Brap/Lumpy idle. What defines how lumpy the idle sounds?

Hi Guys

Curious to know what changes need to made in a Tune to make the car sound lumpier/angrier? I have a 77 RA23 celica with a 1jz with 264/272 cams, it has a nice note but ive heard other similar setups sound much more aggressive. Ive been told its all about the tune an how its setup. Can anyone educate me on this please?

If you get on the "Guild of EFI Tuners" FB page there are 83 comments based on this question. A couple of the blokes really know what they are talking about. Search cyclic idle and scroll down until you find a photo of the rear end of a white Supra.

There's no point in me regurgitating the information but the best sound is from setting up a misfire cycle using timing and the throttle plate where the engine re ingests burnt exhuast.

If that is Kelford cams you are using it has 7 degrees of overlap @.040 valve lift which will help a little.

I've got a ej25 with bc272's and have used the idle ignition control table and put reasonable size timing swing either side of my idle target after setting up open loop idle spot on first. I found if you make the swings too large with a low idle target it makes the engine sound lazy.

It's just a matter of experimenting with the information and use the timing and throttle plate, actual idle rpm to get the sound that you like. One point to keep in mind though even though you're actually setting up an 'unstable idle' in reality it still needs to be an idle that will not let you down at the lights or wherever.

While there are ways to 'cheat' and achieve a lumpier idle from a given setup, predominantly this will come down to cam selection. The cams you're using are quite mild and while you should end up with a nice idle quality that's a little lumpy, these cams alone won't ever be anything too aggressive.

Tuning changes that can help would include using idle ignition control with a reasonably aggressive advance/retard strategy as you move away from the idle target. You could use a 'cyclic idle' strategy which is more commonly utilised to control idle speed with a Group N style antilag where the throttle is constantly held open, however this will result in an idle quality that's pretty obviously cyclic idle and not a large cam to most people who know what they're listening to. If you achieve this by opening the throttle body permanently then also look forward to horrible part throttle driveability.

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Thanks for the info guys. The note i have at the moment is pretty decent after i nagged my tuner to make it sound a little better. Hes not a fan of it personally having originally tuned out any kind of tone. It is a street registered vehicle after all so its not too loud. Thanks