TR6 TR6 Intake Manifold Clean-up

[vettedog72]

Need advise on how to port/polish a manifold. I think I have the understanding on how to match up the manifold to the ports but I do not know what to use to polish the runners. I have read they should be polished to a satin finish rather than a high polish. I also understand that many good manifolds have a design that allows the longest runners to flow at an equal rate to the shorter ones. I hate to do more harm than good with this project so if there is help out there, please let it fly. Also. I need to open the carburetor port to 2" to fit up with some 2" SU's.

 

[Webb Sledge]

Don't know exactly, sorry, but just be VERY careful in doing this. I know that it's very easy to cause detriment to a manifold if you port the manifold wrong. If it were up to me, I'd let a machine shop do the work, but it's your car. Good luck with it, either way.

If I'm not mistaken, Smokey Yunick's book "Power Secrets" has quite a bit of information on this subject. I would recommend buying the book if you don't have it. It's got a LOAD of great information in there. He mostly talks about American V8s, but most of the information can be applied to any engine.

 

[Dave Russell]

I certainly agree with Webb. When it comes to port flow things are counter intuitive. What you "think" should help often reduces power. Bigger is not always better. Bigger reduces port velocity which reduces charge inertia & turbulence. Reducing turbulence causes fuel/air seperation. Reducing inertia decreases cylinder filling, especially while the intake valve is still open as the piston is rising at the start of the compression stroke. Port size & flow needs to be matched to the cam timing & rpm that the engine runs at.

Some engines actually put out more power when the intake port sizes are reduced.
D

 

[DougF]

Read Kas Kastner's Triumph Competition Manual. It should have all that information in it. Written a long time ago, but still very useful information and it pertains specifically to Triumphs. Other useful information also included for varying levels of engine build.

 

[vettedog72]

I think I have a copy of the Triumph Competition Manual but it is remote from me. I will look for it when the Christmas holidays come up. I was hoping some one would have trial and error experience in shaping the ports or polishing the manifold. The high polish vs "satin" finish is kind of new. The helical turbulence is kind of new too. As sensitive as the runners are to size and velocity, it could be a simple and inexpensive way of getting a few more horses to the rear wheels.

 

[trfourtune]

if you have a spare, then it's ok to experiment. otherwise i would talk to an expert or better, get them to do it. did you talk to guys that know? "goodparts"? typically you do not polish the intake. you actually want it rough so that fuel drop-out at low velocities can be picked up. each manifold responds differently to different mods. shape is more important than size. rpm level and engine state of tune must be determined first before you do anything beyond port match, casting irregularities, and carb match. head porting is much more important before manifold. the engine is a system, so one change may not make much difference, but a combination of changes,cam,head,headers,intake,carbs,exhaust, tuned as a whole with matching,complementary changes does make a difference. ultimate flow numbers do not tell the whole story, remember that the intake is not dry air but wet mist.
rob

 

[vettedog72]

Thanks Rob
I am going to enlarge the carburetor side of the manifold to fit up to some 2" SU's and I thought I would check out the fit of the manifold to the ports to insure they match-up. Then I started to think about doing something to the manifold and since have read many articles about the variables but I have not read and specific articles about the ultimate TR6 manifold. I will be using a spare manifold for my mod and I plan a little dyno time before and after the mod. With a little luck, Iwill have the modified manifold fixed up to go to the

I wish some one with a successful experience would write it up for us DIY hackers. The variables seem to be more than I could calculate in calculus! Some how it makes sense that if "stacks" on the stock carburetors can make a difference then doing something to the entire manifold would be even better. (maybe)

 

[swift6]

[ QUOTE ]
I am going to enlarge the carburetor side of the manifold to fit up to some 2" SU's

[/ QUOTE ]

When you enlarge the carb side opening of the manifold be careful how deep into the manifold you go. It's pretty thin over the coolant passages.



[/ QUOTE ] Some how it makes sense that if "stacks" on the stock carburetors can make a difference then doing something to the entire manifold would be even better. (maybe)

[/ QUOTE ]

Two totally different needs here from one side of the carb to the other. The velocity stacks increase the velocity of the air before it mixes with fuel. The intake needs to maintain turbulence to keep fuel suspended in mist form.

Several engine builders I have spoken to that specialize in flow work have all agreed that polished intake manifolds will decrease overall power and driveability as fuel will drop out of suspension and decrease the effectiveness of the air fuel mixture. It can also make for a rather exciting back fire problem with pooled raw fuel in your intake manifold.
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[vettedog72]

I am in agreement with your points. I saw the following artical:
From: pumaracing@aol.com (PumaRacing)
Subject: Re: WTB 2.0 16V 91GLI ported and polished head
Date: 07 Aug 1998
Newsgroups: rec.autos.makers.vw.watercooled

Please, please, please stop using the word "polished" in respect of modified
cylinder heads. Polish is actually bad for fuel drop out and therefore power.
Shape is what matters and how well the valve seats are cut. "Gas- flowed" is
fine. "Ported" on its own is fine. "Modified" is fine. "Polish" sucks.

Dave Baker at Puma Race Engines (London - England) - specialist flow
development and engine work.

With that in mind, has any one tried to put a helix cut in the runners? There are so many "new" processes for power increases that were not considered when Triumph published the racing book. What finish does your tripple manifold have on the inside?

 

[swift6]

[ QUOTE ]
With that in mind, has any one tried to put a helix cut in the runners? There are so many "new" processes for power increases that were not considered when Triumph published the racing book. What finish does your tripple manifold have on the inside?

[/ QUOTE ]

I didn't make any changes to my Triple manifold. I know it's not "polished" but it's been on there for nearly five years so I forget the exact finish inside the manifold. /ubbthreads/images/graemlins/blush.gif

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[Alan_Myers]

[ QUOTE ]
I am going to enlarge the carburetor side of the manifold to fit up to some 2" SU's and I thought I would check out the fit of the manifold to the ports to insure they match-up. Then I started to think about doing something to the manifold and since have read many articles about the variables but I have not read and specific articles about the ultimate TR6 manifold. I will be using a spare manifold for my mod and I plan a little dyno time before and after the mod.... it makes sense that if "stacks" on the stock carburetors can make a difference then doing something to the entire manifold would be even better. (maybe)

[/ QUOTE ]

Hi,

Please let us know how it works out. I'm always interested to hear more about this sort of experimentation.

I've read and heard that larger SUs usually aren't particularly helpful, can actually do more harm than good. But that was a more general comment and not specific to TR6. At one time I was considering a 2" set for my TR4 and was talked out of them. The explanation I got seemed to make sense and was that an overly large carb throat of this type (constant vacuum) actually reduces vacuum effect and that can significantly lower gas speeds right on thru the manifold. The argument was that it's better to match the carb size to the engine, rather than go to as large a size as possible.

Since then, I've had some experience running smaller than usual Weber sidedrafts on my car, which have proven quite good for low to mid-range (street/autocross) where most Weber installations go for a big venturi and high rpm performance. Of couse, Weber are a very different design, with a fixed carb throat rather than variable like the SU, not to mention an accelerator pump, and a throat-per-cylinder rather than, siamesed intake. I have 40DCOEs on the car, which was originally speced to use 42DCOEs and 32mm venturis on a stock engine. I ran 30mm venturis at high altitude, and am going to 33-34mm at sea level on a modified engine. Most seem to go to 36 and even 38mm in 45DCOEs. I have added 40mm velocity stacks to these, but haven't had the opportunity to see if theses make a significant difference.

Also, with respect to velocity tubes, I've heard that, although they can be beneficial on Weber, Dellorto, etc., they are little more than "eye candy" on SUs and Zenith Strombergs, do nothing to improve air flow. This seems odd to me since I'd think stacks would work and I'd like to hear otherwise or see some real life results. I've only got a set of Hitachi SU carbs in the spares pile these days, and don't know if experimenting with those would be very applicable to "real" SUs.

The implication is that the SU throat is about as efficient as it can get, and I've read and heard that a little radius at the very mouth can be useful to improve airflow as it comes over that edge, but not full velocity stacks.

This is all just food for thought. I sure don't want to discourage you from trying things. In fact, I'd like to get some real world data on these issues and will be watching for you, or anyone else, to post some results.

Have fun experimentin'!
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