by "RamblinRover Luxury-Yacht" (ramblininexile)
Published 05/29/2017 at 19:01
by "RamblinRover Luxury-Yacht" (ramblininexile)
Published 05/29/2017 at 19:01
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STARS: 10
It’s a calibrated multi-piece vinyl/polypropylene/polyethylene and steel distraction-maker. Very important in these old cars.
"Die-Trying" (die-trying)
05/29/2017 at 20:24, STARS: 0
i have been NEEDING to get one of those for the truck.... it feels like an old magic fingers while its setting there idling.
adds that nice bit of character......
"RamblinRover Luxury-Yacht" (ramblininexile)
05/30/2017 at 08:46, STARS: 1
Summit has them for $11.99. I picked one up at the retail store, but they’re available for online order - just add one next time you need another bunch of parts.
"Die-Trying" (die-trying)
05/30/2017 at 13:12, STARS: 0
i’m gonna keep my good eye peeled........
"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura)
06/01/2017 at 13:07, STARS: 0
I need one of those.
Do you have any experience with the GM 250/292?
"RamblinRover Luxury-Yacht" (ramblininexile)
06/01/2017 at 13:19, STARS: 0
I regret to say that I do not. The older GM engine I have by far the most experience working on is the 6.2 diesel, and while I appreciate the stovebolts and their descendants, my experience is nil other than having an idea how the timing is set up, same as the Iron Duke with either a Micarta or aluminum cam gear.
Is it by any chance an issue possible to crack with research? I’m generally not too bad at figuring out the right terms and line of attack to find things out.
"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura)
06/01/2017 at 13:37, STARS: 0
It’s an interesting thing. I am corresponding with an older gentleman I met on the Stovebolt Forum who has boo-coo experience in high-end things like NASCAR engine building and such and he poo-poos all of the aftermarket stuff like intake manifolds by Clifford and Offenhauser, multiple carburetors, and so on, saying that none of them are other than a complete waste of money unless you are planning on running them at 6000+ RPM, racing, et cetera. He has a binary set of opinions on most everything...
There is a large body of thought out there that says the 250s breathe poorly and respond well to the manifold upgrades, both intake and exhaust. My OG friend says that multiple carburetors and the like are only used by “...people who don’t know enough about physics and fluid dynamics to know any better.” I am curious whether you have any thoughts on this. His claim that folks who say otherwise “probably have an intake manifold they want to sell you.” Or that installing these parts is akin to installing a 1/2" link in a 1/4" chain and expecting to lift more.
"RamblinRover Luxury-Yacht" (ramblininexile)
06/01/2017 at 14:28, STARS: 0
I know that Ford Thriftpower sixes in a little smaller displacement (the 144 and the 170) respond well to upgrades away from the cast-on intake manifold, which I’m given to understand a lot of the GM 250s have, but if you have a separate intake version, it’s likely a step in the right direction already. There’s a bit of trickiness here, which is probably the grounds for his remarks - on the one hand, it’s a reverse-flow head, which tends to experience flow issues with higher revs, but on the other hand, it’s a single-carb straight six with uneven runner length, which is something of a recipe for poor mixture, especially at low revs. Bolting on a more *open* intake manifold would still see limits from the head breathing and might make drawing of air worse, and bolting on a larger carb makes matters worse at the low end because lower average velocity of air would contribute to bad mixing.
If you get a big enough manifold and carb (and valve upgrades?) to run at high revs, you sacrifice stable low-speed running, and useful low-speed power at correct mix (and efficiency) would best be gained (paradoxically) by having a fairly narrowly piped manifold, bad for high revs.
Of the multi-carb options, if you went with the double single Offenhauser manifold, you’d be in the position of... drawing twice as much air, more or less, to one side of each small carb than the other, which means two different average velocities, which *might* make for uneven draw/mix and would be only limited improvement over an ordinary two-barrel intake. Triple single would be better, but counts as being (I suspect) a good bit overcarbed, so good for medium-high revs but limited usefulness for anything slow.
All this is to say, the head is a bit of a limiting factor, but so is the basic geometry of how much air (relatively little) has to move and how it’s distributed over several inlets. It doesn’t necessarily need *more* air, it just needs to have well-mixed air at a range of speeds and no profound bottlenecks.
The Opala SS (Brazilian Chevy), a sport model which came with the 250, appears to be popular for a conversion to 3x two-barrels, possibly Webers. As long as the two-barrel is small enough that’s not unreasonable, but is serious money for mostly just top end gains and possible low end efficiency - little in the middle and the difficulty of having three carbs properly balanced. The original manifold for the Opala SS appears to be a large square-tube design, which most likely breathes well at medium RPM, but is a bit big for revving low properly, and purportedly has to be tuned for rich running at low RPM. That being said, that style, with a two-barrel, is probably one of the best options. If you have a separate manifold, square-tube style with swept curve runners and a two-barrel, you may be best off trying to optimize that.
Go with a twin-single Offy if you like - it certainly looks neat and would most likely not break the bank - but be aware that actual improvements unless you have one of the worst stock manifolds may be limited. Better mixing to the end cylinders, more unpredictable mixing to the ones in the middle.
Short version: mixing is more important than breathing as such because it’s more of a standout problem, and other than going for a host of tiny carbs (not big/medium ones) and the resultant headaches, it’s hard to address. The best all-around stovebolt might be one with at least two carbs and moderately long runners leading to a redesigned head. Or in other words, doesn’t exist but might look like a Triumph.
"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura)
06/01/2017 at 15:01, STARS: 0
“Doesn’t exist but might look like a Triumph:” classic.
You really laid this out well. Thank you for taking the time.
In the interim, I’ve exchanged a few more lines with my old-timer friend and he is telling me that he thinks he can approach the performance parts company’s gains with the stock carburetor and manifold(s) and a cam and some advance, both of which ingredients are recommended by Clifford and probably do more to increase performance than $2000 worth of their carburetors and manifolds.
"RamblinRover Luxury-Yacht" (ramblininexile)
06/01/2017 at 15:09, STARS: 0
It’s worth note that if the engine is itself drawing air better (see: cam), then air will be drawn better through the manifold and might relieve mixing issues somewhat. I still like the *idea* of multiple carbs, but I’m unconvinced that they’re the best way forward automatically.
In the case of the Triumph, it really does breathe pretty well if the carburetors are right and it’s received an Italian tune-up recently. See also: almost never.