Exhaust Wrap

[Jerryl]

nice parts Chevymd, did you do the uppipe too?

Jerryl, Do you think maybe they didn't really consider the smaller diameter at the ends a big deal since its only taking care of the 3 cylinders? I know its definetly going to choke it a bit, but so does the stock dp, lol. Also, doesn't the postons X-over tube eliminate that? I've got the postons crossover tube, but haven' mounted it yet, or really looked at it closely. .........

Good point! One thing is for sure ...... any change in cross sectional area and path wil effect flow. How much is only a question of relevance.

The question I have (in my mind) is; Is the smaller dia on the X-over a restriction, or not, at 5000 rpm and 25lbs boost? It would take some back-back testing ...... Guess I will never know.

Take a pic of the Poston X-over and post it next to the stock unit next time you have them both off.

 

[b4black]

I am speaking from a common sense point. None of the GM Turbo 3.8 cars had it why question the engineering 20 years later? I did add extra heat shielding for my wires by the turbo. My 2 cents. Brad

They didn't have heat wrap, but I'm pretty sure they were double walled.

 

[tb3]

Ok, jerryl, I went and snapped these just for you. You better feel special! lol :biggrin:

I won't install this till I pull and reinstall the engine. Just don't feel like getting it dirty till then.

Diameter is much bigger, and over all, a much nicer straighter design. Don't know if this was Postons design or not, but if it is, then I do have to give props to them. This has got to be way better flow than the stocker, especially at the higher rpm and boost levels. But, like you, would need to see it on a flow meter. This is the same part number crossover for the poston 86/87 headers, so its obviously interchangeable.
and I know this is a little off the subject. :tongue: but what the hey, theres little traffic in the hot air section anyway. We can start a new post if you want.
let me know if this clears anything up. I'm still not clear exactly what your getting at really, so now I'm curious.

 

[tb3]

They didn't have heat wrap, but I'm pretty sure they were double walled.

well, actually the up pipe and down pipe where wrapped in some sort of wrapped heat insulation (white) with a thick steel braid hose around it. From the factory. They used steel clamps and welded them right to the pipe. I know for a fact they did this on the 84/85's. Not sure if they did that on the carbed stuff. If yours doesn't have it, then it was removed at some point.

 

[Jerryl]

Ok, jerryl, I went and snapped these just for you. You better feel special! lol :biggrin: ...............I won't install this till I pull and reinstall the engine. Just don't feel like getting it dirty till then. ......... Diameter is much bigger, and over all, a much nicer straighter design. ....................let me know if this clears anything up. I'm still not clear exactly what your getting at really, so now I'm curious.

Thanks, and YES, I DO feel special, VERY SPECIAL in fact! :biggrin:
Here is a pic of the stock unit, DS. Speaks for itself.

 

[tb3]

aha! now I'm clear. Thats what I thought you where talking about, those are obviously totally eliminated with the postons. Time and cost must've been the major factor in the stockers being manufactured like that. And I still would think that given the diameter of the tube (which is fairly large considering its only working for 3 cylinders compared to the 2" up and dp that is choking all 6 cylinder gases), that the engineers had any concerns about it when considering the whole picture. Just look at the poor design of the stock hot air headers when observing from a performance standpoint.

One other thing to note, which you probably already know. When you go bending double layered steel parts like that, very strange things start happening quick during the bending process itself. The creases/bends in the metals (which may or may not be the exact same hardness), can make the results a little unpredictable. I'll have to crawl under my car and take some pictures of the center of my crossover and show you what it did when I stretched it.

 

[Jerryl]

aha! now I'm clear. ...... One other thing to note, which you probably already know. When you go bending double layered steel parts like that ...........

Stock X-over = double wall??

 

[tb3]

yes, at least mine is. You should be able to see the layer in the corner of the flange. (might have to clean it up a bit.) Easyer to see if you cut the pipe in half. But, don't do that unless its scrap of course.