FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: janjon on January 02, 2022, 04:54:36 AM
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There's probably a bunch of factors that come into play here, but generally, how much more HP and torque might one expect to see from collector headers on a carbureted engine than one with zoomies? Any input appreciated.
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that's an open ended question have run everything from weed burners' to zoomies to stepped headers only did dyno test on 305 sbc we were running zoomies because there was no min weight to get as light as possible then a rule change they added min weight so we rented a dyno for a day ran test on tube size and lenght collector size and lenght the best results were with small long tubeand a small collector. we won the championship that year i haven't seen anyone running zoomies in that class but they are like sheep and do what the winner does. all this to say headers are better and bigger isn't always better.
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On a carbureted engine, hands down the collector header works better. The signal to the carb is much much better down low. I just had this conversation with Steve Taylor of PRC carbs. The zoomie gains in the upper rpm range are pretty small when compared to the sacrifices at the bottom of the rpm band.
I had a BBC n/a 2 dominators, 1000hp deal and it would barely run with zoomies put a collector header on it and boom it would come to life.
My 2 cents
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About 4-5 years ago we tested collector headers VS zoomies on our dyno.
540ci BB Chevy engine. Tunnel ram with 38sq inch Crower blower hat on alcohol.
The engine made just over 900 HP with the collector headers. No mufflers or extensions of exhaust pipe. Just like on the race car.
We made about 3 pulls and then swapped to the zoomies. These were long tube Gasser/Pro-Mod style zoomies. Same tube diameter.
Lost 40 HP.
The zoomies still went on the car because the cool factor out weighed the 40 HP.
The car sounds better and barely lost a 10th. For us it's all bracket racing anyway.
Matt
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I'll be going for the "traditional" look on my FED with a mild 283 Chevy so Zoomies it will be. HP might be less than I'd have with a collector header but to minimize the potential HP loss I'm using small 1 5/8" tubes to build my Zoomies, which might be a benefit. Most SBC Zoomies I've seen listed and/or for sale are a lot bigger tubes, like 2" or maybe even larger. The small tubes should at least help a little with low-end power. My FED will be for bracket racing too so consistency is really the name of the game.
Lynn
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1 5/8" zoonies is what we had on the 305 sbc and 1 3/4" x 46" weed burners on a 406 sbc fed was for the look and sound
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We are going with collector headers on our NE2 build. This is how we did it back in the 70s. I would rather run a vacupan then a smog pump that is for sure. Zoomies do look cool, but crankcase pressure is something that needs to be addressed.
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Understand it makes difference on a carb motor. My doctor told me with diabetes that I need to limit carbs and I told him I have not had one of those since 1985 and no way I would have one on race car/MPO Zoomies might lose some bottom end, but hey I have 6600 stall converter so who cares about the bottom end. Another consideration is some n0ostalgia classes' don't allow collector headers. Cool factor,weight and sound are other reasons I run zoomies. I know few that have seen cpl hundredths difference but they were bracket and did not care. One more thing is I have built quite a few sets for other racers and me not run ning them would just be a bad showing.LOL
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WITH ZOOMIES You tune for one rpm were as collector type headers the torque and hp band is longer it all depends on what you want or are required to run,(the track was in court) we changed because we had to run mufflers, one guy kept his zoomies ran eight small round mufflers. and like it has been stated small lower powered carburated motor with a low stall convertor need all the help available
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If you are running a carb the collector header will help with tuning ! I tested a to b to a on my car and found no change at all When I built my roomies I laid them out so I would not get fumes in my eyes and I'm very happy with them !
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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
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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.
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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
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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
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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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Tip. Heat the headers before you paint them. In case you haven't heard it before. It Supposedly makes paint stay around longer.
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I haven't heard the tip about heating before painting. Is that using VHT, or was that with BBQ paint? In the past, I've not been pleased with VHT, it just didn't hold up, but RustOleum BBQ paint has held up well for me. I just put on enough paint to cover them, trying to avoid any "build" of paint like one would normally do with rattle can paint. If it doesn't work on these I'll admit you warned me.
Lynn
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if you get them hot and then paint it will last alot longer, i did several sets like that both with the black and silver vht
they also do this with ceramic coatings, you need to pre heat to 1200 degs, then let cool and paint. it burns off all the oils and stuff
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normally i heat the headers on the BBQ then spray usually black then reheat after the paints VHT doesn't always works the best BBQ comes out semi gloss and is easy to touch-up but smells until it's cured
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The Wife is going to know you've been up something when she gets a Zoomie flavored Cheese Burger! ;D
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Another good reason and only counts in one situation. If I build yo a set of zoomies. I need parts. LOL
Honestly I do build them for few guys and even cpl on site. BBC normally about $475 shipped lower 48 $50 of which is shipping. Hemi normally $550 shipped. SBC depends on heads and bolt pattern. Som sbc flanges can be costly for speciality bolt pattern heads.