Carb issue?

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Christopher Vastine said:
I reread the posts and your calculations are based on a flat top piston. I only mentioned kieth black pistons, but not which ones(23cc). I read the 12-1 compression ratio again and thought no way could I be that far off. Punching in the numbers on the wallace calculator with the cam i get the below information. Now i may have done something wrong but i think this is more accurate. A 12-1 cr will not run at this altitude on pump gas and i was building a 10-1 cr motor.

Static compression ratio of 10.1 :1.
Effective stroke is 3.60 inches.
Your dynamic compression ratio is 9.19:1 .
Your dynamic cranking pressure is 158.48 PSI.
V/P (Volume to Pressure Index) is 176
Click to expand...

When you said Zero-deck,yes, I assumed flat tops .
I bet you entered the .050 Ica spec, Didn't you.
The Wallace is not set up for that; you have to calculate and enter the advertised spec. which then comes to;

Static compression ratio of 10:1.
Ica of 81*(see bottom of page) @6900ft
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 6.94:1 .
Your dynamic cranking pressure is 100.49 PSI.
V/P (Volume to Pressure Index) is 82

and if in fact you are at 6900ft with just 10/1, then with the Ica of 81*, that engine should present as being extremely lazy at low rpm. I know of no bandaid for this condition.
Furthermore this would be another, perhaps the biggest, reason that your throttle needs to be so far open to idle. The engine is just not making enough power to idle at a more normal throttle opening.

I highly recommend that you do a compression test ASAP!
With a fully charged battery and the carb at WOT, crank as many times as it takes to get two consecutive same/near same, pressure readings. Warm is better than cold.
For a streeter, Static compression ratio, as a guide to building an engine, is as good as useless.
For a streeter, the predicted cranking cylinder pressure, is a far more useful tool. With alloy heads, it is possible to run up near 200psi, still on pump gas. My engine has run up to nearly 200, and the current combo is a tic under 180, still running on 87E10 at full timing/full load @930ft elevation.

Here's how I figured your Ica from the advertised of;
308/318/112+5

(1/2 intake duration, less the installed centerline, plus 360) less the intake duration, less 180, and finally sign change equals the Ica.
Here's how it looks in scientific notation;
let
Aid be advertized Intake Duration (308)
ICL be the Installed Intake Centerline (107)
Ica be the Intake closing angle

Ica=[(Aid/2-107)+360]-308-180, signchange= 81*
 
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AJ/FormS said:
When you said Zero-deck,yes, I assumed flat tops .
I bet you entered the .050 Ica spec, Didn't you.
The Wallace is not set up for that; you have to calculate and enter the advertised spec. which then comes to;

Static compression ratio of 10:1.
Ica of 81*(see bottom of page) @6900ft
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 6.94:1 .
Your dynamic cranking pressure is 100.49 PSI.
V/P (Volume to Pressure Index) is 82

and if in fact you are at 6900ft with just 10/1, then with the Ica of 81*, that engine should present as being extremely lazy at low rpm. I know of no bandaid for this condition.
Furthermore this would be another, perhaps the biggest, reason that your throttle needs to be so far open to idle. The engine is just not making enough power to idle at a more normal throttle opening.

I highly recommend that you do a compression test ASAP!
With a fully charged battery and the carb at WOT, crank as many times as it takes to get two consecutive same/near same, pressure readings. Warm is better than cold.
For a streeter, Static compression ratio, as a guide to building an engine, is as good as useless.
For a streeter, the predicted cranking cylinder pressure, is a far more useful tool. With alloy heads, it is possible to run up near 200psi, still on pump gas. My engine has run up to nearly 200, and the current combo is a tic under 180, still running on 87E10 at full timing/full load @930ft elevation.

Here's how I figured your Ica from the advertised of;
308/318/112+5

(1/2 intake duration, less the installed centerline, plus 360) less the intake duration, less 180, and finally sign change equals the Ica.
Here's how it looks in scientific notation;
let
Aid be advertized Intake Duration (308)
ICL be the Installed Intake Centerline (107)
Ica be the Intake closing angle

Ica=[(Aid/2-107)+360]-308-180, signchange= 81*
Click to expand...
Correct i entered in the degrees at .050. Compression test results where posted earlier. Cold and dry with full battery was 160ish on all 8 cylinders.
 
With what you have for typical hyd lifter leak down rates these days, I wouldn’t consider a cranking compression test as the last word on how the engine sees the timing events while it’s running, and the lifters are fully pumped up.

You could verify the accuracy of the test by adjusting one pair of rockers so the lifter preload was just up from “bottomed”....... to see if it impacted the results.
 
Dana said:
Why go spend money on a different pcv. There is no crime drilling throttle blades. If you later use the carb on something different, just replace the blades or epoxy them shut.
Click to expand...

A pcv is cheap and can be changed over at any time with a varying sized orifices. You can also use a rubber hose with a designated orifice size without a pcv and run it from the air cleaner and its a cheap alternative. Replacing throttle plates is a PIA and costs money too so does epoxy. What happens if the epoxy comes out.....

Ideally you want all the air to come out the t-slot instead of introducing it into the airstream without fuel entrained in it.
 
Hysteric said:
A pcv is cheap and can be changed over at any time with a varying sized orifices. You can also use a rubber hose with a designated orifice size without a pcv and run it from the air cleaner and its a cheap alternative. Replacing throttle plates is a PIA and costs money too so does epoxy. What happens if the epoxy comes out.....

Ideally you want all the air to come out the t-slot instead of introducing it into the airstream without fuel entrained in it.
Click to expand...
Nah, replacing throttle blades is just nuts and bolts, like everything else. And epoxy done right does not fall out.
 
Dana said:
Nah, replacing throttle blades is just nuts and bolts, like everything else. And epoxy done right does not fall out.
Click to expand...

For some one who does it for a living I'd agree. For some with limited understanding about carbs and tuning its easier to use different pcv's. I know I'd rather change pcv's or orifice bleed sizes than change throttle blades. It doesn't require pulling the carb off to start and can be done numerous times in a few minutes.
 
AJ/FormS said:
When you said Zero-deck,yes, I assumed flat tops .
I bet you entered the .050 Ica spec, Didn't you.
The Wallace is not set up for that; you have to calculate and enter the advertised spec. which then comes to;

Static compression ratio of 10:1.
Ica of 81*(see bottom of page) @6900ft
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 6.94:1 .
Your dynamic cranking pressure is 100.49 PSI.
V/P (Volume to Pressure Index) is 82

and if in fact you are at 6900ft with just 10/1, then with the Ica of 81*, that engine should present as being extremely lazy at low rpm. I know of no bandaid for this condition.
Furthermore this would be another, perhaps the biggest, reason that your throttle needs to be so far open to idle. The engine is just not making enough power to idle at a more normal throttle opening.

I highly recommend that you do a compression test ASAP!
With a fully charged battery and the carb at WOT, crank as many times as it takes to get two consecutive same/near same, pressure readings. Warm is better than cold.
For a streeter, Static compression ratio, as a guide to building an engine, is as good as useless.
For a streeter, the predicted cranking cylinder pressure, is a far more useful tool. With alloy heads, it is possible to run up near 200psi, still on pump gas. My engine has run up to nearly 200, and the current combo is a tic under 180, still running on 87E10 at full timing/full load @930ft elevation.

Here's how I figured your Ica from the advertised of;
308/318/112+5

(1/2 intake duration, less the installed centerline, plus 360) less the intake duration, less 180, and finally sign change equals the Ica.
Here's how it looks in scientific notation;
let
Aid be advertized Intake Duration (308)
ICL be the Installed Intake Centerline (107)
Ica be the Intake closing angle

Ica=[(Aid/2-107)+360]-308-180, signchange= 81*
Click to expand...


So based off what you have posted and a lot of learning on cams thanks to you. I am catching that the cam is a horrible match to the motor. Keeping it streetable on 91 octane pump gas dynamic compression should be between 7.5-8.5. The below cam would be a much better match to the motor and vehicle:

Advertised Duration (Int/Exh): 268/276; Duration @ .050 (Int/Exh): 226/234; Gross Valve Lift (Int/Exh): .494/.513; LSA/ICL: 110/106; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1800-6200; Includes: Cam & Lifters (#71977PR-16)

IVO is 28.0 ° BTDC ( - indicates ATDC)
IVC is 60.0 ° ABDC
EVO is 72.0 ° ATDC ( - indicates BTDC)
EVC is 24.0 ° BBDC
Overlap is 52 °

Static compression ratio of 10:1.
Effective stroke is 3.25 inches.
Your dynamic compression ratio is 8.31:1 .
Your dynamic cranking pressure is 135.34 PSI.
 
PCVs are not gonna solve this man's problems; OP is at 6900 ft elevation, and his engine is starving for air.
He has already stated that the butterflies have to be opened up PAST the top of the transfers, at 26* advance just to keep it from stalling. Just ONE PCV will never meet that demand for air. Even two will not do it. And even if they did, how are you gonna compensate the AFR for that dry air as the throttle continues to open?
_____________________
To Christopher;
IMO, holes in the blades are the BEST option, because as the throttles are opened, they do less and less until by the time the blades stand vertical the holes are doing nothing.
>In your case, because your engine wants so much air, and because of your elevation, I have no idea how much bypass air she will need.
But, it easier to control the cross sectional area with smaller multiple holes than with just one large hole in each blade. So then; I would recommend to drill TWO small holes in each blade, straddling the transfer slot. IMO, you may need more cross-section area, than the equivalent of 4 holes each of 1/16".... I'm guessing.
To start, drill just one hole in each blade, and see how it goes. Again, set your transfer slot exposure FIRST, put your mixture screws to 2.0 turns, and your Idle timing to 16*. If the first two holes are not enough to bring the idle up to 800/850, then drill two more, on the other sides of the Tslots; ONLY two per blade, and try again.
Do not put the holes too close together or too close to the edge of the blades. Chamfer both sides when you are done.
Once you are close, you can try-increasing timing to speed it up, or decrease the timing to slow it down, AND twiddling the mixture screws for fine tuning. If you cannot get into the ballpark, put the timing back to 16*; then increase the hole sizes. On the first cycle, enlarge just one in each blade, to the next larger size by 64ths, so 5/64 inch. If you need still more, then enlarge the other two. Each time the holes get bigger, the cross-section increases exponentially, so it is easy to overdo it, so be careful!
When you get really close, you can vary the fuel delivery; by returning the mixture screws to 2.0, and then, varying the transfer slot fuel, to prevent a tip-in sag.

Caution;
I inadvertently made my holes too big as I was learning this.
To get past this, I chamferred the holes both sides and soldered them closed,then dressed the lumps down; then moved over and started fresh. I chose solder because solder is soft, malleable, and melts at low temperature. My thinking was that if it ever did fall out, it wouldn't hurt my 11/1 engine. It was a bit tricky to get the solder to stick but I got her.
That was year 2000, and the solder is still in there, over 100,000 miles later..

EDIT; added from post #76
BTW
If you are attempting to tune to a vacuum number, with the 7177 cam, you are in a world of hurt. Because it will lead to a massive amount of idle-timing.

I rarely use a vacuum gauge to even observe the idle-vacuum, of an engine with a performance cam.
At 930ft elevation, my 367cuber will idle down to 550 in gear (10.97 starter gear) and pulling itself with no clutch slipping, at 5*advance, with an ancient 750DP, @10.95Scr and a Hughes HE3037AL cam, that is advertised at 276/286/110 and .050s @ 230/236. I have absolutely no clue what the vacuum is and don't care, because the T-slot setting allows lots of tip-in without a sag/hesitation. No, 5* timing is not my normal Idle-timing, which is just what I use for cruising the parking lots at 3.9 mph. My standard Idle-timing is ~14* at 207*F running temperature.
This same 750DP has been on all three iterations; 292/292/108, 270/276/110, and the current 276/286/110.
Only the 270 cam did not require bypass air; Having come from the 292 cam, I did have to solder the holes closed. Going to the 276 cam, I had to provide the bypass again.
Just saying.
 
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Christopher Vastine said:
Advertised Duration (Int/Exh): 268/276; Duration @ .050 (Int/Exh): 226/234; Gross Valve Lift (Int/Exh): .494/.513; LSA/ICL: 110/106; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1800-6200; Includes: Cam & Lifters (#71977PR-16)
Click to expand...
Ok hold on, did you not say 7177 cam? The Edelbrock site told me that 7177 was 308/318/112
I'm in trouble, aren't I,lol

Well that explains the discrepancy between the Wallace predicted pressure and your actual ncompression test numbers. I was wondering how we were gonna resolve that!

Static compression ratio of 10:1.
Ica of 60* @6900ft elevation
Effective stroke is 3.25 inches.
Your dynamic compression ratio is 8.31:1 .
Your dynamic cranking pressure is 135.34 PSI.
V/P (Volume to Pressure Index) is 135

This is closer to your 155psi compression gauge numbers. I still don't know what to make of the discrepancy. The only way I can make the Calculator spit out 155psi is by manipulating the elevation or the compression ratio. And for compression ratio, using your numbers , I get only 9.86, so there is no room for fudging that, leaving only altitude.
In any case
With the new Cam specs of 268/276/110 and 226/[email protected]
I take back all the negativity I said about the previous cam and combo.
Your Ica is now 60*, right on the number I previously posted as the minimum.
This is a great cam-spec; I ran a similar Hughes cam in my 367, and at 11/1 it was a torque beast. I can only imagine what it would be like in a 410 at my elevation of 930ft.
 
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AJ/FormS said:
Ok hold on, did you not say 7177 cam? The Edelbrock site told me that 7177 was 308/318/112
I'm in trouble, aren't I,lol

Well that explains the discrepancy between the Wallace predicted pressure and your actual ncompression test numbers. I was wondering how we were gonna resolve that!
Click to expand...

The current cam is the edelbrock 7177, but i am considering doing a cam swap for a better match. The above specs are a Lunati cam that bring the dynamic compression up significantly. Is recommended for a 2400 stall torque converter with isn't a problem as i currently have a 2500 stall. Previous owner had a 518 built to support 600hp and a 2500 stall. Thank you for all your time and help.
 
Oh boy, the plot thickens :(

Ok , I'm not ready to ditch the 7177 yet. the bypass air will make it idle and you,I assume, haven't even driven yet, right?

But we have a different problem we need to address first.
IIRC you said your compression test results were 155 psi/all; but
the Wallace predicted just 100psi at 6900ft at Ica of 81* which is the 7177 cam (specs of 308/318/110advertised, 234/[email protected]) in at 5* advanced. See this;

Static compression ratio of 10:1.
Ica of 81* @6900ft
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 6.94:1 .
Your dynamic cranking pressure is 100.49 PSI.
V/P (Volume to Pressure Index) is 82

This is too much discrepancy to ignore!
I hate to say this, but something is outta whack, the Wallace has never been this far off base; so either I am inputting erroneous data as concerns the Ica or the Scr or the altitude
OR
your tester is rather optimistic. We are gonna have to reconcile this before talking about camswaps
AND
if the Wallace is right, then YOU are in trouble. But if your tester is right, then I am in trouble.
So lemmee ask you to supply your advertised cam specs, and
your actual elevation,and
your actual measurements as used to calculate your compression ratio. And maybe we can get to the bottom of this.
As to these numbers,in my memory , I have;
total chamber size of; 65head+23dish+6.8gasket+ 0deck= 94.8cc
and swept of 840.26cc, so Scr is
(840.26+94.8)/94.8=9.76
Lessee what you come up with. I'm really interested in the actual elevation where the compression test was done

EDIT;
with 63cc heads, it comes to 10.05



But if you are gonna ditch the 7177, with this really low pressure (100psi), then you need to go straight to a SOLID-lifter cam, with a tight lash, fast ramp design, to compensate for that.
 
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Disregard, as i don't mean to be a pain and really appreciated all your help. Regarding plot thickens previous onwer had nothing to do with the motor just the transmission and rearend before giving up, but still had original motor installed. I built the replacement motor utilizing a local very reputable machine shop to do the machine work.
 
Hey man, I'm semi-retired,covid is a *****, no kids are home for Christmas, I got the day off; and I'd love to get to the bottom of this,
So; I'm here for you.
Besides; I'm tired of playing Spider Solitaire,lol.
 
PRH has the best advise here. Try a carb more suitable for the combination.
Or hand if off to Dana .. someone who knows how to fix it.
Otherwise this thread will expand multiple pages without solving the issue.
 
AJ/FormS said:
Hey man, I'm semi-retired,covid is a *****, no kids are home for Christmas, I got the day off; and I'd love to get to the bottom of this,
So; I'm here for you.
Besides; I'm tired of playing Spider Solitaire,lol.
Click to expand...
I am active duty military, but went to college and was ase certified. Over the last 20 years i have built and restored many cars, but no performance motors other than a few 350's and 400's. I never had an issue like this.

As far as the cr discrepancy heads are 63cc vs 65cc.
Using the Wallace which takes into consideration the head gasket diameter it is 9.8-1.

The only reason for the 7177 cam was that edelbrock recommended it for a match with the heads and intake, but doesn't seem like a good match after all. I found several posts last night from others with similar vacuum issues that had a problem with lifters(coming apart, becoming flat, and other issues). I had one that would never prime after setting the lifter preload and was sent a replacement.

Speaking with two reputable machine shops here that everyone uses to build the race and demolition derby motors they made similar comments to you.

Dynamic compression with aluminum heads 8.2-8.4 and 8.0 for cast iron heads.

My compression test was done cold wide open throttle with plugs removed. Cranked over 4 times watching needle jump and recording the number.
Elevation for my area is 6854ft.
 
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'63GT said:
PRH has the best advise here. Try a carb more suitable for the combination.
Or hand if off to Dana .. someone who knows how to fix it.
Otherwise this thread will expand multiple pages without solving the issue.
Click to expand...

Working on that as well. I have a buddy bringing over a holley 750DP to try, but will be a few days.
 
Christopher Vastine said:
Working on that as well. I have a buddy bringing over a holley 750DP to try, but will be a few days.
Click to expand...

Good move. Try it. There's a reason race carbs are a Holley knock-off.
The Carter AFB/AVS are ok for stockish cams... you're beyond that now.
They can be made to work, as PRH said, but it's not for the faint of heart. (As in NHRA stock and super stock)
 
Christopher Vastine said:
Working on that as well. I have a buddy bringing over a holley 750DP to try, but will be a few days.
Click to expand...

Hopefully it’s one that’s new enough to have 4 corner idle. They didn’t always have that.

The bottom line is, with the right carb, a motor could have 120-130psi cranking pressure, along with 4-5” vacuum...... and still idle just fine....... if the carb is set up to accommodate those parameters.

The Ede carbs aren’t.
 
Race carb?

2D112292-CDD5-446B-98E8-C50EFC389202.png
 
At 6900’ elevation in an engine with 5-6” vacuum?

In any case...... it doesn’t seem to be getting the job done for the OP...... or seem to even be “close”.

Hopefully he can get it sorted out.
 
Christopher Vastine said:
Currently i have low unstable vacuum at idle of around 5-8". The carb will not allow me to adjust idle screw low enough for the idle circuit. This is causing a very rich idle issue. If i hold the secondaries open a little rpms jump and vacuum goes to a solid 10"-12" depending on rpm
Click to expand...

So its 5-8" of vacuum and rich and when you introduce more air it leans out and produces 10-12" more vacuum.

At what rpms are differences?
 
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