Why is the Gen 7 496 such a bad platform to build
11-09-2015, 07:08 PM
#151
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BTW: Can we get a mod to break up this thread ? I would like to see DonziMatt's 8.1 builds and Rage's 8.1 issues discussed entirely but seperately. It would do bhetter justiuce for both. IMHO of course.
11-09-2015, 07:18 PM
#152
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I am not very knowledgeable on EFI mapping, but I personally think, these lean air fuel ratio numbers being talked about, are playing with fire while under load.
Back in the days of carbureted vehicles, spark knock, at low rpm, high load situations, was a real problem. My general opinion, is that while 2200RPM is a slow engine speed, it is not impervious to being rattled to death there, even getting on plane. Some boats can really load the engine down trying to get on plane. With a carb, its very possible that while planing, the loss of engine vacuum, will make the carb go into power enrichment.
When adding power, without adding displacement, or forced induction, you are simply raising cylinder pressure to make that power increase. Looks like you added cam lift, without adding duration. Generally, this will help build more power, esp at lower rpms.
Basically, what I'm saying, is, when the HP per ci goes up, the tune becomes more and more critical. What works at .85hp per ci, may not work at 1.3hp per ci.
I used to believe in textbook AFR numbers I read online. I also used to believe, lean makes big HP numbers, and rich kills power. While quite different than what we are discussing here engine wise, I have witnessed 900-1000hp roots blown carb'd engines, make peak power on the dyno, with an AFR of 11.5. Leaner than that, it lost power. My personal engines, run low 11's currently at WOT. I have had it in the low 12's briefly at wot, and the engines layed down, top speed suffered. I then decided, I'm gonna just start giving the engine what it wants in the fuel, and timing department, and kind of ignore, what the internet says.
Back in the days of carbureted vehicles, spark knock, at low rpm, high load situations, was a real problem. My general opinion, is that while 2200RPM is a slow engine speed, it is not impervious to being rattled to death there, even getting on plane. Some boats can really load the engine down trying to get on plane. With a carb, its very possible that while planing, the loss of engine vacuum, will make the carb go into power enrichment.
When adding power, without adding displacement, or forced induction, you are simply raising cylinder pressure to make that power increase. Looks like you added cam lift, without adding duration. Generally, this will help build more power, esp at lower rpms.
Basically, what I'm saying, is, when the HP per ci goes up, the tune becomes more and more critical. What works at .85hp per ci, may not work at 1.3hp per ci.
I used to believe in textbook AFR numbers I read online. I also used to believe, lean makes big HP numbers, and rich kills power. While quite different than what we are discussing here engine wise, I have witnessed 900-1000hp roots blown carb'd engines, make peak power on the dyno, with an AFR of 11.5. Leaner than that, it lost power. My personal engines, run low 11's currently at WOT. I have had it in the low 12's briefly at wot, and the engines layed down, top speed suffered. I then decided, I'm gonna just start giving the engine what it wants in the fuel, and timing department, and kind of ignore, what the internet says.
11-09-2015, 08:05 PM
#153
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just a couple questions about those piston pics. I am no expert engine builder but looking at the pics it seems the top ring groove is pretty high up and there is not much material left in the valve notch. were the pistons cut for more valve clearance? the shape looks a little odd but it could be the picture. when the engine was refreshed is it possible the ring end gap is tighter than before and the ring butted and pushed on the top of the piston where it is the thinnest? just a couple thoughts and hopefully I can learn something.
11-10-2015, 07:40 AM
#154
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[QUOTE=SB;4374301]BTW: Can we get a mod to break up this thread ? I would like to see DonziMatt's 8.1 builds and Rage's 8.1 issues discussed entirely but seperately. It would do bhetter justiuce for both. IMHO of course.[/QUOTE
Done. New thread:
Detonation Issues - "Why is the Gen 7 496 such a bad platform to build"
Done. New thread:
Detonation Issues - "Why is the Gen 7 496 such a bad platform to build"
Last edited by Rage; 11-10-2015 at 08:03 AM.
11-14-2015, 09:08 PM
#155
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Thread Starter
Second motor is together and running. It went together just as well as the first and lit right off. Cam is off a off a bit which I am attributing to slack in the chain, but just about the same amount as the other motor, so they should be matched just fine.
[ATTACH=CONFIG]547693[/ATTACH]
The only setback I had was when I opened the wrapper on the throttle body it had been damaged in shipping. I am sure I could have sent it back, but instead I though I would try out my metal working skills as it seemed like a waste to junk something that was more or less perfectly fine, I think it came out pretty good, kind of impressed with what I could do with a vice and a couple of sockets for shaping.
[ATTACH=CONFIG]547694[/ATTACH][ATTACH=CONFIG]547695[/ATTACH][ATTACH=CONFIG]547696[/ATTACH][ATTACH=CONFIG]547697[/ATTACH]
And of course, the obligatory first start video.
https://www.youtube.com/watch?v=D9_JbwAh5wE&feature=youtu.be I can't wait to get the Dana exhaust and hear what they sound like then. I am going to have a hard time waiting for spring.
[ATTACH=CONFIG]547693[/ATTACH]
The only setback I had was when I opened the wrapper on the throttle body it had been damaged in shipping. I am sure I could have sent it back, but instead I though I would try out my metal working skills as it seemed like a waste to junk something that was more or less perfectly fine, I think it came out pretty good, kind of impressed with what I could do with a vice and a couple of sockets for shaping.
[ATTACH=CONFIG]547694[/ATTACH][ATTACH=CONFIG]547695[/ATTACH][ATTACH=CONFIG]547696[/ATTACH][ATTACH=CONFIG]547697[/ATTACH]
And of course, the obligatory first start video.
https://www.youtube.com/watch?v=D9_JbwAh5wE&feature=youtu.be I can't wait to get the Dana exhaust and hear what they sound like then. I am going to have a hard time waiting for spring.
11-15-2015, 12:37 PM
#156
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Lookin good Matt! Remember reading that the dbl roller 496 chainsaw were on the looser side when new. Should not be a problem. The tb looks nice, you did well blending it back in. I would not have returned it either. Make sure you post pics and videos when the new exhaust is on.
11-15-2015, 03:54 PM
#159
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I'd go with long tube headers with n/a then. I put CMIs on my stock 496 and sold the aluminum manifolds. I saw zero gain on a stock engine. Modified engine should benefit from the scavenging of headers.
11-15-2015, 04:12 PM
#160
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Thread Starter
I wish I could have afforded CMI's, but I just couldn't swallow 10 grand plus for headers. I think the Dana's will support everything I am going to do with these motors, shave a bit more weight and be an improvement in flow over what I have now. Those CMI's sure do look horny though.
