Cruising Air fuel ratios.

**suffolkauto01** · 10-16-2014

you are syncing the rotor so spark happens at center or rotor you can not adjust timing like that the computer controls that set your timing sync the dis.

**riche** · 10-21-2014

Originally Posted by Fast355

I logged my 5.7 Vortec with a 215/220 cam in it today. 55 mph @ 1,500 rpm with 13% throttle and 45-50 kpa on flat land. 70 mph @ 2,175 and 22% throttle at 45-55 kpa. Cruise timing was 32-39* btdc. 32* @ 1500 rpm and 39* @ 2,150. It wants more but distributor limitations prevent it. 41+ gives misfiring. Stock 0411 van tune only allows 35*BTDC.

Thanks for the reply, I guess that pretty much narrows it down to my cam.
And if I understand you correctly, When I decide to change my cam. You give me a pretty good reason to convert my 8 pin hei to a signal only and add a crank position sensor to take advantage of my ecm's ability to run coil on plug. Since that distributor will only allow for so many degrees before the spark has nowhere to go or jumps to another cylinder.

**Fast355** · 10-21-2014

Originally Posted by riche

Thanks for the reply, I guess that pretty much narrows it down to my cam.
And if I understand you correctly, When I decide to change my cam. You give me a pretty good reason to convert my 8 pin hei to a signal only and add a crank position sensor to take advantage of my ecm's ability to run coil on plug. Since that distributor will only allow for so many degrees before the spark has nowhere to go or jumps to another cylinder.

I am planning to convert to coil near plug aka coil on plug as well. It offers more redundancy, alot more spark energy, and can provide more cruise timing under certain situations.

Your cam seems to be whats hurting the vacuum. My cam is a bit milder, but still pulls strong and is a wide LSA intentionally. My setup is pulling an undergeared brick into the wind and I needed all the off-idle torque I could make. Tighter LSA cams can make more midrange torque, but the ECM seems to like the high, stable vacuum signal better and just runs better all around with the larger, wider LSA cam. I am 215/220 @ .050 on a 114* LSA, 110* ICL where it was 206/210 @ .050 on a 110* LSA, 106* ICL before.

If your ECM can run stock LS1 crank/cam sensors it could run the EFI Connection 24x setup.

I am not sure your static compression ratio, but if it is a under 10:1 with a 108* LSA you are about 10* too large @ .050" on both intake and exhaust for your cruise rpm. You could make the cam work better for you, but it would involve regearing to run 2,800-3,400 rpm at cruise in top gear. Might be worth trying running around in 3rd gear to see if the vacuum and mpg improve with the engine higher up in the torque curve. Your intake and cam are designed to work better at higher rpm than you are running.

Personally I would drop back to something like this cam if you plan to keep the 700r4 and 3.73s in that truck.

EDIT.....First cam I posted was accidentally a small base circle, same grind however.
http://www.summitracing.com/parts/hr...make/chevrolet

**riche** · 11-11-2014

Wow, I didn't get a notification that you replied.
Thanks again for all the advice. Yeah I don't see that point of changing gears, I like to be able to get up to 80+ MPH sometimes and that is around 2,700rpm. When I push it faster it sounds like my motor is trying to kick in secondaries or something. I really need to run a datalog to see what is going on.
And I really appreciate the advice on the cam. I have a decision coming soon, either enjoy the way my engine sounds and not worry about the loss of MPG/Tq. Or bite the bullet and figure out what I am leaving on the table. At the end of the day it is just my weekend cruiser...

**riche** · 05-08-2015

Hey Fast,
I have been thinking. would a cam like this help low end vacuum and help me regain some of my table and still retain some of my high rpm?
http://www.summitracing.com/parts/hr...make/chevrolet
with 1.6 rockers?

**Fast355** · 05-11-2015

Originally Posted by riche

Hey Fast,
I have been thinking. would a cam like this help low end vacuum and help me regain some of my table and still retain some of my high rpm?
http://www.summitracing.com/parts/hr...make/chevrolet
with 1.6 rockers?

I think you would be happier reducing overlap by reducing the exhaust duration rather than making the LSA wider.

http://m.summitracing.com/parts/hrs-110991-08

**riche** · 11-24-2015

Hate to bring this back up after it has been sitting so long, I ended up running across this cam that I got from a friend.
http://www.lunatipower.com/Product.aspx?id=1987
It is a little less on duration then the first cam Fast recommended. But has more lift.
Long story short I am selling that engine and throwing another back together. I was happy with the gains in the map table (for tuning) that I got from the wider LSA and the smaller duration. It did pick up some bottom end TQ but sacrificed top end RPM... Kinda quits pulling not to soon after 5400 rpm.
Also, That cam leaves a little to be desired when it comes to sound... It purrs like a sewing machine. Little to no lope.
I did like being able to cruise at 85 MPH and the engine not having little to no map or zero vacuum almost like it is running at WOT.
It did get 17 MPG on the hwy during the hot rod power tour at 14.7:1 ratio and not even trying to adjust the timing.

So do you think that this cam will have a little more lope, and hopefully allow me to keep some of that upper end TQ and maintain some of the map table?
http://m.summitracing.com/parts/hrs-110991-08
Since it has less overlap than my original cam?
http://www.summitracing.com/parts/hrs-110951-08
I wish there was an online calculator that could spit out vacuum/map at certain RPMs.