ArExSeven88

(i have an 88 n/a) well i wanna just get a custom exhaust cuz im really tight on money and cant really afford any type or rb exhaust or anything like that...i was wondering i go to the local muffler shop what all do i need to tell then..on my past cars ive just let them do it the way they want but with my new rx7 i wanna do it different..i no its not like a reg engine there for i do want them to mess anything up..i wanna be straight forward with them and tell them how i want it done..i dont mind if its loud..i just want the most hp gain i can get sense money is short and i dont have alot of money for mods rite now....i was thinkin about runnin this set up..and correct me if im wrong cuz im new with the rx7 engines... ive been searching and iwas thinkin about runnin 2.5 piping...and then im not sure on what to do with the cast sense of the backpressure and opening the ports..i wanna run straight pipes but i think i might need to get a header before that...im not sure tho so help me out here on that..lol ..and im not sure if i should run a single exhaust or keep the dual... into an n1 sty;e ,iff;er..i really like the way single exhaust looks..would the dual be louder or quieter then the single? we have no emmisions what so ever where i live so loudness or anything like this is not a concern..thanks for the help

SpeedOfLife

iTrader: (16)

I'm regurgitating info, but here goes:
true dual exhaust is pretty freakin' loud with rotaries.
2.5" is probably good, but 3" is very free flowing, especially with no cats

really, I think the basic exhaust concepts are the same between rotaries and piston engines, and it sounds like you have a reasonable understanding. if you like the single exhaust, go for it.

imloggedin

if you wanna do it cheap, do headers to a single pipe all the way back.

if u have the money do true duals mua hahaa

ArExSeven88

if i have 3" piping there still is gunna be enough back pressure? also can i remove all the cats if i dont have headers? cuz what will open the ports up if i take my cats off?

Icemark

This is basic guys... come on. [shakes head]

A 3 inch exhaust the whole way will actually loose power over a 2.5 inch on a non turbo. In fact a 2.25 (I.D.) Exhaust is about the maximum size you want to use.

Now if this was a Turbo, it would be a different situation, but for a non turbo, going to a 3 inch exhaust will result in lower power due to radically decreased exhaust velocity at more than 12 inches away from the engine.

A down pipe will replace the first two cats on a 88 non turbo, then a main pipe will replace the main cat. As far as a cat back I would never go with anything bigger than 2.25 without some major work to the motor, like porting or intake changes or fuel delivery control modifications.

This is automotive 101 guys.

and ArExSeven88 your bump has been deleted, bumps are forbidden here in the 2nd gen technical section. Are you that full of yourself that you think your question is more important than anyone other member's? In addition, your title to this thread is lame. If you want help, put the question in the title instead of something lame like "advice needed" or "help". Please read this thread (that you must have missed) before posting again: https://www.rx7club.com/announcement.php?f=17&a=92

phoenix7

stick with 2.5" pipes. If you do not have emissions laws then I suggest you save for the RB header and midpipe and THEN mate it to your custom catback.

I know flowmaster has some nice flowing exhausts canisters/mufflers that you can look into that will perform well and minimize the noise ( i know you said you don't care but you'll regret it later).

some have recommended Borla's exhausts are an inexpensive alternative also.

I'd stick with 2.5" CATBACK for now and eventually replace the cats with RB Units.

EDIT: Icemark Recommends no larger than 2.25" but I did not notice any power loss with my 2.5" catback in my old NA.


oh and SEARCH next time.

Icemark

Yeah, make sure that we are talking Inner Diameter. Some pipes sold as 2.5 really are 2.3 internally.

ArExSeven88

if i get a catback will there be any hp gains or not really?

Icemark

minor... maybe 5 HP maximum

ArExSeven88

ok so pretty much its a waste of money..like can i run piping from the header back tho or no? and just run straight pipes for the cats?

Icemark

Exhaust changes, like other modifications are more a percentage thing. If the only thing you change is the cat back, you probably won't gain much.

Where you get gains are when you have a whole plan of what your long term goals are.

For example are you going to do porting? are you going to change the fuel system control?are you going to change the intake or induction?

All those add together, so that one gain with conjunction with others will gain you a moderate horsepower increase.

But just removing the cat, or just putting a header on won't gain that much, and using cheap stuff that may not actually be designed for power (such as the pacesetter header for example) may in some combinations actually lower power or change the peak power curve to a spot that is not practical on a street driven vehicle.

ArExSeven88

its just a daily driver..im not gunna use it on track or anything like that..i just want to have a little more power and not spend a ton of money..just u on a little more hp to make it a little more fun to drive..so im not really sure on what to do

Evil Aviator

An unmuffled NA rotary engine is so loud that it can crack the windshields of cars behind it, and it WILL damage the driver's hearing if not protected. Sorry, you need at least one muffler.

You will need an uncollected header ($200-250), a Y-collector ($50-80), one good rotary engine muffler ($100-400), and the muffler shop can provide the remainder of the piping, reducer for the muffler if needed, hangars, labor ($100-200). Unless there is something wrong with your current exhaust system, you may want to just save up some money until you can afford the header and muffler because doing it half-way isn't going to work. Anyway, to answer your question, use 1.75" ID piping for the header and the primary pipes. You can gradually increase up to about 2.5" ID at the end of the exhaust if you like, but 1.75" ID all the way to the muffler will work fine. Collect the primary pipes at 27" piping length's distance from the engine block, or right before the muffler if you can manage 120-124" of piping from the engine block to the muffler.