383 rebuild - kinda whimpy on the dyno?

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Engine details of my project if anyone cares to look. As far as degreeing the cam, I just verified that the ‘straight up’ configuration matched the cam card, which it did.

I specifically chose to stay around a target of 400hp so that I didn’t get into the range where I thought the stock (or close to stock) parts like rods, rockers, drivetrain, etc... would break down. I definitely have to balance cost vs. payoff with anything I’m doing on the car. I’ve recently seen those “push through” push rod pics on stamped rockers :eek:

I’d also say that I relied too much on the race engine building shop for returning to me components and measurements that confirmed the proper compression ratio for what I was after... my bad. When I use online CR calculators.. I can only plug in numbers that I THINK I have, not numbers that I have personally measured. When I do that, I come up with 10:1, and when I guesstimate the cc’s of the valve relief, this brings the cc down to about 9.5:1, which is where I was told I was. I also realized late that I could have been more specific when ordering my head gaskets. I didn’t realize that I could have better specified/measured the bore diameter... I simply ordered the .039” fel-pro for 4.28”. I did not accurately measure the volume of the gasket opening once I got it. So, these are the reasons I say “I don’t know for sure” what the CR is.

So, we’ve established that my heads, rockers, springs could definitely be suspect.

As far as revs during the test... In looking through all of my pulls, it definitely looks like, on many of them, the hp was still climbing when the test was stopped at 5300 rpm.

I’ll just post all my data. I do believe these are all in order of starting pull to last pull...

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Even with stock 906 heads breathing into headers, this combo should be more impressive. If the cam checked out fine, (once in a while they don't quite match the specs on the box) and degreed OK, I would be suspicious of the springs. He needs to provide you with a part number, and check that they match up with the box they came in. Idiots work in automotive manufacturing facilities too. What was the seated and open pressures? Were they too weak for the cam profile?
 
Compression test and apply dynamic compression ratio calculator. Check idle vacuum. If your compression checks out where it should, and your idle vacuum isn't pointing to any intake gasket leaks, then I would suspect dyno error. But still a good idea to check valve spring pressure and consider a rocker upgrade.
 
ir3333 said:
are you sure your builder cut your heads from a stock 93 or so cc's to 79?
Would that much require cutting your intake and maybe shimming your rocker shafts?
i'm wondering about your compression...are you going to check it?
Click to expand...

I’m wondering about the 79cc and compression as well. When I dry-fitted the Intake, I was fully expecting fitment problems, but there were none. I should have looked into it at the time.

I’ve torn the bottom end apart now... going after the main seal leak before looking further into tests, etc. could be a little while. I’m also tearing my deck apart to replace boards. Could be I have too many projects to do any one of them perfectly.

Thanks again for all the feedback and advice. Priceless info guys... that’s why I’m a paid member.
 
It was pretty much leveled off at 5300 so I wouldn't think exceeding that would provide anything useful. Also whether it was 9:1 or 11:1 it's lazy for the sum of the parts. At least IMO.
 
what tuning changes were done between the pulls where HP peaks at 295 at 4800 RPM and those where it peaks at 330 HP at 5300 RPM?

That's a fair amount of variance.
 
YY1 said:
what tuning changes were done between the pulls where HP peaks at 295 at 4800 RPM and those where it peaks at 330 HP at 5300 RPM?

That's a fair amount of variance.
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It was not a typical session. Ron made that clear. It seemed to lose hp when we would run the exact same test back to back without making any changes. I think the only thing that was done during the time you are asking about was changing timing... from 35 to 34 to 36 degrees, then back to 34 again.
 
Valve springs:
Precision Engine Parts - PEP - Las Vegas, NV
Item #: PSK-272-3-7
1.46odx1.06id*110lb.@1.80

Builder said “they use these springs all the time and they shouldn’t be a problem”. 110lb pressure at seat and 230lb open.

I don’t know... a couple of sources told me this isn’t enough of a spring.

B356DE24-2C2C-43C9-A2A9-A79C8CE37511.png
 
Item B. in the article you shared says it all! Good quality name brand springs are much needed, and some heavy duty rockers to match, too.
 
And now on to what I’m guessing is THE REAL PROBLEM... as I was carefully breaking down the bottom end (disassembling rod and main caps) for rear seal complete cleaning and replacement, I found that rod bearings 7 & 8 had spun during break-in. I’d like to be really upset, but this is exactly why I pulled it back out of the car to bench test it on a dyno.

Interesting that, when I tore down the core project block some time ago, this was the same two rods that had spun in the previous life of the block. I had the forged crankshaft rewelded and ground down and polished to .010-under on all journals. New -.010 bearings were supplied by the same builder outfit that had he crank sent out to be refurbished. I also meticulously cleaned all oil passages on the crank after I got it back from the machinist and before assembly.

I’m thinking it also explains why back-to-back dyno tests showed a pretty substantial decrease in HP and tq on subsequent pulls.

What a bummer.

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Tragic! Nothing worse than chasing a bug like that. I'm going to guess oil passage feed problem at number four main in the block feeding excess oil to the top end, or bent rods (if its the same ones) or crank.
 
JAndrea said:
And now on to what I’m guessing is THE REAL PROBLEM... as I was carefully breaking down the bottom end (disassembling rod and main caps) for rear seal complete cleaning and replacement, I found that rod bearings 7 & 8 had spun during break-in. I’d like to be really upset, but this is exactly why I pulled it back out of the car to bench test it on a dyno.

Interesting that, when I tore down the core project block some time ago, this was the same two rods that had spun in the previous life of the block. I had the forged crankshaft rewelded and ground down and polished to .010-under on all journals. New -.010 bearings were supplied by the same builder outfit that had he crank sent out to be refurbished. I also meticulously cleaned all oil passages on the crank after I got it back from the machinist and before assembly.

I’m thinking it also explains why back-to-back dyno tests showed a pretty substantial decrease in HP and tq on subsequent pulls.

What a bummer.

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Were the rods resized?

Not missing a galley plug somewhere?

7&8 are the farthest from the pump. I’ve seen a few 383s spin that pair.
 
mosleyme said:
Were the rods resized?

Not missing a galley plug somewhere?

7&8 are the farthest from the pump. I’ve seen a few 383s spin that pair.
Click to expand...
Yep, the rods were supposed to have been resurfaced and resized to the .010 under crank rod journals. Not having a good bore dial gauge, I didn’t measure, confirm, and document every single thing that I got back. Lesson learned.

I don’t know for sure, but I’m thinking everything should come apart for a good cleaning and confirmation of various component measurements, etc.
 
JAndrea said:
Yep, the rods were supposed to have been resurfaced and resized to the .010 under crank rod journals. Not having a good bore dial gauge, I didn’t measure, confirm, and document every single thing that I got back. Lesson learned.

I don’t know for sure, but I’m thinking everything should come apart for a good cleaning and confirmation of various component measurements, etc.
Click to expand...

Now need to have the rods checked and the crank journals. Everything disassembled and cleaned. You do not want bearing material floating around in your oiling system.

Did you get new rod bolts? New rod bolts are installed before rod resizing. Rod bore doesn’t change with a 0.010 crank, just the crank and the bearing change.

You may have to get the rods resized again since you spun a bearing. Those caps don’t look right, maybe it is an optical illusion with the damaged bearing. I have Eagle rods and the higher rated ARP rod bolts. My bottom end and oiling was designed for 8000rpm. Very important to use the right ARP lube and torque specs.

Do you know how to use plastigage? I check everything when I assemble.
 
JAndrea said:
Yep, the rods were supposed to have been resurfaced and resized to the .010 under crank rod journals. Not having a good bore dial gauge, I didn’t measure, confirm, and document every single thing that I got back. Lesson learned.

I don’t know for sure, but I’m thinking everything should come apart for a good cleaning and confirmation of various component measurements, etc.
Click to expand...
1) One would re-size the rod ID to stock dimensions or a toochie tight for improved heat transfer & crush.
2) The bearings are the only .010" under items.
3) I know I know, everyone including Me has done fine w stock rod bolts for Lord knows how many......
but a set of quality ARP's installed and then reconditioning rods that haven't already spun a set of shells, then torqued by stretch method is really the only way to do it these days for anything that matters.
 
Next;
A) did the chambers get relieved correctly for the 2.14's? Same as camelback Chebbys O/S valves are shrouded unless One does the proper chamber work. They can hurt flow...
B) I have found cyl's representing #3 & #6 to be shallow on a number of 906 castings, but just the same all chambers should be cc'd, and the indexing on the last crankpin may be suspec.........
 
moper said:
It was pretty much leveled off at 5300 so I wouldn't think exceeding that would provide anything useful. Also whether it was 9:1 or 11:1 it's lazy for the sum of the parts. At least IMO.
Click to expand...
started leveling off at 4800/4850, from that point torque took a nose dive.
Reacts like a low compression engine with a poor flowing head.
 
I remember seeing some flow tests on iron heads with porting and valve work, but I don't remember were from. Simply adding 2.14 1.81 valves into decent stock iron head without any other chamber or port work reduced mid lift to peak flow down to near the level of the old pre 1967 closed chamber 516 heads. Even if you have to do it yourself, porting with a set of MP templates will help immensely. Looks like you need to change to heavier valve springs anyway, so it would be a good time to do it. At least the cam is broken in and that is less of a worry ,but if you've got it out anyway, it's still best to treat it like a new one and use break in lube when switching to heavier springs.
 
mosleyme said:
Now need to have the rods checked and the crank journals. Everything disassembled and cleaned. You do not want bearing material floating around in your oiling system.

Did you get new rod bolts? New rod bolts are installed before rod resizing. Rod bore doesn’t change with a 0.010 crank, just the crank and the bearing change.

You may have to get the rods resized again since you spun a bearing. Those caps don’t look right, maybe it is an optical illusion with the damaged bearing. I have Eagle rods and the higher rated ARP rod bolts. My bottom end and oiling was designed for 8000rpm. Very important to use the right ARP lube and torque specs.

Do you know how to use plastigage? I check everything when I assemble.
Click to expand...

Agreed on remeasuring everything now. Also will be looking at oil galleys, new rods, rod bolts, bearings, total reexamination of crank, heads, springs, etc.

Yes, definitely did the minimal tolerance checking... dial gauged crank and cam end play, plastigauged crank and rod journals during assembly. Made sure everything turned freely. Primed oil pump several times and made sure oil psi was in mid 50s during priming. Everything looked great.

Thanks for the well-wishes and tips everyone!
 
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