Cold air intake tips for S30Zs - the CRX solution...

Hi John, out of curiosity, did you need re-jet when installing a cold air intake?
I tried one recently and it behaved horribly, as if the second stage pump jets weren't working. I removed the carbs to check how well the jets were squirting and all seemed to be okay so I re-installed, this time without air intake and velocity stacks and it ran fine. Believing the problem was cured, I then re-installed the cold air intake and it reverted to behaving like a pig. I have even removed the filter and hose and taken the lid off the air box and it still won't run very well.
Now admittedly I made a huge mistake as a friend of mine fabricated an air box from aluminium, which loves to absorb the heat, so I have abandoned the idea of using it but I find it strange that my car simply won't tolerate an air box even when it's just warming up and not really hot. View attachment 32866

if its the same with the lid off, it seems strange. have you tried it with the carb mounts slackened off?
 
I'm not sure I follow Franky ..... If I slacken the carb to mounting bolts I have a greater risk of air leak.

With the lid off, it should perform the same as without the box on, more or less. I’m wondering if when the air box is tightened up it’s twisting anything?

There’s people running modified standard air boxes, with standard size intakes with great results, there’s a thread somewhere with Dyno results on and off and it was much better with the standard (modified) airbox.
 

Peato40

Club Member
@jonbills thought the same and so definitely something I need to check. I will most likely get one of those fiberglass intakes from MR F but I am puzzled with the behavior of this one, especially with the lid off. If air turbulence was been compromised by the shape of this box then I would expect a slight performance issue but this is like night and day ....... it really surprised me.
 
@jonbills thought the same and so definitely something I need to check. I will most likely get one of those fiberglass intakes from MR F but I am puzzled with the behavior of this one, especially with the lid off. If air turbulence was been compromised by the shape of this box then I would expect a slight performance issue but this is like night and day ....... it really surprised me.


That’s why I don’t think it’s the box. You could make that work quite nicely.
 

Peato40

Club Member
The other thing that concerns me about this box is the fact that it's made from aluminium, which of course absorbs heat very well, however I guess there is the possibility to add a heat shield also.
 

jonbills

Membership Secretary
Staff member
Site Administrator
I don't think the box being hot is a problem; I wouldn't think the air is in contact with the box long enough to be significantly heated by it.
It would be easy to test - if the heating aspect is the problem, then it wouldn't be present for the first few minutes from cold start.
 
The other thing that concerns me about this box is the fact that it's made from aluminium, which of course absorbs heat very well, however I guess there is the possibility to add a heat shield also.

I wouldn't say thats a problem at all. it'll be a good % cooler air than no box.

The material isn't the problem, a massive amount of performance cars have cast alloy airboxes.
 

Rob Gaskin

Treasurer
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I'm having difficulty believing that the airbox causes a huge problem. The standard airbox is narrow too.

Is there anything on the face of the carbs that the airbox is blocking off?
 

johnymd

Club Member
That was my thought too Rob but I dont think there is. There are 3 big holes in the backplates but I don't think they are air in.
 

Peato40

Club Member
@Rob Gaskin was spot on.
I drilled holes in the air box to match these highlighted in the photo, which really must serve a purpose so I'm not sure why I didn't consider this before.
Anyway, now the car runs very nicely with entire system installed. I notice it's running slightly richer, so I think it might be worth opening up the inlet to 70mm, which is maximum size that will pass through the hole adjacent to the radiator.

Many thanks for advice and comments.

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toopy

Club Member
Yes, the trumpets are still there, inside the airbox.

Rich, I'm planning on blatantly plagiarizing your rather excellent install and i'm starting to get the bits together :D

I have some short trumpets already that came with my Hitachi's years ago, but i'm not interested in max power so longer ones would be better, what length have you got please? I'll be running 1.75" HS6's, Ive seen 1.5" 2" and 3" but not yet having the air box i don't know what clearance there might be.

Thanks
 

richiep

Club Member
I think I’m running 40mm although they could be a bit longer. There’s tons of room with that size, and you could definitely adjust longer depending on tuning need.
 

AliK

Vehicle Dating Officer
Staff member
Club Member
I think the prices have moved a little since you did this job Richie!! [emoji33][emoji33][emoji33][emoji33]

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And then there is this sort of thing on AliExpress...

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richiep

Club Member
Those eBay listings are nuts! (I've seen them before) You can actually get the right kit from the US for about 50-60 quid including shipping.

We could do with taking a piece as on my car, already cut down to the right length, and have an exhaust place or similar/tubing place copy the bends. You could just do a 3" version as this would suit the majority of applications up to 2.8-2.9L. Larger size for strokers would depend on how the person wants to route the ducting (through an enlarged top rad support hole, a new larger hole in the middle etc).

Then you need a 90deg turn tube for the front side of the rad support, and some sort of rain shield to keep the filter dry.
 

AliK

Vehicle Dating Officer
Staff member
Club Member
Interestingly Richie, I’ve seen similar air boxes with the cone filter inside the box which keeps the pipe work quite clean.

Also another thought to be laughed at - what if you could get a filter to fit inside this box and used a double routing of the pipe to also use the hole below the large one on the rad panel? I did this with my stock intake and used the bottom feed that was designed to go to the manifold for winter warm up. That way, you get cold air into both inlet points. So do you think it’s possible for someone needing the large hole to just combine the two holes with a T piece and put the filter on the inside?
 

tyroguru

Club Member
maybe we should develop some plumbing and add it to the airbox kit.

It would be great if this could be sold separately please. I bought one of these air boxes from MJP last year (prematurely!) so don't need one but would like the plumbing (assuming it's lightweight :) ).
 
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