1970 GT6 MK2

[egret]

My airbox thoughts were as follows.

In theory a big volume (you are limited with what you can do between carbs and wheelarch) will make it a neutral point, which means it becomes the starting point for the really complex induction stuff where you consider pulses and velocities when you need to really consider the momentum of air.

This big airbox is fed by a big tube with a massive cone filter, aiming to minimise any pressure drop between the airbox and atmosphere.  A big cone filter is mounted in front of the radiator so pulls coldest possible air.  This allows you to select a big cheap air filter.  there are many arguments about filter pressure drop vs filtration performance and power etc. etc.  Increasing your filtration area is relatively cheap way to get the best possible outcome.  No way is a K&N developing less pressure drop than a paper filter with 10x the filtration area!

I think I have 3" tubing which looks comically large, but matches the ebay K&N cone I got for peanuts.

Also a 1.3l engine at 6.5k is breathing 70 l/second (assuming 100% volumetric efficiency), or the air going down that path is traveling at 16m/s or 35 mph (feel free to validate my calculations, I got a bit confused at one point, but I think I'm right). The original airbox hoses are about 1" and although there are two, the air is going about twice that speed.  To be clear, the presure drop on this component is likely still peanuts compared to what's happening in the inlet manifold, head around the valves, etc. so is unlikely to be the limiting factor, but it's a relatively easy thing to make better.

The main issues with my working prototype are:

it rubs on the inner wheel arch, not a big issue as it means I've maximised the volume available there. 

It's tight around the radiator brace and radiator so hard left lock means the front of the drivers tire does abrade the inlet tube.  I'm looking at re-routing under the radiator where there's possibly more space, making a new radiator support to give more clearance, and/or making an oval tube to link the airbox to the filter.

I've misplaced the photos of my airbox, I think there are some on here though.

[Gt64fun]

I have also pondered on airbox design and I previously posted this on the TSSC forum at https://forum.tssc.org.uk/topic/12397-air-filter-question/page/2/#comment-195288

My current thinking regarding the airbox as described within the post above. The large diameter (circa 70mm) single pipe is  achieved by flaring out the box at the front end where the wheel arch allows.  

If I make it the right depth it can use either my existing K&N filter elements, or a remote filter at the side of the radiator.

Ian

 

[egret]

This looks great! Much more craftsmanship than in mine, also I think it has a narrower radiator than my spitfire.

In a money no object redesign I'd try a narrower aluminium radiator (with integrated oil cooler) to make more space for this kind of air feedfrom the front.  It's a much more constricted area than I first realised.

 

[Speedysix]

On 7/12/2024 at 3:00 PM, egret said:

My airbox thoughts were as follows.

In theory a big volume (you are limited with what you can do between carbs and wheelarch) will make it a neutral point, which means it becomes the starting point for the really complex induction stuff where you consider pulses and velocities when you need to really consider the momentum of air.

This big airbox is fed by a big tube with a massive cone filter, aiming to minimise any pressure drop between the airbox and atmosphere.  A big cone filter is mounted in front of the radiator so pulls coldest possible air.  This allows you to select a big cheap air filter.  there are many arguments about filter pressure drop vs filtration performance and power etc. etc.  Increasing your filtration area is relatively cheap way to get the best possible outcome.  No way is a K&N developing less pressure drop than a paper filter with 10x the filtration area!

I think I have 3" tubing which looks comically large, but matches the ebay K&N cone I got for peanuts.

Also a 1.3l engine at 6.5k is breathing 70 l/second (assuming 100% volumetric efficiency), or the air going down that path is traveling at 16m/s or 35 mph (feel free to validate my calculations, I got a bit confused at one point, but I think I'm right). The original airbox hoses are about 1" and although there are two, the air is going about twice that speed.  To be clear, the presure drop on this component is likely still peanuts compared to what's happening in the inlet manifold, head around the valves, etc. so is unlikely to be the limiting factor, but it's a relatively easy thing to make better.

The main issues with my working prototype are:

it rubs on the inner wheel arch, not a big issue as it means I've maximised the volume available there. 

It's tight around the radiator brace and radiator so hard left lock means the front of the drivers tire does abrade the inlet tube.  I'm looking at re-routing under the radiator where there's possibly more space, making a new radiator support to give more clearance, and/or making an oval tube to link the airbox to the filter.

I've misplaced the photos of my airbox, I think there are some on here though.

I think I might have seen these pictures across my searches, it was a tight fit! This is the problem on the gt6, a bigger airbox is more desirable but is all down to space. I think this is one of those problems I wanted to solve early, but in reality not going to be able to until I can physically see what sort of room I have to play with in situ. Especially running larger carbs, fortunately without those crappy tt adapter plates for the hs6's thst push them so far back they might as well be outside the car! 

I know what you mean with the tubing, it's very bumpy and not at all the best thing to use, the smoother larger pipe is a much better solution as you've found. I'm definitely in favour of this route, I think the results it will yield are definitely going to be better than just slapping some bank breaking k&n pancakes on and calling it job done. 

 

[Speedysix]

On 7/13/2024 at 12:18 PM, Gt64fun said:

I have also pondered on airbox design and I previously posted this on the TSSC forum at https://forum.tssc.org.uk/topic/12397-air-filter-question/page/2/#comment-195288

My current thinking regarding the airbox as described within the post above. The large diameter (circa 70mm) single pipe is  achieved by flaring out the box at the front end where the wheel arch allows.  

If I make it the right depth it can use either my existing K&N filter elements, or a remote filter at the side of the radiator.

Ian

 

Ian, that's a proper template! The foam is the right way to mock it up, especially with the space limits. That's a extreme close between the arch, nice job! 

[Speedysix]

Thanks for the help on the boxes guys, I think it's one of those issues I need to solve with the engine back in the car. Not too far away hopefully.

The aim was to get the car back on the road for the summer but summer seems to have gone. Anyway, the target is late August at the moment so it's quite an uphill battle!

Smoothed out the manifold ports over the weekend, some very large steps and poor machining from the factory, I corrected them without enlarging the port dia using a 60 grit sanding bit on the die grinder.

You can't see it that well but the flat head of the screwdriver doesn't run smoothly up any of them and goes in about 1mm in some spots. Hopefully this has some sort of effect

I re checked the chamber volumes and gave an average of 34.08cc. So slight increase from before from the cleaning, or just measuring properly this time.

With that it yields a current CR of 9.38:1. Not what we want. So working backwards. I was aiming between 9.5-9.6. Before the target was 9.5, however given this time it's cemented in that we're running a hotter cam, flowed head and slightly improved flow (hopefully), tubular manifold and both port matched to the head( yet to be done) etc, as well as lots else done with the aim of improving the performance, I think 9.6 might be OK.....

Anyway, if we run 9.6;

337.62/(9.6-1)=39.26

New chamber volume=39.26-3.5-2.7

=33.05cc

I have the head setup perfectly level to do it the burette way and measure with a flat edge and digital verniers. My only concern, does anyone know the minimum thickness these heads can go? Really don't want to punch into a water jacket after all this time and effort.

[Speedysix]

Just measured the depth, quite fiddly but end up with a figure of 0.030, 30 thou basically, firs measurement I did came at 0.023, then rechecked and got 0.030. 

Current head thickness is also sat at 3.339"

 

[Speedysix]

Managed to get a few bits done over the weekend, my new wipers finally arrived!

Took a little bit of searching but NOS came in at 5 quid more than a pair from rimmer or canley of the modern type ones. My wiper arms needed a touch filing off them to fit these, hopefully they are an improvement!

The port matching is now complete! Simply used a manifold gasket with all the studs in place

the left is factory, the right is after. Some required quite large amounts taking off, definitely restrictive. Didn't enjoy it either doing it in a full face mask on the hottest day of the year so far, was a very sweaty experience. The manifold I recently acquired matched the gasket I'd say 95%, some had a small amount on the lower edge but given it has a mm or so of movement before its tightened on the studs, I decided to leave it.

The last job which I didn't photograph was removing the square water take off plug from the head, my God that was frustrating. Spent about an hour, eventually got it off by hammering the square end of a socket reducer on to what was left and using the air impact to ease it off. Removed all the guides too so the head is now ready to go to the machine shop when funds permit.

Jacob

[Speedysix]

Managed to get a few bits done over the weekend, my new wipers finally arrived!

Took a little bit of searching but NOS came in at 5 quid more than a pair from rimmer or canley of the modern type ones. My wiper arms needed a touch filing off them to fit these, hopefully they are an improvement!

The port matching is now complete! Simply used a manifold gasket with all the studs in place

the left is factory, the right is after. Some required quite large amounts taking off, definitely restrictive. Didn't enjoy it either doing it in a full face mask on the hottest day of the year so far, was a very sweaty experience. The manifold I recently acquired matched the gasket I'd say 95%, some had a small amount on the lower edge but given it has a mm or so of movement before its tightened on the studs, I decided to leave it.

The last job which I didn't photograph was removing the square water take off plug from the head, my God that was frustrating. Spent about an hour, eventually got it off by hammering the square end of a socket reducer on to what was left and using the air impact to ease it off. Removed all the guides too so the head is now ready to go to the machine shop when funds permit.

Jacob

[Gt64fun]

That's similar to what I found when I did mine. I suppose if the casting and machining is the same it would be.

Bit sloppy Mr Triumph!

Ian

[Speedysix]

On 7/22/2024 at 3:59 PM, Gt64fun said:

That's similar to what I found when I did mine. I suppose if the casting and machining is the same it would be.

Bit sloppy Mr Triumph!

Ian

Not quite modern day standards Everything seems like it had the that'll do approach!

[RedRooster]

DHLAs are the way forward 

[Speedysix]

47 minutes ago, RedRooster said:

DHLAs are the way forward 

If only the budget allowed! I'm going to squeeze every horse out of this boat anchor without going tripple carb

[RedRooster]

I know a bit of a investment, but a carb a cylinder is really the way to go. 

[zetecspit]

1 hour ago, Speedysix said:

If only the budget allowed! I'm going to squeeze every horse out of this boat anchor without going tripple carb

Very good power can be made on a pair of carbs. I know a certain french blue T2000 that makes something around 200bhp on a pair of 1 3/4 SUs. Well known in Triumph circles, and it really is quick. Needs to be revved though.