My 383's performance

[Mr Lee]

Ever since I got my car on the road two years ago, my car has felt underpowered to me.  My Challenger is the only muscle car I've ever owned so I don't really have much to compare it to but...  It's a big block.  I feel like I should be able to smoke the tires without having to drop the clutch, but I can't.  It runs fine, it just feels like it lacks punch.  Maybe I'm crazy, I don't know...  but I wanted to ask others who have a mostly stock 383.. can you smoke the tires without much effort??  Is something wrong with my car?



The 383 Magnum is supposed to put out 335 hp to the crank.
On the chassis dyno, mine put out 232 hp at 4,800 rpm to the wheels.  I let off the gas at 4,800 rpm because my tires are not Z rated and feared blowing a tire but I think this is about where it hits peak power anyway?  Would I have gotten 30+ more hp if I revved it to 5,500 rpm?  I really doubt it but I don't know ?  It felt like it was leveling off anyway.   
I have a 4 speed trans and 3.23 posi rear with 255/60/15 tires.
Changed jetting several times during the dyno run on the Holley 650 double pumper carb. 
Jetted 66 in front, 74 in rear
Timing - ran best at 40 degrees after trying advancing and retarding.
Electronic Ignition with Flamethrower coil
Ballast resistor bypassed
MSD plug wires
Fuel pressure - 7psi

My engine was fully rebuilt by a reputable machine shop and the builder used to be a Chrysler dealer mechanic and racer back in the 70's. 
Bored .030 over and it has a Lunati cam but unfortunately I did not get a cam card and at the time, did not even know to ask for one.  So I don't know the cam specs but when asking him to choose the cam I told him I was more interested in low end vs top end as I did not plan on racing it.  I just wanted a good torquey street engine.

I've done lots of tests and tuning to try and diagnose my engine over the past two years.  One thing I recently came back to was the fact that, with a vacuum gauge hooked to manifold, the needle is all shakey.  It is not steady at all but averages around 13".  I've read that the jumpy needle could indicate a valve train problem, so I did some tests...

First I did a power balance test where you measure your rpm drop starting with a 1,000 rpm idle (with a digital timing light tachometer).  Then ground out one spark plug at a time to see how much the rpm drops (which tells you how much that cylinder is contributing). 

Results - RPM drop per cylinder when spark plug grounded out at the dist cap:
1. 60        2. 60
3. 50        4. 30
5. 50        6. 50
7. 60        8. 30
So, cylinders 4 and 8 seem to be contributing the least here because they had the least rpm drop when grounded.  You would think these numbers might corollate with the numbers of the next test, but they don't...

Then I bought a compression leak-down tester and pumped 100psi into each cylinder and my readings were all between 90-94psi.  So I am losing 6-10% on all cylinders which is supposed to be normal / acceptable. 
psi reading per cylinder from 100psi pumped into each cylinder:
1. 92      2. 92
3. 93      4. 94
5. 91      6. 90
7. 93      8. 90

So I'm not sure what to do next and was wondering if anyone had any suggestions, especially on why my vacuum gauge needle is all jumpy.  I'm kind of stumped.  I don't need 600 hp. I just want to make sure I'm getting everything I should out of my rebuilt engine before I go and install an aftermarket intake and maybe headers.  I've already put a bigger carb on (800 cfm).   Don't know.  I feel like I'm missing about 50 hp. 
Thanks in advance if anyone has a suggestion.

[Mr Cuda]

The first thing I would check is cranking  compression.   It was common for people to rebuild engines with the wrong pistons.
You know,  "those are .030 over but have a different compression height,  oh well."
If you aren't getting a minimum of 145 psi, a performance cam will actually bleed off more vacuum,  and  have no power.
Typically,  wheel horse is 25% less than crank, some say as little as 15%, .

[DeathProofCuda]

 

I'll be interested to see what comes out of this thread.  Seem to be a lot of similarities in the long-term experiences you and I have had with our cars.  I've been going through some similar testing of carb, distributor, and tune combinations trying to improve the performance of my recently rebuilt 383.  Are you using a wideband meter at all?  Have you run your car at the track yet?

I took my car to several test and tune events at the local track last year and it ran consistent with stock 383 times from drag tests back in the day (best time was 14.974/best trap speed was 94.88).  My driving is crap with a four speed so I just focus on trap speed as an indicator of power.  I've never weighed my car, but assuming a weight of about 3,600 lbs that puts me at right about 240 RWHP.  Frankly, I was a bit disappointed to run stock 383 1/4 mile times since my engine has been zero decked, balanced, has 906 heads with a little bit of head work, and a slightly hotter cam.  I'm still running a stock 383 HP intake and running exhaust manifolds.  I was hoping for trap speeds up around 99 to 100 mph.  But all of this testing was done with a Holley 1850 600 cfm VS carb, so I'm pretty sure that I was carb limited at top end.  I've since swapped over to a 650 DP that I'm still trying to tune and I haven't tested it at the track since.  But the 650 DP definitely provides better burn out performance.

Once I figure out where the 650 has gotten me, I'll probably swap intakes for an old Edelbrock DP4B that I have sitting on the shelf.

Oh, BTW, on Nick's garage he recently did dyno testing of a mostly stock 383 and he got 383 hp out of it running with exhaust manifolds, but had to go all the way to 5,700 rpm to hit max HP.

https://www.youtube.com/watch?v=5LeSneOW2WQ

I'd recommend some track time to get a better handle on where you are and what changes make more speed.

[DeathProofCuda]

I'm running 3.91 gears in the rear, and a factory points distributor.  Have a Mopar electronic ignition system to switch over to after I can baseline the new carb and then manifold at the track.

What is your initial timing?

[Mr Lee]

The first thing I would check is cranking  compression.   It was common for people to rebuild engines with the wrong pistons.
You know,  "those are .030 over but have a different compression height,  oh well."
If you aren't getting a minimum of 145 psi, a performance cam will actually bleed off more vacuum,  and  have no power.
Typically,  wheel horse is 25% less than crank, some say as little as 15%, .

Interesting.

I seem to have heard from several sources that there are not a lot of piston choices for the 383 which I can't understand since they made so many of these motors.  I have flat top pistons but don't know anything more than that. 

Cranking compression test - I need to do over again because the first time I did it with the engine cold, but my numbers were between 130-145.  Don't know how much that will increase doing it with the engine warm but, yeah I'd say my compression ratio is probably in the low 9's if I had to guess.  So if that's the case, I guess no matter what I do, I don't have much to work with if I don't have higher compression.   

[Mr Lee]

I'll be interested to see what comes out of this thread.  Seem to be a lot of similarities in the long-term experiences you and I have had with our cars.  I've been going through some similar testing of carb, distributor, and tune combinations trying to improve the performance of my recently rebuilt 383.  Are you using a wideband meter at all?  Have you run your car at the track yet?

I took my car to several test and tune events at the local track last year and it ran consistent with stock 383 times from drag tests back in the day (best time was 14.974/best trap speed was 94.88).  My driving is crap with a four speed so I just focus on trap speed as an indicator of power.  I've never weighed my car, but assuming a weight of about 3,600 lbs that puts me at right about 240 RWHP.  Frankly, I was a bit disappointed to run stock 383 1/4 mile times since my engine has been zero decked, balanced, has 906 heads with a little bit of head work, and a slightly hotter cam.  I'm still running a stock 383 HP intake and running exhaust manifolds.  I was hoping for trap speeds up around 99 to 100 mph.  But all of this testing was done with a Holley 1850 600 cfm VS carb, so I'm pretty sure that I was carb limited at top end.  I've since swapped over to a 650 DP that I'm still trying to tune and I haven't tested it at the track since.  But the 650 DP definitely provides better burn out performance.

Once I figure out where the 650 has gotten me, I'll probably swap intakes for an old Edelbrock DP4B that I have sitting on the shelf.

Oh, BTW, on Nick's garage he recently did dyno testing of a mostly stock 383 and he got 383 hp out of it running with exhaust manifolds, but had to go all the way to 5,700 rpm to hit max HP.

https://www.youtube.com/watch?v=5LeSneOW2WQ

I'd recommend some track time to get a better handle on where you are and what changes make more speed.

Interesting on the Nick's garage thing.  I will check it out.  Wonder what power it was making at 4,800 rpm.

Yes, glad you bumped up the carb size.  I would probably bump it up again to a 750. 

Initial timing is at 18 if I remember correctly, maybe 20. 

I did install a wideband sensor since my Dyno run and have the carb dialed in pretty good and the plugs are clean and light grey.  I have not run the car down the track because the track that is 20 min away closed down for good.  The next closest one is like an hour and a half away.  But maybe this year.   

[Racer57]

I have a stock hp383 with Holley 750 dual feed double pump and I can break tires loose when I floor it from an idle. But, I have a 3:55 rear.

[B5fourspeed]

My first 70 383 Cuda would run 14.2-14.4 at the Fremont drag strip in the early 70's.That was on the polyglas tires.I would run it to 5800-6000 before shifting.I was running with 3.55 gears.

[DeathProofCuda]

@B5fourspeed Was that bone stock or were you running headers and better intake/carb?

[DeathProofCuda]

The first thing I would check is cranking  compression.   It was common for people to rebuild engines with the wrong pistons.
You know,  "those are .030 over but have a different compression height,  oh well."
If you aren't getting a minimum of 145 psi, a performance cam will actually bleed off more vacuum,  and  have no power.
Typically,  wheel horse is 25% less than crank, some say as little as 15%, .

Yeah piston choice for 383s pretty much sucks.  I seem to recall that the KB flat tops would leave your piston pretty far down in the hole.  I went with Diamond pistons, at about twice the price, to get something with a decent compression height.  You also have to be careful about head gasket selection.  With the short stroke of a 383 you loose a bunch of compression if you go with a composite gasket.

[B5fourspeed]

Bone stock.No power steering or brakes.

[DeathProofCuda]

Bone stock.No power steering or brakes.

14.2 seems pretty impressive for a stock 383 car.  I've tried to dig up as many old magazine road tests that I can find from back then and it seems that most 383 cars were running in the mid 14 to 15 range.  I've also scanned through about 20 years of Pure Stock racing results and have yet to find a very quick stock 383 car.  IIRC, the faster ones were earlier A body Barracudas.

[Nepagarage]

Really no experience with a 383 specifically, but am I the only one who thinks 13" of vacuum seems pretty low? Even with a cam in it. Especially since you said it was cammed more for low end/mid range torque. I've seen 15" or more out of strong well sealed V8's that had what most would consider "lumpy" cams. 13" to me would be a race motor just about but most of my V8 experience is with Windsor Fords (302" up through 408"). The other thing is how shaky you said it is. Where are you measuring vacuum from?

[MoparLeo]

  Biggest seat of the pants improvement that can be done on any car is with higher numeric (lower actual ratio) gears. I didn't understand the Z-rating for limiting your engine rpm. Even an S rated tire is rated for 112 mph.
The biggest restriction on making horsepower is the intake and cylinder heads.
An engine is just an air pump and you are trying to move as much air as possible.
The carb controls the amount of air/fuel (in cfm's)you can get into the intake manifold which controls the flow/velocity of the a/f mixture to the intake valve.
The camshaft controls how far open and how long the valves stay open to flow air into and then out of the combustion chamber.
The exhaust manifold(or header) is what draws the spent gasses out.
The more efficiently you can do this cycle, the more power you will make.
The transmission and differential ultimately put the power to the ground. The rear gear ratio and tire diameter will determine how much leverage you are supplying to the tire that is trying to accelerate the car.
Burning rubber just means that you have lost traction.
If you really want to impress, instead of your tires slipping try to make them hook up. Traction is what wins races, burning rubber is what loses them.
Ultimate hook up is a wheelie !
Seems like you spent a long time on a dyno with little to show for it.
A good tuner on a dyno can get your set up zeroed in as far as it will get in a short time.
You need to get the proper carb, intake, cam, head work and headers to to it right.
Not knowing much about the build of your engine like cam specs or  C/R makes it a lot of guess work.F9ind a good tuner and someone who knows a good combo for what you want to do. Gears first for most bang for the buck.[/font]

[cuda hunter]

383's are 3 legged dogs.  I'm curious what you do to remedy your issues.   


Hooking up is the ultimate.  But sometimes, it's nice to throw a bunch of smoke and rubber around at the crowd.  Makes for a fun time.   Sucks when you can't even get your big block to smoke some rubber when you want it to .