347 stroker, vacuum idle problems
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Cross-Country
Joined: Mar 2017
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347 stroker, vacuum idle problems
Video here: https://imgur.com/kLzlivH
The 347 in my 1990 f150 is giving me fits. This is basically a brand new engine, I still have much to do on the truck and the engine has maybe 1h of total runtime. I'm using a sniper efi throttle body to feed it.
My issue lies with vacuum readings, they seem unstable/low at idle but appear to behave properly when I give it a couple blips of the throttle, same with slow acceleration. There is also a noticeable shake at idle. When I rev it, there is no shake, it accelerates smoothly.
I'm leaning towards a problem with the valve train (sticky valves/lash too tight perhaps), but maybe someone here will see something I don't in the video. I should say that I have never put a "performance" cam in an engine before, the cam page on their website states "fair idle", I don't know whether that means I should expecting this behavior or not. I'm mostly concerned about the shake and erratic vacuum.
I don't have a radical cam in it (or do I?), it's a Lunati barebones, specs as follows: Advertised Duration (Int/Exh): 282/292 ;Duration @ .050 (Int/Exh): 218/228 ;Gross Valve Lift (Int/Exh): .496/.494 ;LSA/ICL: 112/108
Thanks in advance for any help.
The 347 in my 1990 f150 is giving me fits. This is basically a brand new engine, I still have much to do on the truck and the engine has maybe 1h of total runtime. I'm using a sniper efi throttle body to feed it.
My issue lies with vacuum readings, they seem unstable/low at idle but appear to behave properly when I give it a couple blips of the throttle, same with slow acceleration. There is also a noticeable shake at idle. When I rev it, there is no shake, it accelerates smoothly.
I'm leaning towards a problem with the valve train (sticky valves/lash too tight perhaps), but maybe someone here will see something I don't in the video. I should say that I have never put a "performance" cam in an engine before, the cam page on their website states "fair idle", I don't know whether that means I should expecting this behavior or not. I'm mostly concerned about the shake and erratic vacuum.
I don't have a radical cam in it (or do I?), it's a Lunati barebones, specs as follows: Advertised Duration (Int/Exh): 282/292 ;Duration @ .050 (Int/Exh): 218/228 ;Gross Valve Lift (Int/Exh): .496/.494 ;LSA/ICL: 112/108
Thanks in advance for any help.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
It's not going to idle like a factoy motor with that cam, 14-15 in/hg and a noticably unsmooth idle is pretty much what that cam is designed to do. The engine shake at idle suggests random misfires which may make the rough idle a little worse than it needs to be, enriching the idle mixture can help with this. That all assumes the valve lash isn't too tight and there are no intake gasket leaks of course.
Logistics Pro
Joined: Aug 2014
Posts: 3,570
Likes: 854
That is how mine ran with a mild cam, 112 LSA, expected behaviour more than likely.
What intake?
Have you dialled in the idle?
Verify timing.
Though I have high acceleration throughout rpm range, not low acceleration.
What intake?
Have you dialled in the idle?
Verify timing.
Though I have high acceleration throughout rpm range, not low acceleration.
Logistics Pro
Joined: Aug 2014
Posts: 3,570
Likes: 854
You have all that as well?
Logistics Pro
Joined: Aug 2010
Posts: 3,718
Likes: 586
From: Chillicothe
The vacuum is about right for that cam.
The idle, hard to tell from that vid, but probably needs more tuning. Sniper TB efi is a glorified carb.
The acceleration being slow:
What transmission?
If auto what stall converter?
Stock stall- yeah that is a problem
2200-2500 probably ok but in a heavy truck may need more. But depends on rear gear.
Stick trans, what gear in rear diff?
Rear gear: Anything less than a 4.10 is a waste of time you need more gear than what came stock.
i have a very similar cam in the 350 my nova. It has a short 26 inch tire with 3.73s, and the stock converter that is in it drags it down till 2500 and it comes on like a light switch. Shouldnt be like that, a stall converter would help a ton.
The idle, hard to tell from that vid, but probably needs more tuning. Sniper TB efi is a glorified carb.
The acceleration being slow:
What transmission?
If auto what stall converter?
Stock stall- yeah that is a problem
2200-2500 probably ok but in a heavy truck may need more. But depends on rear gear.
Stick trans, what gear in rear diff?
Rear gear: Anything less than a 4.10 is a waste of time you need more gear than what came stock.
i have a very similar cam in the 350 my nova. It has a short 26 inch tire with 3.73s, and the stock converter that is in it drags it down till 2500 and it comes on like a light switch. Shouldnt be like that, a stall converter would help a ton.
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Posting Guru
Joined: May 2010
Posts: 1,146
Likes: 17
From: Central Indiana
You said you have an hour on that build. That's not really long enough for a Sniper to learn your engine. Probably looking more at the ten hour range with many starts/stops/freeway/local roads. Your vacuum and idle seem right inline with what the grinder says it is, I don' think you will find better. You also need to heed what was said about the TC and rear gears. As was said in a post above me, 4.10 or better will be needed, this isn't a Mustang. I would go with 4.56 gears and a 2500 stall converter. Add a big trans oil cooler to the list, too. High stall equals high heat.
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