Can Anything be done with my 4.2 air intakes
Discussion
I understand that it is common in some engine tuning to have the intakes machined to match the ports on the engine, thereby smoothing the airflow. Internal polishing is also common. However, I also recall Jules at TCS making some observations about how this could also upset the amount of swirl and hence the petrol/air mixing for Cerberas specifically. Something to do with not enough swirl to begin with...
Hi,
There is a great benefit in opening out the inlets on the 4.2. If you look at the smaller end of the manifold you can see a step of approx 2mm, there is another step just behind the butterflys. If you can find a machine shop to blend this out you will make the internal area larger therefore increasing the amount of air the manifold can flow. This will have a knock on effect with the fueling etc so a trip to Joo's would be in order. I ve just had a manifold ported and it does look very very good.....
BUT........it wasn t cheap
There is a great benefit in opening out the inlets on the 4.2. If you look at the smaller end of the manifold you can see a step of approx 2mm, there is another step just behind the butterflys. If you can find a machine shop to blend this out you will make the internal area larger therefore increasing the amount of air the manifold can flow. This will have a knock on effect with the fueling etc so a trip to Joo's would be in order. I ve just had a manifold ported and it does look very very good.....
BUT........it wasn t cheap
Edited by IanMack on Thursday 27th March 11:18
I don't know .. I do remember wondering at one point if the waisting of the manifold towards the inlet gasket was a deliberate ploy as a fuel tripper to re-introduce any fuel on the manifold wall back into the airstream, but having modded many of the 4.2 inlets and not had any downsides that I know of I concluded it wasn't anything deliberate, or if it was it didn't appear to work!
That's just a smooth open curve so will pretty much flow as much as you want , certainly not a restriction compared to the other steps and diameter changes. I've tried flapwheeling it smooth in the central bit and i'm not convinced it's worth anything. I did my very first set about 5 years ago on a flow bench to see what made a difference and what didn't but I don't think i ever cleaned the middle up and flow tested it.
If I were doing my won inlets I would do the central bit anyway if cost/time wasn't an issue but I wouldn't expect anything from it except the sense of wellbeing from a job nicely done lol.
If I were doing my won inlets I would do the central bit anyway if cost/time wasn't an issue but I wouldn't expect anything from it except the sense of wellbeing from a job nicely done lol.
Only ask because I can remember a number of years ago that I saw a device designed to do that job.
It looked like three spheres covered in grit tied by plastic arms onto a metal flexible metal shaft. The shaft was rotated by a drill and the spheres pushed outward due to their weight but in a very even fashion.
Not since them since and wondered how people did the bit out of reach nowadays.
It looked like three spheres covered in grit tied by plastic arms onto a metal flexible metal shaft. The shaft was rotated by a drill and the spheres pushed outward due to their weight but in a very even fashion.
Not since them since and wondered how people did the bit out of reach nowadays.
Had a brief chat with David Vizard on this sort of thing recently whilst hanging about at Austec waiting for my car.
It went something along the lines of, the gains (flow/cfm) from clearing steps, ridges, profiling the spindle and knife edging the butterfly are about 5 times that you would get from going up one size of throttle body. Which roughly for a 4.2 intake means in theory a cleaned out one will flow more than a 4.5. That is not to say it will flow more than a cleaned out 4.5 body though as its 2mm bigger to begin with, but it is inherently imho a better design and will never collapse on you.
It went something along the lines of, the gains (flow/cfm) from clearing steps, ridges, profiling the spindle and knife edging the butterfly are about 5 times that you would get from going up one size of throttle body. Which roughly for a 4.2 intake means in theory a cleaned out one will flow more than a 4.5. That is not to say it will flow more than a cleaned out 4.5 body though as its 2mm bigger to begin with, but it is inherently imho a better design and will never collapse on you.
Difficult to see how the 4.2 is a better design as the 4.5 is effectively a very short almost straight tube (ok there is a little bump in there but if you take it out you break to fresh air so it has to stay and the way the individual sections line up isn't always great so cleaning the steps out of the 4.5 system is also good, but I can't see how (as std had it been machined accurately) it's worse than the 4.2 which also needs work to make it right) .. but yes the flowed 4.2s will match a std 4.5 .. until you start thinning the 4.5 spindles then the balance returns in the 4.5 inlets' favour again.
I got a 4.2 inlet some time ago with the intention of doing the flow thing.
But I thinned the spindles, and flowed my 4.5 intakes.
When you look at them both side by side I couldn't bring myself to replace the 4.5s with the 4.2s (even allowing for injector placement etcetcetc) cos the 4.5 looks visibly bigger, and not a little bigger. The pipes on a 4.5 would have to deform a lot to lose to those slender 4.2 ones.
The rolling road reports that are printed around would say I'm wrong though.
What about a nice set of aluminium cross over pipes for a 4.5
But I thinned the spindles, and flowed my 4.5 intakes.
When you look at them both side by side I couldn't bring myself to replace the 4.5s with the 4.2s (even allowing for injector placement etcetcetc) cos the 4.5 looks visibly bigger, and not a little bigger. The pipes on a 4.5 would have to deform a lot to lose to those slender 4.2 ones.
The rolling road reports that are printed around would say I'm wrong though.
What about a nice set of aluminium cross over pipes for a 4.5
It is a top area for discussion and exploration, oh for a foundry in the garage 
.
Both set ups have pros and cons, some that I'm aware of...
The injector upstream of the butterfly negates some of advantages of the bigger size of the 4.5 until you are at very high rpm. Equally the butterfly further away from the valve on the 4.2 aids higher rpm. The injector nearer the head and down stream of the butterfly on the 4.2 gives better low end performance etc.
The smaller bore of the 4.2 gives better throttle response and so long as it doesn't limit the peak power flow/output imho the smallest you can get away with is best, a bit like too big a bore exhaust imho.
From Jenvey a 42mm throttle body flows enough for 56hp/cylinder (448hp) a 45mm=65hp (520hp). I think the standard 4.2 is 44mm and the 4.5 is 46mm. That equates to 44mm=62hpx8 (496hp) and 46mm=68hpx8 (544hp) theoretical peaks for the two throttle body sizes.
Whilst all that is theory it does sort of say to me that the 4.2 bodies should not necessary be the limiting factor and if anything give more back in low end and throttle response.
. Both set ups have pros and cons, some that I'm aware of...
The injector upstream of the butterfly negates some of advantages of the bigger size of the 4.5 until you are at very high rpm. Equally the butterfly further away from the valve on the 4.2 aids higher rpm. The injector nearer the head and down stream of the butterfly on the 4.2 gives better low end performance etc.
The smaller bore of the 4.2 gives better throttle response and so long as it doesn't limit the peak power flow/output imho the smallest you can get away with is best, a bit like too big a bore exhaust imho.
From Jenvey a 42mm throttle body flows enough for 56hp/cylinder (448hp) a 45mm=65hp (520hp). I think the standard 4.2 is 44mm and the 4.5 is 46mm. That equates to 44mm=62hpx8 (496hp) and 46mm=68hpx8 (544hp) theoretical peaks for the two throttle body sizes.
Whilst all that is theory it does sort of say to me that the 4.2 bodies should not necessary be the limiting factor and if anything give more back in low end and throttle response.
trackcar said:
Except that they are restrictive in std forms .. not that I'm questioning the Jenvey figures per-se but their numbers that yo're quoting here do not hold true for the cerbie inlets.
As you know all too well Joolz the 4.2 inlet needs a bit of work to flow to its potential with the bottom of the trumpet closing down to around 40mm which puts it back down to nearer 400hp using the , which sort of ties in with some of the late 4.2's topping out around 380hp. HarryW said:
It is a top area for discussion and exploration, oh for a foundry in the garage .
Both set ups have pros and cons, some that I'm aware of...
The injector upstream of the butterfly negates some of advantages of the bigger size of the 4.5 until you are at very high rpm. Equally the butterfly further away from the valve on the 4.2 aids higher rpm. The injector nearer the head and down stream of the butterfly on the 4.2 gives better low end performance etc.
The smaller bore of the 4.2 gives better throttle response and so long as it doesn't limit the peak power flow/output imho the smallest you can get away with is best, a bit like too big a bore exhaust imho.
From Jenvey a 42mm throttle body flows enough for 56hp/cylinder (448hp) a 45mm=65hp (520hp). I think the standard 4.2 is 44mm and the 4.5 is 46mm. That equates to 44mm=62hpx8 (496hp) and 46mm=68hpx8 (544hp) theoretical peaks for the two throttle body sizes.
Whilst all that is theory it does sort of say to me that the 4.2 bodies should not necessary be the limiting factor and if anything give more back in low end and throttle response.
Very interesting stuff and i have to agree with you, but everything is a compromise when it comes to tuning, as you probably know.. Both set ups have pros and cons, some that I'm aware of...
The injector upstream of the butterfly negates some of advantages of the bigger size of the 4.5 until you are at very high rpm. Equally the butterfly further away from the valve on the 4.2 aids higher rpm. The injector nearer the head and down stream of the butterfly on the 4.2 gives better low end performance etc.
The smaller bore of the 4.2 gives better throttle response and so long as it doesn't limit the peak power flow/output imho the smallest you can get away with is best, a bit like too big a bore exhaust imho.
From Jenvey a 42mm throttle body flows enough for 56hp/cylinder (448hp) a 45mm=65hp (520hp). I think the standard 4.2 is 44mm and the 4.5 is 46mm. That equates to 44mm=62hpx8 (496hp) and 46mm=68hpx8 (544hp) theoretical peaks for the two throttle body sizes.
Whilst all that is theory it does sort of say to me that the 4.2 bodies should not necessary be the limiting factor and if anything give more back in low end and throttle response.
I ve had both a 4.2 manifold and 4.5 manifolds flow benched to see what difference there is. Unfortunatly i only have the standard length inlet tubes not Whirlwind or ACT ones, so maybe an unfair comparrison. But after re working the 4.2 we manage to get comparable if not better flow than the 4.5. This involes alot of of machine work including working the bend of the manifold not something i would want to do with a Dremmel on a bench in a shed!! Something i found quite interesting is the butterflies, there not as different in size as you might think. Certainly not worth fitting the 4.5 butterflies into the 4.2. We found ultimate flow by fitting a radius velocity stack to 4.5 manifold, BUT this can seriously affect your midrange and torque (Hence Whirlwind Optimum length tubes)which you cant show on a flow bench.
Both manifolds obviously work and work well, but you also have to consider how the cylinder head flows and how the gases are exhausted to get the true benefit of any inlet weather standard or ported.
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