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 Help Tuning a Rebuilt 350
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  10:17:42 AM  Show Profile  Reply with Quote
I need advice on tuning a freshly rebuilt 350 from my 1970 LeMans.

With the vacuum advance disconnected:
- At 6 DBTDC (17" vacuum) has poor performance and little to no ping
- At required 9 DBTDC (17.5" Vacuum) has mediocre acceleration with a slight ping and still runs at near 200 degrees temp.
- At 10.5 DBTDC (18" vacuum), runs hotter (215 Temp) with more ping
- At 12 DBTDC (18.5" vacuum), runs even hotter with even more ping.

When the Vacuum advance is reconnected, the performance drops and the pinging is much greater.

I have checked for other vacuum leaks and found none. The Quadrajet was freshly rebuilt but originally tuned for a 400.

1969 XS Block 350 with the std 9779067 grind cam. Rebuilt Quadrajet from a Firebird 400 and an HEI ignition.

I have struggled with this for weeks and am at the end of my rope. Please help.

George

Blued and Painted
Chief PONTIAC

USA
3409 Posts

Posted - 20 Apr 2017 :  10:48:11 AM  Show Profile  Reply with Quote
The hei wont work well if connected to the factory resistor or restisor wire. The hei needs a dedicated power source with full battery voltage.
Whats the casting number on the cylinder heads at the center exhaust outlet?



Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  10:50:43 AM  Show Profile  Reply with Quote
The heads are a number 47. Good catch on the HEI. I'll find a dedicated source.

George
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  12:22:58 PM  Show Profile  Reply with Quote
HEI power change to direct battery power made no difference. Should the vacuum advance hose go to the metered post on the Rochester or the straight vacuum?

George
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Admin
Ye Olde Webmaster

848 Posts

Posted - 20 Apr 2017 :  3:00:43 PM  Show Profile  Reply with Quote
George--
The HEI works differently than a typical points distributor. To be specific, the weights operate the same in both, but the HEI is designed to work off of metered vacuum off the Q-jet, whereas, the points distributor was set up, along with the old timing specs, to run off of manifold vacuum.

At idle, you say your manifold vacuum is around 17. The pulse from the carb outlet at idle is zero. Consequently, most HEI run engines want 12-16 degrees of initial advance. Adding the zero vacuum at idle you have only 12-16 degrees. If you keep this concept in mind, you should be able to dial in your timing for good performance.

Vacuum advance increases during part throttle with the Q-jet. Under full throttle vacuum advance falls off while mechanical advance increases with rpm.

So if your mechanical advance is set right, you should see a total mechanical advance of about 34-36 degrees. Most HEIs I've worked with come close to giving 20 degrees advance. Point distributors typically provide more mechanical advance because the initial is set at a lower advance.

HEI's require a full 12 volts to operate. Direct power is needed--no resistor.

The advance curve is another area that can be fine tuned. Most street car engines should have a curve that plateaus around 3000 rpm. Some HEIs I've tested continue to provide mechanical advance as the rpm increases. They should be restricted or limited to around 3000 rpm. The spring tension plays a large part in creating a quick curve. However, there's a fine line between using low tension springs that allow the weights to fly out fast. Typically those light springs don't have enough tension to pull the weights in to close when the engine slows and the car comes to a stop. This results in an inconsistent idle--one that may fluctuate.

I suggest tuning your HEI based on the highest vacuum reading you get from your intake manifold at idle. ( Hook up your vac gauge to the manifold. ) Initial could be between 12-16 degrees. Then hook up your vacuum line from the metered outlet on the Q-jet to the vac canister. Minor adjustments may be needed to the carb to improve idle quality. Make only small adjustments and note what you do. Keep tweaking as needed.

Hang in there--you'll get it.


"Dedicated to keeping the classic Pontiac engine alive."

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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  4:27:34 PM  Show Profile  Reply with Quote
Thanks for the input. Lots to think about. I have three vacuum ports on the quadrajet. I believe the upper left one is metered, so I'll start there. Should I then adjust timing from the get go with the Vaccum attached using a higher rev power tuning?

George
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tjs44
Cochise

USA
413 Posts

Posted - 20 Apr 2017 :  4:50:55 PM  Show Profile  Reply with Quote
Any idea of exactly what your CR is?Do a hot pumping comp test to see what you pumping.If over 175 you might not be able to run pump gas.Tom
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  8:44:16 PM  Show Profile  Reply with Quote
I adjusted the HEI Distributor to the highest vacuum at idle with Vacuum advance plugged. Then I reconnected the Vacuum advance to the metered port on the quadrajet. The engine ran at higher rev, but on acceleration, you got a lot of ping. With vacuum advance still connected I adjusted the distributor to hunt for the highest vacuum, then on acceleration it pinged quite a bit. I gave up for the night thoroughly frustrated. No matter what carb I put on in the past, I still get the same lousy performance. so I know it has to be timing, but I'm stumped.

I am almost reaching the point of putting the old distributor with points back on. Any further advice?

George
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 20 Apr 2017 :  8:46:44 PM  Show Profile  Reply with Quote
the CR should be at 9.25, but Im at 150 psi when I use the compression tester.

George
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Admin
Ye Olde Webmaster

848 Posts

Posted - 21 Apr 2017 :  05:20:09 AM  Show Profile  Reply with Quote
At the highest vac point at idle, what was the initial mechanical advance set at the distributor? How many degrees? What is the vacuum reading at the highest point?

When you have it at this point, what is the rpm at idle?

If you left the engine to idle, how high does does the coolant get, is it running hot? When shut down, how easily does the engine restart? Any kick-back at the starter?

At what rpm are you hearing the pinging? What do you notice?

Using a timing light with vacuum advance not involved, what is the amount of advance at 3000 rpm? Can you tell what it is? Do you have a timing light that will give you that info?

What grade of gas are you burning in the engine? Have you pulled any plugs to see if you are running rich or lean? Have you noticed any peculiar exhaust smell?

When the engine was using a points distributor, did any of these conditions exist or did it occur after the installing the HEI?

"Dedicated to keeping the classic Pontiac engine alive."

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cortcomp
Coyote

USA
5338 Posts

Posted - 21 Apr 2017 :  11:05:08 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Just for giggles, set your timing at closer to 15 and see what it does.
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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 22 Apr 2017 :  08:51:41 AM  Show Profile  Reply with Quote
I dont have an integrated tach with the timing light, but I can scrounge up one.

- 17.5 inch at 9 DBTDC at ~800 rpm
- At idle, ~200 degrees. Easily restarts, no kickback
- 1500-2000 rpm starts to ping
- when at high rev advance is about 20-25 degrees but its off the scale
- 92 octane plus an aftermarket octane booster
- Plugs are burning somewhat lean
- Not a truly rich smell
- Not really

George
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Admin
Ye Olde Webmaster

848 Posts

Posted - 22 Apr 2017 :  09:12:53 AM  Show Profile  Reply with Quote
- 17.5 inch at 9 DBTDC at ~800 rpm--Is that your highest vacuum reading--at 9 degrees advance???

What is the vacuum at 14 degrees?

"Dedicated to keeping the classic Pontiac engine alive."

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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 22 Apr 2017 :  1:30:08 PM  Show Profile  Reply with Quote
20" with lots of ping (vacuum advance not connected)

George
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Admin
Ye Olde Webmaster

848 Posts

Posted - 23 Apr 2017 :  07:08:50 AM  Show Profile  Reply with Quote
I'm thinking your carb is not providing enough gas to your cylinders and the lean mixture is firing a millisecond before the plug is firing.

With a vacuum of 20 the cylinder should be filling to provide a clean burn--but it isn't. This points me to a too lean situation. Your 150 cylinder pressure is not causing this problem--I don't believe it's an octane issue.

"Dedicated to keeping the classic Pontiac engine alive."

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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 23 Apr 2017 :  07:55:11 AM  Show Profile  Reply with Quote
The plugs looked a bit lean. So I shouldn't scrap the HEI and go back to points as a check? I'll start from the beginning and look hard for any obvious vacuum leaks. Starting with the trans shift vacuum line. I also have a breather on the valve cover. Since I dont fun that to the air cleaner, should that now be a one way check valve?

George
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Admin
Ye Olde Webmaster

848 Posts

Posted - 23 Apr 2017 :  11:26:38 AM  Show Profile  Reply with Quote
You could "pop in" the points distributor and see if there's any difference--ping or no ping. If you try it, test the points distributor without vac connected and make sure your dwell is at 30. If it still pings at 20" of vac...you can pretty much conclude that it isn't the distributor(s).




"Dedicated to keeping the classic Pontiac engine alive."

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gmaxiotis
Tribal Scout

USA
10 Posts

Posted - 23 Apr 2017 :  7:29:36 PM  Show Profile  Reply with Quote
Busy day of troubleshooting and it wasn't as successful as I hoped. I an very grateful for all your help so far.

Did a thorough check for vacuum leaks, replaced the carb gasket, put clamps on all the major lines. Installed an older HEI from 1980 with a direct wire from the battery.

Got different results from the 5 yr old aftermarket HEI I measured against in the above data.

Somewhat better performance, but not stellar by any means. Still some rattle at idle and acceleration. Plugs are not too dark, not too light.

Oddly, for now the engine runs a bit better (and cooler) with the vacuum advance disconnected.

For now I'm stuck with average performance using gentle foot when accelerating.

Particulars: Older HEI at slightly faster idle. (vacuum advance connected)
- 15 DBTDC, 16" Vacuum - Low knock
- 18 DBTDC, 17.5" vacuum - more knock
- 20 DBTDC, 18" vacuum - louder knock
- 36 DBTC (est, measured with a gauge), 19" - Loud knock

Older HEI at slightly faster idle. (vacuum advance NOT connected)
- 15 DBTC, 15.5" vacuum - little knock but poor idle
- 19 DBTDC, 17" vacuum - little knock (where engine is now set)
- 24 DBTDC, 18.5" vacuum - more knock
- 30 DBTC, 18.5" vacuum - heavy knock

Re-tuned the Quadrajet idle mixture screws in both cases to hunt for the best vacuum. This is the third carb I have tried (2 Quadrajets and one Edelbrock 1406) and no real change in performance.

I'm still stumped on whether this is a carb, distributor or a combination problem. I no longer have the points, rotor cap, coil to go back to the basics, but I'm tempted to do so if need be.

Ive never been so frustrated in over 40 years of working on cars.

I must now be on the Forum "stump" list. Any thoughts?

George
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cortcomp
Coyote

USA
5338 Posts

Posted - 23 Apr 2017 :  8:35:24 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I was chasing an issue that i had with 3 different HEI units. I put a pertronix dist in (the whole kit, cap and all, not just the ignitor) to gain some room for a big air cleaner (in a trifive chevy engine swap.) Problem solved (stumble at idle, dieseling after shut off.)

3 new different brand HEIs i had all had the same issues (and one, one of the weight posts broke off!) So, it's possible to get bad parts. I would assume this is a combination problem except you didn't have the issue with the points distributor...
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DanM
Buffalo

80 Posts

Posted - 27 Apr 2017 :  09:45:59 AM  Show Profile  Reply with Quote
I'd say Admin has the solution.

You are most likely running very lean.

Your testing of spark advance clearly says your engine cannot tolerate advance. Adding vacuum advance just makes it worse. HEI vs points is a red herring.

You said the carb is tuned for a 400. That could mean a lot of things. My suggestion is to order a collection of primary jets and rods from your favorite vendor and open up the carb and put in a new set. It's an easy thing to do if you just take your time.

If you get a rebuild kit it will have a checklist of 1 to 60 for you to sequentially remove parts then put them back in after you're done. The rebuild kit will also provide you with new gaskets in case you tear any. I'm suggesting you get a rebuild kit not because your carb needs to be rebuilt but because the instruction sheet is worth it's weight in gold. (The paper probably literally weights only a few grams so that's only about $100 in gold FYI...)

The primary jets and rods are cheap, about $6-$10 each so buy a bunch. I suggest getting the richest jets (77, 74, 71) and the richest rods (37, 39, 41,...). You won't need the lean jets or rods because you are already lean (my guess.)

The idle mixture screws can help a little but won't solve your problem. Test your idle screws range this way. You should be able to open them up far enough for your engine to run better and then by opening them up more it should run worse. If you can't make your engine go from bad to better to bad again over the full range of the screws then your idle circuit isn't rich enough. That can only be fixed with some strategically located hand drilling. Don't worry though. You can focus on the part throttle issue for now.

71 LeMans Sport Convertible with 310,000 miles driven year round since 1994.
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DanM
Buffalo

80 Posts

Posted - 27 Apr 2017 :  10:05:52 AM  Show Profile  Reply with Quote
...cont.

You didn't say if the temperature problems are at idle or cruise. We all have temperature problems so don't feel lonely. Temp problems can be helped by using less antifreeze and more water and by using a better water pump or modifying your water pump diverter plate with a few taps of a hammer. Also use a four row radiator not a two row.

Short of removing your water pump or replacing your radiator you should for now drain as much coolant as possible and replace with just water. That alone could solve your temp problems which could also eliminate your knocking problem.

We just came out of winter so many of us have the proper 50/50 mixture of antifreeze to water. that mixture is almost half the heat capacity capability of pure water. (don't use 100% water because you need the anti rust additives in the antifreeze and the 10% antifreeze gives you a slight boost in boiling point which helps inside the head coolant channels right at the surface of the hot metal.)

But the coolant solution (pun) will not likely solve all of the pinging.

Your vacuum numbers at each advance value all make sense to me. The 12 degrees of advance and 18.5" is when I hope you can eventually get your engine set at, once you solve the lean mystery (is it lean? who knows for sure) or your coolant problem (maybe not a coolant problem after all.)

My opinion is the problem is not the HEI or the distributor. The problem is your engine's inability to handle the proper spark advance. Changing the distributors will just change the amount of advance and the advance curve so any results aren't really due to a "better" or "worse" distributor. Eventually you may need to pay attention to how soon the advance kicks in such that you will prefer one distributor over the other or simply modify the HEI so that it adds advance when it should. But for now you can't even run at 12 degrees without pinging or overheating. That's the problem.

71 LeMans Sport Convertible with 310,000 miles driven year round since 1994.
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DanM
Buffalo

80 Posts

Posted - 27 Apr 2017 :  10:21:03 AM  Show Profile  Reply with Quote
One last thing. Back to the basics.

XS block and 47 heads at least match as a '69 engine. You said "freshly rebuilt". And later you said CR should be 9.25. Just for giggles, during the rebuild what deck height did you machine the block to? Did the machinist machine any of the head surface? did you add hardened seats or do any port work? did you have the chambers measured for their volume (cc's)?

150 psi calculates to 10.2:1 if my math is correct. (14.7 psi is one atmosphere so 150 is 10.2:1 right guys?) Are you running 93 octane. My previous 400 allegedly had only 8.9 CR but I couldn't run 91 octane ever.)


71 LeMans Sport Convertible with 310,000 miles driven year round since 1994.
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tjs44
Cochise

USA
413 Posts

Posted - 27 Apr 2017 :  4:55:36 PM  Show Profile  Reply with Quote
I had a 9.5 CR engine pump 200 and had to run race gas.Drive it,get it hot and pump it.Dont guess.Tom
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DanM
Buffalo

80 Posts

Posted - 28 Apr 2017 :  09:52:22 AM  Show Profile  Reply with Quote
From a Honda tuning website and after much research.

"The Evans tuning checklist:
8:1-8.5:1 compression: 150-170 psi per cylinder
8.5:1~9.5:1 compression: 170-210 psi per cylinder
9.5:1~11:1 compression: 210-275 psi per cylinder
11:1+ compression: 250+ per cylinder (highly depends on cams being used)"

There is an "adiabatic compression ratio exponent of about 1.4" which makes the PSI actually larger than 14.7 x CR. Also as we know the cam will create a dynamic CR that is less than the static CR. So, based on engine builders' experience, such as with tjs44 and others, a 200 psi would be a worthy goal nearing the limit of streetability. 150 psi will have left HP "on the table" so to speak. It seems the art is to use a larger static CR and a larger cam such that the net PSI is 180 to 200+ depending on your ability to tolerate expensive gas, pinging, and etc.

So Gmaxiotis: your 150 psi shouldn't be anywhere near the range of pinging due to the engine itself. It also implies your 350 and stock heads have not been rebuilt with efforts to boost CR. But you probably already knew that.
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