All Small Six Winter Project: Better breathing with a large log
- Thread starter awasson
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- large log head
This relates to all small sixes
Just a quick update. I’ve got the head stripped and all of my parts ready but life and work has been busy and I haven’t had the machining done yet. I’ll see if I can get it done in the next couple of weeks.
For the carburetion, I’ve decided that I’ll do a direct 2V mod and bolt the 38/38 onto the log with a phenolic spacer. If I decide at some point I need more carburetion, then I can add outboard carbs between 1 and 2 and 5 and 6 or thereabouts. Probably YF Carter carbs, with progressive linkage so it runs on the 38/38 primaries and then when I punch it, the carbs on the ends kick in, like a 4 barrel.
I had a couple of hours free this morning so I installed the rebuilt rocker assembly with 1.65 ratio adjustable rockers @TrickSix sold me several months ago. I was going to wait until I had the new head ready to go on but I figured my old non-adjustable 1.5 ratio assembly was a little long in the tooth and that it would be worthwhile putting the new ones in. It was…
The results of making this upgrade is amazing. What a difference. The longer rockers let the engine breath better in all modes; idle, acceleration and cruising and it’s even smoother at normal driving acceleration than it was before. It’s really smooth at idle. My engine had some chop to it at idle with the old rocker assembly. It wasn’t horrible with a manual transmission but I think it would have been annoying with an automatic. Now it’s like butter. I can’t get over the improvement.
I also got to do some inspecting. I had the plugs out when I put it through the motions to adjust lash/preload on each set of rockers and they were an off white colour; the center plugs were darker and more tan and the end ones were lighter and more white/grey. This is what I was hoping to see. I’ve got 2,000 miles on them to date and my car does run a little on the rich side.
I used assembly lube to make sure all mating surfaces had lube until the new rocker shaft got pumped up and had the valve cover off when I started it. It gave me an opportunity to check that my pushrods were rotating and oil was flowing correctly. Everything was doing what it’s supposed to so I’m in great shape to go forwards. All systems are go!
For the carburetion, I’ve decided that I’ll do a direct 2V mod and bolt the 38/38 onto the log with a phenolic spacer. If I decide at some point I need more carburetion, then I can add outboard carbs between 1 and 2 and 5 and 6 or thereabouts. Probably YF Carter carbs, with progressive linkage so it runs on the 38/38 primaries and then when I punch it, the carbs on the ends kick in, like a 4 barrel.
I had a couple of hours free this morning so I installed the rebuilt rocker assembly with 1.65 ratio adjustable rockers @TrickSix sold me several months ago. I was going to wait until I had the new head ready to go on but I figured my old non-adjustable 1.5 ratio assembly was a little long in the tooth and that it would be worthwhile putting the new ones in. It was…
The results of making this upgrade is amazing. What a difference. The longer rockers let the engine breath better in all modes; idle, acceleration and cruising and it’s even smoother at normal driving acceleration than it was before. It’s really smooth at idle. My engine had some chop to it at idle with the old rocker assembly. It wasn’t horrible with a manual transmission but I think it would have been annoying with an automatic. Now it’s like butter. I can’t get over the improvement.
I also got to do some inspecting. I had the plugs out when I put it through the motions to adjust lash/preload on each set of rockers and they were an off white colour; the center plugs were darker and more tan and the end ones were lighter and more white/grey. This is what I was hoping to see. I’ve got 2,000 miles on them to date and my car does run a little on the rich side.
I used assembly lube to make sure all mating surfaces had lube until the new rocker shaft got pumped up and had the valve cover off when I started it. It gave me an opportunity to check that my pushrods were rotating and oil was flowing correctly. Everything was doing what it’s supposed to so I’m in great shape to go forwards. All systems are go!
I am following your progress closely. I have the same large log head for my project. Maybe I can drive up and see your car some weekend as I am North of Seattle.
So the 1.65 ratio rockers are a some what significant performance improvement. I have heard that in the past. Could just this alone be a significant performance upgrade even on a stock motor would you say? It also just makes it run better overall apparently so another plus. Nice to hear about this.
I should think simply going from 1.5 ratio to 1.65 ratio improves lift so more of the charge can be pulled in and more of the exhaust can be evacuated.
I think a stock camshaft has ~0.25” lobe lift so with a 1.5 ratio rocker, it’s .375” of valve lift. If you translate that with a 1.65 ratio rocker it becomes .413” of lift.
On my Clay Smith Camshaft, measured intake lobe lift is 0.3075”. Stock 1.5 rocker intake lift was 0.461”. With the 1.65 rocker it’s .507”. Measured exhaust lobe lift on my Clay Smith camshaft is 0.29” and with the 1.5 rocker it was 0.435”. With the 1.65 rocker it is 0.479”. It seems like a substantial improvement.
I also think that because I now have adjustable rockers that my lifter preload is much more accurately set compared to the non adjustable rocker assembly. All around, it’s a big improvement. The exhaust is actually quieter at idle now and sounds less forced.
Appreciate the detailed reply. It's getting more fuel in without getting higher flow carb or bigger camshaft. 1.65 adjustable rockers are now on my planned upgrade list.
You could also back cut the intake valves to increase flow without changing the carb or camshaft. It would also increase the amount of perceived lift. I'll be doing that with mine.
Higher ratio rockers are also beneficial on the big6. 1.5 : 1.65 = 10% increase in valve lift, that is significant. Of course that's 10% more load on the cam journal, lifter and pushrod. Not a problem when all is right.
I read about the plans for your C9 head so your going with the 3 angle valve work and the port and polish on top right? Should be a noticeable performance improvement. Are your 1.65 Adjustable rockers from RAU?
It's a bit of a haul coming up this way. We've got some friends who are just on the outskirts of Seattle and when we go down for a visit, we plan to spend a few days. I haven't take the mustang down yet.
There is supposed to be a Mustang event this summer in Langley though and that is closer to the Peace Arch and the truck border. I'll plan to be there and hopefully the large log head will be on mine by then. I'l keep you posted.
I'm not sure where the rockers came from. I bought the assembly from @TrickSix. I didn't realize they were 1.65 ratio rockers until I looked at them compared to the stock ones and then measured them with a vernier calliper and calculated the ratio. I got fairly long number that began with 1.6428... They look like they're something Ford would have produced. Nothing fancy but pretty bulletproof.
It is not that simple.
As the valve opens the valve spring pressure is equal to the (seat pressure) + [(spring rate) x lobe lift) x (rocker ratio)]
The pushrod and lifter pressure then becomes the above calculated spring pressure multiplied by the rocker arm ratio once again.
The rocker arm fulcrum pressure is the addition of both the pushrod pressure and valve spring pressure.
As you can see, the pressure on the pushrods and lifters increases exponentially with the increase in rocker arm ratio as the valve opens.
Note: There is no increase in valve spring pressure due to rocker arm ratio when the valve is closed.
If you just want to look at the increase in pressures above the installed spring height pressure as the valve opens,
If you go from a 1.5 ratio rocker to a 1.65 ratio rocker the valve spring pressure does increase 10% above the installed spring pressure as the valve opens.
However, the pressure on the pushrod and lifter increases 21% above the initial pressure
and the fulcrum pressure (Shaft, stud or pedestal) increases 31% above the initial pressure as the valve opens.
Makes total sense! Good to know, thanks.
