How much boost can these guys produce? Do they work well on smaller motors?
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They usually are able to make a little more boost than your motor can take. I do like big blowers on all sized motors. I have a 'budget' combination using a 440" Chevy BB and a 14-71 that will run/win in the 8.00 class in a runnerbottom. Yes the offset dist and all the 'up front' costs seem large, but the power and motor life (IMO) is worth it.
Hey George. What about for a smaller motor that is not a max-effort type motor? Is there a point where the additional effort to turn a 14 is not worth it unless you're spinning it enough to make some boost to offset? Sorry, crappy way to ask a question of "unless you're spinning a 14 to make X lbs of boost, the parasitic loss of the blower is too great and you'd be better off with a smaller blower?".
Make sense what I'm asking???
Sorry for the thread jack Mike....john
Main reason for going with a bigger blower like a 14 is if you are planing on making some big big power or you dont want to spin the blower any harder but want to go with more cubes. More cubes will require a bigger blower to make the same boost at the same drive ratio. In theory anyway, every engine set up is different!
A Roots blower should be sized to the engine.
14-71 vs. 8-71 with the same boost pressure in the manifold. The 14-71 will make a tiny bit more power at wide open throttle. The smaller blower spun faster to produce the same level of pressure has more air leakage than the bigger blower turning slower. This additional leakage heats up the air/fuel charge a little bit.
The 8-71 will work better down low and through the mid range RPM. It will respond to throttle better and build torque faster.
With our blower shop hi-helix 14- 71s and billet inner coolers on our Dart headed 565ci mills we have seen as much as 16 lbs and have now run an honest 14 lbs on pump gas and methanol injection for several seasons.
18% over driven.Busted several dry sump 6 drives as well!
Hope this helps!
If a 14/71 putes out 10 lbs of boost and a 8/71 putes out 10lbs of boost are they going to make the same HP? Is the lbs of boost pritty much the same betweetn diferent blower.
Pounds of boost is the same no matter which blower you use, a pound is a pound.
The VOLUME of air changes. A 14-71 will put a larger volume of air/fuel into the engine versus a 8-71.
The reason for using the larger Blower would be that you don't need to spin it as fast to equal the same boost as the smaller blower.
At the lower RPM the larger blower will deliver a larger volume of air/fuel equaling the same boost level as the smaller blower.
I like the large blowers for a few 'good reasons'. How much crankshaft power is used to make the CFM and boost. Internal blower speeds VS mechanical heat and harmonics. Low (engine) RPM intake velocity and fuel mixing ability. I see so many guys turning smaller blowers 'way too fast/hard, and some have 'way too small' of a top. (carbs?) No blower will make any 'clean boost' with small carbs. The blower must have a large air inlet on the top to make boost (CFMs) You can spin any blower very fast, but it also MUST HAVE a large enough inlet (carbs, hat, EFI) to allow the blower to make the air flow. "Sizing the blower" (to me) consists of "how much money do you have?" The bigger the better, smaller blowers just limit your CFMs and so too the boost/heat level you can safely maintain. This ain't normally asperated, this is blowers, and I know the big ones work better. If you are going to tell me that you "just want 5 lbs of boost", fine, go big with little/no overdrive. (sizing?) You can always 'slow down' a big blower with good results. BUT speeding up a smaller blower most often leads to 'high intake temps' and 'tune up' problems.