Flat4x4-again

iTrader: (1)

I've been running Tesco Momentum 99 on my classic since its winter lay off and it has popped and banged more on the over-run / lifting off down the gears than I remember before sports cat days.

Question is, needed to put some BP super unleaded in as I was running low, and the pops and bangs have gone.

I thought it would have been better the other way round ? This sounds like Shell Optimax all over again which my last classic fell out with.

NOSSY_89

I remember from years back consensus was Momentum 99 popped and banged more. I thought so too when I used it but could have been placeebo.

Vxr2010

momentum is a higher octane than bp 99 v 97 , bp has a lot of additives , i was told by the chap who tuned the car to avoid it , if you have no choice not much you can do but it’s not as good , i do quite a lot of miles so with momentum being cheaper than shell plus still a high octane rating then that’s why i stick with momentum

Flat4x4-again

iTrader: (1)

... which is why I thought Momentum would be 'better for it', but BP is definitely a lot calmer when you changed down !

Maybe the lower octane suits the ECU/sports cat better.

NOSSY_89

What do you mean by calmer, no pops and bangs. What was your car mapped to.

Nick_Cat

iTrader: (5)

My classic was mapped by Bob Rawle on Momentum (I don't remember him grumbling about it). The car has a 100 cel sports cat and it pops especially when shifting down after braking hard, e.g. just before a sharp corner.

Flat4x4-again

iTrader: (1)

Sort of what mine does, but without the hard breaking. If I change down and then turn off a road under braking before coming back on the power.

It has standard PPP, but when the original cat downpipe broke at the join, I replaced it with a Cobra sports cat one.

ej20boy

my car actually specifies v power on the fuel cap ,(not a subaru)
but both fuels are 99ron so it shouldn't make any difference

RetroPug

Is the sports cat mapped in?

A decat/higher flowing cat not mapped in plus running the highest octane fuel available at the pump is definitely going to cause some popping.

Vxr2010

nothing that unusual about pops and bangs , just stick with momentum as that’s what it’s mapped for and avoid bp unless no other option 👍 or run it on shell £££🤣👍😁

Flat4x4-again

iTrader: (1)

I didn't think you could remap a PPP? I got this particular classic because I didn't want to go the Ecutek route like I did 15 years ago (which resulted in a new short engine).

NOSSY_89

I didn't know the classics game with a PPP map, thought it was newages onwards. There are other remap options depends what year car it is.

RetroPug

I don't know whether or not your ECU can be mapped.

I'm saying that on a car on a standard map for 95/97, using 99 is more likely to cause the sounds you're describing. In general, so is adding a sports cat but I am not really familiar with subaru engine maps so I wouldn't want to comment on specific conditions.

Basically, I'm saying it isn't surprising that the combination of high octane fuel and a sports cat causes this on the standard map.

Flat4x4-again

iTrader: (1)

... will it do the cat much harm or am I better going to lower Ron 97/98 fuel is where I'm coming from.?

RetroPug

I imagine it depends on exactly how much you're getting, but I don't know- I'm a suspension test engineer!

If it's not excessive then hopefully the cat will be OK, but personally I'd map tweak with a sports cat fitted- I've got one I've been waiting for mapping to fit, that's because I'm worried about it possibly running too lean or having boost spikes though.

Vxr2010

i would stick with higher octane fuel as you don’t want det or other issues , it is slightly pointless adding a sports cat and not remapping as you don’t get the best out of it , a sports cat with out a remap is normally ok on a wrx , on an sti iffy or a jdm sti it will often need a tweak , i would just get the map checked or get it remapped , i am not sure of the years but i believe some older classics can not be mapped ??? , they did do a ppp on the classic it was the first scooby i drove , the boost noise was fantastic 🤣 it was like opening a car boot at 70 mph 🤣👍

Flat4x4-again

iTrader: (1)

Do you know anyone who can sort out my Audi Allroad air suspension nightmares ?

Wurzel

iTrader: (1)

You should try running on Aral 102 then, it sounds like you have antilag on

fpan

iTrader: (11)

Never liked that fuel, the PSI3 I had was showing negative KC values with it.
A friend with a Colt CZT turbo was telling me similar stories.
If I am not mistaken it's made by BP and for some reason Subarus don't like it.

RetroPug

I test the mechanical parts of steering and suspension for developmental purposes on road and race cars, including F1.
I think you need an audi specialist...

Flat4x4-again

iTrader: (1)

No, they are still clueless. Two have tried and failed. I am sure you would stand more chance of getting to root cause

jaygsi

iTrader: (46)

I have a 1998 Impreza with Prodrive ecu fitted, also has a 3" bore exhaust with 100 cell sports cat. No pops or bangs, run on 97 but would prefer 99. Only time it popped and banged is when it had a dump valve fitted. Which has now been removed.

Flat4x4-again

iTrader: (1)

Very similar set up to mine. Would be interested to hear how yours is on 99 when you get chance.