Radien Black

Can someone explain this ?

This weekend i replaced the u-joint in my 86 RX-7 (yes the irreplacible one) courtesy of a blowtorch hammer and a cold chisle and a replacment from Arizona Drivelines (yes another shameless plug)

anywhoo to the root of the problem when i went to put the exhaust back on i removed the mufflers and put straight pipes on it. after that, it now runs like a castrated dog with absolutly no performance and loss of power on hills so i caped one of the exhaust pipes to give it more back pressure and went to the gas station and put premium octane in the car, as opposed to the usual mid grade (yes i know its a horrible thing to use mid grade ) and the power came back for the most part .

can anyone explain this? Does a octane rating make that much difference

95R2-89TII Ground Zero

Octane rating in simple terms is the amount of octane in per gallon of gas. Basically the higher the rating, the higher the ratio. I know that higher levels of octane have been shown to increase power on dyno's...obviously. It runs hotter, and combusts stronger.

DerangedHermit

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

FDreaming

Just go buy the newest issue of Import Tuner (The one with the ugly *** blue gullwing civic on the front, and the scrawny white chick standing in front of it trying to look mysterious) They have an AMAZING article on fuel in there. One of the first worthwhile articles from them in a long time.

Stainless

An octane rating was developed by the petroleum industry so the antiknockquality of a gasolinecould be rated.The octane number is the measure of a fuels tendency not to produce knock in an engine. The higher the octane number the lesser the tendency to knock.

Radien Black

ok i appreciated the explination of the octane rating would that cause majorly significant power increase?

DerangedHermit

I wouldn't say it casues a power increase. An increase in octane gives room for a power increase. A turbo engine isn't going to be able to up the boost if it's going to knock.

SonicRaT

iTrader: (6)

Haha, it's the other way around. You want to run the lowest you can without detonation (knock), for an N/A, there's NEVER a reason to go with anything over '87 (unless you're running some crazy timing), as for a turbo car, it's best to play it safe and take the few ponies lost.

Stainless

The loss of power could be that you have no back presure. Now that you are not running with mufflers. Even the best mufflers have a bit of backpressure.

DerangedHermit

Oh, just noticed he has a 86, thus N/A.

Yeah, just run 87, there's no reason not to.

jacobcartmill

iTrader: (6)

you should be running the LOWEST octane possible unless you are FOR SOME ODD REASON needing to combat DETONATION.

you'd actually LOSE power from using a higher octane, not GAIN power.

alwayssideways

dude is there a way you clogged your exhaust some how???cuz besides taking off your exhaust to do the drive shaft ,. there really anything else i can think of that can contribute to loss of power after doing that

btw i just re read your post. loss of backpressure . that can attest to your power loss

Davidov

iTrader: (2)

Mazda of America has a Technical Service Bulletin (TSB) out for Mazda technicians, that outlines the importance of using 87 octane in Non-Turbo RX7s.

Stock turbocharged RX7s need anything at or better than 91 Octance.
It's that simple.

Evil Aviator

Higher octane pump gas will produce no increase in power whatsoever unless your engine is knocking with the lower grade fuel, causing the knock sensor to retard the timing.

Stock TII's are also rated for 87 octane.

ScrapFC

iTrader: (5)

For a S4 NA, the most likely cause of power loss when running straight pipes is a lack of exhaust backpressure for aux port actuation. Your motor wants as little backpressure as possible, but the aux port actuators need 3-5PSI to open the aux ports and give you your top-end power. If you are going to insist on running such an open system, you need to find another way to actuate them or wire them open.

patman

iTrader: (3)

what he said ^^ lower octane=more power.lower backpressure (to a point) = more power. however, low backpressure on an s4 Na= no aux ports=1/2 th epower u should have. do a search, there are all kind of ways to make the ports open without the converters split air pipe.

pat