Fabricated intake manifold plenum material thickness?

Turbeam said:

The easy way to do this is to use a thermostat housing outlet from a Plymouth Cricket (or Hillman Avenger) that points in the right direction on a whiteblock motor that doesn't use a P/S pump. My photo above shows one of these fitted.

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That's a good idea - I'd love to have a spare cover. Neither if those cars were sold in the US - do you know the model engine used? Perhaps I can reference a US Chrysler product that used the same engine..

As luck would have it, I cant seem to find that formed pc, it may have gotten used elsewhere.

As far as the welding, Ive heard it weakens it, but in real world applications/experience none of my intakes have failed in the 15 years Ive been doing them and some see damn near 30psi daily. Heck, made an air tank for my 4x4, built it, shoved 120psi into the next day, and 5 years, 3 trucks later it still kickin.

lookforjoe said:

That's a good idea - I'd love to have a spare cover. Neither if those cars were sold in the US - do you know the model engine used? Perhaps I can reference a US Chrysler product that used the same engine..

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In the UK, Europe and most of the rest of the world these engines were only used in the Chrysler/ Talbot Sunbeam and the Hillman/ Chrysler/ Talbot Avenger 1300cc and 1600cc pushrod engines. These engines were never fitted to any other models, except for the Pekan that was built in Iran much later, but that is another story.... and they would never have gone to the US.

The UK built Sunbeam was never imported to the US either, but the Avenger model was (just before the fuel crisis) but badged as the Plymouth Cricket, but I don't think it was very successful in that market... bad timing.

It was however built both in Brazil and Argentina as the Dodge Polaris and Plymouth Cricket, and continued to be produced in Argentina for the ten years after VW buying the factory there from Chrysler right up until 1992 simply called the VW1500.

Funnily enough, here in the UK where these engines were originally built, we are currently arranging for a batch of these stat covers, now remanufactured in an alloy with a higher aluminium content, to be imported back over here via a contact in Argentina. If you have any contacts in South America there is a good chance that you could locate a few of these parts there.... they are very inepensive brand new.

Given the limited numbers imported into the US, and how long ago that would have been, I don't imagine that spares availability for these cars is very good now!

I discovered that this stat cover fitted and did the job on a whiteblock engine purely by chance, but perhaps there is another one that could do a similar job on another engine that is more common and more readily available for you?

nathaninwa said:

As far as the welding, Ive heard it weakens it, but in real world applications/experience none of my intakes have failed in the 15 years Ive been doing them and some see damn near 30psi daily. Heck, made an air tank for my 4x4, built it, shoved 120psi into the next day, and 5 years, 3 trucks later it still kickin.

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I don't really think the stress on or around the welds themselves should be a major problem.

The worst effected weld runs on my plan would be those along the top and bottom edges where the U-shaped main plenum section joins the flat (bellmouthed) sections at the front edge of the runners.

If the plenum is very wide and shallow, and high internal pressure is used as well, I can visualise a situation where the top and bottom plenum sections want to 'drum' out and in with pressure change. If these flexing stresses are concentrated at the welds on the joints, and the material there is softer/ weaker, then of course there would be an increased possibility of cracking.

I'm not sure that the magnitude of this flexing would be enough to cause this, at least at the sort of boost levels that I have in mind? If it proves to be an issue, I could always try reinforcing the plenum with some external ribs or something, but if nobody else has thios problem even with lighter gauge material and much higher boost pressures I'm probably just being a bit over concerned about it.

The internal pressure (boost) isn't necessarily a big problem, its the cyclic load from the damn thing vibrating from the engine and usually having an overhanging mass (moment) that can crack the welds. In other words, don't worry about the boost just make sure it doesn't resonate itself to death.

I'll post a pic of my 2j intake, the plenum is completely welded of pcs. And with the cracking, it might be my construction technique. All my runners get pressed through the flanges and plenums walls for welding, not just butted up.

Over a year now, unsupported and lots of boost.

Thanks for posting that photo Nathan, it is quite reassuring. It looks to be of a very similar design of manifold to what I have in mind, but I was thinking that I might need a bit more internal plenum volume ideally.... difficult to tell from the photo.... did you calculate its volume?

The biggest single difference with mine is that it will retain the stock insulation mounting rubbers and the first 'injector' section of the manifold flange exactly as stock so that it can be made easy to remove for access. The plenum section will therefore have to be braced down to the block/ engine mounting bracket position to support its weight and resist any vibration as well as being tied back to the cylinder head to prevent boost pressure simply blowing the manifold off of the injector section flange at the head at the mounting rubbers.

I believe that some others are using the stock octopus manifold on a B6304 while retaining these rubbers without any problems, so I don't really foresee any for this arrangement.

As the intake runners are largely the stock cast octopus parts and as such are quite thick (around 5-6mm on average) I'm thinking of making the runner mounting face of the plenum (that I plan to belmouth) out of 0.25"/ 6mm aluminium to help resist and stresses in that section, also bearing in mind that the whole plenum and runners part of this manifold is being designed to come on and off regularly and that the runners are quite a tight fit into the rubbers so can take a bit of pushing and pulling to remove and refit.

Volume is in the 1.5 Range. I calculate for that to get rough dimensions then work around to make it look nice. The small plenum wall I have is from 3/16, but the whole plenum is 1/8the alum. I feel throttle responce is spot on for the engine package as a whole.

and just for reference, a 2j is a 3.0L.

Do you have shots from the inner of that plenum?

Yes, I'll have to post tonight when I get home.

lI'll have to see if I took a shot with the t/b open, but here's a small. Page thread on the entire build. The last page shows how it looks currently with twelve injectors.

There might be one in my build thread


http://www.supraforums.com/forum/sh...ntake-flange-supplier&highlight=intake+flange

This is my old T6 Intake




The runners were sched 40 which is 0.145".
I believe the plenum was 3/16" which is like 4.7mm

I pressure tested it to 80psi and it did not even blink.

Cheers Kenny, 4.7mm for the plenum walls is slightly thicker than I had in mind, but I certainly won't be anywhere near to 80psi of internal pressure!

Even if my plenum dimensions are slightly less favourable in this respect, it doesn't sound as if the lowish levels of boost that I will be running should give it any real trouble.

I just thought I would ask the question after seeing how thick some of the castings for factory turbo plenums are made, and knowing what a fairly low internal pressure can do if applied over a large enough surface area in other systems.

FWIW 80psi test pressure was chosen based on a safety factor of 3.

If your desired pressure is 20psi, you don't test it to 20.0001psi.

^ True, but testing to that level is really to prove that the manifold will not split, blow or destroy itself in other ways in a one-off highly loaded situation.

If the manifold isn't even showing any signs of minor deflection in the flatter surfaces at those pressures never mind displaying any flexing, swelling or 'inflating' of the plenum in particular short of an actual failure, then I don't think there is any reason whatsoever to be concerned about its longer term use with cyclic load induced cracking at much lower internal pressures.

Given a poor enough plenum shape and enough flat surface area of thin material, even 5psi could be a problem. My intended boost pressure will most likely never exceed 15psi, and I also intend to add some means of overboost protection too, so I really don't think my manifold's design will be different enough from that of most others including your own to run into any problems.

I just thought I'd ask the question to get an idea of how well these fabricated manifolds tend to stand up to longer term use as we often see them being built but rarely hear of how well they perform or survive over a period of time. It would be easier to just build it in thicker material from the outset if necessary, but from the sound of most of the feedback here we don't hear anything more about them because they generally simply don't give any trouble .