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Stroked 383/438" on the dyno

rmchrgr

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Last Saturday my friend and I took his 438" stroker to the dyno to break it in and see what it would do. We didn't set any records but we did OK for a couple rank amateurs - best run of the day netted 442 hp @ 5,400 rpm and 472.7 lb.ft of torque @ 4,200 rpm. Nothing broke, no major leaks or noises, no wiped cam.

This is a pretty mild combination that was meant to be reliable and provide good torque. It's a 1969 .060" over 383 block with a 440 Source balanced 3.75" stroke rotating assembly and OOTB Stealth heads with approximately 9.3:1 compression. Hughes hydraulic cam 228/232 @ .050" with their standard hydraulic lifters and matching single (with dampener) valve springs. The lift is approx. .525" on the intake side. Comp cams Pro Magnum rockers, stock length 5/16" pushrods. Low-deck Performer RPM intake, standard Mopar electronic distributor. Dyno headers were rusty, swap meet junkers with 1 3/4" tubes. We will eventually be using TTi which are 1 7/8" tubes so hopefully that that won't hurt.

For fuel I believe we just used regular pump gas mixed with a little race gas, not sure what the octane level was but figure under 100. I believe the air was pretty good that day. The dyno place is about a mile from an airport, elevation is 361 ft.
  • temperature: 42 deg f
  • uncorrected barometer: 30.057 Hg
  • humidity: 40 %
  • vapor pressure: 0.268 Hg
  • dew point: 20.626 deg f
  • grains: 15.6
  • air density: 103.692 %
  • density altitude: -1,246.421 ft
We used the dyno shop's 'proven' 750 double pumper carburetor. We tried to run a 750 vacuum secondary carb that we intend to use on the engine but it had all sorts of problems. First thing was a stuck float that was getting hung up on a notch on the rear metering plate causing it to gush fuel out the bowl vent. There was enough fuel coming out that it hydro locked the motor so we had to drain the rear two cylinders. I had mistakenly installed a brass float from a different carb which was too big so we switched to a phenolic one that cleared the notch. And even though we solved that issue when we actually got it to run it was popping and struggling so we abandoned it.

We worked on the ignition timing a little bit but it seemed to like around 15-16 degrees initial best. There is an FBO advance limiter plate in the distributor which I believe is set to 16 degrees so figure it ended up at 32 degrees or so. Advancing the timing made the power drop off, we lost 7-12 hp consecutively advancing it to 18 and 20 degrees initial. At that point the dyno operator mentioned it was getting hot and suggested letting it cool off for a bit before making any more pulls. We waited for about 20 min. and tried one or two more runs at 16 initial but didn't gain or lose anything really so we called it a day.

There was one unsolved question regarding pushrod length. We are using "stock" length 5/16" 383 pushrods but they might actually be a hair too long. We had tried to set preload the night before but I had a feeling there was too much because it seemed like we were already at zero lash with the adjusters backed all the way off. I could rotate the rods between my fingers but the rocker arms were solid. When we got there I mentioned it to the operator and he agreed it was too much. We ended up backing them all off fullly to no ill affect since were able to run it up to 5,800 rpm on a few pulls.

He said we might want to double check for proper length before we put the motor in the car by installing a checking spring and grinding down a stock pushrod until we achieve some lash. When we mocked it up I only had a ball/cup length checker so we kind of rolled the dice using the stock ones and it came back to haunt us a little. Again, not a huge deal and I don't think we left much if any power on the table because of it but it may be a worthwhile exercise at least to increase valvetrain longevity.

Worst thing that occurred was taking it off the dyno the dipstick snapped at the base. It was a royal PITA to get it in the block so it was probably brittle already. When we had it tied down in the truck the tube was up against the strap putting pressure on it. Then the headers were not in the right place so we had to bend it out of the way. Kind of inevitable that it would snap.

That's all just wanted to share the results and post the sheet. No, this thing is not going to set the world on fire but it will be way more power than my friend has ever had under his right foot and should be good for block-long burnouts. I'm sure he is going to be happy with it.

- Greg

IMG_2900.jpg
 
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It looks lean between 3,000 -4,000 RPM.
It might make more power if it's richer perhaps that is why it didn't like more advance as well?
 
Cool Beans - Great Job - Good Feeling

Got just under 500 HP on my 383/432 (.030 over)

Same 440 Source Kit

But running Edelbrock E Street 75 cc heads - 10.5 - 1 Compression
Comp XE 275 HL Camshaft
Was done by 5400 RPMs also - 18 initial 34 Total
Edelbrock AVS2 800 Carb
Dyno headers , don’t remember honestly who what

Anyways running Factory HP Manifolds on the street now so obviously down on HP I would assume

I am pretty damn happy other then all the ignition issues that popped up once I got the motor installed in the car about four summers ago

Looking back now I question on why not the 496 Stroker Kit

But wanted the same reliability on the numbers factory block when I built it
 
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It looks lean between 3,000 -4,000 RPM.
It might make more power if it's richer perhaps that is why it didn't like more advance as well?

I asked the operator if it needed more fuel and he said no. This particular carb was something he's had for a long time and has been extensively modified. He claims it works on all sorts of different combos so I had no reason to doubt it.
 
Cool Beans

Got just under 500 HP on my 383/432 (.030 over)

Same 440 Source Kit

But running Edelbrock E Street 75 cc heads - 10.5 - 1 Compression
Comp XE 275 HL Camshaft
Was done by 5400 RPMs also - 18 initial 34 Total
Edelbrock AVS2 800 Carb
Dyno headers , don’t remember honestly who what

Anyways running Factory HP Manifolds on the street now so obviously down on HP I would assume

I am pretty damn happy other then all the ignition issues that popped up once I got the motor installed in the car about four summers ago

Looking back now I question on why not the 496 Stroker Kit

But wanted the same reliability on the numbers factory block when I built it

Very nice.

We chose not to go with the 496" because we thought he'd never be able to take advantage of the bigger volume in a useful way. Yes cubic inches for the win and especially with a heavy car like he has but this may be the one case where that didn't add up. Ideally you'd want to have a bigger cam with something like that but then it snowballs and you start getting into different territory trying to make it efficient with gearing, converters etc. He's already looking at a 2,800-3,000 converter with highway gears, no need to go much higher. It makes a nice flat torque curve pretty low so we were happy with that. This car will hardly ever see north of 4K rpm anyway, just not enough room in the city or even in the surrounding areas.

There's also pretty severe rod angle with the 496" combo that could accelerate thrust-side wear but that's probably a non-issue on a nice weather driver that only sees few thousand miles a year if that. This car is going to be driven on a regular basis. He lives in NYC so will have to deal with heavy traffic on hot days yada yada. With this guy things need to simple and dead reliable.

71 bee, thanks for the heads up sorry 'bout the typo.
 
I think that it will be very reliable. Makes good power at a low rpm, a key for living long… low stress, good for people and engines. Also with that amount of torque, it’s really a lot for street driving. Also since it is the motivating factor for a car, he will be in great surplus of it.

Thanks for posting that Greg.
 
I asked the operator if it needed more fuel and he said no. This particular carb was something he's had for a long time and has been extensively modified. He claims it works on all sorts of different combos so I had no reason to doubt it.

Unfortunately the data suggests otherwise. Trust the data.

Thanks for posting
 
If anything it looks rich and it's very rich on the low end. (11.5)
You probably only spent a couple seconds in the lean area range so I wouldn't base any decisions here on reading the plugs.
 
Plugs were brand new and used for break in then like 7 successive dyno runs. Last time it was running on the stand we briefly checked to see if it would be ok idling at 850 which it did and we shut it down.

These are the plugs that 440 Source recommends/sells so I would think they’d be in the correct heat range.
 
Nice one RamCharger!

I always wanted to run my motors 'on the dyno' but no luck.
What a thrill to see something you built running 'so well'!

That plug look odd and the carb is 'all over the shop'...
Rich and cold, better than hot and lean though...:luvplace:

Best TQ numbers running 'highway lean'...:screwy:
 
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Plugs are Champion RC12YC.

No offense to anyone here but I don't think the plugs are too cold nor is the mixture too rich. The plugs don't smell like gas at all.

Not saying this is a rule but I know from studying the graphs on my EFI that when you go to WOT things lean out until the motor catches up. I suspect if we had a solid roller cam and single plane intake then the A/F numbers might be closer to "optimal" at a given rpm.

That said, the engine draws the fuel it needs. I'm of the idea that force feeding it more to see a "better" A/F number does not make it run better in all instances. Perhaps it is efficient for what it is? It makes 1hp/cubic inch which is usually the standard bench racing yardstick for measuring this kind of stuff.

I've had a/f meters in my cars for years now. You start chasing these numbers trying to make them perfect or whatever but ultimately it may not be what the motor really wants. It's a hard lesson to learn because a lot of what is out there says you need XYZ a/f ratio to make power. Just have to take it with a grain of salt.

I am confident this engine is going to just fine without much tinkering. If something was grossly out of tune it wouldn't have done what it did. That's not saying a whole lot but everyone knows when something is really wrong you can tell right away because it won't run right. Even the pushrod length question proved to be minor because we managed to run a pretty mild hydraulic cam up to 6,000 rpm on a piece that won't hardly ever be run that high. Could we have done better? Probably. Would we have been there all day and night? Yep.

Frankly I was pretty wiped out when we got home. Between getting things ready late the night before to loading up in the AM, driving 40 minutes, unloading and setting up, using our brains all day (!) then breaking down, loading up to leave, driving home in heavy traffic then unloading again...it was an adventure.

Was the dyno place the best? I don't know. The guy was OK and seemed very knowledgeable. At times he was helpful and other times not but we were told at the beginning that it was our show and he was merely there to facilitate. Maybe his perspective is different than ours and that can be hard to crack. I think we acquitted ourselves OK. We didn't go in claiming it was going to do break the dyno. We asked questions and tried to absorb what we could. We learned a lot for sure.
 
Last Saturday my friend and I took his 438" stroker to the dyno to break it in and see what it would do. We didn't set any records but we did OK for a couple rank amateurs - best run of the day netted 442 hp @ 5,400 rpm and 472.7 lb.ft of torque @ 4,200 rpm. Nothing broke, no major leaks or noises, no wiped cam.

View attachment 1197357

Great story, and that's real life, problems happen and we find solutions.

What I can say is, that's good power, but this engine is running very lean under load and it's likely going to hurt the motor if you were to drive it like this. Looking at the graph, from 3,500 to 5,700 RPM you're anywhere from 13.5 AFR to 15.5 AFR, the dyno operator was incredibly negligent for allowing the pull to continue past 4,000 RPM, let alone running it to 5,700 RPM.

The engine will always be the leanest around peak torque, 12.9-13.2 AFR is fine around that point if everywhere else in the curve is 11.8-12.5 AFR. You don't lose that much power running the engine slightly rich @ WOT, but you lose a TON OF POWER and can cause catastrophic damage running the engine lean under load.

Remember as well, the AFR is an overall average of one or two banks (4 to 8 cylinders), most of these intake manifolds will have a deviation of +1 / -1 AFR depending on the cylinder (some a LOT worse). Doesn't matter if you lose one piston, or all eight, it's going to be a bad day. If you're not going to chase numbers, at least put the engine in a SAFE operating range under load, keep it fat and it'll last a long time.

This 'dyno' carburetor needs air-bleed tuning, among many other things to be right on this engine. If this were my brand-new engine, I would be very upset for so little care to be involved in the dyno / tuning process from this shop. Just me though.
 
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Good story.

The two big win-win takeaways.......
It didn’t eat the cam...... no rear seal leak.
Power seems commensurate with the combo.

Dyno sheet critique.......

Imo, the dyno carb isn’t all that dialed in(at least not for that combo).
Big lean hole in the middle.
Builds like that rarely respond favorably to a/f ratios in the 15’s.
Fuel flow between front/rear isn’t balanced that well.

Up towards the top of the pull the a/f ratio is getting more normal, so it’s doubtful a different carb would have yielded drastically different power.

Checking the uncorrected power from the fuel flow and bsfc numbers....... the uncorrected power was actually higher than the corrected power.
You don’t get air like that very often.
At 5400, 94.5 + 88.5/.404 = 452.9hp uncorrected.
 
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