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360 Kinda Slow? |
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WhatISit
AMC Addicted Joined: Aug/07/2017 Location: Phoenix, AZ Status: Offline Points: 0 |
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Posted: May/28/2018 at 3:03pm |
I feel like my Javelin should be a little faster. I'm not very experienced at tuning, so I'm assuming it's a tuning issue. I have a freshly rebuilt (2k miles on the odo) 360 with 9.5:1 compression, Performer intake, Comp Cams Thumpr, Edelbrock Thunder AVS 650, and headers. 3000 RPM stall converter and 3.15 gears. 275/50-15 Nitto drag radials (25.5" tall tires).
I did a couple "unoffical" GPS tracked 0-60 runs and got 6.98 seconds exactly--twice in a row. It felt like it had more power that was left untapped. Like it wasn't getting enough air and was slow to rev. I know 3.54 or 3.73 gears would remedy much of that, but that's for later. I think this is a timing/carb thing. Last I checked, I have about 10 degrees initial timing and I think 36 degrees total. Carb is brand new. All I've done is richen up the mixture a little bit, which seemed to help prior to my 0-60 runs. Is my 360 a little on the slow side or am I just imagining things... |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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That is a little slow coming out of the hole,
could be trying to climb those 3.15's. The intake and carb combo should be helping your bottom end, but might not be a great match for the 3k converter. Converter quality comes in to play too, but I'm not the expert there. Thumper cams use a big slow exhaust lobe on a tight lobe center with the (not as big, but still slow acting) intake lobe to make lots of bad A sound, but gives up a little power to what it could be. Does it feel like it's bogging? What does the Converter's RPM's flash to?
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Since it's a 998 (I just saw your sig) do you have the 2.75 first gear set?
I'm guessing it's not a traction problem(?)
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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WhatISit
AMC Addicted Joined: Aug/07/2017 Location: Phoenix, AZ Status: Offline Points: 0 |
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Sometimes it does feel like it's bogging or stumbling just a little bit right off the line, but usually if I launch at 2500 RPM or so it doesn't have that problem. It's only if I floor it right off idle that it seems to bog. It just feels especially weak climbing from 2000 to 3000 RPM roughly. Seems to have trouble revving quickly in that range more than anything.
As far as the flash goes, I've never really checked, but it's definitely less than 3000. More like 2400, but still sufficient, I would think. It's a Hughes converter, so it should be good stuff. Trans was just rebuilt about 1500 miles ago, too. Definitely not a traction problem. Barely chirps the tires with those Nittos when launching at 2500 RPM. I do have a locker in the rear end, so both tires are getting good traction. Also, I believe it is the 2.75 first gear set. |
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2Busy
AMC Apprentice Joined: Apr/25/2016 Location: Michigan Status: Offline Points: 34 |
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There are kits available with a selection of distributor advance springs to fine tune the timing curve. More advance at a lower RPM may help the low end response. How did you measure the 36 degree total timing?
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PROSTOCKTOM
Supporter of TheAMCForum Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2427 |
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The first major problem I see is the your using a Thumper cam. If you want the lope and mean sound that's a great choice. If you want a performance engine that is the worst choice you could have made. You may not want to hear this, but before you do anything you need to change that cam out.
Tom
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AMXRWB
AMC Addicted Joined: Apr/25/2013 Location: Midwest Status: Offline Points: 1136 |
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I agree with Tom.
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WhatISit
AMC Addicted Joined: Aug/07/2017 Location: Phoenix, AZ Status: Offline Points: 0 |
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Yea, it’s definitely not the best cam. If I built the engine I would have gone with something else. I am seriously considering going with a 3.54 or 3.73 gear.
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5787 |
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There can be some significant gains just from having it tuned right, fuel and ignition.
My understanding is that the thumper cam can make good power at higher RPM, but maybe not the best down low. 3.54 and 3.73 gears do start to cut into your highway cruising comfort levels if that is an issue, really depends how you want to use the car. |
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WhatISit
AMC Addicted Joined: Aug/07/2017 Location: Phoenix, AZ Status: Offline Points: 0 |
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Where I’m moving there isn’t a lot of traffic that goes over 55, so I’m thinking it won’t be too much of a problem.
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