Years ago Ford used extrude honing on the Contour SVT intake and added 5 - 10 HP. There has to be something to the idea of smooth surfaces increasing air speed.
Not intake to head, but when I fitted triple (rebuilt) SUs to replace dual (worn) Stranglebergs, I noticed improvement. Sometime later, I noticed that I had fitted 1 3/4 inch insulators between the SUs and the manifold, rather than the correct 2 inch insulators. I gleefully swapped them out, expecting a big improvement. Nada!
You know you guys are still messing with my head, don’t you?
Wow!!! There is a lot of incorrect stuff in this article.
For a start…turbulent flow to an Engineer is NOT determined by surface roughness. It is determined by velocity, diameter and viscosity.
Typically a Reynolds No. above about 4000 is turbulent. In the jag intake it would be about 100,000. This is nicely in the turbulent regime…and it will stay turbulent at the high gas velocities.
The issue of fuel accumulating on the walls is a red herring. Can the fuel actually “accumulate” on the walls of the manifold…there may certainly be same wall “wetting” that has to be dealt with on cold start…but that’s a different issue.
The discussion on boundary layer is close to correct. There will be no laminar boundary layer anywhere in the inlet system…the boundary layer will be turbulent because the flow is comfortably turbulent.
As an aside…another myth about surface roughness also appears wrongly in this context all the time. A golf ball has a dimpled surface to promote a turbulent boundary layer on the surface of the ball. The reason for this is that the turbulent boundary layer remains attached to the ball for longer than a laminar boundary layer and therefore has a smaller area of “wake” to slow it down. So using the dimpled golf ball as a reason to have rough surfaces on an inlet tube is simply incorrect.
The surface roughness of the inlet tract has a large impact on flow capacity. The surface roughness determines the " Relative roughness" which is then used with the Reynolds No to determine the friction factor courtesy of a famous chart called a Moody Diagram. This friction factor is then used to calculate pressure loss in the piping. That’ s how it works…and it does work because I have used and verified the results several times.
It is amazing how much dis-information abounds on the Internet.
For the agnostics reading this…have a look on the AJ6 Engineering website.
There you can find a picture of a Formula 1 Toyota head with a view into the ports. The guys responsible for this unquestionably know a bit about fluid mechanics!!!
Regards
Matt
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I’ve used trios of 1 3/4 and 1 5/8 size SU’s in triple setups.
The purpose was to improve low end response in sedans.
Surprised the insulators even fit?
The only benefit that is measurable, I suspect Nick, was an increase in my self-esteem. However, since my wonderful opinion of myself is already of galactic proportions, the percentage increase is inevitably miniscule.
Many British bike used cast in situ or bolt-on bifurcated inlet manifolds and there are occasional slight biased flows favouring one cylinder over the other. They can be rectified by “pointing” the carb subtly towards the under-fed side using a very slightly tapered Bakelite insulation spacer.
Looking at the triple SU manifold it appears the knife-edge split into two runners is excellent on the ‘floor’ but compromised and clunky around the upper section where a ’ large blunt face replaces the knife edge.
This is hardly ‘bad’ design, since if there is any tiny effect at all, it is likely to occur only near the red line, which most engines hardly ever see. It’s similar to port-matching, i.e. It is allowed and cumulatively beneficial to do lots of small things as part of engine ‘blue-printing’. In production classes where you are not allowed any serious tuning parts, it’s all you can do but it tends to add up. It’s in a similar league to lining up screw slots or hexagons - done for the fun and satisfaction, not in expectation of any great gain.
I don’t particularly advocate it and only mentioned it because Keith seemed to recall it as me plugging the vacuum holes. I thought I’d better correct that. Club race paddocks (or bench racing pub discussions) are generally full of hocus-pocus and mind games to psyche-out the opposition.
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What about some half twist rifling ??
One per carb 
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I used those on the xjs. they recommend 1 per carb but I have 2 throttle bodies so opted for a total of 3. there was a very noticeable difference after installation of these. my wallet was thick and hard to fold, even uncomfortable to sit on. I purchased those and now its quite thin. sitting in the jag is more comfortable and the weight reduction has improved both acceleration and fuel economy. do not buy the cheap Asian knock offs though. only buy the ‘packaged in america’ version. you can identify the ‘real’ turbulator by the high quality sticker on the base, shiny and boldly says U.S.A. whereas the cheaper ones have a shiny sticker with another country printed there.
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Nick, I ported the head on my E and got 37 more horsepower, 48 mpg, 0-60 in 4.1 sec. and improved staying power in bed. As Jerry would say, YMMV.
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So in reading through all this, the only “definitive” information seems to
be in the response by Matt Furness, which if I read it correctly, states
that porting the system does make a positive difference…of course I
might have incorrectly interpreted what Matt said…could Matt please
verify?
I also asked about what Jaguar did to their racing C’s and D’s…anyone
have and information about that?
I’m getting a headache.
Not that it matters, but not an article; just one man’s post, and opinions, in a forum similar to this one.
Sounds like this is your subject, Matt. So in simple terms what is the best finish for the intact passages? And are there differences for different engine applications?
And if hit with backspin (good!) the dimples help generate lift.
Yes, please, please, please settle this, Matt, if only for the sake of my befuddled grey matter.
Also, what do you think of Pete’s mod? Looks logically like another small improvement.
golf ball decals on each front wing would certainly add horse power
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Have a look at the AJ6 website photo. Smooth is better. And little details even like the angle of the entry to the valve seat can make a difference.
I had my manifolds in my hands about a year ago…but I didn’t touch them because I had too much other stuff to do get my XJS back in action…but if you are looking for something to do…as Nick was at the start of this post…then removing roughness and surface disturbances in the old castings will make a difference. You won’t be faster than a moderately competent modern car…but you will have made a positive difference and will have had hours contemplating a fix for world hunger…
Regards
Matt
Nick forget about the porting and try a big glass of port and then go for a ride. You will definitely notice a difference!
Wow, now that’s a very interesting site/read!
Anyone know what one of the TT systems cost for a 4.2? It must be very expensive.