I have been searching and reading for a couple hours now and have gotten fairly frustrated and more than a little confused.

The good news: I got my blower. Granted its just a Paxton SN 92, but its in great shape and will be a good match for the ZZ1. Better blower is in the future as well as forged pistons.

Bad News: Car is currently carbed. I have a TPI setup but the price of the parts for me to get it on my car is semi staggering considering its going to make it slower with the lack of air flow above 4800 rpm. I had the blower fuel provisions in mind for TPI but doing it for a carb seems atleast mildly more complicated.

I am fairly sure that this information is on this site, its just annoying me that i can't find it. Having all the information in one place would not be a bad idea.

Reading here, most of the people with customish setups for fuel delivery are using Turbos which reach and hold at max boost quite quickly. The Centrifugal S/C on the other hand does not and I am not sure how to supply the required fuel with an injector. For example having one injector on a hobbes switch set to 100% duty cycle would be way too rich at all rpms below redline. What happened to Bhass?

I will be using a water/alcohol injection system and the blower will be pullied for what paxton says is 6 lbs boost. Oh and i will be lowering the compression to approximately 9.3:1 with the same headgasket used on the 80s and early 90s generation corvette.

Tuning the carb in as well as this alcohol injection seems daunting. Do i tune the carb and then start using the water/alky and then tune the carb again and keep going back and forth until its perfect?

I read something about boost referenced power valves in a holley. mine is a 750 cfm 4150. Is this something for me to look into?

Please help me out guys

Since this post, I have gotten my hands on Turbochargers by Hugh MacInnes. I have been reading through how to modify a carb for boost and he shows exactly how to do it and how to make it work to meter the fuel itself without an extra injector.

I suppose i am writing this as much for me as anyone else. Why don't people do this to their carbs to prep them for boosted aps? Botlfed for example put floats inhis and cut off the choke tower. Thats infinitely more simple than this. Why don't you follow these directions? Are they old school and have been proven wrong since the book was writen?

Thats a long quote i typed out...

Well, you asked for it and you’ve got it… my $.02 (but you’ve answered some of your own questions):

First, TPI: If you want to go injected do it, if you don’t, then don’t. The TPI parts won’t hurt you. The biggest reason that stock L98 cars fall on their face before 5K is that the stock heads SUCK! It’s not a problem with the TPI manifold. The flow of the actual stock manifold parts do not become an issue until the high 5K rpm range and about 400hp at the crank (NA).

If you want to run a carb then do that. I don’t really see why a properly modified carb would be any worse then FI with an FPR. It’s really doubtful that either would be perfect, but they can be tuned close enough to work. Within reasonable limits (and 6psi is certainly in those limits), tuning problems with either method are mostly dependant on the person tuning, not he method.

Why don’t people go through the procedure in McInnes? Well, I’d say mostly because people don’t want to do the research to figure out what really works. Also, there are some carbs that seem to deal with boost OK without major mods, specifically the edlebrock carbs and some of the demon carbs.

WRT to water/alcohol injection… well, I would run just water if you don’t really have an issue with it freezing, and then add just enough alcohol to keep it from freezing. OTOH, I wouldn’t waste my time with just 6psi boost, the difference is small enough that you should be able to compensate for any tendencies to detonate with a little extra fuel, colder plugs or slightly less timing.

Also, if the setup is supposed to make 6psi boost on a stock engine I doubt you’ll see that much on your ZZ1, you’ll probably have to spin the blower a little faster.

Well i plan on operating on my carb the way you're supposed to then.

The MacInnes book says I need to move the PCV to the compressor inlet when i do a blow through? What does this mean?

it also says my vacuum source for brakes will be "sporadic, (and) requires check valve."

Explanation would be appreciated.

Also, people report a gain of roughly 75-100 hp using this blower pullied in this manner on a stock engine. With my better flow characteristics, i will make less boost but should have a higher percent gain right? BTW, i can't pully the blower any higher and have it stay 'happy'. Right now it will reach its redline right at 5500 rpm. which is where i shift now. I suppose if reving past 5000 wasn't worth anything i could bring it down for a bit more boost and then never over rev it.

I also have a dual plane intake and you have said a number of times that i have read that a single would be more ideal. Suggestions? It needs to fit under a stock hood.

Thanks

The PVC line that now goes from the PVC valve in the valve cover to the carb has to go to a location in the inlet tract that will not see boost.

Personally, I’d do something different, if nothing else just vent it through a breather or a vacuum pump. That line always puts assorted oily crap into the intake, and on a boosted application just ends up making a mess and making the engine more detonation sensitive, but this is how OEM’s do it.

The plastic fitting on the front of your booster is a check valve. If you let boost into the booster it will at best work against you trying to brake (the boost will push against the pedal rather then with it helping you) at worst will rupture the diaphragm.

I’d leave it like it is and if you have problems then you’ll need to run a vacuum reservoir and a check valve.

Airflow is airflow. What’s important is not the amount of boost but the mass of air ingested an mixed with the proper amount of gas without detonation. Adding a blower of any sort to an engine causes it to make power according to the air being pumped by the compressor under boost, no more, no less. For the most part if you take the same blower and mount it on a tiny engine and a large one they will both make the same power at the same rpm, assuming that both engines have similar combustion efficiencies and you keep the compressor at roughly the same efficiency. Most scroll type compressors are most efficient in the 2-4:1 pressure ratio range (I have NO IDEA where the little Paxton falls, I’ve never seen a compressor map for one), so you usually gain a little efficiency by going with the smaller, less well breathing engine. OTOH, you’ll see less boost/heat on a better breathing engine, so in this case you’ll probably see a couple (say less then 10) HP more on the better breathing engine.

IOW, don’t plan on seeing any more power then any other SN92 installation turning the same RPM.

Well, I’ll still say that a single plane will work better, but a dual plane can be made to work. The fact is that carbureted blowthrough setups in f-bodies are hard to package under a stock hood. The taller bonnet or box over the carb the better the blow through setup will work. I haven’t done this on an f-body so I don’t know what you can really get away with, but if it was me I’d try to find a reasonable bonnet to use and see what combination of carb and intake it will fit with.

The bonnet that bhaas used is about as short as you can realistically go and expect to work well. The fairly common K&N bonnet that you sometimes see is too small and most that use one usually end up getting rid of it after finding that they can’t tune the carb to work right (it’s designed for relocating the air filter in tight packaging situations, not for boost).

In terms of venting the valve cover to the atmosphere, both my valve covers have pcv valves installed. I didn't do this and just haven't gotten around to changing it. The driver's side valve is on one fork of a Y which runs to the brake booster and the carb. I know this isn't right. The passenger side PCV valve is just there; its not connected to anything.

How should I set this up? Vent both valve covers to the atmosphere and just run one hose to the brake booster from the carb?

After reading some more about modifying the carb, i think i am only going to remove the choke tower, put in solid floats, and boost reference the power valves. MacInnes doesn't mention anything about smaller adjustable bleeder valves. Changing the secondaries to be operated by actual boost pressure seems a bit involved and no one else seems to do it. About what Jets on the holley do you think i should start out with. Obviously too rich and then pull the size down slowly until its too lean and go back up one. But where would you suggest i start?

Screw it… I’m getting tired and not making any sense (I was trying to explain how a factory style PVC is routed on an NA and boosted engine). In a nutshell:
- if you don’t care about emissions save yourself the frustration and replace the PVC with brether’s (push in filters…)
- If you care about emissions have a breather or a line going to the valve cover from the filter, and then have the line coming from the PVC valve that should go to the manifold rerouted to the inlet of the supercharger
- If you really care you’ll need 2 PVC valves and you’ll have to route each valve cover to a different point in the inlet system, do a search online for how the Sy/Ty or GN was setup.

To be honest, myself I’d just go with the breathers. PVC on a blown engine is a royal, messy PITA that seems to always clog up and never work right (and this is coming from someone that usually insists in doing things “right,” but in this case “right” is just not worth the hassle).

Brake booster: just run a separate vacuum line from the manifold to the booster. As long as you’ve got a reasonable amount of vacuum at idle and cruise you should be fine. If you have problems (you shouldn't with 6psi, If you do your booster is messed up), then worry about it.

With the carb… same thing as I told bhaas when he asked a similar question. Honestly, I’ve never met a carb that I liked. I can get them to run, but I hate messing with them… I’m probably not the one to give tuning advice on it. Do a search for the blowthrough turbo board and blowthrough turbo Yahoo list (2 separate places, both can be accessed as boards and you can search the archives), they can help you out there.

Thanks for your help.
I think i would prefer to go injected, but i already have everything to set it up for the carb minus some floats and jets so I am going to go that direction.

At some point, a Holley Stealth Ram is in the future.