well before I put on a high flow cat, my mileage was at about 225-270 miles to the tank. I've got a full racing beat racing exhaust, but put the cat where the resonator went. I drove from portland to Seattle (renton, Jimi's Grave and first drive with the cat on) and back, I went 397 miles on one tank!! wtf!! does a cat really save that much gas? I averaged about 85, up and down. occasionally I dropped to third or fourth. I know it's all highway but still 397!!! I've never gone that far in this car even on other highway cruises! can someone explain??

mods:
racing beat exhaust (headers too)
lsd dif
agx sus
eibach springs
one belt (i.e. no ps no ac)
elec. fan
bushings
550 injectors in secondaries, (just experimenting)
I think that's it.

 

Id have to say your car is just ghey and you don't need 550cc injectors in an n/a.

 

225-270mpg? that crazy

 

ok yeah I didn't mean 225-270 mpg. sorry I meant 225-270 to the tank. Suds7 maybe you're gay? thanks for being an ***! obviously I don't need the 550's that's why I said it's an experiment! learn to read!

 

if you are going to keep the 550's buy an S-AFC to save on gas and get more HP

 

actually that's my next step. thanks though. I'm just amazed I got almost 400 miles in one tank. 150 miles more than usual. I just wanted to know if anyone else has checked this.

 

I get 300 miles to a tank what kind of driving do you do?

 

I assume you mean miles per tank. A cat cannot improve mileage because it has no effect on what happens inside the engine. In fact it will probably worsen it marginally because of the reduced VE.

Assuming you used most of a tank (~15gal) to do that 397miles, that's 26.5mpg, which is unrealistically high if you were averaging 85mph. Are you sure about that distance? Waste of time. You are still well within the limits of the stock injectors and without some form of control you'll simply be running very rich above 3800rpm, which will reduce power.

 

I drive fairly hard. I like to slide when I can, usually I go about 10-20 over the limit. anywheres from 1-5 times a day I'll floor it. but usually I keep it in the 2.5-4k rpm range.

 

yeah I'm sure about the distance. the trip there and back plus some extra driving= 397 miles I hit the trip meter as I left the gas station. I monitor my mileage all the time, it's a habit. so it's pretty accurate. damn I shouldn't have told you people about the 550 injectiors. it's just an experiment! I just wanted to see what they would do. but thanks for the help.

 

i would kill for 220-275 miles per tank. Right now I have only been getting about 200 miles per tank. I just changed my oil, oil filter, spark plugs and spark plug wires (oem). I have yet to see if my mileage will improve.

How can I tell if I need to change my cat? I still have the original cat with the original motor with 73k.

My exhaust feels very hot but I have no other fc to compare it to. I am also looking to purchase a high flo cat. Probably the bonez superflo

 

driving like that you should get more MPG than what your getting right now. I drive similarly but I usually drive 20-35 over and floor it often and redline at least once a day.

Santiago

PS_ MODS:
MT Duals
CAI Box(generic filter)
no emmissions
no a/c no PS
stock fan
only 6 vac lines
fairly normal interior(removed arm rest from the middle of the two seats)
SS clutch line
SS oil cooler lines

record is 325 miles from ~15 gal. of 87 octane driving 50-50% city-highway.

 

your O2 sensor can also affect your MPG try changing that and loose the lead foots guys.

 

it's 175 miles to downtown seattle from downtown Portland. plus I drove about 40 odd miles after we got back. so 397 is pretty accurate. sorry if you don't believe it. 26.5 mpg. maybe it was 80 not 85...? I don't know, still 26.5 is good for 70 mph.

 

1. Let's keep this thread on track guys. Abusive comments are not needed.

2. The cat will actually LOWER mileage due to the restriction. Figure 1 MPG.

3. How you drive has a MAJOR effect on mileage. Light-footing it can easily get you an increase of 5 MPG. City = very bad mileage, highway = good mileage. As an example, my Honda Insight gets roughly 65MPG in the city, but around 100 MPG on the highway. Steady state cruising uses a lot les fuel then stop and go.

4. Loose the 550CC secondaries.

 

i made a recent road trip in my 87 gxl with rb road race header, high flow cat, and greddy pe, and i hit 330 miles on just over 12 gallons on one of the long stretches. i averaged right at 85mph also. the total trip was 1300 miles...in one day(that was rough) i was amazed. so it is probably right.

 

well I figured I would get more miles to the tank going there... just not another 150 miles! so I guess I kind of have a heavy foot. but I'm weak!!! so heavy... can't lift off-the-floor haha. thanks for the info.

 

I used to get 275-280 miles to the tank before using pre-mix so that may also help. Try pre-mixing ontop of the MOp system.

 

i have a turbo.....so im not gonna bother tellin how many miles i get to a tank....lets just say its another reason why i'd want to have a NA sittin at home...

 

I agree that almost 400 miles to a tank is not right. I have the Bonex high flow cat, a full RB exhaust, and a newly rebuilt street ported engine with about 3500 miles on it and the best mileage I've gotten, my last tank of 87 octane, was 17.92 mpg. It normally varies between 16.2 and 17.5 mpg. With a 16 gallon tank this means max mileage is 275 miles per tank.

If you really got almost 400 miles we'll be inviting you to tune our rotarties and will be gald to buy your plane ticket and pay your hotel bills. I'll be your agent and will book your lectures and hands on tours throughout the US and Canada!

Bert

 

26MPG is not unrealistic. It's exactly what I get on the highway. This was with mods, just keep the car in tune.

When I'm done modding the car, I'll see how it affects the MPG (New RB Exhaust + Header)

I dont do a 'per tank', I hit the trip meter when I fill up the tank so I know how many miles I've gone. (its a bit more accurate)

 

Oh yeh, I thought I should mention this was at 80MPH with the top UP.

Top down tends to get me .5MPG less