Do i need a blow off valve on my paxton supercharger?

dj65falcon

Well-known member
Ok. I just got done installing a paxton supercharger novi gss on my ford falcon wagon with a 300-6. The supercharger is running at 7 psi..I install a intercooler with all the tubing.. It has a blow thur carb hat from turbonomics. It has a 650 dp. That is made into a blow thur carb.my question is do i need a a blow off valve?and if i do what kind? And how do i hook it up. Thanks for your help.
 
The paxton supercharger novi gss is a ball drive unit and is not designed to operate at boost levels much above 8.
A blowoff valve will keep the pressure level down at partial or no throttle when the engine rpm is up.

The Turbosmart TS-0203-1223 is a good universal 34mm unit at a reasonable price.
It connects between the inlet and the outlet of the supercharger and the sense line connects to the intake manifold.

https://www.summitracing.com/parts/tbs- ... wAodMhYOdA
 
I re-purposed a Tubo-XS BloOff' from a WRX source with a Vortech SC on a 250. Fabbed up a flange on the SC to Carb hat tube ,it senses manifold pressure. The XS uses washers behind a spring to alter the maximum pressure held before release.

The BO' for FI cars usualy need the excess air returned to the intake as part of the MAF metering, carbs can just dump to outside .

haev fun




 
Thanks for the reply. So i need to use one if the supercharger exceeds 8 psi. Mine only does 7 psi.so can i get away from not using one. Since the psi is 7 thank for your guys input
 
djfalcon10":1qdink7n said:
Thanks for the reply. So i need to use one if the supercharger exceeds 8 psi. Mine only does 7 psi.so can i get away from not using one. Since the psi is 7 thank for your guys input
No
It is 7 psi at WOT at high rpm
As you close the throttle you are restricting the outlet of the supercharger and the boost goes high.
The extra pressure needs to be vented out.
 
Just now seeing this post, and noted a comment that excess boost air should be returned to the manifold for boosted fuel injected engines. Mine is Paxton SN89 with MSD Atomic TBI on Classic Inlines head, Duraspark II, and Paxton carb hat with flapper blow off. What does this "returned to manifold" mean for my application? BTW, I've had trouble getting my engine tuned well for acceleration off of idle, and am considering MSD 6AL programmable ignition box so that the Atomic can control timing-or replacing Atomic with a fully programmable aftermarket fuel injection system. Dyno guy says the Atomic limits him from custom fuel mapping, and I have overly rich and overly lean spots throughout rpm range. I've done enough miles that I feel the Atomic self tuning feature would have learned my system if it could.
 
If I'm reading it correctly if the EFI system has a Mass AirFlow sensor the Blow off air should be returned to the intake side of the supercharger through the MAF.
 
Thanks much for your response. The unit has a MAF, but it is in the TB body unlike external ones in intake ducts on factory vehicles. I'll need to research this and probably contact MSD Tech. I simply put a popper type in my carb hat because my Avanti with Carter AFB has only a popper type valve.

Any recommendations on an aftermarket TBI system (I want a retro look) which can be mapped and control timing? To my knowledge, the MSD Atomic cannot be mapped, and only rough parameters in the handheld unit can be varied, with fine tuning done by unit learning without human intervention.

Thanks again,
Mike
 
The Atomic TBI has a MAP (Manifold Absolute Pressure) sensor not a MAF (Mass Air Flow) sensor so the location of the BOV in the hat is OK.

There are only 5 target A/F ratios you get to enter into the system.
Idle, Cruise, WOT, Nitrous and Boost.
You are correct, outside of those 5 fuel control parameters the user has no way of fine tuning the fuel map.

The problem is the Paxton produces a variable boost proportional to engine rpm and the Atomic's ECU only has a single boost parameter to work with so it will only be correct over a short range of boost and rich and lean on either side of that short boost range.

The Holley Super Sniper gives you 4 A/F ratio inputs for boost. 0 PSI, 7 PSI, 14 PSI and 21 PSI

I'm not seeing anything better for the FiTech TBI units.

It would also be possible to use a Multi Port unit that is laptop programmable and adapt it to your Atomic TB.
You have to bypass the ECU in the Atomic TB and wire directly to the injectors and MAP sensor.
 
I'm very appreciative of your advice, and am pleased that you took time to look at this old post which I resurrected. You are certainly correct about the rich-lean spots in the rpm range. We experienced these lean and rich spots on the dyno. In that I plan on only about 5-7 psi boost, it seems that the Sniper won't help me much if three of the boost targets are above my maximum psi. But, hopefully, I'm missing some insight there.

As for an multi-port set up, that is what the dyno tuner suggested for "tunability." But, although recognizing I'd have better performance with multi-port, I really want my installation to have a retro-period look; the "what if there was a Paxton supercharged GT200" type theme. My suspension is Shelby, and I'm going with a minimum options theme.

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What I meant was to use a multiport EFI system to run the four injectors in your Atomic Throttle body.
You would need to bypass the ECU in the throttle body and connect directly to the four injectors.

This way the system would look the same as it is now if your did a good job of hiding the additional wires.
 
So, would the multiport efi be tuned via a custom chip? If the Atomic was to be used for only the throttle body, that seems like a waste. Maybe replacing the Atomic with a different system (multiport?) which allows custom mapping would be better (I would then divert the Atomic to my stock power pack '57 Chev Bel Air).

I'm obviously not very savvy about fuel injection, but I do believe in it for the best fuel delivery! If you have suggestions for a replacement system, aftermarket or cobbled together from a mix of separate parts, I'll research them and work at improving my knowledge.
 
Multiport EFI systems are tuned by way of laptop computer and you have access to all tuning maps and tables.
The MegaSquirt system popular because of it's low price but it requires more work to get it set up.
The Holley HP EFI system comes with all sensors and wire harness.
But you are looking at installing fuel injectors in your intake manifold which is not the look you wanted.

I don't have a combination that will suite you right off the top but will look later.
 
thanks again for the good info which i will use as a basis for commencing substantive research on what's available.
 
so, maybe your initial suggestion to use the Atomic throttle body and control the injectors by separate multiport control is the most straight-forward approach which maintains the boosted carb look and provides custom mapping and control.
 
pmuller9":2vuekflt said:
The Atomic TBI has a MAP (Manifold Absolute Pressure) sensor not a MAF (Mass Air Flow) sensor so the location of the BOV in the hat is OK.

There are only 5 target A/F ratios you get to enter into the system.
Idle, Cruise, WOT, Nitrous and Boost.
You are correct, outside of those 5 fuel control parameters the user has no way of fine tuning the fuel map.

The problem is the Paxton produces a variable boost proportional to engine rpm and the Atomic's ECU only has a single boost parameter to work with so it will only be correct over a short range of boost and rich and lean on either side of that short boost range.

The Holley Super Sniper gives you 4 A/F ratio inputs for boost. 0 PSI, 7 PSI, 14 PSI and 21 PSI

I'm not seeing anything better for the FiTech TBI units.

It would also be possible to use a Multi Port unit that is laptop programmable and adapt it to your Atomic TB.
You have to bypass the ECU in the Atomic TB and wire directly to the injectors and MAP sensor.
Both the standard Holley Sniper and the Holley Super Sniper TBI EFI systems allow for full custom fuel and ignition tuning via laptop software. Both are capable of boost. Regular Sniper works up to 14psig and the Super up to 21psig. They are not limited to only a few A/F inputs and boost pressures.

Fitech EFI TBI "Power Adder" units are also fully tuneable via laptop software and are boost compatible up to 21psig.


The cheapest route would be to use your current TBI and run the injectors inside it via a Megasquirt or Microsquirt standalone EFI. It would require the most custom wiring and tuning, along with a steeper learning curve for a novice.

The most expensive route would be to use your current TBI with another aftermarket standalone EFI control, such as Holley HP. It would also require custom wiring, but has more support and is an easier to learn software and hardware.

Holley Sniper TBI EFI would replace the MSD Atomic and be the easiest and cheapest route for a full TBI system that's tuneable. Holley Super Sniper and Terminator TBI EFI and Terminator Stealth go up in price and features from there.
 
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