View Full Version : Max HP from an intercooled blow-thru P-1SC?

08-02-2005, 11:07 AM
Hey everyone,

I've come across a pretty good deal on a P-1SC with the ATI carb and intercooler. What is the max boost I can run with this unit? I called up ATI and they were not very helpful. I'm looking at about 450hp N/A... ATI told me that it will only flow enough to get about 150 hp from the supercharger... even when intercooled. I don't believe that though... does anyone have any experience here? Also, how is drivability at high boost?


08-02-2005, 11:24 AM
I wouldn't believe ATI's tech support if they told me the sky was blue. :screwy:

I'm running a P1-SCH on my car at 15 psi @ 6700 rpm. Discharge air temps are not bad at all (in the 130F range, non intercooled but with water injection, on a 90 degree day, temp sensor is in the intake plenum right by the runners.) I have not dyno'd the car yet but it's eating enough fuel fuel for over 800hp even at a very conservative .65 BSFC number in the calculations. It should make ~650rwhp when I finally do make it to the dyno, and it drives like it has every bit of that power level.

The guy who helped me pick my combo (Scott @ SDCE) knew my power goals and suggested the P1SCH for my application. He really knows centrifugals and he definately didn't make a mistake.

Boost is really not the key factor you need to look at when sizing the supercharger. The P1SC will support 30lbs of boost but that's only at very low volumes. It will build plenty of pressure but as you open the restriction at the end (engine size) it will take a larger volume of air to build that much pressure up. Theoretically, you could just spin the thing faster to make up for it but there is an upper limit on impeller speed. So at some point you need to move up to a larger supercharger, it will deliver more volume at safe impeller speeds. Volume moved is much more important, boost is really only a measure of air "stacked up" in the intake and piping.

What size engine are you going to be installing it on? That will determine capabilities. I'm running a 4.25" pulley on my P1SCH and could go more if needed (still have about another 8000rpm left safely on impeller speeds.)

The other issue to watch for is intake heating. The faster you spin the supercharger, the less efficient it becomes (look at a compressor map), and the discharge air temps will climb. More heat is less power and a greater chance of detonation. For example, say small supercharger may develop X volume of air at 10psi and a discharge temp of 150F; on the other hand a larger supercharger will deliver that same volume/pressure at a lower 125F. However, with the larger supercharger (especially centrifugal) lower-RPM boost will suffer. You need to find a happy medium. For my application, the P1SCH is a perfect combo of a decent amount of low/mid RPM boost and it also provides plenty of top end boost without overly heating the air charge.

ATI claims the P1SC will flow a max of 1200cfm. It's hard to say specifically how well it will perform in your application because ATI does not have compressor maps available. Shame on them, because that's the best tool for the job to determine if it will work in your application.


08-02-2005, 05:49 PM
Whew, thanks Troy... that's a lot of typing!

I liked how the tech tried to help me... but my words were going in one ear and out the other. We are probably going to be going with a 355 or 383, and it is great to hear that you have experience in this area. Hypotheticals only make me feel so much better. I would go for the D-1SC to be on the safe side (power hungry :) ) but I don't really want to spend another 450 bucks when that could get me a set of rear tires... especially at the rate I plan on going through them :). What is the difference between the P-1SC and the P1-SCH? I could only find reference to the P-1SCH on a dated Procharger page. I doubt they even know that page is still up because none of the links are valid!


08-02-2005, 08:06 PM
The "H" in the P1SC-H designates a "high helix" impeller; i.e. the vanes on the impeller are much more curved than the standard P1SC. This results in better low RPM boost and a bit more efficiency out of the compressor. However, it's more complicated to machine and I believe it was about $200 more than a standard P1SC.

In fact, here's a PIC (http://home.comcast.net/~swedish_chef/stuff/ForumStuff/cwheel.jpg) of my compressor wheel. Note the curvature on every other vane. The standard compressor wheels have nearly straight vanes. This upgrade can be done on any P1SC, all they have to do is swap the impeller. I think the exducer/volute is the exact same, as mine has a printed "P1SC" tag on it with the "H" hand-stamped at the end.

You'll be just fine running a D1SC on a 355 or a 383. You can get away with a larger pulley to make as much power as a P1SC, and it wlll do it at lower air temps at peak boost/flow, the boost will just "come in" a little bit later than the smaller P1SC.

One thing to keep in mind is that ATI's stock bracket and tensioner are, well, junk out of the box. The bracket flexes too much and the tensioner slips a lot. To fix the bracket, you run a brace from the bracket just under the blower to the cylinder head; to fix the tensioner, you convert to a GM spring tensioner. If you dig on my webpage under the "procharger" section you can see pics of both the brace I fabbed and the spring tensioner mod, which was done by SDCE.

The spring tensioner mod is worth every penny. I'm still running the same blower belt after 7000 hard miles and it looks mint and doesn't slip. Guys will burn up belts in under 500 miles with the stock ATI tensioner, and often have slip issues-- and to fix the slip they crank the tensioner down so hard they eat up the front blower bearing.


08-05-2005, 07:29 AM
Sounds to me you would have about the same setup as me... It is very easy to get over 600hp with only 10psi of boost on a 355 with the psc-1 system

try and make sure to say around the 8.5-9.0 compression and use aluminum heads to keep from detonation..

with the intercooler you have you could easily run up to 17psi and make some crazy HP figures... I believe the PSC-1 system can support up to 825hp in a perfect world!

The engine will drive completely normal ,untill under heavy loads when the supercharger creates boost... There is a great misconception that the blower creates boost all the time, WHich it does not!

08-05-2005, 09:50 AM

DO you have the part numbers for the tensioner and pulley you used to replace the ati ones with??

08-05-2005, 01:06 PM
Thanks to both of you guys.

I don't have any technical knowledge in regard to superchargers. So Blown353 thanks for filling in some of the gaps. I'm not going to pretend I understood it all, though :).

I would like to go with a D-1SC, but like I said earlier, its just $450 that I can't spend right now.

Thanks a lot for all of your help and if I have any other questions I'll know who to ask :).

08-05-2005, 09:29 PM
What kind of carb are you guys running?

I'm looking at the 750cfm Holly Double Pumper modified by ATI. I have an opportunity to buy a polished P1-SC w/ 750 cfm Holley and 3.5" inlet/outlet intercooler never used for 2.8k shipped. I don't think I can beat that, and if the carb needs to be modified down the road, so be it.

Does anyone have experience with the ATI carbs?


08-06-2005, 05:12 AM
i am running the 750 DP that ati sells... its a great deal for $425 and really works pretty good out of the box once you change the jets(they dont change the jets for you) I also changed the power valve to fit my camshaft and vacume! The ATI carb is just a basic Holley DP with the choke horn machined off and it has special floats installed and none stick gaskets.. I also think the Proform carb that costs $499 which has special housing and billet metering blocks, would be a great carb as long as you buy the supercharger adapter kit from ATI (gaskets and floats)

Is the intercooler you would be buying made by ATI?

I got a AWSOME deal on my procharger from Frank from prodigy here on this site.. (he is a ATI dealer)

08-06-2005, 08:19 AM
Yes, the intercooler is made by ATI. As far as I can tell, the retail prices for all of the items would be... $4727 and if i got 10% off (shopped) it would be $4253.40... so $2,800 ain't so bad. I had 2.5k budgeted for the supercharger and 500 for the carb. So, it's $200 cheaper than what I had down on paper, plus I get an intercooler! I love it when the budget goes my way.


08-06-2005, 10:05 AM
Do NOT skimp on the carb; it will make or break the whole package. ATI's "mods" are nowhere near adequate contrary to what the "experts" on their "tech support" lines may tell you.

Read here... https://www.pro-touring.com/forum/showthread.php?t=6206

Also, good reading here: http://www.boards2go.com/boards/board.cgi?&user=huntracers

Oh, and back to your very first post about blowthrough driveability-- it is EXCELLENT if the carb prep work has been done properly. Just as I do now, when my car was carb'd I'd drive through town in stop and go traffic with the A/C on with it being 100F+ outside. I also had no problems in the winter. I was able to treat it like a "normal" car and it never had any bad manners or poor driveability. The only real nag I had was that the milled choke horn and the cut-down vent tubes allowed fuel to slosh out the secondary bowl under *really* hard braking which would flood and kill the engine.


08-08-2005, 08:26 AM

My ATI holley carb did not have the vent tube cut down, so i dont have a problem with fuel slosh..

There are alof of guys that can tune holleys just as good as anything.. Just make sure you have someone who knows what there doing tune it..