New Cam & Rocker Arms

[Darwinskeeper]

I'm getting ready to order parts for the next stage in Darwin's evolution. The center piece is going to be the cam change. I'm looking for mileage, so I'm replacing the engine's current Comp 252H grind (206/206 [email protected]; .425/.425 lift@valves; 110 sep) with a milder cam and replace the stock rockers with new Comp Cam Magnum or Pro-Magnum rockers 1.52 ratio on intake side and 1.60 intake on the exhaust. If I use the Crower Mileage Compu-Pro/Level 1, the specs will be (182/190 [email protected]; .391/.413 lift@valves; 114 separation). If I use the Comp Cams 240H, I'll have (192/200 [email protected]; .395/.416 lift@valves; 108 sep). Which one do you think would be better. Any other comments?

 

[T5MalibuWagon]

From what I can understand the wider the LSA the better off you will be. I think that some of the lsx's come with a LSA of 117.5 or something and they get awesome mileage.

I just have to ask, do you think that the gain in MPG will cover the cost of the cam? I dont see that much difference in what you have and what your looking at.

What kind of MPG are you getting now?

 

[Darwinskeeper]

T5MalibuWagon,

The improvement in mpg doesn't have to cover the cost of the changes I'm making. I'm planning to switch the thermostat, add a windage tray, change the carb and possibly upgrade the ignition while I'm changing the cam. Fuel economy is a quest of mine, so if the changes I'm making result in an improvement, I'll be happy with it. As far as whether the improvement in mpg DOES pay for the changes, that will depend on how large the improvement in mileage is and what the price of gas becomes. Between the problems in the Middle East and the increased demand for oil from China and India, I'm planning on the price of gas exceeding $5 a gallon and wouldn't be surprised if it exceeds $10 a gallon in today's money.

Currently I'm getting 20-23 on the highway, about 16-18 in mixed driving and would be doing well to get 15 around town. Part of my problem is that my 3470lb wagon is a bit heavy for a 4.3L V6, and having a larger than stock cam isn't helping matters. Another problem is that the 3 speed manual trans with 2.73 rear gearing means that I really don't have a good gear for driving in the 30-40mpg range around town. I have the choice of puttering around in 3rd and dealing with the loss of vacuum due to high loads at low revs or keep her in 2nd and have the revs higher than I like. My ultimate solution would be to install a 5 speed, but I hope that switching to a milder cam will improve my low end torque situation, making 3rd gear more useable. I also hope that it improves vacuum and mpg at all speeds.

Given your comment on LSA, I take it you think the Crower would be a better choice?

 

[T5MalibuWagon]

I dont really know what cam is what on you poll, I judge cams on duration at .05, lift, and lsa.

I know what you mean about having a 3 speed, I have one in my rambler that I drive daily. I think that a 4 speed would be a wonderful improvement for city driving.

Last time my bu was going with the t5, 2.41's and stock 350 I was pulling down 20 mpg. I think that you might be right about you 4.3 being a little too small. I would go with a cam that is said to make the most bottem end in the rpm that you normally run. As I drive a lot of highway, 65 mph+, that is what I would set it up for. Pick a cam that works for your combo, and what you do with the car. Do you think that the 2.73's are lugging the engine? I said that 4.11's would have probly gotten me better gas mileage than the 2.41's I had. I dont know if I was right but I sure hated the old set up.

 

[T5MalibuWagon]

Im feel like a idiot, I just got the fact that there are only two cams on the poll, and that you are just runnin different rocker ratios.

With that cleared up and you giving me the numbers I would go with the crower for sure, and think that the 1.6 rockers on the exhaust might not be a bad idea.

 

[mhamilton]

Currently I'm getting 20-23 on the highway, about 16-18 in mixed driving and would be doing well to get 15 around town. Part of my problem is that my 3470lb wagon is a bit heavy for a 4.3L V6, and having a larger than stock cam isn't helping matters. Another problem is that the 3 speed manual trans with 2.73 rear gearing means that I really don't have a good gear for driving in the 30-40mpg range around town. I have the choice of puttering around in 3rd and dealing with the loss of vacuum due to high loads at low revs or keep her in 2nd and have the revs higher than I like.

I think you're doing as well as can be expected as far as economy. The EPA ratings for a 1985 Monte with 4 speed and 4.3L were 18/27, with the 3 speed were only 18/23. EPA Ratings

My bone stock 3.8 auto with 2.41 gear was rated at 19/26 mpg. The best I have ever seen was 23 mpg on a long highway trip, but that was with the a/c and some traffic congestion. Usually see 21 in highway/city. City driving does kill economy, since I have no acceleration gear--I either have to dodder along, or floor it to hold out 1st gear. Your manual would already have a lower 1st gear, so not sure if you'll see much improvent in stop and go traffic.

A trans with more gears sounds like it would help. 2nd gear with that axle does seem a bit short, @ 4.0:1. Not sure, I have never noticed a problem at slow speeds with the 2.41... it rolls faster than 35 mph in 3rd, so I'm usually riding the brakes

For comparison, the new Mercedes 3.2L V6 is a 90 degree aluminum block, 3 valves per cylinder, SOHC, 2 plugs per cylinder, with a 2-stage resonant intake, and a 5 speed auto trans. Even with all that and smooth aerodynamics, the EPA ratings for the E-class wagon are only 18/25 mpg. So, you're not really bad at all, considering you have 72ci more than the MB.

 

[80ECLT]

Make it run on e-85... I was seriously going to do that to mine untill I went Fuel injected. Stick it to the middle east!!

Go with an OD trans for the mileage you desire. a T5 and 3.32's will really help. But if you are allready pulling off 23 mpg, thats pretty good for a longroof. If youre really ambitous, install a throttle body injection setup from an 87-95 S-10, or 85-87 El Camino/ Monte 4.3. That will help you pull an od trans as well, plus you could tune the computer for maximum mileage. I had a 92 4x4 s-10 with a 5 speed and TBI 4.3 , it got 23 MPG HWY and weighed a lot more than 3400#'s. Clean, simple, reliable and cheap fuel injection!

 

[ElCaminoBill]

An overdrive trans and gear change would probably make more improvement than the engine mods.

Mine had a 229 V6, 200 metric and 2.41 gears. Now it has a 350, 200R4 and 3.73 rear. The gas mileage is better and fun factor substanially higher. The rear coupled with the overdive's low 1st gear give it a lot of low end. It cruises at 2500rpm on the highway.

TBI, a cam, heads and roller rockers in the my future plans. I'm giving serious consideration to E85. Hot Rod has a good article on it this month.

I also have a 93 C1500 with a 4.3. I'm always looking for ways to improve it too, so keep us posted on progress.

 

[80ECLT]

DK,

Dont forget that if you go with roller rockers, you need to run push rod guide plates, and have the heads machined for them, if you go 1.6 ratio, you need to drill the pushrod holes for clearance because of the offset rocker ratio, and you will need to run hardened pushrods for the guide plates . Also you will need adjustible rocker studs and polylocks. If your motor has threaded studs from the factory, they are 10mm instead of 7/16ths and they need to be machined and tapped for 7/16 threads like mine did. No one makes 10mm rocker studs...

Just for your information if you are planing to do this modification.

Building a V6 sucks because they are so darn expensive compaired to a SBC. But it is fun!

 

[80ECLT]

And you will need different valve covers to clear the darn things! Ask me how I know that!