I am installing a Stillen Supercharger on my car. Word on the street is (from Stillen) that installing headers and high flow cats is a bad idea. According to them their supercharger is designed to operate with a certain amount of back pressure and that by reducing that back pressure I will lose power that the supercharger added. So my question is, is this true? Does anyone have some solid experience with this?

I apologize if this question has already been asked but much like MC Customs, I don't have time nor the inclination to sift through all the crap.

I think you are right, I have heard the same things, I would leave the stock cats and mani's one, If not just for emissions than anything else.

With LTH's, pressure drops and you lose some boost. Solution is to buy a smaller pulley to increase boost. With the headers and smaller pulley pushing the same psi as the stock Stillen kit, it will create more power. PSI to PSI, the headers will create more power on nearly every supercharged application than without... Unless the unit is undersized.

I am running stillen headers and cats with my stillen SC and making great numbers. I do not have any issues at all but I do have a custom tune. what may make a difference if you plan to run headers/cats on stillen's stock tune.

Just to clarify, its not that the LTH's or HFC's are bad its that Stillen didn't design it for those applications. On normal applications improving exhaust flow usually leads to gains on an S/C setup. Hell on my 4 banger S/C, a decat and headers will yield significant positive gains. This was my biggest annoyance with the z34 S/C platforms. You are forced to keep your stock cats which are EXTREMELY RESTRICTIVE and leave power on the table.

Other reasons why improved exhaust doesn't seem to help S/C applications is because VVEL will not compensate properly for the improved flow.

OP since you are in Cali, its probably best to leave the stock exhaust hardware on, are you going CARB certified on the Stillen S/C? If so be wary of the canned tune.

The funny thing about all of these considerations (e.g. actually adding exhaust restriction to make more power) is that the real problem is the inability to control the amount of valve overlap to avoid blowing the boost straight through the motor. VVEL is great for NA but killing us on FI applications. Just look how much more power the 350s are making on the same kits.

Just to add the above comments about leaving the stock mani's and cats on Kelly? You made 405 WHP on a mustang correct with you headers and HFC's correct? I made 412 WHP( 7 SPD AUTO) with stock cats and madifolds. Mustang dyno also. I know every dyno is differnt and numbers will be also, But just to compare I if there where true gains from HFC's and headers I would have expected to see 460sih numbers not close to mine,. BTW car looks the SH#T,, Love everything you did,

Just cause we are talking WHP doesnt mean I can like your ride :)

You will make more power with the headers and high flow cats/ Test pipes with a custom tune not Stillen tune.

RCZ proved this with 445 WHP on a dynoJet.

I aslo made 464WHP dynpjet with test pipes.

It's a vortech V3 Blower it is sufficient enough to flow with that combo. This is done on many platforms with the same unit.

I actually bought RCZ kit and made 20hp more on the same dyno so Stillen makes a good product (as well as GTM) and like everyone else has said it is just the tune because of the restrictions in CA. So it really comes down to personal preference.

Nice numbers just looked at your build very well put together car.

thank you very much. she is a work in progress have just a few more additions before a total paint job to give it a show car finish but I have to pick up another bike to have another mode of transportation before I can start that process. :ughdance:

Hey Guys,

I haven't been able to spend much time on the forums lately unfortunately as I've been buried in projects here but I wanted to jump in and add the "stillen point of view" on this topic.

We do not recommend high flow cats with forced induction. In our experience, they have a hard time living in the FI environment. We have seen Z's/G's, Camaros, Chargers, Corvettes, all different kinds of cars chew through high flow cats when used in an FI application. We basically say, standard OE cats, or nothing...

In regards to the headers. We have seen them used in conjunction with our supercharger and they work fine. Initially the concern was that there may be some boost loss similar to what we experienced on the VQ35 engines. However, on the VQ37 kit this is not the case. We have not seen a significant fluctuation in boost pressure after installing the headers.

It's interesting that OEM N/A cats hold up better to FI than aftermarket cats. I mean, with all of the factory FI cars out there, you would think there would be a supply of FI-capable cats readily available.

Thank You
 

ALL,

I want to thank all of you for your advise and help I think I decided which way I'm going to go with this. I hope to have the car finished soon... I can't wait to see what a difference this all makes. I will post pictures as soon as I can.

Thanks,

Fastlandyacht

I'll let you know about the pulley change also, Just bought mine today. Even tho the is down for the next 3 weeks or so, :(