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360 Kinda Slow?

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Category: Competition
Forum Name: Drag Racing
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URL: https://theamcforum.com/forum/forum_posts.asp?TID=94416
Printed Date: Mar/28/2024 at 11:36am
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Topic: 360 Kinda Slow?
Posted By: WhatISit
Subject: 360 Kinda Slow?
Date 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... Confused

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-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8



Replies:
Posted By: jpnjim
Date Posted: May/28/2018 at 3:39pm
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


Posted By: jpnjim
Date Posted: May/28/2018 at 3:44pm
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


Posted By: WhatISit
Date Posted: May/28/2018 at 4:06pm
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. 

-------------
-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: 2Busy
Date Posted: May/28/2018 at 4:58pm
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?


Posted By: PROSTOCKTOM
Date Posted: May/28/2018 at 5:10pm
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


Posted By: AMXRWB
Date Posted: May/28/2018 at 5:20pm
I agree with Tom.  


Posted By: WhatISit
Date Posted: May/29/2018 at 3:13am
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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-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: WesternRed
Date Posted: May/29/2018 at 3:34am
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.


Posted By: WhatISit
Date Posted: May/29/2018 at 9:35am
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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-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: PHAT69AMX
Date Posted: May/29/2018 at 12:15pm
Be sure valves properly adjusted.
Confirm and nail down the Ignition, Timing, and Advance Curve.
Borrow a known good working 750 Holley Double Pumper.
Bolt it on, set it up buy someone who knows how.
Car all warmed up and run-in a bit with the Holley....
Fuel delivery and regulated fuel pressure nailed down.
Creep up... stop... light foot on brake pedal ( fronts only )...
a tiny little bit of step-in on the carb, then hard to the floor...
using the really light brake pedal with the left foot...
and it'll smoke those tires and walk sideways....
When it's all workin' right how the driver uses his right foot
on the accelerator is what determines the best 0-60 times
because it's his right foot controlling the tire spin throughout the 0-60 run...
Borrow a known good running working Holley 750-800 Double Pumper and TEST...
Or....  the drag launch type test.
creep up... stop... hard on the brakes...
squeeze into that gas pedal and bind that thing up into a tight knot,
that converter, like a rubber band wound up in a model airplane...
wind that converter up hard, knot that car up on those brakes...
then let off the brakes and floor the gas... 60 Feet in 1.8x seconds maybe...
-IF- it bites...

All nothing more than some crazy frustrated car-less internet forum dude's opinion(s)...


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: WhatISit
Date Posted: May/29/2018 at 12:44pm
Well, that brings up an entirely different issue, now that you mention it. I believe I have a bad valve seal on the passenger side (smokes a little at startup and slows down or stops altogether after it's warmed up). Could a bad valve seal affect performance that acutely? 

-------------
-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: PHAT69AMX
Date Posted: May/29/2018 at 1:40pm
A bad valve seal alone, no, but "incorrect valvetrain" yes, performance acutely affected.
What kinda valve seals?  Fresh build, why'd it go bad?.... 
There's a whole buncha stuff to an overall correct properly working valvetrain...
Especially if the motor has been "re-built"... lotta "error opportunities"...


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: one bad rambler
Date Posted: May/29/2018 at 6:53pm
i agree with the thumper cam choice..to me it`s a snake oil circle track cam.... a  comp. 270 or 280 and a little more gear will help pull a little more down low

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68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8


Posted By: one bad rambler
Date Posted: May/29/2018 at 7:06pm
Part Number:30058
Grind Number:LSP-58H
Intake Duration (gross):284
Exhaust Duration (gross):294
Intake Duration (.050”):224
Exhaust Duration (.050”):230
Intake Valve Lift*:.510"
Exhaust Valve Lift*:.510"
Lobe Separation:110
Intake Valve Lash:.000"
Exhaust Valve Lash: .000"
RPM Range
2500-6500
I`m running the same compression in my sons 360...with a 750 dp ...Performer rpm air gap...3,000 stall..3.73 gears..and this Schneider cam....The car was doing a consistent 19.1 1/4 mile before the swap...We can only get better lol

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68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8


Posted By: WesternRed
Date Posted: May/29/2018 at 8:27pm
For the sake of comparison:

Thumpr

Intake Duration (gross): 279
Exhaust Duration (gross): 296

Intake Duration (.050”): 227
Exhaust Duration (.050”): 241

Intake Valve Lift*: .491"
Exhaust Valve Lift*: .476"

Lobe Separation: 107

RPM Range:
2000-5800


Posted By: jpnjim
Date Posted: May/29/2018 at 9:48pm
Originally posted by WesternRed WesternRed wrote:

For the sake of comparison:

Thumpr

Intake Duration (gross): 279
Exhaust Duration (gross): 296

Intake Duration (.050”): 227
Exhaust Duration (.050”): 241

Intake Valve Lift*: .491"
Exhaust Valve Lift*: .476"

Lobe Separation: 107

RPM Range:
2000-5800

^Intake lobe is not terrible for what you're doing,
neither is the intake lift (could be better, but for what is probably a Chevy lobe it could be worse),
the big lazy exhaust lobe is where it gives up everything for sound.

My (probably way too deep) thoughts of why this cam is mismatched with itself:

 overlap is normally helpful (and this cam has decent overlap), 
it lets the strong exhaust signal pull fresh intake charge into the cylinders under the right conditions & RPMs.

With that big exhaust lobe (compared to the intake lobe), exhaust velocities are still lazy at the RPM's the much smaller intake lobe is really starting to work, and could use the benefical scavenging you would otherwise get from the overlap if you had good exhaust velocities.

The cam likely does ok up high because when you get to the RPM that the 241 exhaust is finally flowing great, the 227 intake is having trouble keeping up.
^and the scavenging can finally help the small intake keep up.

But in your case, the small intake manifold and carb probably limit you at that point.

Big exhaust lobes work better with big intake lobes,
and mid size intake lobes work better with mid size exhaust lobes.

Going a little bigger on the exhaust can help, but might give up some torque,
but the 14* more exhaust duration is just there because it sounds better.





-------------
71 P-code 4spd Javelin/AMX
some Jeeps and some Fords


Posted By: PHAT69AMX
Date Posted: May/30/2018 at 12:05am
- I'm sorry, this in no way helps with the original question posted, I got distracted, but I'll leave it here...-
I would really like it if someone made and ran a CAM LIKE THIS...
I got one like this ~1990, Stock AMC Cam Re-Ground by Chet Herbert.
It was a very good cam imho...
The "magic", -IF ANY-, is in using stock lobe centers...
Does look "different" when mapped out as a double 360 graph... ( maybe later )

Chet Herbert AMC V8 A4B 7.0k Max ?, late 80's...
'69 AMC Stock Camshaft Reground, Straight Up,
Self Degree Wheel Measured, not guaranteed...

.512" Lift Intake
 280* @ .005
 227* @ .050 (? 58* ramps) ( assumed symetrical )
 112* ATDC = Intake CL

.529" Lift Exhaust
 295* @ .005
 246* @ .050 (? 61* ramps) ( assumed symetrical )
 112* BTDC = Exhaust CL

IN opens  .050 @   2* BTDC - .005 @  31* BTDC
IN closes .050 @  45* ABDC - .005 @  73* ABDC (DynCR)
          .050 @ 227*      - .005 @ 284*

EX opens  .050 @  53* BBDC - .005 @  77* BBDC
EX closes .050 @  13* ATDC - .005 @  39* ATDC
          .050 @ 246*      - .005 @ 296*

Overlap   .050 @ 15*       - .005 @  70*


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: Red Devil
Date Posted: May/30/2018 at 11:38am
There are several dyno tests on Thumpr cams that seem to show they do pretty well compared to traditional grinds. Expect the tight LSA helps. Where they typically suffer is low vacuum and off-idle, so power brakes won't work well.

With a 3000 stall, I'd be curious if the converter is stalling to where it claims? Should make up for any loss in bottom end and the small runner Performer intake should help low-end torque, but drop off quickly on top end. Tune it first, but expect intake, gears and a bigger carb ... or just go with less cam to suit the rest of the combo and keep it a nice cruiser ... or if otherwise happy with the Thumpr, just run it and have fun.


Posted By: WhatISit
Date Posted: May/30/2018 at 12:34pm
I'm definitely thinking it's a timing/carb tuning issue at the moment. Gonna see if I can get it a little more sorted out this weekend. You guys are probably right that the intake/carb is a little restricting, but I'm just gonna have to live with my combo for now. I'll probably just get it running as best I can with what I have and start saving for a 401 build lol

-------------
-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: amcenthusiast
Date Posted: May/31/2018 at 5:33am
By tradition, with stock type diameter tires, 3.54 to one rear gear will give the Javelin much better acceleration from a dead stop.

IMO, you've learned an expensive lesson; compared to all the money spent to hop up the engine, a gear ratio swap is one the best 'bang for the buck' mods a person can make to their car. ~especially by buying the expensive tall tires.

*you can do the 'rope trick' to install new valve seals...


-------------
443 XRV8 Gremlin YouTube video: https://www.youtube.com/watch?reload=9&v=2DmFOKRuzUc
XRV8 Race Parts website: http://amcramblermarlin.1colony.com/


Posted By: WhatISit
Date Posted: May/31/2018 at 8:53am
Well, it could have been a lot worse. I bought the engine rebuilt and mostly assembled for a pretty good price. If I did it myself I would have gone with a different cam for sure.

-------------
-www.FasterNLouder.com-<br />'73 Javelin AMX 401 V8


Posted By: wantajav
Date Posted: May/31/2018 at 6:15pm
Other things to consider here:

1.check engine vacuum
2.are you getting a good spark (coil, bad ground - I ran a second ground on a Javelin once, etc)
3.bent push rod(s)
4.Carb not opening all the way
5.balancer slipped (wrong timing marks)
6.compression check



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