Technical > Matt Shaff's Engine Shop
Zoomies vs collector headers
lake_harley:
Bolted my exhaust flanges to the heads today and cut the "U" bend, 1 5/8" mandrel bends in half that I'll use to build my zoomies. I think the straight legs of the "U" bend are about 12" long and they're 6" CLR bends, so 90 degrees of a bend are just under 9.5" long. So, that's a total tube length of ~21.5" from the header flange. In my opinion the straight sections being that long is just going to look a bit silly sticking up so high so I'm wondering what the length is on a "typical" length set of zoomies. FWIW, this will be a mild, carbureted 305 and my FED is being built for bracket racing. I've always understood that a longer tube is better for low end power, but I don't want the car to look like a circus calliope.
Lynn
wideopen231:
I build a few setgs to sale. Some custom ordered. No set length.I make some that are as you described 180* bends cut in half,some are mini training wheels(short funny car style). I guess if you leave at low rpm the difference in low end matter, I know most guys running brackets run 5500 to 6700 converters,so low end is useless. With a carb I see where there would be big difference with injection not so much.
Tip if you are adding the straps at end make sure header is bolted down or it will warp the flange. I usually botl flange to 1"x 4" solid steel bar weld up out side,then weld inside and then rebolt and add straps if going to.
lake_harley:
Thanks for the tips on welding steps/procedure. What you describe is pretty much what I had planned to do, only using an old head instead of a bar. It's nice to have confirmation on a plan.
Based on the cam we're going to run a 2400 stall converter has been suggested and planned, so low end is important. But, as fickle as it is, aesthetics will come into play when it comes to tube length. I'm thinking that cutting about 4-6" off of the straight section would have a nice look, but splitting that difference to a 5" cut would take total tube length down to about 16.5" from the flange. Is that flat-out too short?
Thanks
Lynn
wideopen231:
Not reallu I have built shorter,per customer request. Ones i am working on are probably that short. Aluminum tubing is very limited on selection. If you wanted mini training wheels you can use 120* bends,but need 8. Also ta. kes some extra work to keep them aligned and look correct
HAVE FUN. I have to weld up a set this week and got to run ads on cpl sets I have. thread is good motivation, so is need for more parts and money to cover them.LOL
lake_harley:
I ended up cutting off 4.5", so good or bad I ended up with 17" tube length from the flange. Got the tubes tacked up yesterday and got most of the welding done today, but as luck would have it the batteries in my auto-darkening helmet decided they had done enough so I had to go for batteries. I live out in the country and the nearest town that has a selection of stores is 12 miles away. So with the round trip and going to 3 stores before I found the correct "button" batteries it ended up wasting enough time that I didn't quite get the zoomies done. All that remains is facing off the inside TIG weld bead on the head side of the flange. I think I'll lightly bead blast them before painting to give the metal a little "tooth". I have used BBQ paint successfully on other headers, so that's what I'll use on these. My wife is leaving tomorrow for a couple days so after the paint's initial drying time I'll put them in the oven for a good heat cure. It's not like my wife would say NO if she were home, but I'll feel like I'm "getting by" with something in her absence.
On another note, all of my engine parts arrived today so I'll begin engine assembly this weekend. :)
Lynn
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