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Inlet tract tuning


AK260

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Hello gang!

 

My new bad obsession this year is the inlet side! Beyond planning on a new CAI and some David Vizaardry on the carbs, I have a new unhealthy obsession with inlet tract tuning.

 

I have read many references to this not on a Z car, but I am keen to hear from you good fellas as to what we know of, that has been experimented with on a Z.

 

For example, I regularly hear that the stock trumpets are actually very good. But what does that mean? They are no doubt very good for stock engines / cams / exhaust combo etc but what about modified engines with more overlap and duration?

 

It’s common knowledge that long stacks give you better mid range and short ones are good for top end BHP + the end mouth shapes are also pretty important but has anyone done any real back to back fact based analysis on the Z and on a modified engine? And what were the findings for an ideal length for that spec of engine?

 

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I’m tempted but the fully radiused 50mm MSA ones but there are others out there including “12 second dual SU Nom’s” baby ring toss mod!

 

https://www.classiczcars.com/forums/topic/60086-velocity-stacks/

 

 

Some links of interest below and some interesting results ....

 

A geeky read ...

 

https://core.ac.uk/download/pdf/82364512.pdf

 

 

A great read ...

 

https://www.emeraldm3d.com/articles/emr-adj-length-intake/

 

A good watch ...

 

 

 

A mind boggling calculator ...

 

https://www.classiczcars.com/forums/topic/60086-velocity-stacks/

 

Ps. I absolutely LOVE this thing machined but the UK MG guys from scratch!

 

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Thanks dude. Not sure how I missed that in my googling hours!

It’s one to read carefully - I just read the first 4 posts and it seems like a brilliant discussion with lots of good info!

I was shocked to find my tapered 70mm ITG HS6 horns caused the car to feel flat EVERYWHERE and made the reversion at low revs even worse. Then I measured them to discover the throat went down to 40.5 on 44.5 mm carb openings reducing surface area by 17%!!!!


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Then I looked at the stock back plate on the air box to discover the opening is larger than the cab mouth so in effect a step causing frictional losses / vortices + an expansion wave all of it’s own! So I will be reaming out / tapering the carb mouths to match the exact dimensions of my home made aluminium back plate for my new plenum and the horns I finally go with.

Here’s my new airbox / plenum with home made 4mm aluminium back plate.

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[mention=32052]AK260[/mention] how’d you make the plenum?
cc: [mention=23457]Captain Obvious[/mention]



This was a box developed a few years ago by the racers in the uk’s Zclub.net before my time with Zs. I believe they did a lot of dyno testing and fine tuning - which proved that it added some significant ponies and eliminated some dead spots they had. It eventually became the “club airbox” offered at cost to paid up members.

We recently did a couple of batch runs but not sure about plans for the future.

The original design has a fibreglass back plate and clips to hold it on. I wasn’t a fan of having nyloc nuts where they “may” get sucked in. While this has never happened to anyone yet, I still set about making my own back plate for it.

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My interest in the inlet tract beyond the additional few small ponies (and detail OCD) is to reduce the carb standoff and reversion I get around 2.1-2.5 and 3.1-3.5 K rpm. My torque curve currently has 3 peaks.

On the airbox, it has an 82mm ID / 86mm OD mouth. Most early S30 owners replace the air tube on the left of the car and reduce inlet pipes down to 76mm to get through the hole in the rad panel. On my ‘77, the hole on the left is 91mm in one direction and 110mm vertically. I’ve opted for 90mm ID 2ply flexible silicone ducting and an AP2 S2000 air filter.

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Why that filter? Well, the S2K head flows just north of 300cfm and at max revs it’s doing close to 290. My head at a theoretical 83% VE and current bhp output is doing a theoretical 277. The filter flows more than enough for my requirements, is very cheap compared to a K&N, filters better than a K&N, doesn’t need oiling, has a built in velocity stack and an 87mm OD / 83mm ID flange. The down side is that it’s a BIG old beast, puke green and has prosthetic limb coloured plastics (which will get a coat of black paint)!!!! On the upside, it will be hidden behind a front facing 190mm heat shield to protect it from water and stone chip damage, something like this in black. I don’t want anything visible through the grille!


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Well, I appear to have thread jacked myself!! ;)

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4 hours ago, AK260 said:

I was shocked to find my tapered 70mm ITG HS6 horns caused the car to feel flat EVERYWHERE and made the reversion at low revs even worse. Then I measured them to discover the throat went down to 40.5 on 44.5 mm carb openings reducing surface area by 17%!!!!

Similar problem but the opposite, when I was using SK triples the front edge of the chokes had to be tapered down so it flowed into and matched the bottom of the trumpet, the Ramair foam filter wasn't ideal but worked well enough.

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Similar problem but the opposite, when I was using SK triples the front edge of the chokes had to be tapered down so it flowed into and matched the bottom of the trumpet, the Ramair foam filter wasn't ideal but worked well enough.
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Ooooh! That’s really nice work there! What did you use to get such a good finish / result?

Not a chance. We already talked about this....  I'm not getting pulled into a carbon fiber layup project.      default_<img%20src=.gif' alt='default_ROFL.gif' alt='default_rofl.gif' alt='ROFL'>.gif'>.gif' alt='ROFL'>.gif'>


I’m not sure what you gents have discussed in the past but this airbox, while it looks carbon is all fibreglass. I have to say, I would prefer it if it was just smooth.

I REALLY love the one @HS30-H has on one of his cars and wish it was more readily available. I’d gladly pay top dollar for that item! 9f0c0529219494acf02d9d08b55697d4.jpg&key=f5782564b1a4951dde294b836739a70c17c67b935e34710858b7c873540973b6
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Ps. Beyond the issues people have quoted with them deforming and collecting / dripping the fuel from the standoff mist, the thing I really don’t like about the Ram Air filters (or any trumpet filter) is the sucking of hot air!!

I am planning on getting a couple of temperature sensors under the bonnet to measure what temps I’m getting. While doing my search, I came across this VERY good thread / experiment.

https://www.jaguarforums.com/forum/xjs-x27-32/under-bonnet-hood-temperatures-166641/

Mr. Vizzard has a chart showing that for every 11c drop in intake charge temp, he gained 2.2% HP. Now imagine ambient 25c and under bonnet temps of 68c as an example. That’s 6.6%!! On a 200bhp engine that is worth 13 ponies. 13 very easy and cheap to have ponies.

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I know all of this is old hat but I’m always intrigued at how few people care. I guess not everyone is chasing ponies and prefer the sound. And oh what a lovely tune it is too!!

[/Rant off]





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Somebody on a different forum measured under hood temperatures for Z's and found that when the car was moving the air under the hood equilibrated to outside air temperature.  It got replaced faster than it could be heated.  Non-moving might be a different story, can't remember what he found there.  His conclusion was that relocating inlets was not worth the effort.

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Somebody on a different forum measured under hood temperatures for Z's and found that when the car was moving the air under the hood equilibrated to outside air temperature.  It got replaced faster than it could be heated.  Non-moving might be a different story, can't remember what he found there.  His conclusion was that relocating inlets was not worth the effort.


That’s really interesting! Something I have to prove to myself ;)

In all seriousness, my under bonnet temperatures get horrendously elevated standing still. Since I made my own heat shield, the carbs not longer get hot. In fact, they are fridge cold to the touch after a good blast!

Also with the biggest hole at the front of the car being the radiator and a fan constantly sucking air through it, I have always imagined hot air being pushed into the engine bay more than fresh cool air. Having said all that, if someone has measured it then there is fact there.

I’m still keen to try it out and prove it to myself. I want to put the factory air box back on and have a sensor inside it, got for a drive, then repeat with the CAI and compare and contrast!
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