: Performance mods!

01-11-04, 09:25 AM
A lot of guys do mods on their cars to increase performance.....The question here is....Do they work as intended? Or cause problems with no appreciable performance gains The real answer is that the modifications usually offer little to no gains and can seriously compromise the overall capability of the vehicle. I'll try to explain it here with two common mods that we hear about a lot here...Exhaust and air box mods... Any system on the car has to comply with a myriad of specifications..most of which you would not even know about !! Things such as emissions, fuel economy, driveability, coldstarting, water intrusion, dust intrusion, induction noise, etc. must all be balanced.

Any exhaust system that significantly reduces exhaust backpressure will be louder...so...most owners will not put up with the noise. Many "performance enthusiasts" even find the noise to be objectional for daily use. Loud exhausts are fine for a Friday night cruiser but a pain to put up with in the daily commute.

Changes to the induction system significantly reduce it's effectiveness at attenuating induction noise, preventing snow and water from entering the engine and cooling the PCM that is in the induction system on many vehicles. Water intrusion is of particular importance as the engines with highly tuned intakes are very susceptable to "gulping" a slug of water from the plenum thus hydrostatically locking the engine and destroying it in all likelyhood.

Understand that most, if not all, of the aftermarket pieces that you see that advertise significant gains for a simple modification have HIGHLY exaggerated claims.
Understand that any passenger car is an extreme compromise in it's design by definition. It is engineered to accomodate use by the general public in a wide variety of operating conditions. Any given car off the assembly line could be shipped to Alaska, Northern Ontario, Florida, California or the Middle East. They are all engineered to work in all the areas. Obviously snow intrusion is something that the Saudi's are not interested in but they do care about dust intrusion clogging the element... Florida owners don't need block heaters and could care less about cold cranking capability but the owner in Alaska cares about the ability to start at -40.

Any modification to the existing factory systems will probably seriously compromise performance of the system in another area. If you realize this and can accept this (and accept responsibility for any resulting damage that occurs) then modify away !!! Just don't expect huge gains with simple boltons because all the "low hanging fruit" has been picked on modern engines and very little is left on the table without compromising noise, idle quality , durability, etc. The Northstar , in particular, makes over 1 HP per Cubic Inch from the factory. Gone are the days of buying a 350 chev with 160 HP and making huge gains with simple bolt ons.

Don't forget that the power and torque characteristics of the engine are more important than the absolute HP number. In the Northstar's case you have a 280 cubic inch engine pushing (pulling..??) a 4500 pound car around. A lot of work went into maximizing the torque curve to get the performance that the vehicle exhibits. You can change cams, make 100 more HP on the dyno, and the car will be slower due to the severe loss of low end torque that will result. Not a good idea... Sounds good in the ads, and looks good on paper but drives like Sh*t. Remember, people buy HP but they drive torque...so torque is what you need.

One of the popular mods is cutting up the air box to "let more air in". I have seen some testing with modified airboxes and have yet to really see an improvement the performance of the vehicle under carefully controlled conditions... Yet major gains are "reported" I suspect due to the increased induction roar...no doubt it sounds fast...but it isn't. And it will drive around fine for years until you happen to accidentally drive thru that 10 inch deep puddle of water in a cloudburst and drown the engine and hydrostatically lock it due to the modified airbox.

Try not to freak out here and start screaming about the super power that you produced with a simple airbox mod or bolt on exhaust....The gains are just not that significant! If you like the extra noise...Fine, but remember it's noise not power....There's a difference!

01-11-04, 10:46 AM
Great post, kc.

I agree, the airbox mods are not what they're cracked up to be (no pun intended). A good cold air intake system yields at best a 10-12% boost in hp, but torque is sacrificed in the process. So, like you said, noise ain't power.

01-11-04, 02:58 PM
Great post..... Airbox mods are about the most worthless thing you can do, along with performance air filters..... You might be able to squeeze 1 hp (3hp with placebo affect :) ) out of a filter, but you can also really dirty your MAF, TB and plenum....

Unless your talking about stuff like NOS, or forced induction, most cheap mods may give you extra HP, but move the torque curve up in the upper RPMs.... That doesnt really do anything for daily performance!!!

01-11-04, 03:33 PM
Great post..... Airbox mods are about the most worthless thing you can do, along with performance air filters..... You might be able to squeeze 1 hp (3hp with placebo affect :) ) out of a filter, but you can also really dirty your MAF, TB and plenum....

If you get your MAF, TB, and plenum dirty then I suggest you stop drowning the filter with the oil. I got 2 of these filters but I got it more mostly because I don't need to throw it away. A light coat of the oil is all that is needed. I check it every time I change the engine oil.

01-11-04, 03:51 PM
My mods all seem to work well together,probably going to do NOS also. I think it is the combination of the mods. I am also doing powerstop rotors,drilled and performance calipers. I agree that the advertised performance gains are too high.

97 concours
01-11-04, 05:55 PM
Removal of the honey comb mesh on the MAF seem to help a bit. Me and a buddy both have Northstars. One night before going out to play I decided to remove the honey comb mesh. We raced before and after. Before the cars were about even, after my car pulled him about 2 full honest car lenghts consistantly. After he removed his we were back to dead even, therefore, I would say that it did seem to make a difference, especially in the higher rpms.