Split pin crank
Discussion
I've often wondered about the 75° AJP8 engine. It's an interesting choice, and the only other non 90° V8 I know is the RPE Powertec V8 at 72°.
As far as I'm aware (correct me if I'm wrong), given that it's 75° and flat-plane, the firing flip-flops between every 75° and 105°. With exhaust pulses being out of sync, there is no merge X/H/Y pipe in the system and it's a "true dual", which gives the Cerbera engine a very distinctive sound. Almost like 2 4-cyl engines firing slightly out of sync.
However, part of me has been thinking. If the Lamborghini 5.0 V10 is 90°, with 18° split crank pins to even the firing, could the same thing be done with the AJP8? Given the money to get a custom crank, and work on the ignition and ECU tuning etc, could you do a custom engine build with the split pin crank and make it an even firing engine?
I don't claim to know the first thing about physics (Did my GCSEs a while back), or engineering, so I am wondering about harmonic balance or things like that. I'm not sure how the differing firing order would affect the balance of the engine or things like that.
I'm not saying I WANT to do it or WOULD do it, but I have a rather active imagination and get to thinking about things. Could anyone shed any light on whether this would work, or do I need to shut my brain up?
As far as I'm aware (correct me if I'm wrong), given that it's 75° and flat-plane, the firing flip-flops between every 75° and 105°. With exhaust pulses being out of sync, there is no merge X/H/Y pipe in the system and it's a "true dual", which gives the Cerbera engine a very distinctive sound. Almost like 2 4-cyl engines firing slightly out of sync.
However, part of me has been thinking. If the Lamborghini 5.0 V10 is 90°, with 18° split crank pins to even the firing, could the same thing be done with the AJP8? Given the money to get a custom crank, and work on the ignition and ECU tuning etc, could you do a custom engine build with the split pin crank and make it an even firing engine?
I don't claim to know the first thing about physics (Did my GCSEs a while back), or engineering, so I am wondering about harmonic balance or things like that. I'm not sure how the differing firing order would affect the balance of the engine or things like that.
I'm not saying I WANT to do it or WOULD do it, but I have a rather active imagination and get to thinking about things. Could anyone shed any light on whether this would work, or do I need to shut my brain up?
I can't answer your question, but I can confirm that the AJP8 does sound like two 4 cylinder engines slightly out of synch
You can hear the ignition going in and out of phase as the revs change (like the devil trying to tune a violin), it is a truly wonderous sound, certainly not a classic crossplane V8 sound at all
You can hear the ignition going in and out of phase as the revs change (like the devil trying to tune a violin), it is a truly wonderous sound, certainly not a classic crossplane V8 sound at all
If it was a true big bang engine there might be some traction benefit, but the ignition events are only 15degrees separated from where they would be on a cross plane v8 at 90degrees apart, and the rate of burn means there will be power stroke overlapping because the power stroke is more than 90 degrees of crank rotation, so in terms of what the tyre sees it won't be much different to a cross plane v8 anyway ? I'm not sure you could ever get a big bang v8 to work ? what would the mechanics of that be i wonder? Also big bang engines work well on bikes because of the low inertia and momentum of lightweight bike drivetrain and wheels / tyres .. not quite so true of cars systems which tend to store lots of energy and therefore tend to not respond quickly to rapid power on/off events.
Also, because the sequential ignition events are only 15deg away from the 90 degrees of a crossplane there is opportunity for high exhaust pressure in one pipe to migrate to the other pipe via an cross link H pipe, and this has been demonstrated to work in reality for about the past 15 years. A true x pipe as seen on cross plane v8s doesn't seem to work well, but my H/X hybrid works very well.
Also, because the sequential ignition events are only 15deg away from the 90 degrees of a crossplane there is opportunity for high exhaust pressure in one pipe to migrate to the other pipe via an cross link H pipe, and this has been demonstrated to work in reality for about the past 15 years. A true x pipe as seen on cross plane v8s doesn't seem to work well, but my H/X hybrid works very well.
Edited by spitfire4v8 on Friday 12th February 09:10
Surely we know from musical references that the devil considers himself a great violin player, at least in Georgia 
although if we are doing devil based lyrics for Cerbera owner ship it's probably
Please allow me to introduce myself
I'm a man of wealth and taste
I've been around for a long, long years
Stole million man's soul an faith
although if we are doing devil based lyrics for Cerbera owner ship it's probably
Please allow me to introduce myself
I'm a man of wealth and taste
I've been around for a long, long years
Stole million man's soul an faith
spitfire4v8 said:
The H linked decats work very well. I have evolved the design over the years but yes keep the H linked pipes .. you will hear all sorts of experts saying they dont work on a cerbera, and yet they do. Quieter and more power than straight decats. Ive sold loads over the years.
spitfire4v8 said:
The H linked decats work very well. I have evolved the design over the years but yes keep the H linked pipes .. you will hear all sorts of experts saying they dont work on a cerbera, and yet they do. Quieter and more power than straight decats. Ive sold loads over the years.
I fitted a hybrid X/H to mine, and I can confirm it does quieten them down a bit, and I am adamant seat of the pants dyno says it makes more power too. Wheelspin is noticeably easier to provoke.spitfire4v8 said:
The H linked decats work very well. I have evolved the design over the years but yes keep the H linked pipes .. you will hear all sorts of experts saying they dont work on a cerbera, and yet they do. Quieter and more power than straight decats. Ive sold loads over the years.
I just about remember reading a blog type post explaining your thinking behind them, but I cannot find it anywhere nowIt's essentially that the exhaust downstream on the cerb is the restriction, especially the s bend under the front of the diff (even worse on replacement intermediate pipes using crush bends) and anything that you can do to even out the pulses / share the flow between the pipes helps improve hp.
It's also why the H pipe works best on the 2 1/8th inch 4.2 exhaust and not as well on a 2.5inch system - on the 2.5inch system the flow downstream is not as compromised. In fact on the 4.2 the H pipe worked so well i supplied a different ecu chip to tweak the fuelling on the 4.2s
the standard 4.5s always run so rich that anything that weakens the mixture is a good thing!
We tested all this on cyclone1's cerb about 15 years ago where the best power we made was with 2 straight pipes straight out under the boot floor proving that the bends were indeed a restriction.
After that 350Matt suggested linking the two pipes together, and the rest is history.
It still makes me smile that people are experimenting with H pipes and X pipes when all this was done 15 years ago and well documented. What I never appreciated back then though was that the best way was to combine the two.
It's also why the H pipe works best on the 2 1/8th inch 4.2 exhaust and not as well on a 2.5inch system - on the 2.5inch system the flow downstream is not as compromised. In fact on the 4.2 the H pipe worked so well i supplied a different ecu chip to tweak the fuelling on the 4.2s
the standard 4.5s always run so rich that anything that weakens the mixture is a good thing!
We tested all this on cyclone1's cerb about 15 years ago where the best power we made was with 2 straight pipes straight out under the boot floor proving that the bends were indeed a restriction.
After that 350Matt suggested linking the two pipes together, and the rest is history.
It still makes me smile that people are experimenting with H pipes and X pipes when all this was done 15 years ago and well documented. What I never appreciated back then though was that the best way was to combine the two.
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