Holley 1850-5
Hi All,
I just inherited a Holley 1850-5 it has vacuum secondary's . Has anyone used this on a 340 4 spd ? I always liked mechanical secondaries myself. Also 600 CFM. It's a street car no strip but maybe a touch small with 20 over with Eddy heads . I am looking for some gas mileage .My AVS is giving me issues after a rebuild so I thought I might try it. I'm thinking Looking for a few opinions.
Thanks
Actually I now think the carb is fine. I just went through the motor, 20 over KB pistons, Same crank, same cam, Eddy heads 60175, Motor sounds good at idle but acts like a severe vacuum leak or like timing marks are off. Stalls , won't accelerate properly. I know I aligned it correctly for stock setting. Timing is at 8 BTC 35' Total. Motor was tired but ran good but sat 10 years before rebuild.New Gas tank and stock fuel pump . I have 15 in. of vacuum at idle. Not sure if this is low for stock 1968 4 speed cam but can't recall what it use to run at . Comp to me is little high at 180 . In the process of moving so it's been hard to get to work on it. Have no Mopar mechanic friends to help .
Well I bump stopped #1 cyl. and found the balancer off 5 degress. So i guess when I was running at 8' for 100k miles it was actually at 13. Guess that's why it ran so good prior to rebuild. Motor still not right. Also at 800 rpm I have 13 in. of vacuum not 15 as previously thought. I might try a different dist. I have just to eliminate any possible issue there. I'm having a hard time thinking water port may be leaking into intake from intake gasket and not oil as well. I forgot to spin the motor while plugs were out so I guess I'll try that next.
With 13"@800@13*@180psi,this should be a dynomite combo.
With the balancer index off, you will have to fix the power-timing, as 40* is too much. The Eddie heads don't need much more than 32*.
Steam out the tailpipes at this time of year, with lots of humidity in the air is normal, especially during the warm-up period.
"Eddy heads 60175, Motor sounds good at idle but acts like a severe vacuum leak or like timing marks are off. Stalls , won't accelerate properly." This obviously is not normal, and I think 13"@800 is perhaps a lil low for a stock 340 cam @13* Idle-timing. Between what I believe and what you are experiencing,and the fact that additional timing didn't improve the situation; I have to conclude that you have a modest vacuum leak somewhere.
I would carefully examine the
PCV system first. If you have a brake
booster check the line and especially the ends,then clamp it off and note the engine idle speed and quality change. If none then remove the clamp. Then check any other
vacuum lines and circuits that may be on the intake or carb. If all is good there,then move on to the
carb base gasket,
the intake ports and especially the underside in
the valley. To check the valley, I put a vacuum gauge on the dipstick tube, then flip the PCV out of the valve cover, then seal both valve covers. Now start it up and watch the gauge; there should not be any vacuum developing in the crankcase, in fact, without the PCV, it should actually begin to build a pressure in there. That would be what I would expect to see. If you see pressure,
do not let it it exceed 3 to 4 psi, as excessive pressure will blow out something; be it seals, or gaskets.
I could be wrong on suspecting a vacuum leak, so if you don't find one then you can move along to the carb. But you can't start working on the carb until you are sure you don't have a vacuum leak. Well you could if you don't mind chasing your tail for a few hours.
And it is imperative that you know EXACTLY what your idle-timing is, and that starts with finding true, #1-TDC.I don't know what "bump-stopping" is, just make sure you done it right. With 180psi, I would advise against too much more than 13* idle-timing as, the low-rpm when you engage the clutch or try to drive slower than curb idle speed, will get real jumpy; and with 3.23s @ 650 rpm, your minimum road-speed will be about 6mph. After that you will have to slip the clutch. I have to crank mine back to 5* with my dash-mounted dial-back timing device, so as to delay the jumpiness to 550rpm@ 4mph, Yeah they run down there if you get the t-slot tune right, and very sweetly I might add.
So once you have your power-timing limited to 32/34 with the idle-timing at 13 to 15, then just make sure it doesn't come in too fast for 3.23s and a 4-speed. If you have 28* by 2800, that is fast enough.
Now,after all that is done, you can attack the carb.
But first; as to gas-mileage with a 340,with the stock cam, IMO forget about it. And the reason is, I recently found out, is because the cam is a lot bigger than the specs indicate. Mopar calls that cam a 268/276/114+4 but it is rated at at .008 tappet lift, and on that cam it is a looooooooong way from .008 tappet lift to intake actually on the seat.And it's the same deal on the exhaust side. So if you work out the valve events on that cam with the advertised numbers,and in at 110, you get ; intake duration of 268*, exhaust of 276*, compression of 116*, power of 104*, and overlap of 44*; which on paper looks pretty good.
What you don't see is; firstly, that exhaust duration from sealed to sealed is actually an awful lot shorter than 104*, which means an awful lot of energy still remains in the expanding gasses when the exhaust valve actually opens. I'm gonna guess that that the valve actually opens as early as 90*ATDC....... which is fine for making power at high revs...... but for you at 65=2600rpm, it is lousy. Wait, make that; really lousy.
Another thing you don't see is what is actually going on at TDC-Overlap. The advertised is only 44*measured at .008 tappet lift/.012 valve lift. So the valves are not actually closed YET!! Again, I'll guess that this sealed to sealed time is actually closer to , eh, actually I can't guess on the sealed to sealed, it could be flipping huge.
So, now with manifolds this is not a huge deal with that early opening exhaust valve, but your intake manifold is still gonna see a lot of EGR at low rpms, hence the 13" at 800rpm. But that EGR wreaks havoc on tuning the carb, especially with the ring seal that is required to make 180psi. This all adds up to very poor engine efficiency at low rpms.
But with headers it gets worse. Now the pipes, inertially tuned, are pulling on the carb during overlap, pretty hard; which is not just 44* seat to seat but some much much bigger effective amount,at low rpm, where there is plenty of time to yank A/F charge on thru.
To get the best from this cam, in terms of fuel mileage, you need a cruising rpm that is at least as high as your vacuum peak, which is the lowest rpm that reversion is mostly stopped. So rev it up in neutral and watch the vacuum gauge. The manifold vacuum will rise to a plateau and then begin to fall. You wanna cruise on the plateau. The next thing is, on the plateau, you wanna give the engine the timing it craves, and that could be as much as 55/60 degrees. You might only have 26*@2600 in the mechanical +initial, so the rest has to come from the Vcan. But the biggest Vcan I have seen was 20*, which I have modified to 24*. So about the most you can get is 26+24=50*. To get more, you would have to increase the Idle-timing, and/or speed up the rate of advance. If you did both, you might get as much as 20+8+24=52* @2600 which is still not enough, but now you have the added problem of the jumpiness at 650rpm that 20* initial brings on. IMO, it is better to leave the initial at 14 and mess with the rate of advance, to achieve the same end-result of 28@2600.
So that is why IMO, you will never get great mileage with the factory cam and 3.23s and a cruise rpm of 2600.
Now throw into the mix, the 1850 carb, which has a fairly rich low-speed circuit, made worse by the cam, and forget mileage. You need that metering-rod carb so you can really lean out the cruise circuit....... but you can't lean it out until you get the timing maxed out. Then you lean it out. Then you increase the timing so you can lean it out some more. Then you hit a wall that no more timing ,nor any less fuelling, gets you any better mileage, and now the car doesn't even want to accelerate to cruising speed anymore, unless you get up on the mains........ and there goes the mileage!
IMO
I would pull that cam in a heartbeat. You can make equal or better power WITH better mileage, with a more "modern" cam.
This does not speak to your current tuning problems, tho, I'm jus saying, not to expect much from the Mopar factory cam (used no less),in terms of fuel mileage.
Don't even think about swapping the 3.23s out for 2.94s or less, it will only make less mileage on account of they will put you on the wrong side of the vacuum-plateau. Instead; drive faster lol.
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In the 60s, my dad and his brothers used to buy big-motor Buicks and Olds and such, cuz, they said, they got best mileage at 85plus mph. At 60 they sucked gas.But they had a hard time keeping tires on them in those days.
I have a recipe for 32mpgs from a high compression 367......... I'd like to try it with a 3.79 stroke 340 one day,lol. That could be a 396 cuber at 4.08bore....... Yeah, 396......that has a nice ring to it.
