Re: long rod 400, 915 heads
[Re: hemienvy]
#2747218
02/27/20 09:57 PM
02/27/20 09:57 PM
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Joined: Jan 2004
Posts: 8,637 fredericksburg,va
cudaman1969
master
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master
Joined: Jan 2004
Posts: 8,637
fredericksburg,va
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Be interesting to know what power it will make at rpm. One of the reasons for the long NASCAR rod in the hemi. Let us know how it works out.
Last edited by cudaman1969; 02/27/20 09:59 PM.
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Re: long rod 400, 915 heads
[Re: AndyF]
#2747222
02/27/20 10:10 PM
02/27/20 10:10 PM
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Joined: Jun 2016
Posts: 920 Washington
hemienvy
OP
super stock
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OP
super stock
Joined: Jun 2016
Posts: 920
Washington
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Andy, you are right.
My understanding is that under conditions that marginally favor detonation, that detonation is more likely at lower RPM. As RPM rises, even though you approach, and pass, the torque peak, the danger of detonation goes down. This is likely due to increased mixture turbulence, and decreased time for bad flame front to propagate.
Is this correct or old wives' tale ?
If I was targeting 12:1, I would have no chance, but at 10:1 I thought it would be managable with enough cam duration. The other guys evidently had good luck at 230-degrees; I guessed that the long rod deal would require more duration to stay out of detonation, maybe 240~250 min ?
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Re: long rod 400, 915 heads
[Re: AndyF]
#2747226
02/27/20 10:19 PM
02/27/20 10:19 PM
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Joined: Jan 2007
Posts: 728 mi usa
old yeller
super stock
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super stock
Joined: Jan 2007
Posts: 728
mi usa
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I don't think your question makes any sense. The camshaft doesn't change the compression ratio. If you put a big cam in a high compression engine you can reduce cylinder filling at low speeds, but as soon as the engine comes up on the cam you have a high compression engine. Sorry but that answer makes no sence either....my 400 is a 12.5 pump gas motor.....cam shaft....316/340......682/687...with a lobe separation of 115....if the lobe separation was smaller the motor would never work with pump gas...So yes the cam shaft does have something to do with Compression....And i'm out....got no time to debate with garage racers or dyno people....have a good night
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Re: long rod 400, 915 heads
[Re: hemienvy]
#2747264
02/28/20 12:38 AM
02/28/20 12:38 AM
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Joined: Jan 2003
Posts: 31,200 Oregon
AndyF
I Win
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I Win
Joined: Jan 2003
Posts: 31,200
Oregon
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Andy, you are right.
My understanding is that under conditions that marginally favor detonation, that detonation is more likely at lower RPM. As RPM rises, even though you approach, and pass, the torque peak, the danger of detonation goes down. This is likely due to increased mixture turbulence, and decreased time for bad flame front to propagate.
Is this correct or old wives' tale ?
If I was targeting 12:1, I would have no chance, but at 10:1 I thought it would be managable with enough cam duration. The other guys evidently had good luck at 230-degrees; I guessed that the long rod deal would require more duration to stay out of detonation, maybe 240~250 min ? Sure you can put a big cam in it and kill off the low end torque but then you have a soggy bottom end that isn't any fun to drive on the street. If you are building a street car then cam it for the street and use premium fuel. If you can't afford premium fuel then lower the compression ratio to point that is safe to drive. A camshaft R&D project is really expensive and unless you have some decent test equipment you aren't going to know what is going on anyway. If you are planning on going EFI and have knock sensors on the engine then go for it. You can use the knock sensors to change the AFR or the timing. If you just have old school distributor and carb then how are you even going to know if you're on the ragged edge of detonation? If you just have to build the combination that you're talking about then go ahead and build it but plan on starting off with higher octane fuel and then gradually trying different mixtures of fuel until you find out what it will run on. If it was my car I'd use a Sniper and a Hyperspark distributor so I at least had control over the AFR and timing. A knock sensor would also make sense.
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Re: long rod 400, 915 heads
[Re: AndyF]
#2747282
02/28/20 08:11 AM
02/28/20 08:11 AM
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Joined: Nov 2011
Posts: 291 PA
Harry's Taxi 2
enthusiast
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enthusiast
Joined: Nov 2011
Posts: 291
PA
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Andy, you are right.
My understanding is that under conditions that marginally favor detonation, that detonation is more likely at lower RPM. As RPM rises, even though you approach, and pass, the torque peak, the danger of detonation goes down. This is likely due to increased mixture turbulence, and decreased time for bad flame front to propagate.
Is this correct or old wives' tale ?
If I was targeting 12:1, I would have no chance, but at 10:1 I thought it would be managable with enough cam duration. The other guys evidently had good luck at 230-degrees; I guessed that the long rod deal would require more duration to stay out of detonation, maybe 240~250 min ? Sure you can put a big cam in it and kill off the low end torque but then you have a soggy bottom end that isn't any fun to drive on the street. If you are building a street car then cam it for the street and use premium fuel. If you can't afford premium fuel then lower the compression ratio to point that is safe to drive. A camshaft R&D project is really expensive and unless you have some decent test equipment you aren't going to know what is going on anyway. If you are planning on going EFI and have knock sensors on the engine then go for it. You can use the knock sensors to change the AFR or the timing. If you just have old school distributor and carb then how are you even going to know if you're on the ragged edge of detonation? If you just have to build the combination that you're talking about then go ahead and build it but plan on starting off with higher octane fuel and then gradually trying different mixtures of fuel until you find out what it will run on. If it was my car I'd use a Sniper and a Hyperspark distributor so I at least had control over the AFR and timing. A knock sensor would also make sense. I was wondering how long till the EFI sales pitch showed up. Don't forget to mention TrickFlow heads too. his idea of 10-1 with pump gas will work just fine with his thoughts on cam timing and a little slower distributor advance springs. I didn't see it mentioned, but the weight of the vehicle it's going in will also have some bearing.....detonation is load dependent to some degree. I have a 4100 lb. pickup with 906 heads a little over 10-1 and with the little bit of ethanol (5%) now in our pump gas, it's detonation free at 38* total timing...in the heat of summer 85-90*
Last edited by Harry's Taxi 2; 02/28/20 08:22 AM.
'86 Maple Grove KOS Mopar low qualifier......true street legal with no power adders.
NOS-used when losing since 1940.
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Re: long rod 400, 915 heads
[Re: Harry's Taxi 2]
#2747314
02/28/20 10:27 AM
02/28/20 10:27 AM
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Joined: Aug 2006
Posts: 2,141 junction city oregon
viperblue72
top fuel
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top fuel
Joined: Aug 2006
Posts: 2,141
junction city oregon
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My opinion is that it will run on pump fuel just fine. If it pings just back off timing a bit, but I doubt it will. Although every combo is different. I ran a 12.7 to 1 383 on pump gas for over a year and didn’t have a problem. That happened because I didn’t know what was in the motor when I bought the car. But it also had a 5200 stall and 590 cam, 4.56 gears and 2800 pound car. When I tore the motor down I found it had 20+cc domes and 915 heads. Seems to me you should be able to make it work. You haven’t mentioned the rest of your combo.
Last edited by viperblue72; 02/28/20 11:04 AM.
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Re: long rod 400, 915 heads
[Re: hemienvy]
#2747952
03/01/20 09:43 AM
03/01/20 09:43 AM
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Joined: Jan 2003
Posts: 10,081 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,081
Frostbitefalls MN (Rocky&Bullw...
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While not the same engine family, a 408 i built had somewhat similar specs. Iron EQ heads, 10.1/1 compression, 235/249/107 cam in at 105. Made max torque at 4600 max hp at 5700. It ran well on pump 93 e10. My opinion on why it ran well is the three way combo of cam, converter and timing curve. With that cam it didn't have very high cylinder pressure till 3000 plus rpm, the converter was loose enough the motor never saw less than 4000 rpm at full load. The timing curve was conservative with 14 initial and 30 total in at 4000 rpm. It also had vacuum advance working. 30 total was the best timing on the dyno with a mix of 2gal 100 +3gal 93 pump. The motor never pinged on straight 93e10 driving. So the final combo means a lot to me. A buddy built a 451 with 906 heads, kb reverse dome pistons with tight quench, heads were from Herb McCandless; plunge cut in the bowls, .030 shaved to make them flat. The dyno operater was afraid it would not do well with over 10 compression but it ran excellent on 93! So i like the idea of picking the cam you want to run, be conservative on timing curve and total, and some kind of knock sensor for tuning since detonation isn't heard until it is past the point it can start to do damage. Good water flow through the motor cold air intake are also important.
Last edited by gregsdart; 03/01/20 09:45 AM.
8.582, 160.18 mph best, 2905 lbs 549, indy 572-13, alky
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