Engine is back! - ClassicOldsmobile.com

Engine is back!

Old June 15th, 2018, 06:26 PM
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Engine is back!

After more than 4 months at the machine shop the engine is back home. I had to have the crankshaft drilled for the pilot bearing when the build veered to using a 4 speed. Wish I would have just had it done when the engine was originally assembled (and would have saved $522.50.)

After 5 years of working on this engine I would love to tell you that the engine sounds mean. But I can't, because I never got the opportunity to hear it run. The plan was for them to call me when the engine was ready to go on the dyno. I hadn't heard anything from them so I just stopped by and found out that the dyno run had already taken place! Still pissed a week later.

The layers of disappointment grow: Aside from the pilot bearing cost (my fault for not anticipating it,) not getting to hear my engine run, and the cost of the dyno (65% more than "estimated" before hand,) he tells me that the cam is probably holding it back. Great.

Block is .030 over, aluminum heads, Edelbrock performer intake w/ Holly Street Avenger 870. The dyno numbers are: Peak HP 392 @ 4700 rpm and torque is 478 @ 3900. I was hoping for around 450 and am a little disappointed. Hell my wife's GMC Acadia is 310 HP with half the cubic inches.

Options are #1, replace the cam with something better while the engine is out of the car. Current cam JM20-22 specs are 226/230 @ 050. I really don't understand the numbers and I'm hoping that someone could point me in the right direction. Even if I do change the cam I don't think it will go back to the dyno because of the cost.

#2 leave it alone and drive it to see how it responds. This is probably a year or two away as I'm just starting to work on the rusty floors.
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Old June 15th, 2018, 06:37 PM
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While its out of the car and the motor is fresh, replace the cam while its still accessible and if you can afford to. Otherwise you'll be forever kicking yourself for not doing it when you had the chance.
Now the seed of doubt has been sown in your mind you'll be thinking it everytime you drive the car.
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Old June 15th, 2018, 07:07 PM
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Thatís really low for corrected power. Piston? Compression?
With mostly similar equipment Iíve made 415/530 with iron heads, corrected. Something ainít right.
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Old June 15th, 2018, 10:37 PM
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Originally Posted by cutlassefi View Post
Thatís really low for corrected power. Piston? Compression?
With mostly similar equipment Iíve made 415/530 with iron heads, corrected. Something ainít right.
Hypereuectic alloy pistons 14.5 cc dish, heads 77 cc. Estimated compression ratio 10.1:1. Also have MSD 8566 distributer. It was supposed to be dynoed with Hooker 1 3/4 comp header but he never switched out the used, same sized headers that I had bought just for the engine break in.
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Old June 16th, 2018, 06:25 AM
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That is very low. Mark did a 9 to 1 422 ci 350 stroker that out performed your build. I would seriously consider a roller cam, I am biting the bullet on my next build. No break in worries, more lift, power and better manners. Talk to Cutlassefi about one, it should make a very big difference. Oh and I blew the doors off one of those 310 hp GMC Acadia's, like it was standing stll with my 88 when it ran a 9.4 in the 1/8, to make you feel better.

Last edited by olds 307 and 403; June 16th, 2018 at 06:31 AM.
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Old June 16th, 2018, 07:21 AM
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A few issues/questions;
870 or 780 carb? Says both in different areas.
Your bsfc is low, which is normally good. BUT you're not making any power, did you have a wideband on it?
Are all the parameters set correctly, fuel weight, bore, stroke? Did he dyno it at 1000rpm/sec? That's what it looks like. That'll make for lower numbers.
Header concern is unwarranted, won't make that much difference.

Last edited by cutlassefi; June 16th, 2018 at 07:25 AM.
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Old June 16th, 2018, 09:10 AM
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Its also not about peak numbers, but the curve and where the power comes on and how much avg in the curve. The EMC is average in the band or curve, and not about peak numbers. You will spend a lot more time between 2500 of 4500, then you will above it. That engine is also not tuned yet for max power, and its sure not the cam numbers you have. Those are already larger than many a very fast street Olds has in them, that have relatively smooth idles.


Dynos can tell you the truth, or whatever they want you to hear (happy dynos).
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Old June 16th, 2018, 11:03 AM
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Originally Posted by cutlassefi View Post
A few issues/questions;
870 or 780 carb? Says both in different areas.
Your bsfc is low, which is normally good. BUT you're not making any power, did you have a wideband on it?
Are all the parameters set correctly, fuel weight, bore, stroke? Did he dyno it at 1000rpm/sec? That's what it looks like. That'll make for lower numbers.
Header concern is unwarranted, won't make that much difference.
I will double check the carb but it is supposed to be an 870 and I assumed it was transposed number on the report. Is that an inputted parameter that would affect the dyno or just a reported number?

As far as the other things this was my "firstborn" and have yet to ever attend a dyno session. I don't know what bsfc stands for or what the "wideband" is.

I do see that the dyno report was originally 7 pages but was only provided with 3 that were printed. I posted all of what I got. I will go back and ask for the complete report. What other questions should I ask?

I'm sensing that you and others might feel that the cam may not be the only source of the low numbers and I am getting concerned that the problem might be deeper (and more expensive.)
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Old June 16th, 2018, 11:28 AM
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Originally Posted by rpinnt View Post
I will double check the carb but it is supposed to be an 870 and I assumed it was transposed number on the report. Is that an inputted parameter that would affect the dyno or just a reported number?

As far as the other things this was my "firstborn" and have yet to ever attend a dyno session. I don't know what bsfc stands for or what the "wideband" is.

I do see that the dyno report was originally 7 pages but was only provided with 3 that were printed. I posted all of what I got. I will go back and ask for the complete report. What other questions should I ask?

I'm sensing that you and others might feel that the cam may not be the only source of the low numbers and I am getting concerned that the problem might be deeper (and more expensive.)

First of all stop worrying. You are closer to having it running then you were, and you haven't even got the car ready yet by miles. The cams not it, but it may be installed wrong on timing. Ignition timing might be WAY off.
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Old June 16th, 2018, 12:47 PM
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First thing I would look at is what a compression test shows and also what temp oil pressure is at. Also what aluminum heads and from who?
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Old June 16th, 2018, 07:35 PM
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You need to confirm the carb size and rate of pull.
A wideband will tell you air/fuel ratios.
And your builder shouldíve verified tdc on the balancer, then checked timing from there.
Still lots of variables here.
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Old June 16th, 2018, 08:10 PM
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Originally Posted by cutlassefi View Post
You need to confirm the carb size and rate of pull.
A wideband will tell you air/fuel ratios.
And your builder shouldíve verified tdc on the balancer, then checked timing from there.
Still lots of variables here.

Lots and lots and lots Just sticking advance weights can cause lots of grief. Non opening secondaries, or cam degreeing, to far off one way or another. A few valves not set right. And on and on it goes.
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Old June 17th, 2018, 01:04 AM
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Originally Posted by cutlassefi View Post
You need to confirm the carb size and rate of pull.
A wideband will tell you air/fuel ratios.
And your builder shouldíve verified tdc on the balancer, then checked timing from there.
Still lots of variables here.
I double checked the carb and it definitely is a 870. I saw that the electric choke had been zip tied open for the dyno run but would think that would have no effect on numbers. I removed the break in headers from the engine. There was a couple of spots where the headers hadn't sealed against the heads. I was surprised that the coating on the break in headers wasn't more discolored than it was.
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Old June 18th, 2018, 02:19 PM
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Went back to machine shop and got the full report printed. Carb size is a typo, it is a 870. He said didn't use the wideband but optimized timing and jetting (not sure what that means.) As far as rate of pull I think he said 600rpm/sec but also said it was in the report which I don't know what I'm looking for. He still says it's a too small cam for the cubic inches.
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Old June 18th, 2018, 03:10 PM
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Originally Posted by rpinnt View Post
Went back to machine shop and got the full report printed. Carb size is a typo, it is a 870. He said didn't use the wideband but optimized timing and jetting (not sure what that means.) As far as rate of pull I think he said 600rpm/sec but also said it was in the report which I don't know what I'm looking for. He still says it's a too small cam for the cubic inches.

I would guess the a/f is off and or timing. You have a torque dip for one between 2800 and 3900 and the torque and HP are lower than would be expected in that cams range. But then again that torque at 2800 it shows would make it run strong on the street and you can tune it once in the car.
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Old June 18th, 2018, 03:15 PM
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I have the JM 18-20 in an 80 GMC with stock converter & 3.73 gears. It is 0.060 over 455 with 10.2:1 compression & ported C heads. Running an Edelbrock performer & an 750 AED carb & MSD electronics & headers it put 540 ft lbs to the ground on the chassis dyno @ 3850 RPM.Very nice truck engine.


https://classicoldsmobile.com/forums...ck-engine.html


I appologize. I made a mistake. I was thinking about FLYWHEEL number not the wheels. Obviously a huge difference. I should have read it again before I posted. Thanks for catching my blunder.

The observed values for this engine were 325 hp @ 4500 & 427 TQ @ 3500 rpm to the ground. This was in Lethbridge AB & the net flywheel numbers in Lethbridge were 406 hp & 534 TQ.


Sea level corrected the flywheel power was 447 hp & 587 TQ. I do not recall what the correction factor what that day. Corrected altitude in Lethbridge is usually between 3500-4500 ft.

Those are the numbers that were provded to me. I will look to see if I can find the dyno sheet.

A lot of people are down on some of the old Mondello camshafts. I agree that there are better choices but I have had reasonable success with the JM 18-20 in my truck engine & I do have the JM 22-25-10 in the 455 in my 65 442 (no dyno work done on that car).
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Old June 18th, 2018, 05:08 PM
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Youíve got issues. Youíre only using 164lb of fuel.
Divide that by your bsfc of .487 at the end of the pull and thatís only 336hp. Something is wrong.
You show an air/fuel so he must have a wideband or an airtight room with the stack/turbine to measure airflow. But nonetheless you may want to ask your dyno guy why it goes from dead lean to pig rich.

Last edited by cutlassefi; June 18th, 2018 at 05:16 PM.
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Old June 23rd, 2018, 04:44 AM
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I asked him about the optimized tuning and he said that he increased the carb jet size until power had began to drop.

I bought most of the parts myself without solicitating much input from anyone before I even knew that classicoldsmobile.com existed. The heads, cam and rockers were sourced from the wrong Mondello (again before I knew about the problems others have had) and now wonder if there was something wrong with the parts. This engine was assembled in 2014 and sat untouched (and unrotated) for years. Could it be a stuck valve or would that have shown itself during the break in or dyno run? Or is it a timing issue, the cam installed incorrectly or the timing way off? The engine builder is not an Oldsmobile guy but he does build engines and has been doing so for at least 20 years.

At this point I don’t know what to do. I don’t know if it is a fuel, spark or compression issue. If I knew it was the cam I would have Mark set me up with something more appropriate and may yet. But I don’t want to throw good money after bad especially since I haven’t even heard it run yet. Please tell me what to do.
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Old June 23rd, 2018, 04:55 AM
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Originally Posted by rpinnt View Post
I asked him about the optimized tuning and he said that he increased the carb jet size until power had began to drop.

I bought most of the parts myself without solicitating much input from anyone before I even knew that classicoldsmobile.com existed. The heads, cam and rockers were sourced from the wrong Mondello (again before I knew about the problems others have had) and now wonder if there was something wrong with the parts. This engine was assembled in 2014 and sat untouched (and unrotated) for years. Could it be a stuck valve or would that have shown itself during the break in or dyno run? Or is it a timing issue, the cam installed incorrectly or the timing way off? The engine builder is not an Oldsmobile guy but he does build engines and has been doing so for at least 20 years.

At this point I donít know what to do. I donít know if it is a fuel, spark or compression issue. If I knew it was the cam I would have Mark set me up with something more appropriate and may yet. But I donít want to throw good money after bad especially since I havenít even heard it run yet. Please tell me what to do.
What does your dyno guy say about the hp/tq Numbers? Is his dyno known to be pessimistic?
Check cranking compression first, then make sure all the plugs were firing. Then go from there.

Last edited by cutlassefi; June 23rd, 2018 at 05:49 AM.
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Old June 23rd, 2018, 05:12 AM
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Another thing to look at is the pushrod length.

If they are too short, you want gey full power.

Built a 455 with ported iron heads, the same cam, an O4B/Q-jet, and W/Z manifolds that made 420HP on the dyno.
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Old June 23rd, 2018, 08:17 AM
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I would put it in the car and start driving it, and see if it meets your needs. More changes can happen down the road in the future if you think they are needed.
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Old July 1st, 2018, 11:39 PM
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Originally Posted by cutlassefi View Post

What does your dyno guy say about the hp/tq Numbers? Is his dyno known to be pessimistic?
Check cranking compression first, then make sure all the plugs were firing. Then go from there.
He said that the dyno might read a few hp low.
I checked the compression of each cylinder and these are the results:

1 175 2 170
3 160 4 155
5 155 6 155
7 155 8 150

The engine is just sitting in stand and not installed. I'm not able to run it to warm it up so these numbers are a cold engine. I probably also messed up by leaving the carb cap on during the test.
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Old July 1st, 2018, 11:44 PM
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Originally Posted by rpinnt View Post
He said that the dyno might read a few hp low.
I checked the compression of each cylinder and these are the results:

1 175 2 170
3 160 4 155
5 155 6 155
7 155 8 150

The engine is just sitting in stand and not installed. I'm not able to run it to warm it up so these numbers are a cold engine. I probably also messed up by leaving the carb cap on during the test.

Those numbers look fine, for most Oldsmobiles, and even more so possibly for a cold dry engine.
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