i have a 93 rx-7 twin turbo w/ an apex'i cat back exhaust and custom k&n intakes. i was told that after replacing the intake and exhaust i can't do anything else to the engine until the computer was upgraded. is this true? i was told i stand a chance of blowing up my motor if any other modifications were made b/c the air/fuel mixture would not be right.

 

This is correct. The stock fuel system will only support to about 14.5 PSI, and the combo of a higher flow intake and exhaust can generally cause boost spike/creep into the 14PSI or higher range. An aftermarket comp that will also control boost will give you control over this, as well as give you the ability to fine tune the motor so it is running at its optimum level with the mods that you have.

If you want to run higher boost on a regular basis you need to look into upgrading the fuel system. I.E. bigger injectors, pump, etc.

 

In my experience 2 mods and you're ok. But different cars do different things. For instance, my rex has all of the usual bolt-ons, Intake, DP, high-flow cat, cat back. In the summertime, my A/F gauge said everything was A-OK, but when the winter got here, my rex was sucking in cold dense air, and producing more HP than the stock computer could handle, and I started leaning out. But, to answer your question, 2 mods, and you're ok for now, but after that you're taking chances w/your motor, also get an A/F ratio gauge to give you an idea of what you engine is doing.

 

The general rule of thumb is two modifications and then you have to get an ECU upgrade. What you said below is true, you will be running too lean to do any more upgrades. Now that being said, I am running a downpipe, high flow cat and an intake without the ECU upgrade. I am pushing it and plan on getting the upgrade soon. Besides running to lean, you will also be running to much boost. I added a Defi boost gauge to monitor my PSI and am running at 12lbs. With my mods and 12 PSI, I am pushing it. Read more on the web site about your options for the ECU. Either get a computer or a programed chip.

 

Yes to true, The Mazda RX-7 is very well tuned to achive 255 hp, However adding two mods does seem to jump the cars hp significantly. The result more air same amount of supplied fuel. This in turn gives you a situation that our beloved Appex seals like to snap crackle and pop too! Leaning out the engine is one of the great destoyers of the rotary engine. I have the Petit upgrade computer for my car. It really seems to run rich but the chip set on the board was only for my timing chip not the fuel one, and hence I don't really know if Petit does anything to the fuel maps or if the fule maps just follow suit in accomidating the timing. Any ways It works But unless you like the sound of shotguns (backfiring when foot is of the gas) You may want to order a computer elsewhere. However on a plus side it really shoots out a sizable flame which tends to get tailgaters off my butt!

 

HUGH do u have a cat? or how are u shooting these flames . wasnt sure if its possblle to shoot one with a cat

 

Actually I have a custom 3" stainless exhaust it's 2 pieces right off the engine. No cat so maybe thats another reason I backfire so darn much!

 

The general rule of thumb is three mods before you have to upgrade your ECU.

I'm running a Pettit Cold Air Intake (3 K & N filters), a 3" SS downpipe, and an Apexi Dunk Catback.

My boost runs 11-9-11

No probs!

Also, added the power pulley, ACT Clutch & 8.5# flywheel.

 

...backfiring...something I do quite a lot...when I backfire in a tunnel...sounds like a shotgun going off...very loud

 

So far the only performance upgrade I had done was an HKS downpipe. this was before the water seals went and the car went into the shop. While in the shop I had it street ported by Dave @ KDR. Do I need to go with an ECU next. Also the car is an auto. Any opinions on that? Thanks guys

 

if you have the port done...whoo hoo..youre gonna love it when you get that ecu on there....the stock piece of **** doesnt read the port at all and the ecu upgrade will make a really nice difference in performance. a realllly nice difference.


good luck.

jason