Vacuum on 1968 GTS 340 4 spd.

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Kendog 170

Kendog 170

Let the boy go !
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Anyone have a stock 1968 Dart 340 4 spd ? I was wondering what your vacuum reading is. I bored mine 20 over with eddy heads KB pistons same cam . My vacuum is only 13 at idle. Engine Acts like it has a vacuum leak but cant find any. This includes putting a vacuum gauge on the dip stick tube after sealing valve covers and vacuum ports.I cant remember but I thought it should be around 16 In.
Thanks
 
Kendog 170 said:
Anyone have a stock 1968 Dart 340 4 spd ? I was wondering what your vacuum reading is. I bored mine 20 over with eddy heads KB pistons same cam . My vacuum is only 13 at idle. Engine Acts like it has a vacuum leak but cant find any. This includes putting a vacuum gauge on the dip stick tube after sealing valve covers and vacuum ports.I cant remember but I thought it should be around 16 In.
Thanks
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That's about all my pure stock 340 4sp back in the day would pull. No worries. Same with another friend of mine. with his 69 340 4sp Dart. We compared and the best at idle was 13 - 13.5 Cars ran great.
 
Kendog 170 said:
Anyone have a stock 1968 Dart 340 4 spd ? I was wondering what your vacuum reading is. I bored mine 20 over with eddy heads KB pistons same cam . My vacuum is only 13 at idle. Engine Acts like it has a vacuum leak but cant find any. This includes putting a vacuum gauge on the dip stick tube after sealing valve covers and vacuum ports.I cant remember but I thought it should be around 16 In.
Thanks
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At idle in gear?

Which cam do you have?
The early cam?
 
did your compression change?
actually your vac sounds about right
automatic cam would be more
a more modern cam would be more as yours has unnecessarily long ramps, more overlap than required
did you get any quench (depends on which head and which pistons and your attention to detail)
 
As already asked, where's your initial timing?
 
Sorry for the late response. I'm at 16' initial.All in at 35' I think I'm around 10.8 CR. Comp test at 180 PSI. Rebuilt the stock 600 cfm Carter then tried a 625 Eddy I rebuilt but engine acts like vacuum leak . Runs the same with both carbs. New wires ,cap and rotor. Plugs. Idles good but will surge at times. Motor won't go at WOT. Old timing chain and new chain set the same. Motor ran good but was tired before rebuild. Found crack between 5 & 7 on X heads that's why I went with the Eddys . Haven't check fuel pressure yet but just a New stock Carter pump stock filter.
 
Do you have a PVC valve from another SBM engine? If so, it may be one with a higher transition vacuum level, like 14-15" from a 318. If so, it be wide open at idle instead of closed down to the lower idle flow level, and that will dump extra air into the intake. Pinch down the PCV hose and measure how much the idle vacuum changes.

Also, the secondary throttle stop screw may be too wide open. This can cause low vacuum by 1-2" and cause associated off-idle problems.

Can you explain the "won't go at WOT" comment a bit more? Just dead feeling? Won't rev past *** RPM? Misses and stumbles?

New lifters on the cam or the same ones in the exact same holes?

Premium pump fuel? Which Eddy heads? The one with the 'open chamber milled in them. That is an awful lot of timing to put in for true 10.8 SCR on pump fuel, especially if it comes in early. Just concerned that it is on the edge of detonation.
 
Same stock Non adjustable hydraulic Rockers with same push rods.I replaced the lifters with new set (Comp Cams) that I originally bought for my 440 .Same part number CC822-16 and lubed cam lobes and lifters. Motor sounds nice at idle ,no ticks or skips.Premium fuel. Almost like not getting gas at wot no power like timing chain off a tooth. I rotated the motor numerous times to double check marks when I assembled the Timing gears. Car is not yet registered. I only drove it a few miles each way for a front end alignment with a borrowed repair plate. I may register it so can drive it more but Winter and salt on roads makes me want to wait till spring.
 
I think edelbrock heads require adjustable rockers.
 
The heads don't 'require' adjustable rockers per se, but it makes adjusting everything a lot easier. Otherwise, you may well be changing out pushrods.

You can do an approximate check on cam timing by:
- Find TDC on #1 by using a piston stop; don't count on the damper 0 mark as it can move/slip. By using the piston stop, you will be able to verify the damper 0 mark to be sure your ignition timing is actually what you think
- Once you find true TDC on #1, remove the driver's side valve cover and look at the position of the intake and exhaust rockers on #1. If both are fully closed, then rotate the engine 1 full turn to get back to TDC, and look. The 2 rockers ought to be open a slight and almost equal amounts. The intake might be a bit more open.
- One thing that can throw this off is if either lifter on #1 leaks off pressure when sitting. To avoid, this, run the engine a minute or so before doing this test.
 
I did use a piston stop already and found Balancer was off 5' degrees. I remarked my damper . I thought originally my timing was set at 8' BTD but was actually at 12' I now had bumped to 16' to see if it helped but didn't so I'm going to pull it back a bit .I did not no how to check the cam but know will check that with your suggestion. Thanks !
 
I would also try checking the lifter preload, not much else at this point. I can pretty much guarantee with your Eddy heads and new head gaskets the pushrods need to be a different length, most likely shorter. Were the heads milled at all? I kind of hope so TBH, I have a pair of Edelbrocks that just got done and my machinist said the decks were super crooked, had to take off .008" to make them flat.

If the pushrods are long enough it could be causing some of the valves to hang open just slightly which would make sense with the low vacuum and weird running issues.

OH yeah and once this is figured out get a new harmonic damper on there pronto, from here on out the outer ring will just keep slipping which is no bueno. You'll keep chasing timing marks that move and the crankshaft might eventually get damaged.
 
MOPEkidD-3 said:
OH yeah and once this is figured out get a new harmonic damper on there pronto, from here on out the outer ring will just keep slipping which is no bueno. You'll keep chasing timing marks that move and the crankshaft might eventually get damaged.
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Good point... not to mention that if the ring has slipped and the rubber is cracked between the outer ring and hub, then the damper is no longer doing its job of the damping the internal high frequency crank vibrations. BTW, if you want to keep the old one, it can be rebuilt at a place like Damper Doctor; there may be other rebuilders too.
 
Kendog 170 said:
I did use a piston stop already and found Balancer was off 5' degrees. I remarked my damper . I thought originally my timing was set at 8' BTD but was actually at 12' I now had bumped to 16' to see if it helped but didn't so I'm going to pull it back a bit .I did not no how to check the cam but know will check that with your suggestion. Thanks !
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This is just a rough check to find gross errors in cam timing. And if the intake and exhaust valves are way off from each other do 2 things:
  1. Push down on both rockers on the pushrod end to see if they are soft; this is just to see if either lifter has likely leaked down. The both should be firm.
  2. If the lifters are firm but the 2 rockers way off from each other at TDC, then rotate the crank to get them level with each other. If the chain is off at the crank sprocket by 1 tooth off, then you should rotate the crank approximately 15 degrees + or - to get them level with each other.
 
Ok, turns out my vacuum gauge was messed up. I have 8" of vacuum. And yes I do plan on changing the balancer. So much for bolt on replacement heads if I have to change pushrods and or Rockers. My fault for not checking. I think 1st I might try putting .010 Rocker shaft shims in to see if vacuum changes at all After I do the cam check just to see if there is a change in vacuum . Sadly I never checked pre-load thinking direct bolt on ect: motor wasn't decked .I dont have a sm. blk. adj. pushrod to check preload . But I agree maybe intake valves not fully seating as I cant find an intake leak . Anyone selling some decent 273 Rocker assemblies? I see a few on E-bay. I don't have money to throw around right now but I do have time. I'll order a shim kit and adjustable pushrod for now to check preload. I do appreciate the advice. I'll keep you posted.
 
Oh, reason moneys tight is wife out of work with government shutdown so not spending at the moment .
 
You can check preload without a checker.
  • Loosen up the rockers on a side and find a lifter that is on the base circle of the cam
  • Put shims under the valve for the corresponding rocker to juuust take up the slack on the pushrod side
  • Lay a razor blade or other sharp edge across the valve cover surface and holding it steadily against the pushrod, rotate the pushrod to put a mark around it. (And there are a variety of ways to make this refereence mark on the pushrod...) You can put a reference pointer (a piece of bent wire) to the mark under a valve cover bolt.
  • Bolt your rockers back down, and see how far the mark has moved down. As a double check, start engine to pump-up lifters (no need to rev it or run it after getting oil pressure for 5-10 seconds), stop engine, put that lifter on the base circle again, and see how far down that mark on the pushrod is now. You can leave the the pointer on when you start the engine if you just idle it; oil usually just dribbles out of the stock rockers at idle.
 
Wow! That's awesome advice. I will try it. So I think I'm looking for about .050-.090 preload anything more would potentially hold intake from seating and or bend push rod ? Thanks again.
 
The lifters' pistons 'typically' have a gauranteed range of up to .120-160".... But some have more. Running the .050" to .080" range gets you roughly in the middle of the 'typical' range. Also note that is can vary between each rocker/pushrod/valve, so if you can do a couple of valve this way, it would not hurt. A valve sunk into the head from a valve job can stick up further than its neighbors and push the pushrod in even further; deck heights can vary; rocker and rocker/shaft wear can vary.

And, the pushrods typically only bend if things get so out of whack that a valve hits a piston.

If you have an old spare pushrod or just buy a cheap new one, you can make your own checker by cutting out a 1" section up near one end, threading the inside, and putting a piece of skinny all thread between the end with locknuts. That is they are!
 
The heads are New so hopefully not much variation. I thought of making a pushrod as you mentioned but only have two sets of ball and cup type.
 
Ok, so I didn't have much luck scoring and measuring as you suggested but I did install .030 rocker shims on one side and started it up and every lifter was ticking . I did let it idle enough to be sure lifters were pumped up as well . I removed the shims and motor back to nice and quiet.Maybe a little short if anything. Now comes the strangest thing. I decided to do a compression check and found left bank all averaging near 175. When I check right bank all about 145! WTF ! I could have sworn I did both sides when I check it last July , I must be losing my mind.I didn't deck the engine. I used EDL-7326 that came with the heads they say .050 . Could I have swapped the FEL-8553PT head gaskets .039 that came with my Felpro set? I measured .065 uncompressed on each of the Felpros I still have.:BangHead:
 
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