Anyone have some numbers for shorties vs longtubes on the same/similar car? Seems the general impression is the longtubes have minimal hp gain but significant torque gain.. I'm thinking about pickup up a set of bbk's this winter, just pondering if it's really worth it.
from a dyno runs book i have, it gains a little hp, not much though, but a good amount of lowend tq. between my longtubes and my old equal length headers, on my gtech comp., at 2900 it made close to 40 rwtq more, by 3200 it was making 20 rwtq more but from 3750+ basically made the same power. the MPH i was running was basically the same in the 1/4, but with less traction at launch. im sure with more traction i would have MPH'd higher as well.
It really depends on the app. On a basically stock 6k rpm combo you won't see much difference between shortys and longtubes. So longtubes wouldn't be worth the headache. The more radical you get with your combo though, the more difference you'll see. Expecially like a high rpm naturally aspirated combo because they rely on good scavenging. If I stuck shortys on my car, I'd probably lose at least 20 horsepower.
It really depends on the app. On a basically stock 6k rpm combo you won't see much difference between shortys and longtubes. So longtubes wouldn't be worth the headache. The more radical you get with your combo though, the more difference you'll see. Expecially like a high rpm naturally aspirated combo because they rely on good scavenging. If I stuck shortys on my car, I'd probably lose at least 20 horsepower.
A friend of mine just got done building a 331 with AFR 185's and Holley intake combo. It had a custom Cam Motions cam and FRPP 1 5/8 shorties with a VRS x-pipe. it made 390 RWHP and he was looking to break the 400 mark so he felt the Long Tubes would get him there. He bought a set of 1 3/4 BBK LT's and a matching x-pipe and dyno'ed it again. Under the same conditions it made 390 again and only gained 3 to 4 FT Lbs throughout. Needless to say he was not satisfied so he searched for the problem. It came down to the collectors on the headers not being big enough. So he cut them off and put on a set of Flowmaster collectors and got rid of the "Ball Joint" connector. Back to the Dyno and resulted in 405 RWHP and gained another 15 ft lbs.
Just saying to do your homework when selecting a header as they are not created equal. The diameter and fit is not the whole story. Look at the collectors.
It came down to the collectors on the headers not being big enough. So he cut them off and put on a set of Flowmaster collectors and got rid of the "Ball Joint" connector. Back to the Dyno and resulted in 405 RWHP and gained another 15 ft lbs.
Just saying to do your homework when selecting a header as they are not created equal. The diameter and fit is not the whole story. Look at the collectors.
That's a good point also. The Mac and BBK headers both have like a 23/8" ball collector. Another problem with the BBKs is how they are welded on the inside of the header flange. I used to run their 13/4" Longtubes and the inside of the tubes at the flange had huge welds sticking out into the port. I had to do a ton of grinding to make them match my ports. When I switched to the Bassani step headers, I saw a nice difference on the dyno.
To confirm what the other guys are saying here, on a relatively mild 347 build up (400 crank HP), MM&FF tested unequal shorties, equal-length shorties and long tubes (all 1 5/8ths primaries) and long tubes with 1 3/4 primaries with dyno runs on the same engine. All 4 sets made within 3 or 4 HP and torque of each other at peak. However, the 1 5/8" long tubes were MUCH stronger at low rpm - at 3000 they were making almost 40 lb-ft more (the 1 5/8). Unfortunately the goobers running the test seemed to miss that "minor" difference, and didn't run the test at any lower rpms.
The bottom line is that it's really a case by case. Primary size, collector size, collector type/configuration and length can really have an impact on a higher output motor. Most folks find out what works best by experimenting. I suppose some of your custom cam designers might have the ability to model some of those details to try and help you predict what's gonna work best.
In general - long tubes are gonna be your best bet regardless. On milder motors, even if the peak isn't much improved, the bottom should be. And as power levels increase, they'll show more benefit. Wish there was room on mine...