need help building a tuned intake for inline six 8

[madaz]

Hi all I’m new to this forum. I think it’s the best forum around I love learning thing like this. So anyway I’m currently designing a tuned intake for a inline 6 the car is a XF Falcon (Australian car) the engine is a 250ci 4.1lt inline 6 OHV (250 crossflow).
I want max torque at around 2000rpm the car is driven daily not a race car
I have searched eng-tips looked at a few articles like tea Integra.
From those calculations I need an 52cm long runner.
The car will be running a 350 Holley.
The runners will be the same size as the ports I don’t know how big that is I’m trying to find out.

My questions are:
Will bends effect the bower band or effectiveness? (They have to be bent to fit under the bonnet).
Do velocity stacks help make more power/torque?
I can make it with some adjustability would this be a good idea?
What shape plenum and how big?
How much does size of the runner effect power band?

If there’s any thing else you would like to know just ask.
Any help at all is appreciated.

 

[GregLocock]

Some people, with far more time and money on their hands than you will ever have, have spent a long time optimising that manifold. Stick your head under a BA and measure it up.

"Will bends effect the bower band or effectiveness? (They have to be bent to fit under the bonnet)."

No

"Do velocity stacks help make more power/torque?"

Interesting question. They are part of the primary length of the runner, so they do affect the VE vs speed graph. I think they'll be better in terms of max VE, but only by a smidgeon.

"I can make it with some adjustability would this be a good idea?"

Those wacky kids in Geelong seem to think that adjustability is a good thing, that's why they fitted a BBM

"What shape plenum and how big?"

Excellent question. Shape - don't know. Volume, use search engine.

"How much does size of the runner effect power band?"

in terms of area? or literally the shape - round vs square?




Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

If you look at the inlet manifold on an EA falcon you will get some ideas.

Tuned length is normally aimed to work near peak power rather than peak torque. That way they don't need to be nearly 2' long.

Nice smooth swept bends will only have a small effect on power.

The whole idea of velocity stacks is to improve power.

Some OEM manifolds automatically adjust at a set engine speed. They don't spend that money unless it works.

Shape is normally a log shape or box shape.

For steady state power, the bigger the better, but there is a diminishing return. I think at least the volume of 2 cylinders would be minimum and over engine volume would be pointless. The bigger the plenum, the more the signal to the carb is filtered and the slower the throttle response.

If I wanted maximum torque at around 2000 rpm, but better than stock power, and wanted carbies rather than EFI I would use 3 X 1.5" SUs on individual ram tubes.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[thundair]

I work on Land speed motors and we have looked at tuned length to catch the reversion wave at the right moment.
The 1st wave say is 35" and the 2nd is 20" and the 3rd is 13" for a specific RPM.
Looking at these hypothetical lengths the problem lies in the RPM that you are turning in between the idea length.
We concluded that unless you are spending a lot of time at the same RPM and you have access to a Dyno that you are better off with the short stubby Velocity stacks and a huge air box.

Maybe posting this will bring a better understanding, but I spent a lot of time with Jerry Branch at Flow-metrics and I have just enough knowledge to get me in trouble..

I don't know anything but the people that do.

 

[MikeHalloran]

For a street car, you want a wide powerband, so maybe you don't want every tube to resonate at exactly the same rpm.

Which may be why Chrysler used long, gently curved tubes in the manifold for their old slant six. Take a look.





Mike Halloran
Pembroke Pines, FL, USA

 

[madaz]

Thanks for the help guys

"We concluded that unless you are spending a lot of time at the same RPM and you have access to a Dyno that you are better off with the short stubby Velocity stacks and a huge air box."

The engine spends most of its time a 2000 peek torque is at 2000-2400 max power is at 3700 and redline is at 4000.
That’s why I thought if tuned the intake to 2000 that would be the best way to improve torque.
So will having short runners and a huge plenum have the same effect long runner’s small plenum?
Bye huge air box you mean plenum I’m assuming so how big is huge

"For a street car, you want a wide power band, so maybe you don't want every tube to resonate at exactly the same rpm.
Which may be why Chrysler used long, gently curved tubes in the manifold for their old slant six. Take a look."

This was very help full I see how 1, 6 are tuned for low rpm
2, 5 midrange and 3, 4 high rpm great idea thus giving a wide power band.

Some OEM manifolds automatically adjust at a set engine speed. They don't spend that money unless it works.

Shape is normally a log shape or box shape.

For steady state power, the bigger the better, but there is a diminishing return. I think at least the volume of 2 cylinders would be minimum and over engine volume would be pointless. The bigger the plenum, the more the signal to the carb is filtered and the slower the throttle response.

If I wanted maximum torque at around 2000 rpm, but better than stock power, and wanted carbies rather than EFI I would use 3 X 1.5" SUs on individual ram tubes.

I didn’t mean on to fly adjustability I meant fixed just enough to make up for any errors and bends.
The shape will be log between 1.2 and 4.1 sounds good.
Have you ever tuned triple SUs before I have and I never want to do it again not only is a single SU hard to tune then you multiple the problem by 3.

In terms of area? or literally the shape - round vs square?
Sorry I meant area they will be round same as the ports.

Thanks again all big help.

 

[patprimmer]

I have tuned triple SUs once.

I put them on the car, tuned them once then left them alone. They worked great for years with only the occasional topping up of the dash pots.

SUs only require a lot of tuning if you think you can improve them with unnecessary adjustment. You just chase your tail and end up untuning (new word)them.

Once you have the correct main jet, the correct needle and the needle is centralised in the jet, the rest is not critical. the spring should be about right, but so long as it is not to soft, it will work OK. Once the spring is selected, it never needs adjusting.

The dash pot should be filled with oil occasionally, like about every time you change oil.

Air speed at idle should be reasonably equal, but in reality, if it's off a bit it makes little difference, but this is the same for any carby.

If the throttle plungers lift at different rates, that does not matter and in fact it is the carby reacting correctly to variations in airflow in each manifold runner.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

"The engine spends most of its time a 2000 peek torque is at 2000-2400 max power is at 3700 and redline is at 4000. That’s why I thought if tuned the intake to 2000 that would be the best way to improve torque."

I think it is a good move

"So will having short runners and a huge plenum have the same effect long runner’s small plenum? "

No, not by any means. Huge plenum is bad anyway. The most important length is that from the valve seat to the first major change in area, typically where the runner hits the plenum, or the end of the velocity stack.

"By huge air box you mean plenum I’m assuming so how big is huge" several multiples of the engine capacity.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[IceStationZebra]

I think you guys missed the boat on the whole long/mid/short runner idea on the Dodge/Chrysler slant 6 or any other engine for that matter. If you want equal length runners you have very few choices except a long plenum with parallel runners. This is very impractical on a production engine running only one carb.
- The manifold will be roughly twice the size of a traditional manifold.(more weight, cost, packaging problems, potential cracking, etc.)
- Fuel distribution will be a big problem. The fuel to the end cylinders will have to make a sharp 90deg bend causing the fuel to puddle. The front cylinder nay lean out some during hard acceleration.
- Tuning for a specific RPM has already been done and didn't prove that successful. Look at the Dodge 413 cross ram. It was pushing into production as a technical marketing gimmick even though one of the engineers on the project had proven that an equivalent engine with a conventional manifold could out accelerate it - its torque under the curve the matters.
- An engine with an abrupt torque peak can be a bear to drive on the street. I had a 190hp GM W41 quad 4 that was a dog util 4000rpm, and than you better hang on. OK for racing but hard to control in the rain and snow. The only saving grace with the limited slip differential! I would think if you are using an automatic trans that you would need to retune it also.

You asked if bends would hurt power - I agree with everyone who previously said no IF it doesn't hurt fuel distribution or cause puddling.

If you go with the 3 carb set up by all means use the long plenum/equal length runner idea.

Also, you didn't state your whole plan, but the engine should be optimized as a unit. If you upgrade the intake you should also look at the exhaust, head flow, and cam.

 

[madaz]

I think you guys missed the boat on the whole long/mid/short runner idea on the Dodge/Chrysler slant 6 or any other engine for that matter
No I understand but there will be little effect it’s a big compromise just for a broad power band.

Also, you didn't state your whole plan, but the engine should be optimized as a unit. If you upgrade the intake you should also look at the exhaust, head flow, and cam.
2.5" exhaust, mild cam, mild head work, 10:1 comp.

I think it is a good move
Thank you at least some one thinks so

I put them on the car, tuned them once then left them alone. They worked great for years with only the occasional topping up of the dash pots.
Yes but tuning them is the hard part

 

[Marquis]

My questions are:
Will bends effect the bower band or effectiveness? (They have to be bent to fit under the bonnet).
Do velocity stacks help make more power/torque?
I can make it with some adjustability would this be a good idea?
What shape plenum and how big?
How much does size of the runner effect power band?"

Hi,
Bend radius do effect the power band as they assert a loss- but this is usually associated with higher rpm (about 4500 rpm onwards). At the kind of engine speeds you’re talking about it’s not that significant. The only thing I’ll say, is that you seem to be designing the intake for carburation. I would assume therefore that it’s duties will be split between providing some degree of intake tuning and also supplying fuel to the cylinders also. With this in mind- it would mean that the intake should be shaped for “wet flow” in mind considering both cylinder to cylinder fuel distribution and air flow tuning effects. Because of this inlet manifold symmetry and keeping the manifold section velocities up could have more importance. One of the advantages of fuel injection over NON-,multiple carb set up- and not often voiced- is that the duties of air flow ram tuning and fuel delivery are no longer combined.

I would make the plenum” torpoedo” shaped if possible, this gives a nice more rigid structure with less flat sides which would be better for Noise vibration and harshness. As for volume- I’m assuming that the carburetteur butterfl (ies) is/are upstream of the plenum- in which case you should consider throttle response. This is dictated by the volume from the throttle butterfly to the inlet valve- or the “Throttled volume”. From the experiences of engines I’ve worked on I would aim for 2.5 times your engine swept volume as the TOTAL Volume from back of valve, including the inlet runner and plenum up to the throttle butterfly or less. But use this value as an upper limit.
The size of the plenum will effect the powerband- the Euro 3 litre Euro M3 uses a plenum volume of 14 litres- but it has individual throttle bodies and fuel injection. You have other concerns such as cylinder to cylinder fuel distribution and throttle response.

I’m not quite sure what velocities stacks are, but best for power are tapered runners that are as straight as possible- however – you engine speed range is low- so bends would make a big difference and you have to consider the effect on “wet flow”.

I realise a lot of the recommendations I’ve given are from an OEM perspective, slightly idealised and perhaps not that easily achievable for a home grown modded application like this but they give you something to aim for. I’m also following similar procedures for my straight six, but Ive got access to a flow rig, and mine will rev to 8000 rpm

 

[IceStationZebra]

Madaz, sounds like a good balanced plan. I think that Marquis restated/expanded on my fuel distribution concern in a much more elegant manner than I did. The reason I am especially concerned with that aspect is because you want it to be a dailey driver. If it was a race car or street/strip project you could live with a more temperamental set-up.

"Do velocity stacks help make more power/torque?" - could you describe what you are calling a velocity stack? In USA this is generally a bell mouthed pipe attached to the carb inlet, but could also describe the inlet to each runner inside of the plenum. If used on the carb inlet it is generally used to smooth the air into the carb making it flow more efficiently - a good thing. If the entrance to the individual runners - a good thing but more complicated to do than a plain radiused runner inlet that is part of the plenum wall.

"I can make it with some adjustability would this be a good idea?" It never hurts Then you can test with real world results. Will a little forethought you could easily adjust the plenum volume/shape and the runner length.

"What shape plenum and how big?" From what I have read you want at least 1x engine displacement. But if you make a split plenum you can easily make a spacer to play with this.

 

[patprimmer]

Fuel distribution and constant depression are the reasons I keep harping about 3 SUs.

It will work, in fact, it will work great. It won't be hard to tune if you just leave it alone.

I know guys who will set them up in Sydney. You just bolt them on and set the idle speed.

1.5 SUs are dirt cheap from any specialist BMC wrecker as all the boy racers want 1.75s and 2"

I set up a UC Torana. I used a Blue motor 3300 cc capacity.

Flat top pistons for 10:1 comp.
3 X 1.5" SUs on an aftermarket manifold for a red motor, ground and welded a bit to fit the blue motor head.
Stock valves, back cut to narrow seats and improve low lift flow.
Custom exhaust with 1.625 primaries.
A very big hydraulic cam (for a daily driver) 48/85 with 0.480 lift I think with asymmetric lobes and asymmetric inlet and exhaust, ground by Wade Cams in Abbotsford near Melbourne's CBD
Rhodes lifters
A Toyota HiLux 5 speed gearbox on a Dellow adaptor.
3.55 final drive, 3.55 low gear.
205 60 14 tyres.

It pulled easy from 1000 rpm in 5th gear, and ran all the way out to 6000 rpm.

It was good on fuel.

It was easy to drive.

It had heavy steering and bad brakes as it was a Torana after all.

My brother taught his 70 od year old mother in law to drive in it without a harsh word. It pulled that well.

Sorry to harp, but I really believe it will give the result you want at the budget you seem to have.

I set up another Torana 3300 red. It was a company car, so stock looking was critical. I used a 350 Holley (as it took a stock holden air cleaner cover, and adapted it to a stock Torana GTR manifold I also did a mild cam (20/60) and I used a stock GTR twin branch exhaust manifold. It went quite a bit better than stock, but compared to the above engine, it lacked bottom end torque, top end power, smooth pulling and economy. It lacked in all these areas to a considerable degree.


Holleys are great in the middle of a V8 which is short compared to an inline 6 and where bonnet clearance is an issue, but they leave the centre 2 cylinders rich and the end cylinders lean on an inline 6. You can offset this with good manifold design, but you can't fix it and get equal length at the same time. I reduced distribution problems on my inline 6 with 350 Holley by running about 0.007" bigger jets in the outboard choke, as it lined up more with the end cylinder runners, but any puddled fuel was still right in front of the centre 2 cylinder runners.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[OP800]

Max torque area is the engines best efficieny range.
Any thing you do the keep mixture speed up, helps enhance torque.
Same goes for the exhaust. Keep the tubing diameter small to keep the gas speed up without going into restriction.
Look at most modern engines, they have intake tuning of one sort or another.
Ford 4.2 had dual runner control.
For 5L has tuned intake as well as many other models but these are all FI and dry flow manifolds.
The only way you will know if you are improving anything is by dyno testing.
The length of resonace tuning for the first wave is quite long. As you go to second and third resonance, the returns begin to diminish quite rapid.
The dual runner control was more for intake flow speed than changing resonance. Even the Corvette used it.
One trick used some time ago was to put fine wire mesh across the intake ports to keep the mixture more in suspension if you don't care about losing a little top end power.

 

[madaz]

OOne of the advantages of fuel injection over NON-,multiple carb set up- and not often voiced- is that the duties of air flow ram tuning and fuel delivery are no longer combined.
I m going to go for efi now I didn’t realize how much of a compromise a carb manifold is.

I would make the plenum” torpoedo” shaped if possible.
So start as a log then taper it into a point? Wouldn’t this favor front cylinder?

As for volume- I’m assuming that the carburetteur butterfl (ies) is/are upstream of the plenum- in which case you should consider throttle response. This is dictated by the volume from the throttle butterfly to the inlet valve- or the “Throttled volume”.
This will still apply because I m only going single throttle body. Will the placement of the throttle body make any difference?

Then you can test with real world results. Will a little forethought you could easily adjust the plenum volume/shape and the runner length.
What do you think the easiest way to adjust plenum volume?

Any thing you do the keep mixture speed up, helps enhance torque.
Taperd runners will be not adjustable so they will the same size as the ports.

 

[Warpspeed]

Going EFI is a really smart move, and these days it will probably cost less if you take tuning multiple carbs successfully into account. Really good drivability and fuel economy are far easier to achieve as well.

You can only do so much with tuned length, a bigger factor is port velocity, but you will be pretty much stuck with what you have anyway.

Looking at some charts I have here, something in the region of 24" to 28" should suit your requirements best.

28 inch length:
5th pulse 1,928 rpm
4th pulse 2,642 rpm
3rd pulse 3,464 rpm
2nd pulse 3,857 rpm

26 inch length
5th pulse 2,076 rpm
4th pulse 2,846 rpm
3rd pulse 3,730 rpm
2nd pulse 4,153 rpm

24 inch length
5th pulse 2,250 rpm
4th pulse 3,083 rpm
3rd pulse 4,041 rpm
2nd pulse 4,500 rpm

As Thundair stated earlier, one length will create a series of tuning humps (and dips) at various different rpm. As rpm rises, there will be less time for multiple reflections, so you go from say five reflections, up to four, then three then two.

 

[Marquis]

Torpedo shaped means- a general shape devoid of flat surfaces, with rounded edges- this is stiffer and a more rigid structure than a flat sided boxy log.

Tapered runners give a big benefit on engines with dry flow.

 

[Alchemi]

What your trying to make is called a Helmholtz Resonator, a good read of how this works can be found here

http://www.grapeaperacing.com/GrapeApeRacing/tech/inductionsystems.pdf

- the short of it is you need very long runners for low peak torque ranges, the tube diameter is very important, the theory only works with upto 4 cyls - so you would be looking at a dual plane setup (not a bad thing), each plenum should be the same volume as the # of cyls its feeding and then the runner feeding the carb/TB has to be a certain size - but is easily made adjustable for tuning.

Im contemplating making one for my 265 Hemi 6 with a similar rev range, 1500-3500 with 2000 being where most of the works done at, but the evils of turbo charging (for economy, when done the right way) are beconing - which negates the Helmholtz maths

 

[Lou Scannon]

"the evils of turbo charging (for economy, when done the right way) are beconing - which negates the Helmholtz maths"
Care to elaborate?

 

[Alchemi]

Ok, the "dosent work on turbos" info i got was anedocial, so have done a bit of digging and have come up with the following.

The runner length theories still work but the speed of sound coefficient needs to be changed due to the increase in air temprature, there is a formula here

http://en.wikipedia.org/wiki/Speed_of_sound,

and an online calculator here

http://www.school-for-champions.com/science/sound_speed_gas.htm

Humidity has an effect too, as the actual air is less dense and sound travels through water faster. This is important to me as i wish to use alot of injected water, however the only math i can find that is suitable

http://www.rane.com/pdf/eespeed.pdf

is a tad beyond my excel programming skills. There are a heap of online calculators but they are only acurate to around 40c. 0 to 90% humidity only increases speed by 5 fps @40c but the output temp on a turbo is much higher than that. The water injection would drop alot of temp off (hopefully) which will screw with the runner length again.

Where I think it starts to fall apart is the "tuning" port to the plenum, this works like a port in a speaker box and thus allows some free air movement, A turbo at either end of this pipe would cancel out this effect??

Im not too sure how it would work out if you try to put a 20"x1.4" 0r 2 20"x1" pipes - aprox size for a 4L@2000 rpm, onto a 2" turbo outlet, or if you would have to include the internal flow of the turbo in the tuning pipe length.

I would think that a smaller plenum would be better vs lag, but havent found any definitive evidence either way.

Basicly there are a heap of unknown variables, a bad thing when your trying to make such a precision item. Any one got some answers??