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What's holding it back |
Post Reply | Page 123 4> |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5787 |
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Posted: Oct/25/2014 at 5:44am |
What's holding me back, ran the car up on the dyno on Friday and I must say ther results are a little dissapointing, conservative dyno perhaps, but even then, it seems a little below expectations.
Engine specs: 343 block, 360 crank, 4.155 bore, all up 375 cubic inches and 10.5:1 compression Edelbrock heads, basically out of the box. Airgap manifold Holley 750 4150 vacuum Secondary Street HP carby, http://www.summitracing.com/int/parts/hly-0-82750/overview/ 1/2" 4 hole phenolic carb spacer Hooker 1 5/8" headers modified to match dogleg exhaust ports 3" pipes back to crossover then twin 2.5" pipes from there back, free flow mufflers Crane Hydraulic Roller HR-224/339-2S-12 http://www.cranecams.com/product/cart.php?m=product_detail&p=24174
Rest of the driveline: BW M12 Auto, stock convertor rebuilt with increased stall (don't know the specs) AMC 20 diff, 3.54 gears 275/40/17 rear tyres I have had it dynoed a couple of times and no obvious issues with air/fuel or timing, running 14 initial, 32 total with the vacuum advance connected. It's making full throttle and no restriction with the air cleaner. Ran 13.1 @ 106 last time out, 69 Javelin, around 3600 lbs with driver. That's about all I can think of spec wise, any thoughts on what's holding it back would be appreciated.
Edited by WesternRed - Oct/25/2014 at 5:49am |
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Dave Z
AMC Nut Joined: Jul/02/2007 Location: Massachusetts Status: Online Points: 300 |
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I'd try 32 deg. total timing with the vacuum disconnected.
Dave Z |
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401MATCOUPE
AMC Addicted Joined: May/20/2010 Location: Salisbury, MD Status: Offline Points: 5370 |
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Are you sure the distibutor timing is correct??? Cam timing is correct?? thinking maybe the outer ring on dampener is slipped giving you in-correct actual timing. There are some guys on here that should be aboe to help, I agree with you, looks like goods bits in the engine and sure seems like your performance is way off. I think your torque converter maybe a cause of a lot of loss. Go back to basics and double check everything....that has helped me when stumped.
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Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
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amx2bfast
AMC Apprentice Joined: Aug/07/2013 Location: middlesex nc Status: Offline Points: 217 |
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I think something was not right with your rpm reading. I believe that HP and torque should cross at 5250 rpm. When my dyno was running and I got readings like that, something wasn't set correct
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1975 gremlin
1973 javelin 1976 pacer wagon |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5787 |
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It made a couple more HP with the vacuum advance connected than without apparently. It has a new rebuilt damper after the ring slipped on the previous one, TDC was checked on installation. Two different dyno places have tuned it now, both recommended for carby capability. These guys didn't find much to change from the previous tune. Made more HP last time (272), but different dyno som maybe just calibration. It's peaking about 150 rpm lower this time, but appears to make more early on, hard to tell as this one was based on RPM, the previous one on road speed. Have changed the diff gears (previously 2.87) and rebuilt the auto since the original dyno run, also changed the exhaust, was 2.5" all the way previously.
Cam was dialed in on installation and checked out fine. I'm thinking heads, intake and headers should support 400 HP (at the crank), so that sort of leaves the cam and tuning.
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wantajav
AMC Addicted Joined: Sep/04/2009 Location: PA Status: Offline Points: 1150 |
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Random thoughts:
106 in the quarter is a hard running car Stock/large diameter/tight TC and heavy M12 internals are sapping some power Are you sure you are getting the valve lift you think, might want to check that/lash/pushrods, etc I don't see what air-fuel ratio you had. Need different jets? Different dynos give different results, maybe yours would test higher on someone else's machine. Mike |
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scott
AMC Addicted Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3498 |
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Did you try running more total timing? 34, 36, 38?
What distributor are you running? |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5787 |
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It's running a Mallory HEI distributor.
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jcisworthy
AMC Addicted Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2805 |
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Hp and torque are scaled on opposite sides of the print out that is why they do not cross over.
I would try more timing if you have not, that can pick you up a bunch if the engine wants it. Those heads should want 34 degrees maybe more.
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tsanchez
AMC Addicted Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4302 |
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When you say cam is straight up, do you mean at 112 or at 107, it's supposed to be at 107
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