45mm Weber DCOE Ram Tube lengths

[Whittie]

Hey All,

Just started pulling the motor down as part of the rebuild and I'm looking at all aspects of it and I came across the interesting conundrem of Ram Tubes. The Ram Tubes on the car are SUPER long, and this would not normally be an issue, but I've put those cylindrical K&N type air filters that have the chrome plate on the ends. The ram tubes come within probably 1-2cm of the chrome plate and I can only assume that this is killing engine power.

So, I was wondering what length people use on their motors, what effect the length has on the motor (from a fluid mechanics point, so long as it's smooth and well rounded I can't think of anything it would do). Also, if anyone knows somewhere reputable to buy them, the places in the UK want upwards of 20 pounds each plus shipping for these things!!

The tubes will be inside the air filters so colour really doesn't matter, but if the cost is irrelevent, blue 

Cheers

[Scoota G]

These ones i got from   aholguin8877  on ebay but he dosen't have any listed at the moment.  Cheapest by far.

[Whittie]

Cheers Scoota!

Unfortunately, they are about the same length as I have at the moment, so probably no good for me. I'll keep an eye on his eBay postings, maybe he'llpost something more like 30mm

Another quick question, do the tubes slot into the weber at all? I've found some that do, some that don't and now I'm confused.....

[luvemfast]

30mm ram tubes for triple 45's would be too short wouldn't they?
I would have thought you'd need 50mm long.
Maybe you need to change the way you filter the air?

[Whittie]

30mm ram tubes for triple 45's would be too short wouldn't they?

Well I don't know, that's why I'm asking before I buy anything

Why exactly would they be too short, what effect does the length of the tube have on the air flow? LIke I said, physically I can't imagine it has any effect but how much drag there is on the air, which is a function of the shape of the curved section, not so much the total overall length.

**EDIT**

Well, I've done a bit of looking around and it seems there is a whole art to intact tuning, much the same as exhaust tuning!

On a very basic level, long intake = low rpm torque, short intake = high rpm torque..... That is a gross simplification, but works much the same as exhaust header and collector lengths.

I have a very long carbie manifold on the car, so I think what I will do is try and get some 45mm long (square) ram tubes with an eliptical inlet shape and switch over to running sock filters. The K&N filter was burn't from a few backfires and needed replacing anyways, so no huge cost there, I just need to find some decent and cheap velocity stacks....

[luvemfast]

I'm sure someone with better knowledge can chime in here.
Its all about air speed/velocity.

I have 40mm carbs at the moment, they have 25mm ram tubes.
Its more common for the smaller carbs to have shorter tubes for the reason that these carbs give good torque, but die off as they struggle for volume of air.
The larger carbs come into their own at higher revs, which is why they have longer horns.

Thats my air horns for dummies explaination of the day
(comments made above are purely my misguided beleifs and can be disproven quite easily as I'm an idiot)

[Scoota G]

I think that Ram Tubes would be specific to engine design, exhaust, head mods, compression. I bolted mine on cause i loved the look since i was a pimple faced teenager. Now i've got the ram tubes and the pimples . . .  they show up in the oddest of places   

[Gareth. J.]

Longer ram tubes give better low down torque, shorter give top end. I ran nothing for 18mnths then bought 105mm ram tubes on my old 40mm dellorto's, these were pretty close to the strut tower, but ok. There was no difference in top end but low down was much improved. The minimum clearance for uniterrupted flow is meant to be around 25mm from the face of the tube otherwise you'll get too much turbulence, which is bad. I based my reason for picking long tubes on the V8 supercars, they shift a 7200rpm and run longer ram tubes.

I got the 105mm ram tubes from Steve Newing at EFI Hardware in Melbourne. The bottom pic is my dellortos on Rev's zed after I sold them.

[peter mc]

one time i spent the hole day on the dyno with a l28 with 45dcoe and i try ed every combo of ram tubes to see wot would happen i was very surprised to find very little improvement. in the end i went with the long ones as it had a bit more at 3500 -4500 but it was very marginal only 4 or 5 hp between all of them . air cleaners were more important as i found some losing up to 15hp over others. also efi hardwear no there stuff they can tell you wot you need length wise

[Whittie]

Yeah, it's not a huge difference, but certainly worth looking at if you can get them cheap.

OK, so next question would be what air cleaners?!

I have the K&N's but these are no good with my ram tubes, so I'd need smaller ram tubes. The other option would be sock filters.

The big thing with my car is it still sneezes a bit sometimes out the carbies when it's cold so I don't want to set filters on fire or burn big holes in them everytime I start the car, so something a little resilient would be good.

What would be your recommendation there Peter, keep the K&N's or go with something like a sock filter, and then what brand? Should you oil them or not (I'm thinking oiling will kill performance, but increase filter life)?

To be honest, I'm thinking keep the K&N's and go with like a 25mm ram tube. The manifold on the zed is super long and the long ram tubes almost hit the strut tower, much like Scoota's pics there and I wouldn't mind some more top end in the car, it falls off pretty steeply at around 6500rpm, but that is likely just the cam restricting things.

[peter mc]

the K&N filter with ram tube was not that good. was down on power over sock and tubes both need heat protection for best results. a plate under the manifold that extends all the way under the socks is best .

[peter mc]

allso the longer manifolds can run shorter tubes with good results  and short manifolds need long tubes funny that...

[Whittie]

Hey Peter, thanks for summing that up and putting detailed results, not just "i think this was better". Numbers are always better than guesses.

As for the ram length depending on the manifold, the reading I did says that the length of importance is the total length from the inlet valve to where the ram tube starts to curve, that entire section determines the length of the intake and thus the harmonics. So, if you have a long manifold and a short ram tube, then you would need a long ram tube on a short manifold to get the same total length from the inlet valve to where the ram tube starts to curve.

Given I have a long manifold, I would like to try the shorter tubes, but I think I'll just get sock filters and leave it at that for now, I don't have free dyno access to work out the differences between changes.

Another thing of note, is that you get a greater impact with a long tube than a short. So, the torgue gain at lower revs is higher than the torque you gain at higher revs. Also leans me towards just keeping the long ram tubes.

[twosixty]

You can have a look at this, which should answer some of your questions re intake bellmouths and distances to airbox/airfilter.
http://www.bgideas.demon.co.uk/tmanual/Tm_Ch2.pdf

They give a rule of thumb that you should allow at least the bore diameter gap inbetween the end of the ram tube and the airbox (KN filter in your case).
There are also plenty of information and calculators available on the net about optimum runner length measured from valve to airbox (or air supply with assumed zero velocity).

Considering the importance placed in having a fully rounded bellmouth, I would assume that a filter sock over ram tubes would severly reduce the speed of the air coming around the bellmouth, negating any positive effect that it would provide. That said, we are probably talking 3/10s of FA noticeable change.

Keep reading if you feel like having a bit of a snooze:

An estimate of the first harmonic length for our L6s with a warm cam is somewhere around 3.3m, which is an aweful lot of runner. You can halve that figure to get the second harmonic length, and again for the third and so on. The gains from capturing that first pressure wave is estimated to be up to 10% gain, but diminish as you aim for the higher/shorter harmonics. Generally the 3rd and 4th are the only practical harmonics to be able to capture (about 0.8m & 0.4m, for about 4% and 1% estimated gain).
This is all estimated on the peak power rev range, so you can pretty much throw it all out and just go for the longers runner/airbox tubing that you can fit.

This site has some good reading and easy calcs http://v8soarer.com/intakerunners/index.shtml

Hope that helps.

[peter mc]

All we have to do is copy the race cars from the 70s and 80s BRE and the like, they all had long manifolds.
We are not doing anything new guys!