blower is installed?

Also, did this used SN93 you've purchased come with all the necessary parts (ie. brackets, belts, pulleys, hoses, etc...) you'll need, or are you going to need to source that stuff?

[timdpetty]

thank you,
the engine is together and running at this time. I was just wondering the tune with adding sn93?
I bought it with all papers and brackets, I think. I was thinknig the engine will need more fuel for more boost and how will the computer adjust for more air and fuel?

thanks ,
tim

[pavement pounde]

Then the kit was not complete.
For most Chevy engines Paxton used a aluminum spacer under the trottle body with 2 or 3 injectors controlled by a little computer.
Vortech did the same on Chevy and Mopar.
Or go with bigger injectors and do ecm tuning yourself, there is a lot to be found on the net.
Check the F body forums.

[Michael]

Then the kit was not complete.
For most Chevy engines Paxton used a aluminum spacer under the trottle body with 2 or 3 injectors controlled by a little computer.
Vortech did the same on Chevy and Mopar.

That may be true on some F.I. applications but all of the Paxton SN-based kits for TPI engines that I've seen didn't include secondary injectors/plates. They relied on larger injectors and ECM tuning.

The difficulty timdpetty will face is that he's running a '92 TPI setup, which uses a MAP sensor. These are a bit trickier to tune properly. Pre-'90 TPI setups used a MAF sensor, which responds better to forced induction tuning since the computer bases the engine's fuel and ignition requirements on actual airflow into the engine; MAP-based systems use manifold pressure correlated to airflow based on pre-programmed tables. That's not to say the MAP-based system can't be tuned to work, it's just going to be a bit trickier to do so.

My advice to the O.P. in this case is to sort through what you've purchased to ensure that you have everything you need to at least physically bolt the supercharger to the engine (ie. belts, brackets, hoses, fasteners, etc...). Post pictures of what you've purchased here on SCH - I'm sure several people here can help identify whether or not you've got everything you need to install the system. Once that's sorted out install the system as it is then take the car to a tuner shop that has experience with supercharged cars in order to tune the ECM. It may take a couple of dyno runs in order to log enough data to program the ECM to run the engine properly.

You could also contact Greg Carroll @ Blowerworks and see if he'll sell you an off-the-shelf ECM PROM - it'll be the same as what he supplies in his Stage I L98 supercharging kit. This will get the car running much better than if you were running a stock tune, however to really get everything running correctly, you'll still need to enlist the help of a tuner shop.

My only concern would be the size of the fuel injectors you have. However, given that the SN93 will only see a maximum of about 6~6.5psi, the 24lb. injectors you have will more than likely suffice with respect to the fuel demands of the engine. You could step up to a set of 30lb. injectors just to stay on the safe side, but I don't think that's necessary.

[zipnz]

Tim, looks like you are on the same path that i took. In the begining i started out with a tpi setup on my 68 camaro. I have a 350 in my car with edelbrock rpm heads and the same exact xfi cam u have with 1.6 rockers.
Even though the paxton really woke the tpi up i still suffered the power dropping fast over 4500 rpm because of the long and small runner tubes. in the future i feel you may be wanting to look into a different intake as in my motor it was built for 6000 rpm redline but the power dropped off dramatically before 5000 rpm.

With my tpi i originally started with the factory computer but with the addition of the paxton the factory computer has no mapping when getting into boost.
I then switched to a megasquirt II stand alone system that handles all fuel and ignition mapping. The switchover had some small teething problems but i love the ability to change any map setting at will and the ability to data log my drive and look at all my paramiters in real time after the drive.

24 lb injectors are stock for the 350 tpi system but they may be running short when getting into boost. i have 30lb injectors on my setup and have hit over 100% duty cycle on my injectors during a few data logs and i may upgrade to bigger injectors sometime in the future with my quest for more power.

To overcome my shortfalls with the tpi manifold i ended up switching to a edelbrock pro flo xt mini ram style intake. with this switch i have a better setup and it pulls really hard all the way up to 6000 rpm.

mike

[Michael]

24 lb injectors are stock for the 350 tpi system

Stock TPI injectors are 22lbs., not 24lbs.

Most people swap the stock Lucas 22lbs. injectors for 24lbs. units (typically choosing Ford Motorsports/SVO injectors) when it comes time to replace them. Those old Lucas disc-type injectors don't last long, and tend to develop leaks when used with modern 'ethanol enriched' fuels. The common belief is that the higher fuel rate of the 24lbs. injectors will provide a bit more power. Unfortunately, that doesn't happen since the ECM is programmed to run with 22lbs. injectors, and it has no way of telling that higher flow rate injectors have been installed; the only way any benefits are gained is with proper ECM tuning (ie. telling the ECM that the injectors have been upgraded to 24lbs).

The reason I suggested the 24lbs. injectors would be sufficient with the SN93 is based on the L98 TPI Stage I blower kit from Greg Carroll @ Blowerworks. This kit makes 6psi. of boost - the same as a Paxton SN unit - and does not include upgraded injectors (reusing the stock 22lbs. units). Blowerworks does however include upgraded injectors in their Stage II kit (8psi of boost) and beyond.

However, if your experience is such that you're finding 30lbs. injectors inadequate under boost, then by all means I'd suggest timdpetty reconsider the use of 24lbs injectors and instead upgrade to either 30lbs. or even 42lbs.

BTW - how much boost are you running with your SN93?

[zipnz]

Michael i beleive you are right about the 22lb injectors, some reason the number 24 was stuck in my head.
If tim is able to aquire a eprom this might be the most economical was to get his system together and the 24lb injectors might be adequate because of the performance limitations of the tpi.


I would like to share a 7 second snap shot of a data log i did a couple months ago.
There is a lot of usable information in this shot were i took a blast through first and second gear. The vertical line shows the values of the graph in that point in time.
You can see that at that point in time my,
Rpm in yellow was 4748.
The map sensor in light blue recorded 151kpa which is about 7.5 psi of boost.
The duty cycle in light green is 102.1% . (100% is considered wide open).
The air fuel ratio in red is 12.4.
And you can see in this particular tune in dark blue i have the timing pulled out to 23.8 degrees with this amount of boost.
Another bit of usefull information you can see that my boost starts to drop off after 4800 rpm because of belt slippage.
The values on the far left are the max readings during my total data log.