With any stock head and not just mopars, air flow and cylinder filling is less than optimal. That is why you want to squeeze what you do have as much as possible.
Disappointing dyno results
- Thread starter jawbone
- Start date
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Saw your post on compression. What did I miss in my calc?
Your right. I am very frustrated. So much so I would rather start over on a different engine.
I think my dyno guy is OK but like said earlier, he should have installed cam. That is my fault for at the time did not know one hade to degree a cam. Not that it's very difficult but was involved. Likewise to cc combustion chamber. I enjoy learning new things.
I do want to run my AVS. Based on numbers, I see why he want to run smaller carb but think he is going do the wrong path.
A few degrees of cam timing will not give you that much deviation from a stock 340... There is either something totally broken or you need to try a different place to dyno it.
Do you want to buy a cam???? At this point, to buy a ne cam is cheap for what I have in this engine.
That cam should only maybe shift the stock 340 curve down in the RPM band just a little bit.. likely on the street you would not even notice it if you don't wind it out much.
No, I'm stalled on my 340 build lol with mojo lacking.
What I was trying to convey is that if it cant be "fixed" by tweaking/tuning and it indeed needs a cam change, you wont be happy going thru all the effort/energy to install an underpowered 340.
I know, easy for me to say and spend your $$.
Good luck.
What I was trying to convey is that if it cant be "fixed" by tweaking/tuning and it indeed needs a cam change, you wont be happy going thru all the effort/energy to install an underpowered 340.
I know, easy for me to say and spend your $$.
Good luck.
He should have jetted and re rodded your avs.
A smaller carb is just going to hurt more. Avs has 554 cfm and on a dual plane each cylinder only sees 277 cfm.
Your cam definitely needs to be degreed in with a degree wheel. That is your first step.
Second step is to check distributor advance curve and set timing.
Third step is to tune your avs and adjust the secondary air door. If it opens too slow and does not open all the way you will never get all your horsepower.
A smaller carb is just going to hurt more. Avs has 554 cfm and on a dual plane each cylinder only sees 277 cfm.
Your cam definitely needs to be degreed in with a degree wheel. That is your first step.
Second step is to check distributor advance curve and set timing.
Third step is to tune your avs and adjust the secondary air door. If it opens too slow and does not open all the way you will never get all your horsepower.
Hi Jim. You got me thinking. Understand people intentionally vary cam timing to suit their needs. Am I understanding that correctly. If so and like you said the curve would change but never look like mine meaning something is totally wrong.
I can't live with myself knowing the curve looks tike it does.
Please someone with real world experience jump in here but if I move the timing +/- 6 degrees it will NOT devastate the curve like that in the simulation model. Your curve is totally crazy. All it really does is shift the peak around, it does not make it collapse like yours does.
I agree. If anything, the stock AVS is too small, not too large. Even for a stock 340.
Back in the day, I ran a 780 Holley and an aluminum intake on an otherwise stock low compression 72 340. It ran very well.
Everyone is hung up on the cam or Air/Fuel.... i would be dropping a different dist into it... I know the timing was checked but it almost seems like it's pulling a ton out for some reason.. which would leave it rich and the weird curve and all that. i'm rarely right though..
tell us about your ignition and distributor setup......
Beat me to it by one minute! Something is wrong... everything about the mechanical build seems like it should be close to a stock 340.....
yeah... is it me or is this thread have a bad vibe? not the OP/topic just a lot of arguing and not much actual help other than theorizing... just my .02.. i'm having a meh day though
Jawbone, i don't wanna read back again but don't think it was asked.. does your dyno guy run any type of MSD box or any type of electronic controls on his dyno? What dist setup did you use... this all looks like pulled timing..
that cam isn't bad enough to kill a motor that hard... and the carb would have to be a dominator set on kill to be that bad.
that cam isn't bad enough to kill a motor that hard... and the carb would have to be a dominator set on kill to be that bad.
yeah... is it me or is this thread have a bad vibe? not the OP/topic just a lot of arguing and not much actual help other than theorizing... just my .02.. i'm having a meh day though
Yea and what do I know... all I have been doing is blocking for the last 3 months, I have filler dust brain....
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Yea and what do I know... all I have been doing is blocking for the last 3 months....
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Jesus man.. **** that.. i would rather dive headfirst into transmissions and axles than do body work... hate it sooooo much
That thing looks amazing though
Oooh, that trucks gonna be a beaut!Yea and what do I know... all I have been doing is blocking for the last 3 months....
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junkyardhero
Well-Known Member
unless i missed it, you have a stock AVS no? those are rated at like 630cfm
the only 4 barrels smaller than that would be a holley 450 or 390
remember 340's came factory with 800cfm TQ's
it's not the carb. not with those numbers.
Funny you should ask. Just got off the phone with gear head friend from work. He is concerned about timing as well. The engine is making use of Prestolite dual point that Ray at Halifaxhops rebuilt for me. Do not know how much advance engine guy has dialed in at the moment but first on my list to ask when I see him again.
Hops knows his ****, but ignition timing would explain every issue you are having..... could be something there...
Can you have a timing light on the engine the next time you run it on the dyno and write down what the advance is for different RPMs?
Prestolite dual point rebuilt and setup by Halifaxhops.
What did you set the initial timing at?
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