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Help with Cam selection (again) |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7901 |
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1815 |
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As a ballpark I do not suggest more than 230 degrees intake on a hydraulic. Above that means you are looking for pretty serious power at rpm levels that get problematic for a hydraulic lifter. My opinion is only go bigger than that with a hydraulic is when the rules require it.
Can it be done - yes. My opinion is if you want a cam that big go to a solid, and add 8-10 degrees to compensate for the different take up ramp. A solid will have a better rpm band, both high and low as the idle will be better with an equivalent solid. I did break my own guideline on my own build with a 232 degree cam, but not by much. There are also some efforts to mitigate the hydraulic problems with light valves, beehives, and good rocker gear. It worked, and the engine pulls clean to 6500 without obvious signs of lifter collapse. The power curve does not nose over. It made 567 hp @ 6050 rpm. The discussion of how it sounds is a different one. So to me 236 is a pretty radically big cam for a hydraulic. |
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JERSEYJOE
AMC Addicted Joined: Oct/23/2008 Location: TUG HILL NY Status: Offline Points: 1718 |
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I would stay wit something abound 224-228 degrees at .050 and lift in the .500 range max 112 centers
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1985 J-20 PLOW TRUCK
1977 CJ 7 360 T-18 D 300 1970 AMX ex-SCCA car SPEED COSTS MONEY HOW FAST DO YOU WANT TO GO? |
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AMXrated
AMC Nut Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Bullet Cams said the cam they spec'd would have best power between 2,500-5,500 RPM with 6,000 being about the max.
Howard estimated 2,000 - 5,500 RPM. Not sure either qualifies as "low" as in "low to mid level power". But I suppose everything is relative... Probably my fault for not giving them a target RPM range to work with. It's been a long time since I did any real engine work or owned a performance vehicle--What is a good RPM range for "hot street"? 1,500 to 5,000? Seems like I'd want it to idle around 750-800, right? Also, think I want to stay with hydraulic lifters. The solids are interesting, but don't think I want to have to worry about adjusting them even though the car probably won't see a lot of use. A lot of good, helpful info so far--Thanks!
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You can have my Hurst shifter when you pry it from my cold dead hand.
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6746 |
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1500-1600 bottom and 5500-6000 top would be my aim. Idle with this would have to be about 800 as you state.
You won't get full use of the 750 CFM carburetor but that's not the point of what you state you want the car for. A 650 CFM would be a better match but not worth the change for the little difference it would make, and you already have a 750. |
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Those two custom cams are using wide lobes in order to get the DCR down, as the static CR is so high. I'd try to get the static CR down then take another look at cam selection. Probably the easiest way is to open up the combustion chambers to 62-65 cc, as the de-shrouding will give you more flow anyway. In my opinion the EVO number of 58 is just too high for your application. That's going to bleed off cylinder pressure and kill low RPM torque, trading it for reduced high RPM pumping losses. And it will also be ludicrously loud. Not simply lumpy/rumbly, but ear splitting, wife complaining, neighbors calling the cops kind of loud. Even the EVO of 54 from the Howards cam is just too much. Howards was using their standard 842 lobes on that custom cam too, not their 904 Mopar lobes. An easy way to spot their 904 lobes is that the duration at 0.050 numbers are even numbers, while all of their other lobes have odd numbers. I think they actually call them Mopar 0.903 lobes. |
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1968 AMX 390 w/T5
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AMXrated
AMC Nut Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Well...now I'm worried. Not so much about the wife or neighbors, but I don't want my eardrums split.
I was trying to compensate for the lower CR AMC implemented in the 72 360, but obviously have went too far with the Wiseco flat tops. Probably why guys build their engines around the cam and not the other way around. Geez, I really don't want to have to machine the chambers on the heads--just got them back from the machine shop..I think before I do that, I'd like to take a shot with a stock cam and see what the result is. If I have to open the heads and buy another cam later, then so be it. I'm already over budget on the engine work any way. Based on the replies I have received on this post, here is what I think is a summary of recommendations on what I should be looking for: Duration @ .050 of 224 - 230 max .500 lift max 112 LSA 1,500-6,000 RPM .904 lobes And (if all that is correct) I am wondering if something like the Lunati 10100702LK might be in the ballpark with these specs: Hydraulic Flat Tappet Duration @ .050: 220/226 Gross Valve Lift: .507/.527 LSA/ICL: 112/108 RPM Range: 1,600-5,800 Lobe width: .904 Obviously the lift is a bit higher than recommended, but not horribly high. I've read some reviews on it and people say they have been disappointed in the idle being smoother than expected. But, not every set-up is the same either. Anyone have any thoughts on that cam or used it in the past? Thanks.
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You can have my Hurst shifter when you pry it from my cold dead hand.
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7901 |
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I believe Howard's also has a 223 -.480 or so lift on 114 centers. Not a modern fast acting cam, but it at least has a late closing intake, a reasonable idle, and not a tremendous amount of lift. It's similar to the Chevy 350/350 and L82 cam and also the AMC Group 19 cam I believe. That is what was considered a good hi-po replacement back when the car was new. I would appreciate Greyhound's opinion.
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1982AMCConcord
AMC Addicted Joined: Jul/13/2012 Location: Kenosha, WI Status: Offline Points: 1286 |
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I'd also like to mention... I've talked to Howard's several times and they will custom grind whatever you want for only $150... and they grind in house... They don't repackage Eddy or Summit or Crane etc... So just FYI...
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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I'm still hung up on the compression ratio though. With iron heads and standard 93 octane fuel 9.5:1 is what most people consider the limit. Are you going to run octane booster in every tank, or maybe race fuel? We have ethanol free 93 octane here at the pumps, but that's as good as it gets. I think someone mentioned E85, but in my mind more ethanol is not a good thing with our old tech gasket materials, fuel pumps diaphragms, etc.
Granted you can back the timing off if it's pinging, but then they tend to overheat. Overheating and pinging = new pistons. Another thing to consider: The single plane intake manifold will have a more aggressive idle than a dual plane intake, so if you really want the beefiest idle sound possible you might want to go with the Torker.
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1968 AMX 390 w/T5
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