14 replies to this topic

[AdamLarnachJr]

The first time I experienced the backfire during the shift was when I saw the Lola B2K/10 Judd at Sears Point a year or so ago. It amazed me how awesome that sound was and felt, but I noticed that it didn't happen with the other LMP's such as the Audi, Panoz, and Chrysler's. I then went to the CART race in Lagun Seca and heard the same thing out of the engines, now my question is, does the backfire only occur in high rpm engines?

I noticed the BTCC last night, and decided to watch it and they were making the same sound too, but I could not find it on any other production or sports racer.

Why does this occur on some engines and not on others, and more importantly how do I get my car to do it:) jk, but seriously, what causes this? High rpm's? Does it only happen with sequential transmissions?

Any input would be appreciated.

Thanks a ton.

[swoopp]

Backfires are quit common on race engines. When I went to Laguna Seca the Audi's backfired.
Backfires occure because there is more fuel than air in the combstion cycle and the unburned
fuel dumps into the exhaust pipe where it is burned, BACKFIRE!! When the throttle is closed
it takes a second for the injectors to react to this new fuel demand( or lack there of), car runs
rich for a few seconds and BACKFIRE. Run your street car rich and you will get it to backfire.

[AdamLarnachJr]

I understand that part, and yeah I saw lots of backfiring even in the sports cars, but it wasn't exactly when it was shifting, take for instance when the Lola was shifting you would get that loud bassy backfire that sounds really trick, I assume its because of the instant change in rpm, but this happened with no other vehicle when I saw the ALMS race other than the Judd, it sucks too because my video camera doesnt pick up that frequency:(

[david_martin]

Most likely due to the way the engine ECU has been setup. If the ignition system has been programmed to provide a short retardation or cutout during upshifts (to assist "clutch free" gear engagement or in concert with a semi-automatic gearbox), then some overrun will occur because of this and produce the backfiring you hear.

[AdamLarnachJr]

Interesting, thanks for your replys. I just always wondered why I could only hear it on the engines running 10,000+rpm like the Judd and Champ cars, as I noted, I never noticed a backfire during a shift with the Audi's, Cadillacs, or Panoz Fords (the sound of them would probably mask any backfire)... but thanks for the input.

[H. Eckener]

Turbos generally don't get along with backfires.

[AdamLarnachJr]

Hmm, ok. But the Champ cars were backfiring during every single shift, and these are turbocharged engines backfiring dozens and dozens of times per lap.

[nzkarit]

race turbos often keep putting fuel in even when off the gas, to keep the exhaust pressure up to help reduce turbo lag.

[H. Eckener]

Yes. Notice the liberal use of "generally" in my message. The fact that the Panoz Ford big blocks are NA could also be pointed out as well. Ask yourself what materials do they use specially for race built turbos, how often do they rebuild them, and could there be various degrees of magnitude for a backfire. Try it out on a turbo street car and see how long it takes them to cancel your warranty.
Yes some turbo race cars use the principal of backfire as an "anti-lag" device. But, how many street cars use the concept?

[AdamLarnachJr]

I was just asking about them not saying you were wrong. I don't know what you meant with the small block Fords but I havent heard a backfire from them, and as I said before it may be masked because of their non cross over exhaust which sounds like a bunch of Harley Davidson's.

Again, thanks to all for your input, its much appreciated.

[MRC]

Hello,

Backfires will have a more detrimental effect on the thrust journal if the oil pressure is kept low. While this is not usually a problem, cars utilizing a pre-turbo restirctor (or with excessive restriction caused by some other means) can suffer from excessive oil blow by past the compressor seals. From my understanding, set ups that suffer from excessive oil blow (past the compressor) will sometimes use a different seal setup and/or a lower oil pressure to the turbo. Turbos can be run with very low oil pressure, if they are treated carefully. Turbos with a ceramic hybrid ball bearing can handle higher thrust loads, with poorer lubrication. I have heard of people using carbon seals in the past, but I do not know if that is common today. This may or may not be somewhat of a reason for the LMP cars to not be burning as much excess fuel in the exhaust, thus trying to reduce the load on the thrust journal of the turbo.

[Jhope]

I hope all of you have had the pleasure of being in a braking zone during an F1 event or test session. sweet god that backfire sound is nice.

[JForce]

Originally posted by Jhope
I hope all of you have had the pleasure of being in a braking zone during an F1 event or test session. sweet god that backfire sound is nice.

Not yet, but I've got tickets at turn one, at the end of the pit straight at Melbourne...I lie awake at night wondering what it will sound like....

On a slightly different note....
Drill a hole in your exhaust pipe, and screw a sparkplug in....connect to the battery via a cabin-mounted switch...and you can get that lovely "Grease is the word.." flame shooting from your exhaust effect....

[AdamLarnachJr]

Hehe:) Here in the states they have a special section in Police HQ for people like us

That sound is the most awesome sound I have ever heard, the way it coincides with the shift, shoot I even got some people to like road racing because I told them that sound was a hydraulic valve shooting tons of pressure to jam the gears together. The drag guys aint so sharp sometimes I tell ya... hehe.

If anybody want's, I have some awesome sound clips from my Laguna Seca trip of the champ cars going from abotu 170-50 before the cork screw.

Cya

[confucius]

Originally posted by Jhope
I hope all of you have had the pleasure of being in a braking zone during an F1 event or test session. sweet god that backfire sound is nice.

droooooool

My friend has a turbo Nissan 180SX, and just two days ago while we were at a beach house, he took it for a cane around the block. It backfired and popped like anything, and we could hear it from a mile away...sounded awesome. I didn't think anything of it then, but this discussion got me thinking that I'd never heard that noise on any other road car before.