nm9stheham
Well-Known Member
Thanks... exactly the numbers I assumed for the DCR numbers. Pretty common numbers on factory cams.
Large rpm drop
- Thread starter Charlesvolare
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nm9stheham
Well-Known Member
Yes... at light cruise, you're still partly on the transition slots...for a Holley at least.
Wyrmrider
Well-Known Member
110 because that's where the multi lobe "gang" master is set at
they would have tho grind the intakes (or exhausts) then reset the gang master
or use a cnc grinder
or perhaps they are getting cores pre roughed in at 110
whatever - it's a cost- profit thing not a performance thing
they would have tho grind the intakes (or exhausts) then reset the gang master
or use a cnc grinder
or perhaps they are getting cores pre roughed in at 110
whatever - it's a cost- profit thing not a performance thing
I wish I was there to help tune this car. I don't believe the above banter about the camshaft has much relevance to the idle problem
But, carry on...……..
But, carry on...……..
yellow rose
Overnight Sensation
It can be but I seal off the top of the piston with grease to eliminate crevice volume. You can calculate that too later on, and it also matters how far out of the bore the piston is, because sticking the piston out of the hole will reduce crevice volume.
yellow rose
Overnight Sensation
I agree. But he's what I consider short on ignition timing and IMO he is killing power doing that in the places where most guys claim to want the power (and I'm using "guys" in the most broad sense of the term and I'm not trying to label the OP and "that guy" because he hasn't really asked that yet).
I'm a firm believer if you do it correctly you can run the OP's CR on pump gas and and run what is considered full timing.
You just need to be careful moving the intake closing ahead trying to do something you don't need to do when the CR is that high, which is cover up a power loss because most guys don't have the CR they think they have.
Charlesvolare
Well-Known Member
Here's where I'm at:
Pulled the carb, lots of transfer slot exposed. Squared it up, figured out how many turns from 0.020" to 0.040".
Put it back on the car, fiddled around to keep it running. Transfer slot at 0.040" secondaries barely cracked open timing at 30*, idle mixture screws 1 turn out from seated, fuel pressure at 6psi, float level checked, 14-15 inhg on vacuum gauge plugged into full manifold vacuum. ~600 rpm in neutral, ~450 in gear, nothing higher. Black, rich smoke in exhaust, enough to fog surrounding neighbors.
Pulled the carb, lots of transfer slot exposed. Squared it up, figured out how many turns from 0.020" to 0.040".
Put it back on the car, fiddled around to keep it running. Transfer slot at 0.040" secondaries barely cracked open timing at 30*, idle mixture screws 1 turn out from seated, fuel pressure at 6psi, float level checked, 14-15 inhg on vacuum gauge plugged into full manifold vacuum. ~600 rpm in neutral, ~450 in gear, nothing higher. Black, rich smoke in exhaust, enough to fog surrounding neighbors.
yellow rose
Overnight Sensation
Whoever suggested to take a look at make sure the power valve isn't hitting the boss in the main body is a good idea. Many of them hit that boss, and it will allow a big fuel leak that will drive you nuts.
If that is not the case, the next thing to look at is the Idle Feed Restriction in the metering block.
I looked at a 750 Holley a few weeks ago that had HUGE (and by HUGE I mean MASSIVE) IFR's in it. They measured with pin gauges at .060 and they should be .035-.037ish. So almost double the correct size.
If you have 4 corner idle, you need to verify both metering blocks for IFR.
If you find they are sized wrong, you can use brass set screws to correct that.
Also verify the Idle Air Bleed sizing.
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Did you try closing the secondaries.
Charlesvolare
Well-Known Member
Yep, wouldn't idle.
Charlesvolare
Well-Known Member
I pulled off the primary metering block, and it looked wet in the pv cavity. That sound be dry, shouldn't it? Fuel in there would go straight into the straight to the intake manifold. It looks like my metering block isn't adjustable but it also looks like it hasn't been tampered with, I'll dig out some pin gauges and check all those sizes
Correct it should be dry.
I beleive there are two styles of PV gasket. One better matches PV's with rectangular holes, the other with round holes.
Commonly the PV gaskets split when removed, but I don't think this is any of it.
.040 is a lot of T-slot exposure, especially on a newer holley.
Which List number is this?
If you can take a picture of the block.
I'm not ready to blame carb....yet...
Charlesvolare
Well-Known Member
Charlesvolare
Well-Known Member
Using the gasket on the top, which should be the correct gasket
Pressure and float level are good to know.
These should result in the proper fuel level.
The way to check that is at the site plugs. Depending on the carb, fuel should either be just below the plug, or in the mid area of the glass.
And previous it was:
20* @ 1200 rpm
T-slots @ something much more than .040"
~600 in gear
14" in at 600 rpm is pretty strong. That should be enough to pull fuel through the idle ports.
I'm not thrilled about 30* BTC to get that though.
I was expecting 9 to 12" Hg with somehting close to the 20* BTC at 800-1000 rpm.
I'd try some air first. Crack the secondaries more (2 corner idle)
I should have asked, is there a PVC valve?
Charlesvolare
Well-Known Member
Yes PVC, but wasn't hooked up at the time, vacuum gauge was on that port. Didn't idle too much different with pvc plugged in before the gauge was connected
Bingo! That's critical!
Hook the vac gage to one of the low ports on the carb base*.
Either use a PCV or a fixed orifice.
From Chilton's General Manual 1970.
Fixed orifice sizes to substitute for PCV Valve Testing at idle:
Engine (cid) Hole dia. (in) fractional drill
90 to 140; 0.056 - 0.075 or 1/16
141 to 200; 0.074 - 0.088 or 5/64
201 to 275; 0.087 - 0.099 or 3/32
276 to 350; 0.098 - 0.112 or 7/64
351 and up; 0.111 - 0.125 or 1/8
Notice the equivalent PCV fixed orifice is about the same size as drilling holes to let more air in.
*
*
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Yes it looks correct.
80508 is a 4160 vac secondary.
At the moment don't know how it differed from the List 3310
-2 is revision.
Early revision is generally better IMO. So far so good.
If you are going to measure with pin gages, might as well map everything out.
My spread sheet looks like this. Not all of it is important.
I use the same sheets to document changes. Then I add test letter-number and date to the column.
Charlesvolare
Well-Known Member
Update: couldn't find pin gauges yet, put it together with new gaskets, new 6.5 power valve just to check. Plugged in PVC and pulled vacuum cap of front port, right below where check ball port to power valve is and gas came out of cap.
nm9stheham
Well-Known Member
Ruptured PV diaphragm from a backfire..?? Never had that happen myself, but supposedly a common issue for these PV's after a good backfire.
I don't understand needing 30* advance for this latest idle number, with this cam and this SCR/DCR, and the secondary slots closed off. Something sounds fishy in the timing advance measurements....??? Or just super rich with the PV problem....
I don't understand needing 30* advance for this latest idle number, with this cam and this SCR/DCR, and the secondary slots closed off. Something sounds fishy in the timing advance measurements....??? Or just super rich with the PV problem....
It seems like a combination of the excess fuel and the PVC not hooked up.
That carb has the backfire check valve, so if there is a damaged diaphram, its not from backfire.
I've had occassionally leaks into the PV cavity - its always something like the block not sealing or PV not sealing to the block.
The impressions on the block gasket look good, that's why I think its the PV gasket or somehting like that.
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yellow rose
Overnight Sensation
The quickest test I use to verify the power valve isn't hitting the boss is to take the gasket off the metering block, and with the power valve installed with the gasket under it (some guys, for some reason, do this without the gasket under them power valve and I don't know why) stick the metering block up on the main body.
If it wiggles at all, the power valve is hitting. Your metering block isn't billet and they are a bit more conforming so the power valve can be hitting and you may not have an external leak.
Thats the quickest way to verify the power valve isn't hitting the main body.
Wyrmrider
Well-Known Member
.
Engine Specs:
360, 11:1, magnum heads, comp cam (specs inn picture), 750 holley (tuned with wideband, still slightly rich at idle I believe is idling off main circuit)
I went to the comp cams lobe catalog and looked up your HR lobes
nmbr dur .050 .200 lobe 106 110 1.5 1.6 1.7
3314 276 224 145 .335 .068 .055 .503 .536 .570
3315 282 230 151 .340 .078 .064 .510 .544 .578
small block buick journal used for stroker chevies
MI 27.1 (13.4 opening 13.7 closing
just using a regular sbc journal 3192 would have given you 152 @200 and .567lift with a 1.5 rocker on the intake
using a BBC or Mopar sized journal I do not see one for 1.5 rockers
a faster lift rate
3007 270 220 145 .357 .062 .049 .536 you could get same at .200 with 5 degrees less seat if you needed more dynamic compression and a little more lift
3009 276 226 150 .359 .072 .058 .539 or at the same seat duration if 276 is the right number
MI 26.6 (13.1/13.5) on these (which you may not want to do with the heavier mopar valves)
lots of other choices
run what you have
let's see how it works
should be reliable even if it's not perfect but who knows
Engine Specs:
360, 11:1, magnum heads, comp cam (specs inn picture), 750 holley (tuned with wideband, still slightly rich at idle I believe is idling off main circuit)
I went to the comp cams lobe catalog and looked up your HR lobes
nmbr dur .050 .200 lobe 106 110 1.5 1.6 1.7
3314 276 224 145 .335 .068 .055 .503 .536 .570
3315 282 230 151 .340 .078 .064 .510 .544 .578
small block buick journal used for stroker chevies
MI 27.1 (13.4 opening 13.7 closing
just using a regular sbc journal 3192 would have given you 152 @200 and .567lift with a 1.5 rocker on the intake
using a BBC or Mopar sized journal I do not see one for 1.5 rockers
a faster lift rate
3007 270 220 145 .357 .062 .049 .536 you could get same at .200 with 5 degrees less seat if you needed more dynamic compression and a little more lift
3009 276 226 150 .359 .072 .058 .539 or at the same seat duration if 276 is the right number
MI 26.6 (13.1/13.5) on these (which you may not want to do with the heavier mopar valves)
lots of other choices
run what you have
let's see how it works
should be reliable even if it's not perfect but who knows
Have you VERIFIED your timing is correct? As in with another timing light? Preferably one with a fixed (non dial back) setting.
You can also verify this by finding TRUE TDC with a piston stop.
You can also verify this by finding TRUE TDC with a piston stop.
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