Headers vs Zoomies

[Fired Up]

My motor is a BBC 468, single 1050, around 750hp in a Canyon flat. 106 at 10:02 is the best at the races. Was running Basset (dry) headers and had the chance to test with some Rewarder zoomies today at the lake. Since my last test session with headers the only change was the weather , today about 80-85 degrees, last time about 95-100. Jetting (92), gears (12%), prop all the same. With the zoomies the motor wanted to idle much higher (about 1900 initially ), my idle with headers is normally around 1400. She was a dog compared to before with the Headers. Real bog when I hit the throttle under load. Did some idle mixture adjustments and the idle increased to 2500rpm's, sounded better,improved some performance, but really lost about 600 rpm's on the burnout (6100 down from 6700). Zoomies lose that much power in a carbureted set up??

[Moneypitt]

Wow, that much increased idle speed? It sounds to me like the motor liked the slight backpressure with the headers. Also the tuned tubes aided in the higher RPM cylinder flow demands. A good set of tuned headers is a big plus in a N/A motor, as you found out. The cam overlap is best utilized with the scavenging effects of the headers, something a blown application doesn't need. It is possible you could tune to the zoomies, but it may also require a cam change to get back to the same performance the headers gave you. I am by no means and expert on zoomies, and am kinda generalizing... Perhaps Fiat or Art will jump in here and help with some actual experience of a N/A motor using zoomies. BTW, how did it SOUND?.........Ray

[GofastRacer]

Zoomies are for a blown motor, N/A motor needs a certain amount of back pressure, also collector lenght on the headers make a difference. Take them off and put the headers back on!..

[GofastRacer]

Wow, that much increased idle speed? It sounds to me like the motor liked the slight backpressure with the headers. Also the tuned tubes aided in the higher RPM cylinder flow demands. A good set of tuned headers is a big plus in a N/A motor, as you found out. The cam overlap is best utilized with the scavenging effects of the headers, something a blown application doesn't need. It is possible you could tune to the zoomies, but it may also require a cam change to get back to the same performance the headers gave you. I am by no means and expert on zoomies, and am kinda generalizing... Perhaps Fiat or Art will jump in here and help with some actual experience of a N/A motor using zoomies. BTW, how did it SOUND?.........Ray
Ray, unless it's blown or on the bottle zoomies don't work on a N/A motor, went thru that many moons ago!..

[Paul128a]

My guess is the same, you need the backpressure on a N/A motor. I tried this before on my little 350, I had 31 inch headers running dry. I made a bit more power when I had them water jacketed with wet muffler tips.

[Animal Magnatism]

You often see headers on blown motors too. If they help scavenging on N/A motors, why not blown motors. There is the pressure on the intake pushing out the exhaust gasses, but if the exhaust pressure is pulling as well, doesn't it all help??
-- Or is it like putting a fan on each end of a tube. If you have a fan on one end pushing 100 cfm, and you put a fan on the other end pulling 100 cfm, you don't get any more flow. It stays at 100cfm. So with the blower pushing 1000 cfm, Headers that would normally pull 200cfm make no difference. Is this a fair analogy?? ( have I answered my own question??)

[Moneypitt]

Ray, unless it's blown or on the bottle zoomies don't work on a N/A motor, went thru that many moons ago!..
Art, I kinda knew that, but without actual first hand experience I wasn't going to say point blank they won't work. In hindsight, I guess the idle circuit couldn't handle the extra air they flowed at idle, therefore it was lean, way lean, at an idle, and that is why the idle increased so drasticly. Then as the motor started to come up under power he lost that overlap induced induction, and it layed down......As I said, there has to be a way, but not with the same set up as an engine that ran well with headers, in other words, if you designed and planned an engine to run with zoomies, (cam, heads, induction, etc.) then headers would not work as well as the zoomies, but here we have the opposite..........and IMO,(.02 cents), NA engines like/need the tubes tied together, and enough overlap to use them.......Ray
Question answered Sam?

[Fiat48]

My motor is a BBC 468, single 1050, around 750hp in a Canyon flat. 106 at 10:02 is the best at the races. Was running Basset (dry) headers and had the chance to test with some Rewarder zoomies today at the lake. Since my last test session with headers the only change was the weather , today about 80-85 degrees, last time about 95-100. Jetting (92), gears (12%), prop all the same. With the zoomies the motor wanted to idle much higher (about 1900 initially ), my idle with headers is normally around 1400. She was a dog compared to before with the Headers. Real bog when I hit the throttle under load. Did some idle mixture adjustments and the idle increased to 2500rpm's, sounded better,improved some performance, but really lost about 600 rpm's on the burnout (6100 down from 6700). Zoomies lose that much power in a carbureted set up??
Never heard of such a thing. That much change from headers to zoomies. Faster idle. Mixture adjustments and we get 2500 idle?
I am wondering what corrected altitude was between where you were before (95 to 100 degrees) and where now (80 to 85 degrees).
I think you need to do this at the races when there is only a slight air correction factor between runs of trying the zoomie and the headers. Id try that before calling a true judgement on the difference between them. Timeslips.
Now that said.....generally unblown tunnel ram motors like the headers IF the header is correct for the motor. Injected motors unblown can actually like zoomies if you are working with tuned lengths. But that is another story.
I made many back to back runs with zoomies and headers and found no difference in time slips. But I attributed that to not the right header.
A lot of guys used to cut the bassett collectors off...1 inch at a time till the boat slowed down or picked up. I know some guys found a little bit there. In the early days of UGF I picked up just over 1 mph when trying zoomies. I left them on there because the boat was easier to work on. The right header...it may have gone faster.

[W.O.T]

good post i always wondered about them both. nice avatar animal magnatism!

[GofastRacer]

A lot of guys used to cut the bassett collectors off...1 inch at a time till the boat slowed down or picked up. I know some guys found a little bit there. In the early days of UGF I picked up just over 1 mph when trying zoomies. I left them on there because the boat was easier to work on. The right header...it may have gone faster.
We used to take cheap ole paint and painted the collector, then watch for the burn line that would be the spot to whack it off!.. Never could get zoomies to work as good as headers, even with different cams and stack heights, the idle changed a tad but that was easily taken cared of with a slight tweak of the barel valve!.. When it comes to working on stuff, the zoomies do make life easier!..