Cats off lost 5-7 PSI

[ken sampson]

I removed my Cats per the recommendation of my tuner. I am running a Whipple 2.3L and 425 RWHP so he said I would tear them up if left on so I replaced them with test pipes. I lost between 5 and 7 PSI just from the cat removal. I just found a way to get the boost back. I used the CC inserts. This also brought down sound very nice. Now back to the tuner.

 

[C-speed]

From my experience, if you are losing boost due to an exhaust mod, it sounds like you are running way too aggressive NA cams on an FI application or you have dialed in way too much overlap on the cams.

In either situation, on FI applications, you want short(er) duration and high lift, otherwise your car will run like crap under boost, or not build (much) boost at all as both intake and exhaust valves are open at the same time (overlap) for far too long.

Aftermarket NA cams are "generally" long duration/high lift and will NOT work for boosted applications.

Ask you tuner if he's done that.

 

[CarCrazed4Life]

I've also lost PSI while maintaining or increasing HP on a BMW FI car, but I was always told a small drop is expected due to increase flow of your setup... however 5-7 seems like alot...

 

[ken sampson]

I am running 19PSI so I lost between 4-5 on the low and mid range and 6 to 7 on the top end. I have stock cams. All is ok now after installing the inserts I got it all back.

 

[jdnsx]

Ken,

I don't think you want that boost back??? The only reason it is there is because you are "clogging" the air pump with a restrictive exhaust. It would probably be better for you to tune for 13-14 psi with the open exhaust. The motor would be happier and you might even make more power.

.02 cents
Joe

 

[jorligan]

I'd have to agree with Joe. It always kinda surprised me that you are running such high boost with a built motor and getting low hp numbers. I thought that it was related to the SC design and restriction on the intake side but now that you removed your cats, it sounds more like it was the outflow. I am running only 13 lbs of boost on my turbo setup and getting closer to 580 rwhp. My car is running really rich so I suspect that I will get more with a retune.
Tim

 

[ken sampson]

I'd have to agree with Joe. It always kinda surprised me that you are running such high boost with a built motor and getting low hp numbers. I thought that it was related to the SC design and restriction on the intake side but now that you removed your cats, it sounds more like it was the outflow. I am running only 13 lbs of boost on my turbo setup and getting closer to 580 rwhp. My car is running really rich so I suspect that I will get more with a retune.
Tim

I take it your not running any cats? What are you running for timing?

 

[jorligan]

No cats. Using the MSL-AEM for now, plan on changing over to the FI/C in the near future. Originally had been planning on using the TEC3 like you (bought a unit from GJ right after you did) but my tuner was more comfortable with the AEM.

 

[Mark911]

Any time you increase the volumetric efficiency of the engine (less exhaust restriction in this case), absolute boost pressure will drop. This is a desirable condition as you should be seeing at least the same total air flow (if not more) at a lower pressure with the benefit of associated reduction in air temperature. Lower air temps allow more aggressive tuning before the onset of detonation, which should result in increased torque and HP.

 

[ken sampson]

I will bring the boost back down by removing some of the insert restriction.
It just seemed like it lost so much power. I guess when I tune again I will get it all back and more with less boost? I hope.

 

[supergoji]

I will bring the boost back down by removing some of the insert restriction.
It just seemed like it lost so much power. I guess when I tune again I will get it all back and more with less boost? I hope.

you wont get it all back since you are running NA cams. you want FI cams.
as C-speed and Mark911 just explained to you. I would also think it would be healthier for the engine to have the proper cams and tuning if you are attempting to make that type of power, it also makes more sense.

 

[ken sampson]

Maybe you misunderstood something. I have stock cams so C-speed said if I was running larger cams. He also said I may not get boost and the car would run like crap. My car runs perfectly fine and has 19 PSI. Then Mark stated that I would get The HP would return and some. This sounds correct.

 

[nsxotic911]

I will bring the boost back down by removing some of the insert restriction.
It just seemed like it lost so much power. I guess when I tune again I will get it all back and more with less boost? I hope.

Yep - you'll be able to run a more aggressive tune. This is why race cars have a straight pipes (or very limited restriction) and engines, when they are put on dynos, they don't have a full catback exhaust on

Restricion limits power, in general. However, you need to tune your car for that.

As a quick note.. when I put my test pipes on, I've found that I actually may have gained some boost Not quite sure yet b/c I can't hold my foot down at WOT for extended perio of times while trying to make out my analog Defi gauge on the a-pillar, and try to distinguish between .4 or .5 or .6 bars...

Anyway - test pipes are a good thing, just get the car retuned.

 

[C-speed]

As a quick note.. when I put my test pipes on, I've found that I actually may have gained some boost

Ya, on turbo cars, especially if you are running an internal wastegate, opening up the exhaust and relieving any backpressure may cause you to gain boost. This is mainly due to the fact that the internal wastegate (sucks ), and it is creeping or spiking beyond the boost limit of the wastegate since the turbo can spool that much quicker now and the wastegate can't flow/bypass the exhaust fast enough to limit the boost.

When that happens, you can either port the wastegate bypass port on the exhaust housing a little (may or may not fix the issue), or switch to an external wastegate (100% fix).

 

[nsxotic911]

Ya, on turbo cars, especially if you are running an internal wastegate, opening up the exhaust and relieving any backpressure may cause you to gain boost. This is mainly due to the fact that the internal wastegate (sucks ), and it is creeping or spiking beyond the boost limit of the wastegate since the turbo can spool that much quicker now and the wastegate can't flow/bypass the exhaust fast enough to limit the boost.

When that happens, you can either port the wastegate bypass port on the exhaust housing a little (may or may not fix the issue), or switch to an external wastegate (100% fix).

I have CT SC Whipple "High Boost" buddy

 

[C-speed]

Maybe you misunderstood something. I have stock cams so C-speed said if I was running larger cams. He also said I may not get boost and the car would run like crap. My car runs perfectly fine and has 19 PSI. Then Mark stated that I would get The HP would return and some. This sounds correct.

Actually, i said "If you are running AFTERMARKET *naturally aspirated* cams".

ie: more agressive than stock, naturally aspirated application cams - if you try to use those on an FI setup, your car will run like crap, split and sputter or buck under boost or not boost at all, due to the (excessive) overlap.

Aftermarket FI cams are NOT the same as aftermarket NA cams.

FI = high lift, short duration
NA = high lift + (typically) long duration = BAD for FI

 

[C-speed]

I have CT SC Whipple "High Boost" buddy

hehe oops. Well, in that case - your gauge is broken