Odd fire V8 (flatplane 75 degree)

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jonfx4com
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Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

I have an MS3 and I plan to use it on a TVR AJP engine which is a 75 degree V8 flat plane crank engine. The firing order is 1,4,5,2,7,6,3,8
with the odds on the left bank and evens on the right. the firing angles are 75 degrees / 105 degrees. looking at the ECU setup I think I can do this with the MS3 but I wonder if someone could look over my basic settings for engine and ignition to see if I have got it right so far. It uses a crank wheel with 60-2 teeth and I think the first tooth after the missing ones is 180deg BTDC.

I know much of what is in the MSQ other than the basic engine/wheel/ignition settings is rubbish so pay no attention to the rest.

Advice much appreciated, it's my first MS3 project and my first odd fire project so I'm struggling a little.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

Looks like I'm on my own with this one. It's now installed but awaiting coil drivers before I can test. Got a nice clean tach signal and all sensors calibrated nicely.

One more question, I'm using the mainboard inj1/2 for my odd/even banks and dual widebands. Can I use fuel trim tables per bank, the throttle bodies are particularly difficult to adjust. Balanced at idle can be way out at half throttle and with one VE and AFR table it will be hard to get it right.

I cant see how to do it in tunerstudio.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

Small correction.

With sequential off and cylinder trims on the inj1 and inj 2 trim tables are enabled but the manual says they will not be.

The cylinder 1-4 trims and cylinder 5-8 are greyed out.

So the real question is will the inj1 and inj2 tables work in batch as it appears or not work as per the manual.
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Re: Odd fire V8 (flatplane 75 degree)

Post by grom_e30 »

can't be much help here, but what car is the engine in? is it the 4.2 or the 4.5 ajp8?
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

Hi, its the 4.5.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

Cerbera
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Re: Odd fire V8 (flatplane 75 degree)

Post by Six_Shooter »

I believe the cylinder trims will only work when there are multipoint injectors (one per cylinder) being used, since the settings are cylinder trims not bank trims.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

scrdump.jpg
In batch fire with trim turned on it shows inj1/2 trim tables available. Is this a new addition? Seems to suggest trim per bank in none sequential is now possible. The wording in the manual is a little unclear.
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Re: Odd fire V8 (flatplane 75 degree)

Post by Six_Shooter »

My bad, yeah that would do bank trimming, I didn't even notice that as an option due to the way I have my TS setup to not show unused settings.

I just went and quickly changed some setting in an MSQ to enable the inj1/2 trims and it would work the same was as cylinder trims, but just for an entire bank.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

Up and running! some weird figures to get the ignition right though. Had a look at my spare engine and the first tooth is 300 deg BTDC. The offset angle for the odd fire does not seem to be the "small angle" as stated in various places buth rather the first angle from spk A to spk B which I suppose may or may not be the same angle depending on the application. In mine the angle is 105 as it fires at 105-75-105-75....

Not tuned yet as EGOs not yet connected but starts, idles and revs cleanly. Keeps its temperature and all fans etc working as expected.

A big thanks to all those whose efforts have gone into Megasquirt. Very impressive!
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Re: Odd fire V8 (flatplane 75 degree)

Post by creposuke »

Hello, I dig this post because I just buy a cerbera ajp 4.5 and I want to install on it. I already megasquirt my miata na so I know basics.
Unfortunately less people megasquirt cerbera than a miata so I need some advice before blow my engine ^^
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

My advice, be very careful. This is no simple 4 cylinder even fire engine. It is a screaming race engine and it uses AlphaN as it has no MAP or MAF sensors. There is also some electronic stuff to deal with like ignitors. You may also want to look at adding idle speed control as the AJP is a real bitch when it's cold. Make sure your throttle bodies are in good condition or getting the cylinder trim correct can be made very difficult with out of sync throttle plates and spindle air leaks. The AJP bodies, especially the 4.5 version are really not good. I would like to change them to something better engineered and more reliable but space is a big problem. Get some reliable electrical schematics and study them well. You will see some stuff on the ECU that is not the same as on the car, TVR often changed things without telling anyone. For example, on the schematics you will see and engine idle stepper. It's not there, never has been!


Don't run it lean and don't do power runs until you are confident of the timing on both banks or you will have a mess of broken engine internals and they are not cheap to fix. Get your injectors cleaned or replaced, mine were badly out of balance with each other. It also needs a good gulp of fuel to start up, disproportionately more than any other engine I ever came across. Don't try sequential you will need massive injectors to get enough fuel in in the short time available and idle fueling will become near impossible to control. Lose the Cats unless you want the floor on fire, the factory heat shielding is garbage.

They are my tips.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jsmcortina »

jonfx4com wrote: Don't try sequential you will need massive injectors to get enough fuel in in the short time available and idle fueling will become near impossible to control.
Could you explain why?
These have individual ports don't they? Not siamesed? In which case sequential provides better control, not less.

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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

The engine does not use (as standard) a manifold referenced fuel pressure regulator. I tried big enough injectors to get enough fuel in within a small overlap of either side of the inlet valve opening and it was happy enough at running speeds but at idle it needed fractions of a mS and became exceedingly hard to regulate to within anywhere approaching what might even sympathetically be called an emissions pass. With a better FPR setup it may be doable but the vacuum signature is pretty pathetic even with the pill pot method and the later software smoothing and MAP sample timing methods.

It has big throttle plates, very short intakes, according to my calculations they are about perfect for 10k RPM but it redlines at 8k all of which make it a bit of a pig to tune and make it behave at low revs. You also have to give it a lot of retard to reduce the power at low RPMs or it kangaroos like hell because of what I think is reversion due to the throttle angles, you can see the fuel sitting above the trumpets in a nice little cloud. Retard the timing a bit and it forces a wider throttle and the problems are masked nicely but that means a big transition from dolloping in more fuel and burning it inefficiently at 1600 RPM to trying to control tiny opening times as the speed drops slower down to idle.

The factory setup uses retard to control idle speed, I suspect that was too overcome the problems with having no useful vacuum signature, bump the throttle open a fraction and pull some timing to drop and stabilise the idle.

It's a rather old fashioned 2V/cyl race engine doing 95BHP per litre so making it behave for road use is always going to be a challenge. If Al Melling who designed it is to be believed it was designed to be bolted up to a transaxle for Lola for an F3000 and never intended for the road. 120KG dressed and a real pig to work on as it was supposed to be hanging out the back not shoved in the front.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jsmcortina »

Not an easy engine to tune, but I'm not seeing any reasons why batch fire would be better than sequential.

James
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

An injector big enough to inject enough fuel with WOT during the time the inlet valve is open must necessarily be bigger than one that is open for 85% of the engine cycle. At idle it must necessarily be open for a miniscule time especially if you cannot drop the fuel pressure with manifold vacuum to increase the effective dynamic range. I have done several engine with MS with both sequential and batch but none has put up a fight like this one.

Did I miss something fundamental there, genuine question, if I have it all wrong I would like to understand better.
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Re: Odd fire V8 (flatplane 75 degree)

Post by jsmcortina »

jonfx4com wrote:An injector big enough to inject enough fuel with WOT during the time the inlet valve is open.
Are you perhaps confusing direct injection with sequential?
Sequential does not require oversized injectors.

James
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Re: Odd fire V8 (flatplane 75 degree)

Post by jonfx4com »

I agree, it doesnt if you don’t care if the valve is open or not but then is there any advantage over batch?

I thought the point of sequential was to be injecting the fuel into a fast moving airstream not having it hang around in the port behind a closed valve?
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Re: Odd fire V8 (flatplane 75 degree)

Post by jsmcortina »

jonfx4com wrote:I agree, it doesnt if you don’t care if the valve is open or not but then is there any advantage over batch?

I thought the point of sequential was to be injecting the fuel into a fast moving airstream not having it hang around in the port behind a closed valve?
Yes there is an advantage over batch. Each cylinder gets its fuel at the same time in relation to its TDC firing and you get more consistent operation.

James
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Re: Odd fire V8 (flatplane 75 degree)

Post by billr »

James, let me give it a try...

With batch, you are guaranteed to be injecting fuel on some cylinders (all?) at times other than that "intake open" period you are desiring. Sequential gives you the best chance of hitting that timing and minimizes the size of injector needed, since there are fewer "dead-times" for each cycle. Likewise, keeping the total injection period in one single lump (sequential) avoids really small non-linear and less consistent pulses at idle.
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