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Not trying to be facetious, but it just depends on the application. There are a lot of camshaft theories that just can't be generalized. |
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In an optimum situation, a small cubic inch engine with a small intake port volume should gain torque and throttle response. If the overall combination is not optimal, then one could go one way and the other could go the other. Just depends.
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Ok dont know if this will help at all. If 2 cams were identical except for separation angle. And installed on the same intake center line. The one with the narrower separation angle would open the intake at the same time as the wide one. But it would have more overlap and a later ex opening. The narrower one would also have more valve closed time during the compression and power stroke.
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1. Overlap can make/break vacuum, which is necessary for accessories like power brakes. 2. You can have too much overlap (either by narrow LSA or by large advertised durations) which will push the charge right out the exhaust instead of using it for power-making. That's why engines with really large or tight LSA cams sound so radical at idle, they are inefficient. 3. Overlap can be your friend on a large intake port, such as in the case of a 4V 351C head or a Tunnel Port FE head. With the valves open at the same time, the exhaust can scavenge the intake charge on a port which is otherwise too large and too slow on velocity, which will help fill the cylinders. |
Brent i think you meant Less overlap gives you vacuum.
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Brent guess i was thinking more overlap at idle the less vacuum.
Hey its been good spending the last couple of day with you guys ! |
You aren't wrong, I just worded it goofy and it wasn't clear.
As an aside, increasing the overlap doesn't mean that you lose your brakes, they will remain functional for quite a while. On a 445 FE, 65° of overlap still gives you 14-15" of vacuum if the engine is sealed up tight. |
Seems like I have heard that Webers don't like the LSA to be less than 108-110 degrees... trying to remember where I got that info. Sound right?
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Webers have very short runners, essentially non-existent for all intents and purposes. Tighter LSAs increase overlap, which can introduce some reversion into the intake manifold. Reversion doesn't matter at 7000 rpm, so you cam the engine for its intended purpose if it's a race engine. If it's a street engine, then it needs to be cammed to minimize reversion. Most guys think, "Oh it's got Webers, I need to go 112-115 LSA", but again, it's totally dependent on overlap. |
Just talked to the engine builder, my build specs say Dart Iron Eagle, but the heads are WP Windsor Jr 180 cc with 58 cc chamber. According to what I can find they flow 226 cfm at intake and 144 cfm at exhaust. Not the best, they have not been ported. The question is, do we port these or if available get the Dart Iron Eagle 200 cc heads with a 58 cc chamber that flow 285 cfm at .700 lift without porting? WE might be stuck with these heads, as supplies are drying up. Luckily we were able to find a block and it will arrive January 4. Some suppliers were telling him not until March 2021 at best due to the factory being shut down, or at best running on low production line numbers.
Brent, the builder and I both agree that the cam is wrong and he does not know anyone that builds cos for Webers anymore. He said that the last one he had built for a SBF with Webers was 25 years ago and he recalled that it was not as aggressive as this one, nor were the originals this aggressive either. So, start putting on your thinking cap. If available, new heads would be cheaper than porting the existing ones. Thoughts? The connecting rods will be similar to what you do, in that they will be longer due to shortened piston height and the crankshaft being lightened. Jim |
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Jim |
Dart IE heads havent been available for the past year and still aren’t. You’d be best off porting what you have.
I do *really* long rods on my 289’s. Longer than what normal guys do, at 5.700” length. It requires a SBC rod and some rod narrowing with some non-typical bearings. Be happy to help with the cam when it comes time. |
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https://jiminglese.com/ Jim Inglese 242 SE Mimosa Place Lake City, FL 32025 Email: jiminglese@att.net Telephone: (203) 623-0659 Fax: (203) 315-6224 |
Brent,
Ok, looks like we might be porting. He has them in the cleaner right now. Will let you know what we come up with. I believe that the rods that has on order are 5.04" from what I recall. Luckily he has not ordered the valve train parts yet. What would be an estimate of turn around for the cam, once we have the flow numbers? Jim |
5.400”?
Cam takes about a week and a half. |
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Jim |
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