No Bottom End
- Thread starter Mopar-Charger
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JoeSbee
Active Member
Do you still have your old carb? Is the new 750 dp manual secondaries?
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I ask because back when ...... I listen too what I was told with a build(top end). Not knowing I put on a 650 DP DF Manual sec. Which was too much fuel with stock converter off the line.If you still have your old carb bolt it up and see what you get. Won't cost you anything, maybe a gasket.
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I ask because back when ...... I listen too what I was told with a build(top end). Not knowing I put on a 650 DP DF Manual sec. Which was too much fuel with stock converter off the line.If you still have your old carb bolt it up and see what you get. Won't cost you anything, maybe a gasket.
Mopar-Charger
Well-Known Member
I have a stiff spring that kicks in when the secondaries open. With the Vacuum secondary carbs, secondaries wouldn't open any bit until over 4k (at least on my car, not the best vacuum). I won't necessarily fully jump on the gas completely maybe just open the primaries off the line (you can feel in the pedal when you hit the secondaries. I thought about it, but I got the same bottom end response with the vacuum secondaries vs Mechanical. Only difference I felt was the topend was 3x that of the vacuum secondaries.
I'm still aiming towards either ignition or torque converter. I just bit the bullet and bought a complete MSD set.
Double Pumpers are all manual secondary's, that's why they need 2 accelerator pumps.
JoeSbee
Active Member
The MSD won't hurt, I wonder about the cam . Might not be what you want for your app. I don't like the low vacuum ,Have you put a vacuum guage on it ? Whats the pull? I would start there. You can throw alot of money at it
Mopar-Charger
Well-Known Member
I'll have to check again, it was pulling like 7 but I found a leak later. I'll check it again when I get home tonight.
Mopar-Charger
Well-Known Member
In neutral I idle round 750 RPMS, in gear I do about 550. Give or take 50 RPMS on both.
440roadrunner
Well-Known Member
Assuming the cam was ADVANCED and you put it back to zero, that action would normally KILL bottom end.
Mopar-Charger
Well-Known Member
So what would the difference be from ust advancing the dist 4 degrees more? I'm not exactly sure how cam degreeing works? I had stock heads with a performer intake with the cam advanced at 4. The reason why I put it back to 0 was because the timing was never constant, but that was because the timing chain was stretched.
When changing the degree you only have to take off the pulleys, water pump, and timing cover?
When changing the degree you only have to take off the pulleys, water pump, and timing cover?
Hemirunner
Well-Known Member
You changed the valve events (particularly the intake valve closing) which has a huge effect on torque and you moved the usable power up into a higher rpm range. It may well be an animal with all your changes but unless the converter and gear are matched to the rest of the package it will run poorly. All parts of a combination (including the driveline and chassis) have to be matched.
Mopar-Charger
Well-Known Member
So you're saying 0 Degree advanced is (3000-7000RPMS)
While 4 degree advanced would be (2000-6000) - Per Se
I have a 3.55 posi rearend and a stiff chassis (not drag or track quality)
While 4 degree advanced would be (2000-6000) - Per Se
I have a 3.55 posi rearend and a stiff chassis (not drag or track quality)
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Yup, advancing the cam usually improves bottom end. Use a degree wheel when doing this that way you know exactly where it's set. Also, what is your cranking compression? I'm betting it's less than 140 psi.....
Mopar-Charger
Well-Known Member
I'll buy a gauge and check. Any specific ones you recommend?
Also, I'm sure how to exactly use a degree wheel? Will a comp cam degree wheel come with directions?
Also, I'm sure how to exactly use a degree wheel? Will a comp cam degree wheel come with directions?
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I like gauges that are NOT made in China
There's a lot of info on the net about how to use a degree wheel. Many folks will say you don't really need one.....and so long as the cam is ground like it's supposed to be, and the sprocket key ways are where they are supposed to be and the alignment pin on the cam is where it's supposed to be....you don't really need to use a degree wheel but after 30+ years as a machinist, I've learned that nothing is perfect and when you have as many machine operations involved in producing a cam and it's associated parts, the margin for error can be quite high. I know many who have engines that didn't run well after assembly and they chased their tails trying to find out why by changing things like converters, gearing and a number of other fairly expensive parts. I always used a degree wheel on a new build no matter if it's stock.
niteshift70
Well-Known Member
If your cranking cylinder pressure is low, the cam may be to radical for your application. The Whiplash series cams from hughes are designed for lower compression (close to or at stock.) They are fairly radical, but they have minimal overlap built it to maintain cylinder pressure. The only thing is they require matching springs from hughes that are made to handle the radical ramp profiles and lift.
niteshift70
Well-Known Member
Crank keyways, timing gear keyways and alignment dots, and cam bolt holes are not always perfect due to manufacturing tolerences. Degreeing the cam, like he said, will help detect those problems so you cam compensate for any issues you find. Plus, you can take the opportunity to double check the position of the timing mark on the balancer in relation to the tab. If it's off, you can paint over the old one and mark the true zero in relation to the tab.
440roadrunner
Well-Known Member
Just google "how to degree a camshaft" There's videos and instructions "all over" Comp cams, etc
https://www.google.com/search?num=2....0....0...1c.1.64.hp..1.24.1818.0.ALU9mSKIsK8
So how I read this is. You don't really know which cam, converter, head flow, or compression ratio. How do you know the compression is 8.5-1? Did you CC the heads and measure deck clearance? I would bet not if you don't understand degreeing a cam and don't own a compression gauge. Lots to learn here. Go slowly. You need to get good data for diagnosis or the results are worthless. The best you can do now is compression test it. My bet is 125 psi or less. Advancing the cam may help. But if you didn't degree it you have no idea if it is advanced, retarded or straight up. There's a great deal to learn from the results of this build. The bottom line is a big cam, low compression ratio, big carb, tight converter, high rear axle ratio won't be very quick. None of it matches up well. It can be band aided and get better, but not great. Like I said before. A TQ carb, more aggressive advance curve are probably the two easiest low cost steps.
Doug
Doug
Mopar-Charger
Well-Known Member
I ran a pretty quick 1/4 with this set up. If I can remember it was a 13.4 @102 MPH. But that was like the day after I put it all together running out the headers.
This might be why I didn't have a bottom end. This wire is from #7 plug looked brand new with some gas residue.
I will probably still look at degree the cam. I've looked into buying a degree wheel and the tools necessary to do it. I do intend on doing it.
Here's a video of the idle a week after the rebuild. IF you guys have an ear for telling the cam.
https://www.youtube.com/watch?v=oz8QWKUhuJE
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