Technical > Matt Shaff's Engine Shop

Zoomies vs collector headers

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hemidakota:
MPH was the same that day, but I don't think the tune where it needed to be, was still a little lean. Just got it close on the last pass. 60' was better by .05 and it picked up 3 mph on the last jet change. There was just not enough time to make enough changes to get it happy.

Roger:
The reason I asked about the MPH was because of some other pieces of anecdotal information I’ve seen on some other web sites, including the performance boat sites. They tend to indicate the same things you voiced; bottom end torque takes a bad hit with zoomies but the top-end power doesn’t seem to be affected. Their words:

“1984 UGF back to back runs: 129.31 headers & injectors (staggered tubes), 130.81 Bassett Zoomies 2-1/4. No other changes.”

“Our Unblown Gas Boat has a 555 Chevy… was man-handling our drag boat out of the gate. The boat came out so hard that it was out of control…installed a set of zoomies and a prop…the boat now leaves the gate under control…was almost 4 tenths better than we have ever ran…pulling about 8300rpm in the lights.”

“Had the same deal on one of my hydro engines. Collector made more on the dyno, zoomies faster in the boat. I wasn't racing a dyno so I ran the zoomies.”

The Stahl Headers Newsletter this thread was based on made mention that zoomies ran “quite well from 3500 to 4500 and from 7000 to 7500.” Your experience and the ones I found seem to indicate that once you’re into that 7000-7500rpm range the zoomies may have little effect on top end performance, just as stated in the newsletter. That leaves the 5500-6500rpm range where Stahl says that the performance on a 406” SBC will see “as much as 45 to 50 HP difference between 5500 and 6500.” The 383” SBC engine I’m assembling now will operate in that 5500-7000rpm range to run the 8.5 quarter index and the 5.50 eighth index. Should be interesting, will run the tests again next year with the new engine and will post the results.

Roger

PSweeney:
I've also tested zoomies and headers before.  There is no one single theory as there are so many contributing factors from car to car.  Headers came out marginally better for the engine I was running, but no amount of power increase would make me run them on a digger again, just looks plain wrong.

Guido:
There's allot of great info on this thread! I am running a sbc with a small blower and was wondering about what size of tubing, I have 2" that are approximately 16" from the flange to the tip. Would a 1 5/8 or 1 3/4 work better?

JrFuel Hayden:
If you were not runing a blower the tubing size would make a difference depending on head air flow and RPM, however since a blower doesn't need exhaust tuning, so keep the 2" and spend your money and time on something else to make your combo better. One thing I would look at is your converter, so many racers I know have said the biggest improvement in performance was their converter change.
The goal should to better match your stall to your engine power curve. If your cam/motor comes on at 6,000 rpm, and you have stall of 4,000 rpm, guess what will happen.
I've had great returns on ET using A-1 Converters in WA. 360-574-9966.
BTW I run 2 1/8" zoomies aimed at the top of my slicks [ layed-back] on my all iron 23° raised runner injected alky Heritage JF, good for 9800-10,000 rpm, running low 7.0's, 188-190 mph.

Have Fun
Jon

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