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PostPosted: Thu Jul 25, 2019 10:01 am 
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Joined: Mon Oct 23, 2017 9:53 am
Posts: 230
mcbain wrote:
Hi,
I'm stuck on what I hope are some tuning issues with my 351 Cleveland, and am looking for some help or ideas from some old pro's. If I set the timing advance to anything less than 20 deg, it will backfire out the tailpipe at idle. This seems wrong, as from what I understand initial timing for a Cleveland is supposed to be around 14 deg. If I bump the idle timing up to around 24 deg, it runs better, but this seems like an insane amount of advance. I have all the vacuum ports on the carb plugged, and the vac advance on this disty plugged. If I put a vacuum gauge on the full manifold vacuum port of the carb (or in the port on the intake manifold) I see the need rapidly bouncing between 6-9 in Hg. Rapidly. This seems really low, but I do have an aggressive cam in it. The rapid fluctuations in vacuum don't seem right though. Here's some specifics on my setup:

There's only about 400 miles on this newly built motor. It seems to pull pretty good on the road, but admittedly haven't pushed it too hard during the break-in period. Idle is very poor and changes from one stop light to the next. Might idle fine at one light, then a few miles away, it wants to die. Over-heating issues at sustained highway speeds (longer than 20 minutes), made me stop driving it to look deeper. I've got a 3-row radiator, and am blaming it for the over-heating, but wanting to get the other timing and vacuum issues resolved before tackling that. Along those lines - thinking about getting a 4-row Champion radiator and a high flow water pump. (using a standard Ford water pump today)

I've got the distributor installed such that the vacuum port is pointing to the drivers side, instead of straight forward. Does that matter, as long as I've got the rotor pointing to #1 at TDC? I've read in forums that this is a no-no, and also that it doesn't matter as long as you observe the correct firing order and point the rotor to the right cylinder.

I'd like to use the vac advance, but when I connect a line between it and the timing port on the carb, it runs even worse than already. Interestingly, if I take the power brake vacuum plug off the carb, the engine runs a lot better at idle.

It looks like MP4 file attachments are not allowed, otherwise I'd post a video which shows the vacuum gauge rapidly jumping between 6-9 in Hg. Is this expected with such a setup?
Any ideas what's going on with my timing? 24 deg initial just seems outrageous.

Sorry for the long post. Congratulations if you've made it this far! Appreciate any ideas. Disclaimer: I don't know what I'm doing! Just learning as I go. I've probably created a mess here, but don't have any Ford buddies to come over and help me with this.

Your power valve is opening at idle. Thats all it is. Put the 3.5 in and you will be fine. Just went through exact same problem with another guy. Once valve opens it just creates more issues and you end up chasing your tail.


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PostPosted: Sun Jul 28, 2019 10:35 pm 
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Joined: Sun Apr 21, 2019 9:09 pm
Posts: 17
Thanks for the input on the power valve. I suspected the same thing, and bought a 2.5 and 3.5. Tried both, and although neither seemed to solve my idling problems, the 3.5 gave me the best overall performance. With the 2.5 value, I could feel an intermittent hesitation at low speed highway cruising. I'm pretty certain the stock 6.5 value was opening during idle.

I read a couple old Holley books on the 4160, and both recommended drilling small holes in the primary throttle plates, to let in more air at idle. Since I could see my engine idle much better when I opened the power brake vacuum port, it seemed to make sense that my engine setup needed more air at idle too. So I drilled a small 7/64" hole in each primary plate. The books suggested drilling bigger, but I wanted to take small step, and it did seem to help some. I read some forum posts that recommended against drilling holes in the throttle plates - so there you go. I may drill them out bigger at some point, but leaving them as-is for now.

As a general update on my situation, I've given up trying to get the engine to idle at 900 RPM with this cam. I settled at about 1000 RPM for idle and it's doing much better.

After talking to a Cleveland guru at a local drag strip, he was not surprised at all about needing initial timing of 25 deg advance. He said to give it more if it isn't pinging, or use higher octane fuel (>93 pump gas) with the additional advance. I've got mine at about 25 deg initial advance now and it seems to be doing better.

I did get the 4-row Champion radiator for Fox body mustangs, as well as the Flow Kooler high-flow water pump, and these seemed to have solved my heat issues. I just didn't have enough cooling capacity before. I've read on forums that boring the 351C to .060" over can lead to heating problems. The theory is that thinner walls lead to localized boiling in the water jacket because there's less metal to spread the heat along the cylinder walls instead of going out straight to the water. Higher pressure from the high flow pump in the water jacket raises the boiling point, supposedly suppressing the localized boiling. I'm not sure I buy these theories, but that's what my research found on the topic.


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PostPosted: Sat Aug 17, 2019 9:12 am 
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Joined: Mon Nov 05, 2012 3:54 pm
Posts: 70
......over-heating issues at sustained highway speeds (longer than 20 minutes), made me stop driving it to look deeper. I've got a 3-row radiator, and am blaming it for the over-heating, but wanting to get the other timing and vacuum issues resolved before tackling that. Along those lines - thinking about getting a 4-row Champion radiator and a high flow water pump. (using a standard Ford water pump today) ".....

Head gaskets on correctly? Tabs must be showing on the lower front edge of each head.

http://351c.net/board/uploads/monthly_2 ... 83130b.jpg

Pics are of a Windsor engine yet the tabs also apply to all SBF's.

https://www.cjponyparts.com/pub/media/i ... 0111-6.jpg


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