I read all the time that you have to match your cam carefully to the heads that you are using, yet I hear often of guys that are running unported iron heads with cheater type cams (KB107, Poston 112, etc.) that are running the low 12's, high 11's. Is it possible to "get around" poor breathing heads with this type of cam, even if you're sacrificing idle quality and have to use a higher stall converter? When I run a typical combination through desktop dyno, these types of cams don't make a lot of power, and they seem to sacrifice the torque curve to make a few more hp in a higher rpm range, but in actual cars, you see guys running pretty fast with them. Can someone explain this to me? It makes no sense to me that a near-stock iron-headed motor with, say, a poston GS112 with 244, 264 duration would run faster than the same motor with the TA413 (234, 244), or Poston GS113A (232, 246) cams. The torque curve is killed by the intake duration, and the heads don't breathe enough to support the duration used. Is there really some cheating going on with these type of cams?
I have a stock set of 71stage 1's(I hand cleaned the bowls a little), and run a GS113A and it pulls like a freight train( it gets a 4700lbs. car into a 13.79 with no gear and a 3000stall(I only have a 2.92:1 posi).
the 107a has a lot of duration to make power from stock heads, even stage 1 heads with a little port work only need about .500 lift, dura tion is were its at, and the 107 lobe is for high rpm h.p. and it needs alot of stall and gears, and idles at 1100, low vacumm, just my 2 cents. talk to the tec. guys at the companys that sell these buick parts, or the ones that build engines, they really know BUICKS
It was just kind of a general question. I know that these cams seem to work. 3 examples: 1. 70 GS- 430, full weight (4100 with driver) 9:1 compression. Gasket-matched heads, headers, B4B, 1" spacer, Q-jet, 3500 stall, 3.90 gears- 12.20 best, 12.5's typical. It actually idles at around 800. 2. lighter 70 GS- was going mid-high 12's with a hemi killer. Switched out to a 107 and went 12.0's. 3. 3400 lb. car, fairly stock motor, non-ported iron heads, poston 112 cam. Car runs 11's! It just doesn't seem possible, considering that these cars have near-stock heads. How is it that the cams can make them perform like this? Can duration make up for head flow?
Having more overlap will certainly help pull more fresh air into the cylinder. And you can add a lot of exhaust duration to overcome the usual shortcoming in exhaust flow. Is that what you mean? -Bob C.
Steve, I am by no means an expert... But IMO.. When you say "near-stock iron headed motor", I just want to clarify somethings. The stock iron heads unported won't flow at high lifts (like ABOVE .500 lift). That's why duration is increased. To "cheat" the engine into believing that the cylinder heads flow better than they actually do. With any action comes a reaction, the longer (and/or) a valve is open, the more opportunity there is for air/fuel to enter the cylinder. But there are consequences also. Like you said, but that's kinda harsh. Should be more like altered and/or moved depending .... Generally speaking, increased duration moves the torque peak up the RPM range. This is why lower rear gears, higher stall converter, increased static compression, ignition timing changes, ect. are required to realize any real performance gains. So "stock or "near-stock" engines won't realize any performance gains from a KB 107 or Poston 112 UNLESS matched to the proper components, and would probably SUFFER. I know from my personal experience that very little is actually stock to get into the low 12's-high elevens. I can honestly say that almost everything in my car from the air cleaner to the tires has been altered/modified or replaced to obtain this goal. Some changes I made weren't necessarily for actual performance GAINS, but were done for strength, reliability, consistency. Sorry for the long post guys, please remember that I said that I am NOT an expert. I hope I helped some, and did not confuse or say anything in error.
you would have to treat your engine like a winston cup restrictor plate motor, i can give you a number of a cam designer if you wish to pay a little extra for the proper cam. other choices are comp cams tech line, or crane cams tech line. good luck
Lift is not as important factor in making power as duration is. Duration is the amount of time the valve is open. The idea of these "cheater cams " was simple, the sanctioning bodies said that you could only run x amount of lift in the stock classes, typically no more lift than the stock cam, but they had no stipulations on duration, so cams were designed with low lift but long duration and of course the engines made more power. The valve being open for a longer period of time is still going to allow more air into and out of the engine, even if the head flow is not good. There really is no such thing as the head won't support that much duration, it's just that using a big duration cam on a stock head will produce only useable power at higher rpms, so if you try to do this with a stock converter and small rear gears, the car will be a pig until you can get up into a decent higher rpm power band. As stated in some other posts, when you go way up in duration, your torque peak will come in at a higher rpm, so to get everything to work, you need a higher stall converter and more gear, you want to get the engine into it's power band sooner. The down side is these cams have a very lumpy idle and give rotten gas mileage for a street car. Now while these profiles will make better power with stock heads, they will of course make even better power with better flowing heads. With really good flowing heads, you can cut back the cam , have a better idle and economy , and still make killer power , because the heads flow better in the first place. Everything with making power has to do with air flow into and out of the engine, period, whether you do this with a big duration cam and stock heads or with a conservative cam and good flowing heads, both will kmake power, streetability between the two will be the big difference. I hope this helps answer the original question asked. Jim Burek P.A.E. ENTERPRISES
Thanks... that's exactly what I was asking. So, if I don't mind the problems with this type of cam, it's a good way to go faster without having to get ported heads, right? And, if I understand what everyone is saying then, it does this by shifting the powerband up, and making it peakier? Thanks for the replies.
