exhaust question

[sidewaysFC]

I just put an open 2 1/2'' open exhaust on my 88 na rx7 and now I have like no torqe under 4000rpm . so my question is would the lack of back pressure this exhaust has kill my low end torqe. and I messed around with my aux ports a little bit but that didnt do much.

[BoostedFC]

Well our cars lack in the torque department from the start, but reducing the back pressure can result in loss of low end torque. What did you do to the aux ports?

[sidewaysFC]

I hooked them up to the air pump with some pluming parts and an adjustabul valve but im haveing a hard time adjusting when they open cos they should open around 3500rpm but I need to work on a better setup to adjust that. but I dont feel much until I get up to 4000rpm so should I make so back pressure some how?

[BoostedFC]

Remember there will be sacrifices to be made. The loss of low end torque in exchange for top end power. In general racing you will be spending more time in the upper RPMs so some parts are designed in this manner. Piping size, muffler design & exhaust routing (tuned exhaust) is the only way to get the best performance to specific needs. Most off the shelf systems were made to make power, but not always be the best design for every situation.

[sidewaysFC]

nice I like that answer. Yea I gess your rite ill have to play around with the six ports and the exhaust system but im not in the low end when Im raceing anyway.

[BoostedFC]

Another thing to think about is rear end gear ratios. Higher ratio is referred to as lower gearing (geared down) and lower ratio is referred to as higher gearing ( geared up)... nice and confusing! Okay now look the bigger/higher the ratio the quicker you will get to speed, but for a trade off. Here's the trade off you may get to speed sooner, but your top speed will be reduced & gas mileage be affected. On the other hand running a lower ratio will enable higher top speeds & gas mileage, but sacrifice how quick you get up to speed. This is where torque is affected.

BTW the tire diameter will affect speed too. By increasing the diameter you can pick back up some top speed or in reverse by reducing tire diameter.

[sidewaysFC]

We just started going over that in my auto shop class to day acculey im going to be rebuilding and shiming my lsd in the near future so I im looking into doing that im going to be puting a higher gear ratio in it because higher ratio benifits with torqe dosent it for better excelleration because im all about excelleration , so if I did that would that put me at a higher rpm in each gear .does that put any more load on the engine or does the fact that I would be at a higher rpm stop that .and how do I change the ratio like do they sell differnt sized ring and pinion gears.

[BoostedFC]

Scroll down to bottom of page for rear ends. http://www.mazdatrix.com/g5.htm
there are a few other options I will get back to you on though. Interchanges can be made from vehicle to vehicle.

Yes the higher the number the better the acceleration.

[sidewaysFC]

ok so it says a 89-90 non turbo has a 4.30 insted of a 4.10 would that be my best bet

[sidewaysFC]

and ive never taken one of these diffs apart before is there any thing special I need to do or do I just take it apart put the new stuff in it and put it back together.

[BoostedFC]

Well if I can remember it's not all NA 89-90 RX7's the 4.30 with LSD was only in the GTUs not the GTU or any other NA model. If you got your hands on the whole differential just swap it, buying the ring & pinion is not that hard if you are mechanically inclined. I'll see if I can find a write up on this for you. Also Mazdatrix sells a 4.77 & 5.12 ring & pinion set if the car is not going to be street driven all that much & top speeds are of no concern. Would be great for drag racing.

[sidewaysFC]

can I use my lsd with a 89-90 ring and pinion gear cos I dont want to use the viscaus lsd they use or are there any 89-92 that use a 4.30 and a clutch type lsd

[BoostedFC]

You can use the ring & pinion.

[sidewaysFC]

awsom ill have to find an 89-90 diff.

[BoostedFC]

Make sure it's a GTUs to get the 4.30 ratio.

[sidewaysFC]

are gtus the only one with the 4.30

[BoostedFC]

As far as I remember yes only the GTUs not the GTU or any other model. I think all the rest are 4.10 ratio unless they were automatics & they have 3.90 ratio

[sidewaysFC]

a 3.90 sounds like it would have relly good exelleration will that work in my car

[BoostedFC]

3.90 ratio is working in the wrong direction if you are looking for acceleration. Higher the ratio the quicker the acceleration & lower top speed. The lower the ratio higher top speeds but slower acceleration. The 4.10 that you have is better then the 3.90 for acceleration & the 4.30, 4.77 & 5.12 ect are better over the 4.10's for acceleration.

[sidewaysFC]

o does 3.90 mean 3.9 . I gess ill just stick with the 4.30 then will I see a big increas in acceleration