The DYNO, it WORKS! 383 test mule pulls a load.

[IQ52]

After the SuperFlow 901 setting in the corner for some five years, it's finally up and running. Made a pull on a stock '71 cast crank 2bbl 383 using a '69 4bbl intake and an 850 Mighty Demon carb (yeah, yeah, I know, but it is the only stuff we had laying around). 318 lb-ft and 266 hp.

 

[RustyRatRod]

That's great, Jim. I know yall are excited.

 

[cdr]

that is great MR JIM

 

[Meep-Meep]

I know the feeling of getting a high dollar piece of equipment working for the first time. Congrats! Looking forward to some results.

 

[super-bee_ski]

Yaaaaay!

 

[rsd859]

Nice!

 

[IQ52]

Well the dyno owners are learning what can go wrong with a used dyno. Had trouble getting the dyno to hold a consistant load. Sometimes it would hold the engine to the 2500 starting rpm and other times no. When it did hold the starting load and rpm it would go to 4400 rpm, stall there, and then take off to the upper rpm limit of 5000 rpm we had for the 383. Disassembled the absorber and found the main seal blown out. We got dyno scattered all over the shop until the replacement parts get here.

When we installed the old 1971 383 we have been using for a mule, we used it "as is" from the old '68 Chrysler we found it in. Put the timing light on it and it had only 20 degrees total advance. With the total at 36 degrees, it now has 387 lb-ft and 281 hp. Kinda wondering what readings we'll get when the absorber is working properly.

 

[RustyRatRod]

So I take it that these are rear wheel readings and it's a chassis dyno? I sure wish we were closer. I'd love to come be a fender lizard.

 

[IQ52]

No Rob, this is a SuperFlow 901 engine dyno.

 

[RustyRatRod]

Oh ok. I'm not that familiar with dynos to spot them with part numbers. Thanks.

 

[IQ52]

Well the temperature and humidity sensors are working now so we don't have to calculate (or quess) vapor pressures anymore.

I've always wondered what the difference would be in engine power by only changing the cylinder heads and nothing else. We've a pair of 915 heads flowing:

.100...........76
.200.........153
.300.........214
.400.........253
.500.........280
.550.........285

The 383 test mule on the dyno right now has stock 346 heads on it and they should be flowing around:

.100..........61
.200........130
.300........188
.400........213
.500........227
.550........228

Wonder what would happen if we just swapped the 346 for the 915 and did nothing else? Hafta round up some gaskets!

 

[Meep-Meep]

I can send you some gaskets!! And if you were closer I'd help do the swap. So those 915's look like they have been worked a bit. Normally I just do a tried and proven pocket port and that's it.

 

[IQ52]

We're attempting the head swap tomorrow. Gunna use 85 octane like we've been running for all the tests and see what happens. I have no idea what the cam is, I think its just a stock 2bbl cam.

 

[kdtjb]

Jim, let me know when all is right. I'll bring the heads you done for my old motor and we can see where it's at, Kent. P.S. new motor is in and I'll be in Anaconda next week end, come on up if you get the chance.http://www.lostcreek-raceway.com/Schedule/2013_LCRA_SCHEDULE.pdf

 

[IQ52]

Will do Kent. Oh, and Dennis of Praxair was here at the shop last week and spoke of you..

 

[IQ52]

Got 10 pulls in on the dyno yesterday. Very interesting.

The 383 had been rebuilt in the past. Camshaft with .280 lobe lift intake and exhaust. 346 heads with 87cc chambers and .038 deck height for 8.7:1 compression. The ported 915 heads we put on were 82cc, using a .050 gasket we ended up with.......uh......8.7:1 compression. We used 85 octane and pulled the engine to 5,000 rpm. With the garbage stock rockers we were getting around .400" valve lift.

So NO COMPRESSION INCREASE, airflow increase only gave us this:

346 heads, 69 4bbl cast intake............................283 HP
915 heads, 69 4bbl cast intake............................305 HP........+22 HP

346 heads, Holley Street Dominator intake...........303 HP
915 heads, Holley Street Dominator intake...........329 HP........+26 HP

Unfortunately less than we had hoped for but significant none the less. If we had started with a bigger cam the gains could have been greater as the flows were really starting to take off after .400" lift. Sounds like we need to do another test!

BUT, swapping to the Street Dominator and ported 915 heads picked up 46 HP. That'll wake up a low compression 383. Where is the single plane M1 and the RPM Performer? Gettum off the shelf!

Interesting also, though flow bench tests showed the stock 1969 4bbl intake to limit the flows through the cylinder head to 207 cfm, still the iron manifold made 30-40 lb-ft more than the Street Dominator at 3,000 RPM and 20 lb-ft more at 3,500 RPM. It lost all the advantage buy 4,000 RPM and the Street Dominator made such huge gains the next 1,000 RPM, that the averages for the Street Dominator were +12-14 lb-ft over the 2,000 RPM test range. The stock manifold is great if you are idling to the grocery store for a quart of milk, you just can't beat it for that.

 

[Meep-Meep]

So at 5000 RPM you got 22 and 26 HP respectively? And would it be safe to say that below 5000 RPM the increase is basically nothing? Even the best case of 46 HP @ 5000 RPM may not have produced anything earth shattering from off idle to 3500. At that point saving the ported heads and street dominator for another build would be my recommendation. Now take that stock 383 and put steel shim gaskets and a mild cam WITH the 915's and dominator and see what you get.

To me the results comparing the stock intake to the dominator are very useful because of the RPM at which the extra 30-40 ft-lbs come in. Like you said for a street car it's good, and for most people who spend their driving time on the street, this is good news. Again, I will say leave the 2 BBL engine alone.

Using my own 440 as another data point I'll add that running the factory iron intake wasn't hurting me too much, or not enough to care. But I do have a non stock cam - very mild one - but not stock. Taking all the info above into account my position remains that changing the cam only is the greatest bang for the buck upgrade as long as the change is within reason. And adding head work, compression and exhaust just makes it that much better.

 

[IQ52]

I guess i'm not advocating a darn thing, but I'm a racer kinda guy, or I wouldn't be testing with my old 750 cfm Murry Jensen NASCAR carburetor. I'm listing the dyno results. Here is a list of torque increases from 3,000 RPM to 5,000 RPM by only changing to the ported head.

3,000............+2
3,100............+10
3,200............+5
3,300............+6
3,400............-2
3,500............+4
3,600............+12
3,700............+10
3,800............+11
3,900............+12
4,000............+8
4,100............+10
4,200............+9
4,300............+12
4,500............+17
4,600............+20
4,700............+31
4,800............+24
4,900............+23
5,000............+22

 

[Meep-Meep]

Before I continue I want to say I appreciate you doing the work and posting the results.

I'm seeing your results and tying everything together and learning stuff in the process. Those are small gains vs. the amount of work one must do to get there.

Putting the engine back to the 346 heads (same 8.7:1 CR) but only changing the cam may produce a better result, and if you are willing to do that I will help with the expense. Do you have any mild cams lying around?

 

[IQ52]

I wish I could. The 383 is off and the 451 stroker with the 906 heads is on right now.