[johnta1]

Cleared it up some.


Lots of stuff looks suspect to me?

[steve25]

Judging by those numbers the carb was flooding out.

The first thing I would do is change your oil and filter.

[Bill Hanlon]

I'm no dyno (or any other kind of) expert, but I would think the engine should use more fuel at higher rpm (4600) than lower rpm ( 3400).

[JLMounce]

Was everything hooked up during the dyno to where those numbers can be trusted? The BSFC numbers are frighteningly high. To the point that I'm not sure how they even kept the thing running.

That carp needs a serious overhaul and while QJets in general are not junk, the one you have probably is; in it's current state.

[JLMounce]

Originally Posted by Bill Hanlon

I'm no dyno (or any other kind of) expert, but I would think the engine should use more fuel at higher rpm (4600) than lower rpm ( 3400).

Yes, but not always. What may be going on with this graph is that the throttle was snapped open at the start of the run and there is a rich tip-in event happening.

If you lob off the first couple rows and the last couple rows, the engine's fuel consumption from a trend perspective seems okay, outside of the fact that it shows to be incredibly rich.

It is possible though that certain engine combinations could use less fuel at higher rpm's than lower rpm's. Peak Volumetric Efficiency typically occurs at the same time as peak torque. If VE falls off significantly after peak torque, it's possible to need less fuel at that point, even with more revs.

[SRGN]

I'm surprised it made what it did if the AF data is correct. Get the air fuel straightened out by fixing or replacing the carburetor, get the timing where it needs to be, and see how it runs. That's what the dyno is for, finding an resolving issues. Don't go crazy over dyno numbers, I've never pulled into the staging beams and seen a dyno in the other lane.

[scott70]

The only numbers that look right are the oil pressure numbers.

[mgarblik]

With a Q-jet, Fuel A should show all the fuel being used. Fuel B should show 0 and be plugged off. The BSFC is crazy high. The fuel B numbers are contributing to this. The one page printout does not show any air flow numbers. Did they have an air hat on the carb? If not, that's another reason the numbers are so weird. Allot of wrong stuff going on with that printout. It's a computer . Garbage in, garbage out. As mentioned, the only usable data is the oil pressure. Spark plugs should be coal black. If not, the data is completely useless.

[Skippy597]

I'm surprised they even bothered with the pull with it being so rich.

[steve25]

All of the BSFC numbers are at least 2.5 times higher than they should be at a minimum.

The only two good things I see on that sheet is that the oil pressure is good , and that judging by the torque and hp numbers at 5000 rpm is that at least the dyno correction factor used on that day was not set to make the motor a paper / print out hero.

That being said I would have preferred that the pull went to 5400.

Maybe one other good thing is running that rich the motor was not pinging or knocking.


Was that hopefully the only pull that was made?

[Stan Weiss]

Originally Posted by mgarblik

With a Q-jet, Fuel A should show all the fuel being used. Fuel B should show 0 and be plugged off. The BSFC is crazy high. The fuel B numbers are contributing to this. The one page printout does not show any air flow numbers. Did they have an air hat on the carb? If not, that's another reason the numbers are so weird. Allot of wrong stuff going on with that printout. It's a computer . Garbage in, garbage out. As mentioned, the only usable data is the oil pressure. Spark plugs should be coal black. If not, the data is completely useless.

OK lets do some math. The dyno sheet is hard to read so I may have gotten a number wrong. Lets look at peak Hp - 4300 RPM.

Using Fuel A plus Fuel B and the shown BSFC we get 181.95 Un Corrected HP

Using Fuel A plus Fuel B and the shown A/F ratio we 2036.9 lbs/hr Air or roughly 445 SCFM

Using 181.95 Un Corrected HP and Fuel A we get a BSFC of 1.14097

Using Fuel A and the shown A/F ratio we 1712.7 lbs/hr Air or roughly 374 SCFM

I get a 1.053 Correction Factor

Stan

[mgarblik]

Originally Posted by Stan Weiss

OK lets do some math. The dyno sheet is hard to read so I may have gotten a number wrong. Lets look at peak Hp - 4300 RPM.

Using Fuel A plus Fuel B and the shown BSFC we get 181.95 Un Corrected HP

Using Fuel A plus Fuel B and the shown A/F ratio we 2036.9 lbs/hr Air or roughly 445 SCFM

Using 181.95 Un Corrected HP and Fuel A we get a BSFC of 1.14097

Using Fuel A and the shown A/F ratio we 1712.7 lbs/hr Air or roughly 374 SCFM

I get a 1.053 Correction Factor

Stan

Thanks for doing the thinking, {math} for me. Made some sense out of that mess. I am a little puzzled by that fuel B. It should be zero and blocked off 100%. A Q-jet only has one inlet/fuel bowl. Certainly has some problems there. Some dyno, some carburetor, some engine? I think it's all because it's a Pontiac!!

[78w72]

The secondaries in that pic definitely arent fully open... but they look to be at least 3/4 open and I doubt that is the cause of the low numbers. The internal set up/tune could be the cause.

If you have the money/time for another dyno session, would try different carb or have that gone through by a pro. Surprised they didnt swap on a different known good carb if it was that bad.

[chiphead]

Originally Posted by steve25

Judging by those numbers the carb was flooding out.

The first thing I would do is change your oil and filter.

Yeah that's pig rich. That mixture, low air flow and low compression will yield inaccurate dyno numbers. As more experienced members said, the dyno cell setup looks suspect.
I'd go so far as to say negligence by the dyno operator. With numbers that far off, they should abort the test and regroup with another carb, or tell the customer to bring another carb. That's time and money wasted making pulls like that.

[RocktimusPryme]

[QUOTE=78w72;6611969 Surprised they didnt swap on a different known good carb if it was that bad.[/QUOTE]

Thats what I was thinking. Even if it used a spread to square spacer that would kill a little power by itself it would at least let the engine run reasoanably well to identify the carb as the issue or not.

[JLMounce]

Originally Posted by 78w72

The secondaries in that pic definitely arent fully open... but they look to be at least 3/4 open and I doubt that is the cause of the low numbers. The internal set up/tune could be the cause.

If you have the money/time for another dyno session, would try different carb or have that gone through by a pro. Surprised they didnt swap on a different known good carb if it was that bad.

Originally Posted by chiphead

Yeah that's pig rich. That mixture, low air flow and low compression will yield inaccurate dyno numbers. As more experienced members said, the dyno cell setup looks suspect.
I'd go so far as to say negligence by the dyno operator. With numbers that far off, they should abort the test and regroup with another carb, or tell the customer to bring another carb. That's time and money wasted making pulls like that.

Originally Posted by RocktimusPryme

Thats what I was thinking. Even if it used a spread to square spacer that would kill a little power by itself it would at least let the engine run reasoanably well to identify the carb as the issue or not.

Are we actually surprised by this? I've never known anybody that makes a blanket statement like "QJets are crap" to be arbiters of knowledge and attention to details.

The carburetor here is at least partially, if not completely to blame for sure, but the dyno operator (same as the engine builder?) didn't care enough to do anything other than shift any and all blame.

Had a shop carb been put in place and the engine only made 5-10 more hp, that person may have more explaining to do.

This build to me is a bit off the rockers in general. The compression is anemic, the cam choice is suspect, why it needs a a .060+ head gasket is beyond my comprehension.

This has the hallmark of a lazy build that somebody didn't really want to take seriously. Who wants to wager it's got 8 eyebrow pistons in it?

At any rate, at least the engine makes good oil pressure. If this was me in this situation, the engine would never go back to that particular builder. My process would then be the following:

-Remove heads and check to see how far in the hole the pistons are. Calculate compression with a FelPro 8516 head gasket, reinstall heads with new head gaskets
-Pick a new cam that is appropriate for the compression (probably a Butler 067 or 068 hyd roller)
-Have the QJet professionally rebuilt by somebody like CRK performance, or rebuild it myself per Cliff R's book.

Then I'd reinstall the engine and go have fun.

[RocktimusPryme]

Im not above being lazy, heck my little YT channel is at least half about getting solid results for low effort inputs with a bunch of little paint projects I do. But I cant imagine wanting my name anywhere near that dyno sheet. There is no way I wouldnt have put a shop carb on it just to prove the engine I built wouldnt run reasonably well. If im on record as saying the carb is junk, you can bet Im going to put a working carb on it so I could spike the football about it.


I agree, if it were me I would evaluate swapping to a thinner head gasket if not the gasket and cam. Its just not that much extra work with the engine out of the car. That said, if you put a functional carb on it and it runs fine......dont be above just running it and enjoying your car. Would you be maximizing the engines potential? No. But dont let great be the enemy of good if it gets your car going down the road.

[chiphead]

Originally Posted by JLMounce

Are we actually surprised by this? I've never known anybody that makes a blanket statement like "QJets are crap" to be arbiters of knowledge and attention to details.

The carburetor here is at least partially, if not completely to blame for sure, but the dyno operator (same as the engine builder?) didn't care enough to do anything other than shift any and all blame.

Had a shop carb been put in place and the engine only made 5-10 more hp, that person may have more explaining to do.

This build to me is a bit off the rockers in general. The compression is anemic, the cam choice is suspect, why it needs a a .060+ head gasket is beyond my comprehension.

This has the hallmark of a lazy build that somebody didn't really want to take seriously. Who wants to wager it's got 8 eyebrow pistons in it?

At any rate, at least the engine makes good oil pressure. If this was me in this situation, the engine would never go back to that particular builder. My process would then be the following:

-Remove heads and check to see how far in the hole the pistons are. Calculate compression with a FelPro 8516 head gasket, reinstall heads with new head gaskets
-Pick a new cam that is appropriate for the compression (probably a Butler 067 or 068 hyd roller)
-Have the QJet professionally rebuilt by somebody like CRK performance, or rebuild it myself per Cliff R's book.

Then I'd reinstall the engine and go have fun.

This. Not trying to upset the OP, but this whole build sounds like a DGAF special. Somebody who doesn't know better would run this engine until he got tired of it. It's like a 2.8L V6, it'll run forever because it's not going to make enough power to hurt itself. Maybe the shop is used to big Mopar? Those put the pistons way down the hole to lower compression.

Seriously though, if it's got good pistons in it, you've got a fighting chance. Swap on a set of heads with 75 to 85CC chambers, a Summit 2802 cam and let it eat. 370-410 HP like falling off a log.

[JB Eng Wis]

Ideas.... Re Dyno someplace else.... change your oil and filter,,, re prime.... And im sure things are going to BETTER

[TinRabbit]

Thanks so much fellas for alllll the info and thoughts on this. I too was surprised when I got the call it was done only to show up with it sitting on a stand ready to load and with those dyno sheets as they were, no prior call as to a potential carb problem or issues in general hence why it is now in my shop instead and asking here for better assistance.
First and foremost the carb problem, Ive contacted several places to see if they had something on hand but looks like I'll be sending this one out and waiting several weeks.
As far as the camshaft goes, I really thought I was getting a roller very close to the 068, when I saw the 106 seperation I wasnt sure why they went with that.
I am not opposed to a cam swap to get back on track of where I was initially wanting to get.
As far as a fresh dyno shop I do believe there is one very close that also has a wheel dyno in his shop, warrants a call on Wednesday!
Thanks again, I will keep adding pics as its opened up and some details what I find along the way