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Baseline settings for triple OERs


AK260

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Hello wise ones.

 

I have a friend who is about to install his triple OERs onto a brand new high-end engine for his first start up and initial run-in.

 

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But given what a critical time those first 20-30 mins are, there isn’t much latitude for messing about to get them dialled in.

 

So, I have advised he starts with his good known SUs set a little richer (say 3 turns down) than previously to account for a more thirsty engine and then once initial run-in is complete, he can swap them out. Also easy to get the adjustment right quickly with his afr guage.

 

However, what if? What if he threw on the OERs and kept them there from the very beginning? How do you set them up so that the engine starts and is able to rev out to say 4k rpm without being overly lean or rich?

 

Has anyone set a “base tune” on these carbs either off the car or with the engine off and is there any advice for my buddy?

 

My assumption is that you can turn all mix screws out equally from closed to a ball park / best practice first setting, balance the throttles to “nearly there” using a feeler gauge.

 

Or is it just a bad idea to start the engine and run-in with the OERs?

 

I know there are different / opposing religiously held views on how to run-in an engine but that’s almost irrelevant as the engine builder has recommended the start it and hold it at xK rpm for y minutes. (My personal church preached a different method but let’s not get into that as it will divert us from our purpose).

 

Or indeed, am I asking a question asked many times before and can be pointed to a previous thread?

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42 minutes ago, heyitsrama said:

Borrow the OERs from him and let him borrow your nice SUs. :^) 

I like the way you think!!!! 👍

 

22 minutes ago, jonbill said:

sell the OERs and get ITBs and injection. 

And there speaketh the voice of experience! 

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16 hours ago, Patcon said:

I would use the SU's if the engine isn't too wild. I think it will be hard to get the OER's close enough

I have to agree with that - but never having set up a set of triples, I wasn't sure if I was being pessimistic 😉

 

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Lot's of jetting in DCOE style carbs. Somebody really familiar with DCOE's might get the jetting pretty close first try but I would try it. Much less getting them balanced on a break in run. The nice thing about SU's is their simplicity. Mixture is easy to fatten up or lean out.

I will violate religious protocol and say I'm not sure how critical a continuous break in run is. I have broken in a number of engines and never had a failure due to the break in period. These engines are incredibly tough...

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At the risk of starting a heated debate, please help me understand this - why can carbs be better than ITB / injection?

Except for the obvious other points, I had always understood that DCOE carbs suffer with reversion / standoff when the air pulses back and forth past the jet. Not forgetting low air velocity atomisation issues (read below 4k rpm) if not choked right down - which in turn takes away the benefit of better breathing up top. But an injector isn’t affected by how many times the air passes it back and forth or by the shockwaves in the same way as a carb jet. It just injects fuel once, at the ideal time and with great atomisation.

So what am I missing?

I’m not questioning factual experience but I’m keen to learn.

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Not only that but I can set up a fuel table to fuel at different levels across a myriad of throttle positions and refine that fueling based on O2 feedback. Fire right up when cold and idle perfectly without any choke.

Anecdotally, I would think if carbs were superior then somebody, anybody would still be installing them on new cars...

Now, don't get me wrong, I like carbs. I have SU's and may run some triple webers, but if I get an opportunity to got ITB's, I will and not look back

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My non-expert thoughts on the matter? Most of the fuel injection systems have a long-ish intake tract and some sort of air flow meter along the way towards the air cleaner. Both of those restrict the air flow. Might not be much restriction, but it's more restriction than a short stub of a carb throat running wide open.

For example... When they went to the fuel injection in the 280Z, each cylinder got a whole lot less throttle plate cross sectional area to the air cleaner than they did when they were running carbs. In addition, the fuel injection system has that AFM flapper thingie which adds some restriction.

So while it's absolutely POSSIBLE to design and install a FI system that provides no additional intake restriction over a typical set of carbs, I think it's cheaper for the manufacturer to use something that shares components like throttle body and air flow meters. 

I don't think the manufacturers went to fuel injection because of performance. I think it was because of driveability, fuel economy, and emissions.

So I'm no expert in the field, but my take is that for most stock automobiles these days, if you're willing to forgo wide temperature range drivability, fuel economy, and emissions... I think you can get better straight up raw performance from a carb or a bunch of carbs.

Maybe a set of ITB's and a huge MAF that doesn't provide only negligible restriction could be the same as carbs?

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My understanding of ITB's is there is only a butterfly at each bore the same way a DCOE would be. There is a map sensor and a throttle position sensor. Using those inputs as well as rpm a fuel map determines fueling. No MAF used.

I agree that fuel injection was developed for better economy and broad range drive-ability. I also believe that all out power is better produced with fuel injection. Atomisation is much better at 40-50 psi than 3-4 psi. It would be interesting to see some dyno work using the same engine from carb to FI

Somebody like Eiji probably already has this info as he sells the Jenvey ITB's

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I've heard that carbs can get better atomisation than injection. certainly the airflow through the venturi isn't the same as on ITBs. perhaps helps to vapourise the fuel. 

anyway, ultimately if they both deliver the same amount of air and fuel as each other, then they will produce similar power, all other things being equal. 

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Speed density systems eliminate the need for MAF. 
Carbs require taking into account the TAL factor where ported EFI does not need to deal with this . 
Less parts to go wrong with EFI . Temp compensation is automatic . 
 

I would break the motor in with the simplest method possible - SU’s 

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The good news is my friend has decided to use his SUs for all the reasons mentioned until the initial running in period is complete. Thanks all for the advice and an interesting discussion - so far ;)

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Great video! I forgot I'd seen that before

Picked up 2.5% with ignition upgrade

5.7% with EFI

At the end of the video in their summary,  they say that the numbers don't tell the whole story. Mid range power is better. Drivability is better. Sounds better and fuel economy should be better.

That all sounds nice

 

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1 minute ago, AK260 said:

The good news is my friend has decided to use his SUs for all the reasons mentioned until the initial running in period is complete. Thanks all for the advice and an interesting discussion - so far 😉

What kind of rpm do you need to hold?

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Well I’ve just been sent the builder’s pamphlet / notes on their recommended running in procedure and it’s quite the opposite of what I had been told before (or misunderstood). Frankly I’m horrified as it goes against every grain of what I’ve been taught, BUT he builds engines so he knows what is best for his engines.

The procedure is to fire up and let it idle for 20-30 mins, then baby it along at constant revs for 200-300 miles.

I’ve always been told that you need to get the rings to expand under acceleration and seat under deceleration but NEVER to be left idling or steady state as it’s just polishing the bores.

I know I didn’t want to get into this but there, I’ve done it myself! :p

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Im ok with the babying part to some degree, but I agree on accelerating and decelerating to set the rings. The idle part wouldn't be my choice.

What kind of warranty is he offering?

Motors are motors. His shouldn't need a special procedure compared to someone elses.

@Diseazd

What is yours or Eijis preffered break in method?

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8 hours ago, AK260 said:

The procedure is to fire up and let it idle for 20-30 mins, then baby it along at constant revs for 200-300 miles.

While I am hardly an expert on the topic, I know enough to know that's exactly what you don't do when breaking in a motor. I'd be questioning the credibility of the engine builder if he told me that, and would likely ignore his instructions. 

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