Author Topic: vortec headed 383 has no power  (Read 20477 times)

Offline 305chevy c-10

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vortec headed 383 has no power
« on: May 13, 2014, 08:30:35 PM »
got my motor running but it has no real power .it picks up speed fast but  this thing wont even break tires loose .vortec heads ,373 gears ,th350 trans , roller cam,1.5 roller rockers,air gap intake ,1" spacer and 750 holley carb .i bought a trans that supposed to have 25-2800 stal in it .the only thing i can come up with for why it make no power is that the trans may have a stock coverter in stead 25-2800.i thought with a stall it takes a while for truck to move once it put in gear and rpm reaches stall point .my truck does not hesitate when its put in gear its ready to move .my cam has a range of 24-5600 rpm .would a stock stall cause me to not have no power until rpm reaches above recomended stall piont .CAM SPECS BELOW
HOWARDS 180305-08
 
NA
 
282
 
282
 
229
 
229
 
.480
 
.480
 
108
 
104
 
Hyd.
 
Hyd.
 
1
 



2400-5600
 
Choppy idle, strong low & mid range performance. 2500+ stall
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Offline LeftysRodandCustom

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Re: vortec headed 383 has no power
« Reply #1 on: May 13, 2014, 08:48:45 PM »
This thing should be a screamer with or without the stall converter. All of your combination seems to be well chosen for the total package. No crazy cam stuff or non streetable parts. A stall converter basically just has looser tolerances on the vanes inside it so that it locks up at a higher rpm than a stock one with tighter tolerances. They will still grab and drive somewhat easily on the low end, especially a mild one like yours as opposed to a wild 3500rpm+ one. The converter is essentially just a cetrufugal pump. If you brake stand it, and i dont mean sit and burn the tires, but just allow the stall to slip up to its rated lock up and then let it fly it should show you what you want to know. Timing and carb tuning should be looked at closely also. Thats a pretty sizeable holley and maybe the lack of vacuum on the bottom is causing it to hesitate.

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #2 on: May 13, 2014, 10:05:56 PM »
Well i was expecting a screamer when i first drove ,but nothing . :'(
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Offline rich weyand

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Re: vortec headed 383 has no power
« Reply #3 on: May 14, 2014, 12:43:53 AM »
would a stock stall cause me to not have no power until rpm reaches above recomended stall piont

No, the cam spec says you will have no power until rpm reaches the recommended stall converter rpm.  That's what "recommended stall converter rpm" means.  That "2500+" stall speed torque converter recommendation says it all.

I had the same problem with the GM 350/290 hp engine.  It was a two-lane terror.  The 50-90 times were incredible.  Getting off the line?  Not so much.  All the hot rod guys will tell you, horsepower gets the headlines, but torque is what you drive.  And those cam specs you have are close to the cam specs in the GM 350/290 engine.  Yes, vortec heads help a lot, but still.

As one example.  The 1970 Hemi Cuda was a very fast car.  426 hemi, 425 horsepower.  Mopar guys drool when you talk about that engine.  The 1970 Chevelle LS-6 was a very fast car, rated by GM at 450 horsepower.  They both completed the quarter-mile in the low 13s, in darned near a dead tie.  In contrast, the 1970 Buick GS 455 Stage 1 was only 360 hp, but it had 510 lbft of torque at a low 2500 rpm.  It was a quarter-second slower than the Chevelle and the Hemi Cuda in the quarter-mile, but it would positively smoke both of them in the 1/8th mile.  Gonna race in circles?  Hard to beat that hemi.  Drive on the street?  I'll take the Buick.

What I did was swap out the cam in my 350/290 (yeah, the cam I paid $500 extra for over the 350/260 hp base crate engine) and put in a torquer cam.  I gave up a little horsepower, and there's no "choppy idle", but I am getting over 420 lbft of torque at 2500 rpm.  So my cam is in the middle of its torque curve at the same rpm that your cam specs say is where your torque curve starts.  When you think about it, it makes sense.  Unless you are a circle-track racer, you are almost always in the 1500-3500 rpm range in normal driving; that is, in the lower half of the working rpm range.  And "choppy idle" means the engine doesn't like to run at low rpms.

I just ran a dyno simulation on your setup and ran through some choices on a cam selector.  Put a Comp Cams 12-408-8 cam in there.  350 hp at 4500 rpm is cool, but 494 lbft of torque at 2500 rpm will make it a serious launch vehicle.  Note: Recommended rpm range: 1000-5000 rpm.

The 12-408-8 has a .480/,487 lift; if you can't go that high you could use the 12-409-8 cam at .458/.458 lift.  You come down to 345 hp at 4000 rpm, but you keep 491 lbft of torque at 2500 rpm. Same recommended rpm range.

Even with the cam you have, however, you should be getting a bit over 400 lbft of torque (probably at around 3500 rpm) and maybe 380 hp or so.  It won't be as quick as a more torque-oriented cam with a lower peak-torque rpm, but it shouldn't be a slug.  So here are some other things to think about.

The air-gap manifold will keep the carb from overheating, but it will also keep it from getting to operating temperature very quickly without warm-air induction.  The original air cleaner had warm-air induction off the manifold until the carb was up to temp.  I have the air-gap manifold, and in cold weather the engine always ran like it couldn't warm up.  I put the stock warm-air induction back on, with a cold-air induction tube to the radiator bulkhead, and that helped a lot -- the carb got to temp quicker, and then it stayed at optimum temp as the thermostatic air cleaner dialed in the induction temperature.  Then I put an electric fan on it that is temp-controlled to maintain engine temps at operating temp and that helped as well.

Another issue to look at is ignition timing.  You should be able to run 16*-18* of base timing on a SBC, with 20* of vacuum advance.  Just keep advancing the timing 2 degrees at a time until you start to get pinging under low rpm heavy load, then back it off a couple degrees.

Plugs and wires and coil matter a lot too.  What plugs are you running?  The AC Delco R45TS is probably the right plug, or even better the Autolite 26.  I am running Taylor stainless steel conductor wires instead of the crappy resistor wires, and an Accel high-voltage (tan color) distributor cap and rotor with the Accel 48000 volt coil.  I can give you part numbers if you want.

Finally, where do you have your vacuum advance connected?  It should be to manifold vacuum (the lower port, under the throttle plate), not "ported" vacuum (the higher port, above the throttle plate).  Connecting the vacuum advance to ported vacuum will give you off-idle hesitation and boggy starts.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #4 on: May 14, 2014, 06:56:30 PM »
my vac advance in connected to top timed spark port.My brake booster goes to port on intake.my trans vac goes to full manifold vac on lower front of carb .pvc goes to port on back of carb .
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Offline rich weyand

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Re: vortec headed 383 has no power
« Reply #5 on: May 15, 2014, 12:31:05 AM »
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline ohio hab

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Re: vortec headed 383 has no power
« Reply #6 on: May 15, 2014, 06:02:12 PM »
Check timing, initial and total. Make sure mechanical advance in distributer is working all the way. I agree with previous post's, this should break the tires loose with ease.

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #7 on: May 15, 2014, 08:49:17 PM »
Motor was built a year ago . Guy dont remember where cam was set .(degrees).another guy installed the motor and set timing without knowing how cam was degreed. I have 9 keyway dbl roller timing set (+-8 degrees) .lsa is 108 i think Howard's cam  told me to set it on 104 .i really feeling this is why i have no power .i will get to the bottom of this .
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Offline LeftysRodandCustom

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Re: vortec headed 383 has no power
« Reply #8 on: May 16, 2014, 10:23:42 PM »
With that said I'd pull the cover and figure out where your cam is degree'd in at. Unless this thing lives on the strip I dont see any reason to move it from standard, and until you know what its at for sure then you cant time it correctly.

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #9 on: May 17, 2014, 10:41:29 AM »
Can this be done with motor in truck or will it have to come out
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Offline LeftysRodandCustom

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Re: vortec headed 383 has no power
« Reply #10 on: May 17, 2014, 08:37:56 PM »
Yeah it can and thats a matter of preference. You'll need to pull the water pump, balancer and drop the oil pan to get the timing cover off. Might be alot easier out of the truck but it doesnt have to happen that way. With the cover off you can just check the keyways and timing marks to see where you are and go from there.

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #11 on: May 17, 2014, 09:21:12 PM »
Great im getting some one to look at at it to give me an estimate on what he will charge to do this .hope its not to expensive.just ready to feel 450 ft lb. of torqe .atleast thats where i hope its at with my setup.$300-400 should handle this fix i hope .
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Offline HAULIN IT

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Re: vortec headed 383 has no power
« Reply #12 on: May 18, 2014, 08:36:32 AM »
That should be a very nice working engine...something is wrong with the basics. Cam timing, ignition timing, engine sealing. Does the engine operate "normal"...as in, idles fine (not all rough & the engine shaking around), goes through the RPM range smoothly, ect.?

The ideal converter would optimize the components, however there should be plenty of torque there to put a smile on your face with even a stock converter...It's 383 inches, good flowing heads & a nice sized cam for the combo & 3.73 gears...it should make a very nice running/driving truck.

Before you take anything apart, I would suggest you do a compression test...it will/could help you down the right path. A leakdown test or simply an air tank plumbed into the sparkplug hole will tell you if you have a valve or ring sealing problem. A dial-back timing light so you can check timing at 2000, 3000, ect. will be next. Keep us posted, Lorne

Offline 305chevy c-10

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Re: vortec headed 383 has no power
« Reply #13 on: May 18, 2014, 03:42:32 PM »
Yes operates fine just no power .dont know how true it is but i always heard as young boy that when water drips from tailpipe that s  a sign of good compression .i know people have different labor rates but whats a reasonable price to degree a cam ?if thats the problem.i read that being +/-1 degree would not make alot of diff except maybe track time, but  performance wise no .for instance mine should be 104 ICL which is +4 advanced .a 103or105 would be ok .anything beyond that performance will suffer greatly.
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Offline LeftysRodandCustom

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Re: vortec headed 383 has no power
« Reply #14 on: May 19, 2014, 02:01:43 AM »
My setup is similar but smaller in inches,358, with dart SHP heads a smaller 600 holley with vac secondaries, and an M21 trans backed up by a 4.11 posi. When I step into this thing with no assistance from the clutch or brakes she flat out boils the tires through 1st and 2nd and then slips em for a good 20ft before they grab in 3rd. There is no reason why that 383 shouldnt do it just as well on any converter really. As for the cam degree, I dont know your level of comfort so dont let this be an insult at all, but if you're comfortable tearing it down that far it really isnt difficult to do for a street engine. You just line up the marks on the crank gear with the corresponding marks on the cam gear and set it for 0 not + or - anything. Guys correct me if I'm wrong on this next part, but the distributor makes one revolution per trip through the firing order. So when setting the timing there as you will have to do either way, you can get way beyond a few degrees of adjustment out of it. If you arent comfortable, the going rate in any shop in my area is every bit of $40/hr and theres several hours involved here, especially if they're going by what the book estimates it to be and not actual time.