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emripires

Info on long runner manifold.

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In very, very general terms the longer the intake length from the valve to atmosphere the more torque your engine generates at lower speeds. Peak power is usually dropped to a slightly lower RPM as well. This would benefit a street engine that has to work hard at all RPMs

 

A shorter intake length moves the peak torque and power higher in the RPM range but suffers from torque loss in the mid range and lower. This would favor a non stop race car engine that is not driven at mid RPMs or lower.

 

An engine that is over cammed and very peaky in power delivery at high RPMs can show a smoother and higher torque range at low and mid range with longer runners.

 

In some cases and at some RPMs, you can get better than 100% volumetric efficiency. That's more air than the cylinder can hold at one atmosphere.  Like having an invisible turbo charger.

 

This only applies to engines with individual runners and throttle bodies.

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Mostly urban myths...

 

Ideal intake length (first wave) is very long even for cars that turn 10,000 rpm.

2nd, 3rd, and 4th wave (each provide less, and less power) are used by people that have space restrictions, like fitting under the hood of a car.

Nascar engine builders mostly use 3rd wave to fit under their hoods.

 

A first wave induction, for 272 cams on a 4-valve head, to turn 10,000 rpm is 30" !

And that is dependent on cam timing (advance, retard, and lobe separation).

My 620 with 292 cams, to make max power at say, 7000 would require 13.4" runners by using the 3rd wave (this is from valve seat to the open end of a stack)

 

A dead stock L4, with say 248 cams, and max power at about 5000, would need 21" runners, also 3rd wave.

To drop max power just by 1000 rpm (to 4000), you have to add 5.5" !

In other words, it really isn't possible to really gain anything.

Just use what fits. Apply your time to actual tuning, and time on a dyno, or at a drag strip.

Learn how to dial in air/fuel ratios.

 

Any intake length tuning, to really work, need the exhaust also tuned, and a lot of experimentation with cam timing in reference to crank, and lobe separation. Also, compression ratio requirements change with cam timing.

 

Oh, and as Smokey Yunick said about exceeding 100% cylinder filling efficiency.....

Bull Shit, will never happen.

Should read his book. Just wish he had stuck more to tuning secrets, and less of the sexual adventures of those who built, tuned, and raced Indy cars back in the 50s through modern day.

 

But if you want to waste time with figuring this stuff, here is a neat on-line intake length calculator:

How to calculate intake tract length

 

Edited by G-Duax

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 That's why I said in very very general terms and left the actual lengths out. It's not a wives tale and length tuning does work. Knowing Smokey he was simply on to something and was throwing others off the scent. He was a master at bull shitting.

 

00DSCN4189small.jpg

 

Lots of engine makers have and do today, include intake tuning to smooth out and lengthen torque peaks and troughs. It's free, never goes out of tune, nothing to wear out and there for the taking.

 

47791530d1399152929-1986-88-tuned-port-i

 

 

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the NissanComp manifold was a a longer type.

Be honest I like the short Mikuni ones as it fit better w/o hiting the brake master

what ever is cheaper makes it Ezer but short wouldbe my pick for your truck. In a L motor the HP/torq gain you wont be able to tell as much I think. Just putting the carbs on will feel like a 50% improvment

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I have never liked that gooseneck intake.

 

X2 on the Mikuni intake. Less fitment issues and a pretty good all around performer.

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Last time I visited Rebello Racing, Dave told me about a manifold they are using now in lieu of the Mikuni intake. It is a short runner intake that is available new and is relatively inexpensive. I can't remember the brand, but if you call them, I'm sure they could sell you one.

 

He also told me that they work better than the Mikuni intake, so win-win.

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G-Duax, any idea how you calculate runner length when terminating runners into a common plenum with a single throttle body? Thanks

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Use that same formula in the link I posted, as any wave activity is lost once it hits a larger volume plenum.

 

And Mike, when writing his book at the end of his career, I doubt Smokey was worried about misdirecting competition.

Having played with intake & exhaust tuning, running dynos, and field testing for 50 years, I've learned a little about sorting out the bull shit from the truth.

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You need to make the plenum large enough to simulate open air but the formula would be the same. If the plenum is too small a volume it will act like an extension of the actual runner and the other runners will add their pulses making it impractical.

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Thanks for the info guys,

What effect would a inlet restricter before the throttle body have on all this?

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Not much when you look at the history of intake restrictors.

Do some reading on the subject when it was first introduced into the world rally competition years ago.

The people who had $$ to experiment in the off season had come back with soe enormous plenums, and ended up loosing very little power.

 

Many racing organizations like SCCA (stupidest car club of America) now forbid large volume plenums behind the restrictor.

What happens is that a restrictor flows better when it's at constant flow, opposed to surge flows created small volume between valve and restrictor.

I have personally played with this, both on the dyno, and at the track, as many other people have, and it works well.

That is why people who write rules for the likes of scca (who also are your competitors - gee, why is this allowed?) have cracked down on it.

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Plenum shape is important too. If the runner opening is too close to the roof of the plenum, you will have distortion from possible reversion. Runners should also protrude slightly into the plenum with a velocity stack shape. Even a simple radius will help.

 

You can see the small radiused "stacks" in the baseplate of this plenum I built a few years ago.

 

1GRFE_Intake004.jpg

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11 hours ago, G-Duax said:

Not much when you look at the history of intake restrictors.

Do some reading on the subject when it was first introduced into the world rally competition years ago.

The people who had $$ to experiment in the off season had come back with soe enormous plenums, and ended up loosing very little power.

 

Many racing organizations like SCCA (stupidest car club of America) now forbid large volume plenums behind the restrictor.

What happens is that a restrictor flows better when it's at constant flow, opposed to surge flows created small volume between valve and restrictor.

I have personally played with this, both on the dyno, and at the track, as many other people have, and it works well.

That is why people who write rules for the likes of scca (who also are your competitors - gee, why is this allowed?) have cracked down on it.

I have an acquaintance with a GT2 car, and with tiny plenum increases ( because of hood height), .5" here 1" there, was able to pick up about 25 hp.

Pretty impressive considering we originally thought it would be a waste of time for the small size increase. His was plenum on top of ITB's.

  In my situation with a single throttle body, would having a large "after" plenum have adverse effects on throttle response?

Would having a large volume of air space between the restrictor and the throttle body help?

 

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No, because how fast the actual air flow speed, and the change in pressure actually is

Issues in throttle response are typically due to ECU programing, or using carbs feeding the plenum.

 

On EFI systems, the injectors are usually right at the intake port, and the ECU (especially like an aftermarket stand alone) should anticipate thee engine's need for more fuel as the throttle is opened quickly, and the resulting decrease in vacuum. This in turn increases injector on time to add fuel as the air flow suddenly increases.

 

On a carb set up, like the old tunnel ram manifolds, the accelerator pumps had to supply more fuel, but unfortunately they were on the inlet side of the plenum, and the air in the plenum, and intake ports could be too lean, unless you ran an overly rich idle mixture.

 

To get a better idea on this, picture s Slinky (the old kids toy that was a spring made of flat wire.

Stretch it out. That is the vacuum in the plenum at off throttle.

Let go of left end, that is a sudden opening of the throttle.

An EFI system should instantly increase fuel delivery at the right end.

On a carb system, the accelerator pump is at the left end, and even if it has perfect linkage, and the pump starts spraying as soon as the throttle plates open, the fuel has to travel the length of the system before the engine ever gets it, even though the air flow into the engine starts to increase as soon as the left end of the Slinky is released (throttle plates opened).

Edited by G-Duax

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Interesting stuff, thanks for the info guys!

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Here is a set of long runners from am L block I bought just to keep them from being scrapped.

004.jpg

 

006.jpg

they even have fins inside them to help the air spin/mix??

007.jpg

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The first time you showed those, I thought you were making a joke. I still can't believe they exist. If there is ever a museum for Datsun engines, you should donate them.

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:lol: They will not work on any of my 520/521s as I have power brake boosters in the way, they were on a 510 in Nevada I believe, the stock L block manifold just cleared the engine compartment sheet metal, I used to have a photo of them but that was in another email account I do not have anymore, I do not remember who I bought them from anymore either, but it was someone on Ratsun.

 

 

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2 hours ago, Stoffregen Motorsports said:

 If there is ever a museum for Datsun engines, you should donate them.

 

 I can think of other places to donate them......

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those need to get run on a dyno mule to see what effect they would make...

 

maybe those had something to do with a propane setup possibly?

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Or cow magnets taped to a fuel line......

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... or strut braces.

... or hood pins

... or catch cans

.. or

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