Winter Work
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From: wisconsin
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From: Western South Dakota
I read somewhere but I can't recall exactly where,but it was a bunch of dyno information,that a guy had screaming eagle heads,an andrews EV 27 cam, Mikuni carb and ignition,but I'm unsure if which but the dyno pull showed 85hp and the torque wasn't far off of that. I'm going to have Branch Flometrics do my heads when I get that far. There is alot of power to be made from headwork. By the way the 85hp motor was with a stock bore and pistons. I'll see if I can find that info.
That is where you should probably start is the headwork, and add to your motor from there, rather than the other way around. However, don't be deceived by "flowed" heads. It's more in the porting than anywhere else.
http://www.bigboyzcycles.com/showthread.php?p=17
It should be further understood that a set of heads does not act the same on a flow bench as it does on an operating motor. A flow bench has a set pressure at which airflow is measured. An operating engine develops vast and very rapid changes in pressure depending on where the piston is in the cylinder (how fast it is traveling). From the time the piston hits bottom dead center until the time the intake valve closes, the only force keeping that cylinder filling, is inertia. A slow moving large port moving the same cfm of air, as a fast moving small port, will have less inertia and consequently less cylinder fill and power. Thus, fast moving air in a small port may actually fool an operating engine by giving it more air than a slower moving large port that actually flows more volume on a flow bench.
Don't let other shops lead you to believe that flow numbers are the final word in power. Furthermore, don't let someone tell you that you need a certain amount (cfm) of air on a flow bench to meet your design horsepower needs. The odds are that if you do, the numbers given will be more than you need, and your motor will never even use it all unless you are revving it to 7000 rpm. Even then, faster moving ports with less flow will create the same power sooner, with more torque across the entire power range. So, instead, concentrate on obtaining reasonable numbers with the smallest port possible. This means, don't buy heads from anyone who just hogs out the port and achieves big numbers.
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lionsm13 has a good point. This is illustrated in the Toyota 4AGE motor's development over the years. These are 1587 CC, 4 valve per cylinder motors with the heads designed by Yamaha. The first version is known as the "Large Port" and was developed in the early 80's. The intake ports are really huge. It made 112 HP and needed half of the port closed off at lower engine speeds in order to get some useable torque out of it. They called this sytem TVIS, Toyota Variable Induction System. The next version is known as the "Small Port" and made about 130 HP with much smaller ports, introduced in 1989. The next 2 versions had 5 valves per cylinder ("20 valve") and did 150-160 HP, with ports more the size of the Small Port and came out in 1991. At their maximum HP, a 20 valve has a volumetric efficiency greater than 1. That is, they flow more air into the motor than the 1587 CC piston displacement, like with forced induction but without the blower.
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It makes perfect sense. Great information. I talked to a sales rep from Revolution Performance at the 105th celebration, and he wanted to sell me a a port job, bigger valves,different cylinders etc. I explained to him that I want to drive this thing not drag race it and he kinda shrugged me off. I did a little reading on Branch Flowmetrics and was thinking of calling them and explaining to them what I'm after which is a street engine.I think I will be looking much closer at BigBoyz and maybe I will be able to do everything this winter that I planned and a port job.
Have you had personnal experience with this company and how was it. I really appreciate all of the information that you have provided.
Thank You
Have you had personnal experience with this company and how was it. I really appreciate all of the information that you have provided.
Thank You
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