Vectortrex

iTrader: (1)

I've read a few posts indicating this might be normal for older rx7s, but nothing on FDs so I'll jump on the newbie sword and ask I suppose.

I've noticed occasional "popping" from the exhaust when the engine is decelerating out of gear. This seems to occur more frequently if the AC is on, though can occur without it. A typical scenario would be accelerating in first to 3k rpm then switching to neutral.

It's not too bad, as I only get one or two pops as the engine winds back down to idle. Idle is smooth and there aren't any other signs of the engine running poorly. Temps are fine and vacuum is normal.

Should I be worried, or is this just another "rotary thing"? My biggest concern is the potential abuse the main cat could be taking.

Car details:
- Precat removed, main cat assumed to be original
- Racing Beat exhaust
- All emissions gear present and still working (as far as I know. Passed emissions inspection less than a year ago)

lduley

iTrader: (1)

With the exhaust you have, it doesn't surprise me that you get little backfires

Only other thing you could do is get a wideband and see if its running rich

Or do it the cheap way and look at your plugs

BLUE TII

iTrader: (9)

Don't worry that is normal.

I read a review of the Japanese late model FDs by a Western journalist where the journalist noted this "raucous" exhaust popping in a new stock press fleet FD.

If you have any exhaust leaks or modifications this will be much more pronounced.

It is also more pronounced with the JDM FD or with removal of the US Spec cat-ed downpipe.

Only other thing you could do is get a wideband and see if its running rich

Well, that is just it- stock FDs do run very rich everywhere except on freeway cruise.

lduley

iTrader: (1)

true, actually all rotarys run rich

after I hit submit that crossed my mind

Vectortrex

iTrader: (1)

Thanks, I'll continue to ignore it then unless the situation gets worse.

Might be worth adding this to the new member/third gen FAQ, even if it only occurs after deleting the pre-cat and/or exhaust work, I imagine that's increasingly common in the ever-shrinking market of running FDs.

lduley

iTrader: (1)

Its not just FD's, its rotarys as a whole due to their design with ports instead of valves

Best way i can describe a rotary is like a 2 cycle engine, theres usually alot of unburnt fuel that goes out the exhaust, which is hot, which ignites it. When you have a full OEM exhaust you don't hear it because the cats muffle it, you remove them, and especially with a header that gets hotter than a manifold, you hear it, and it happens more.

Now if your shooting fireballs out the back on a stock car, then worry about the engine health

Sgtblue

iTrader: (16)

Believe any porting may also contibute.

patmac21

on deceleration my fd makes LOUD pops, along with fire. so pronounced it shakes the car

BLUE TII

iTrader: (9)

In my experience that is usually from an exhaust leak.

Its pretty fun.

My last exhaust on my FC was all v-bands and zero leaks so it didn't have that kinda fun.

Vectortrex

iTrader: (1)

That is way beyond what I get. Mine are more like coughs.

Rx7ADK

iTrader: (4)

normal if nominal

FDRX794

iTrader: (2)

It should be normal and porting does make it pop more usually