Thanks. Good question about the distributor. How would the curves compare between egr and no egr? And I assume verifying the timing set means pulling off the front of the engine to visually look at it?

 

The emissions engine had various vacuum devices built inline outside the distributor that depending on the emissions configuration had influence on the timing .. The sum of these dictated the final distributor timing curve .. When you remove these items the curve will be off .. So to to get the motors efficiency back the distributor should be recurved if it wasn't done by the PO already ..

Unfortunately yes but it will give you a chance to replace the front seal and inspect your harmonic balancer more closely for slippage ..

 

I've read a lot of debate about the cam timing. Generally Ford retarded the cam 4* for emissions. I think it had a slight effect on efficiency, good or bad being the debate, but essentially all it did was move the power band up around 500rpm and slightly lower the dynamic compression. This would make the engine make slightly less peak torque and often a couple extra HP at the top of the RPM band.

I didn't go to the trouble of pulling my timing cover to find out on my Comet. Playing with Engine Analyzer, retarding the camshaft on my old 302 is almost a wash on the torque, average torque increased from 230 to 232 but peak torque was 280 @ 3000 in both. HP goes from 199 to 203 when retarding the cam. The biggest difference was at 1500RPM where I lost 3 ft lbs of torque.

I have seen the opposite on larger motors, but I don't have the correct specs on the 351M. I could probably get them, just take some digging.

Edit: The timing curve is pretty conservative in the first place, mostly due to emissions. The EGR system should allow for a more aggressive curve, but I'm pretty sure they didn't do that, think they went the other way. You should be able to crank the timing quite a bit. EGR would even help in this regard, essentially adds in dead air that can't preignite, so you could push the timing harder.

 

The whole point for the OP is to have the motor run as as efficiently as possible through the whole 34*-35* with the motor he has .. I agree having an egr installed correctly would help fuel efficiency at cruise speeds but that is not the case with this motor and intake .. Taking back the 4* timing retard is a good step in the right direction with the 335 and 385 series motors IMHO

 

My above mentioned 302 got 24mpg on the highway with the retarded cam timing. It makes less dynamic compression which means the engine doesn't have to push as hard to run itself.

There is obviously a sweet spot. My 302 isn't a power house but it gets excellent mileage. The 351m might not get the same results, but my 302 does fine with the 4* retard in timing. I'm hoping to get similar results with my new engine. We'll see.

I know the point is mileage, that's why I put in my experiences. His engine may not benefit from retarded cam timing but it isn't universally bad.

 

You've got me thinking more about the timing set. It's been in the back of my mind for a while as an unknown. Similarly, I don't know whether it still has the stock camshaft or not. With the Edelbrock intake and headers when I got it, I'm inclined to think they may have upgraded the cam as well. So I'm thinking if I go to the trouble of taking the front of the engine apart, I'll probably just put in a new cam and lifters so I know what I have. Something else for the long-range project list . . .

 

I totally agree "it isn't universally bad" and your point and post are well taken .. I think the OP's work and data will go a long ways to clarify the mystery as does your info on the 302

 

More than just one way to find out, take off the valve cover and measure the rocker where it pushes the valve, turn the motor until it opens, find the difference on both the intake and exhaust.

The approximate lift will give us an idea of what cam is in there. Some have the same lift across multiple cams, Comp Cams does that, but Edelbrock tends to have very specific lift for intake and exhaust on each camshaft. On a small block, a .456 lift would likely be a 268H, .5 could be a 270H or one of many, but it is at least narrowed down.

The Edel cams for the SBF have .462 intake and .480 exhaust. Might be interesting trying to get very specific numbers from the rocker arm, but we could at least get in the ballpark. I never tried this with my Comet, but I'm thinking I might. Never thought of it while I was tinkering with it. The timing cover has been off of my Comet, but it behaves like a stock cam, falls off hard above 4500, gets creamed by an Edel RV cam.

 

This method along with a degree wheel would tell you if cam is retarded 4* or not as well. Assuming you know what cam it is.

 

A couple of great ideas to spare taking off the front of the engine. I'll give those measurements a try the next time I pull one of the valve covers off. Which will probably be soon since one has a bit of a leak and needs a new gasket.

 

Yesterday I tackled replacing the fixed IABs as suggested by whc8100 many posts ago. Much easier than I was expecting. Initially I was thinking I'd use a few drills to gradually enlarge the holes up to the size needed for the 10-32 tap. I started with a #36 in the pin vise which worked fine. The next size up grabbed well enough that I could pull out the entire brass IAB. On the right is the drilled out IAB while on the left you can see the IAB on the end of the drill bit.



It turns out the IAB hole in the main body is just about the exact size needed for the 10-32 tap so I went ahead and started the threads. However, I ended up running the drill in the hole to remove the step that the IAB sits against. This way I didn't need to run out and try to find a bottoming tap. Below is a picture of the brass set screws in place. I iterated a few times between putting these in and cutting a thread or two so the top sits flush the aluminum. I then used the pin vise to drill the set screws.



I measured the original IABs at 0.079" so I decided to drill the brass set screws with a #46 drill which increases the cross-sectional area by 5%. I also verified the IFRs are 0.029" so the inserted #30 gauge wire drops the area by 12%.

With the change to the IAB size above, the immediate impact was the idle AFR went to about 15.5 - 16.0. I was then able to back out the idle mixture screws about 1/8 of a turn to drop the AFR to about 13.5. So now I'm sitting with the screws just shy of 1.5 turns out which is good. Most surprisingly I was able to drop the idle speed to about 600 RPM which is a first. I'll have to think more about how the IAB size affected the idle speed.

 

Interesting.
So your IFR should be around what, .027, .025?

The one thing that does worry me is how will this affect driving at lower elevations?

I would think it would lean out a bit, but as the air is thicker it might cause it to pull more fuel. The humidity here might actually work against the thicker air, effectively leaning it out. I still think that 90% of your work should be almost universally applicable though.

 

Got the numbers from my 4160, turns out I've got 62 primary jets in there. I think if I can get my idle running leaner I'll be getting pretty decent mileage out of it.

Since I can't make it ping I wonder if I could go leaner. I need to get an O2 sensor.

You've started something man!

lol

 

Yes, the #30 wire in the IFR reduces the effective area to that of a ~0.027" hole. As for the impact of elevation, the air density at sea level relative to here is about 10% greater. Hence, I'd expect that enlarging the IABs would not be needed. Similarly, dropping a few jet sizes (as in the Holley manual) wouldn't be needed either.

I think you should definitely get an O2 sensor - I don't see how I'd make any progress without it. It has certainly sent me in the right direction by reducing the IFRs and now increasing the IABs (which looks to be a positive change). Otherwise I'd been guessing as the plugs aren't colored differently enough to help.

So far I'm running with an AFR of about 15.5 to 16.5 while cruising around 1500 RPM. Every now and then it will pop up to 17 with no indication of detonation. Given most of my commute has me running between 1200 and 1800 RPM, most of my attention has been on the idle/transition circuit. In hindsight I should've started here instead of the main jets. They're only playing a small role in my usual running which explains the weaker effect when I changed those relative the effects I've seen with the IFRs (and hopefully some with the IABs).

 

The larger IABs had a positive impact on the MPG. I'm a bit surprised since I can see this affected the AFR (less rich) between idle and my usual cruise RPM, but the the engine doesn't spend much time in this range. But maybe this change and being able to drop the idle RPM to 600 is enough to be impactful for my usual commute through town.



Since it's still rich between 600 and 1200 RPM, I'd like to open up the IABs a bit more. The challenge right now is a #45 drill would be an 8% increase in area (from stock), but a #44 would jump up to 19%. I have a feeling the later is too much and the former might not be enough to detect a difference (5% to 8%). Time to think how to hit something in the middle.