What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

how much performance without hurting mpgs or emissions?

All good points have been said. But like others had said its the whole.package.
I had a 185 HP crate engine get 14 mpgs and a 300 HP 327 get almost 20 mpgs.
I don't see why everyone wants fuel injection all the time
 
have you looked into some timing adjustments. that made a real difference in the mileage in my k5.

i got the weight/spring kit. it was cheap and most likely youre distributer needs them rebuilt anyways.

then i put on a adjustable vacuum advance kit. then you can adjust it so the timing is as far up as possible when not under load, but drops back when the throttle is down.

i also put a msd modulein it but thats kinda expensive compared to the other stuff. the weight kit is $15. the vacuum can is about $35. i think the module was $70

i think that with the q-jet might get you a noticeable difference without tearing the engine down or spending hundreds of dollars.

i dont see a 350 crate engine getting much more efficient without a head and/or cam change.
 
i would hate to see you dump a bunch of cash to add efficiency and have the mileage stay the same. im sure power/driveability would be better, but it is what it is.

and no 454 will increase mileage. they are just too inefficiant and too many cubes.

a 465 swap might help since t400s suck so much power. but the big gear split with a small block and a heavy truck might hurt in-town mileage, but increase highway
 
Yep, nothing is ideal. And I wont be dumping a ton of money into it...cause I don't have any.:haha:

The question was both for me and theoretical- at what point does economy drop as performance increases? What is the sweet spot for max torque and max economy and at what rpm does that happen?

Honestly I don't need much more performance for what I ask my truck to do currently. Sure its slow up the grades and could use a couple more mpgs. But, you make do...
 
I have wondered the same thing about economy and power. My truck with a cheap rebuilt 350 and stock parts, 5200 lbs and only a th400 at the time, got 7-8 mpg. With my 383 (edelbrock heads, cam and intake, good headers, and a Gearvendors overdrive) I got 8-10 mpg and the truck weighed 6500lbs with tool boxes and a ladder rack added to it.

My new engine is a 406sbc with a comp cams 270 magnum cam that is installed 4 degrees advanced. The edelbrock heads and intake have had a ton of work done to them including anti-reversion work done to the intake valves to make the cam sound a bit smaller and to keep it burning cleanly for smog, valves and intake manifold have been thermal barrier coated. CR is 10:1 and the squish quench is about 30-35 thousandths. The flat top pistons stick out of the hole about 5 thousandths. The cylinder pressure should be in the low 200's. And the VE could be at 100% or more, based on similar engines from the same head porter. I am running a 600 cfm edelbrock 1400 carb and get 10mpg, and I don't drive it nicely. This engine is a night and day difference to my 383 as far as torque goes. I think the high torque/lower hp numbers help with fuel efficiency.

My manifold vacuum doesn't drop below 5 inches at 5500 rpm. This shows that I need a bigger carb. I am going to try a holley 750 vac secondaries. I may gain the bit of power that is lacking due to the small carb, but I wouldn't be surprised to see my fuel mileage drop.

This engine hasn't been on a dyno. Very similar engines (impersonator 406 I and II) made 525 ft. pounds of torque at 3500 rpm and 420-498 hp at 5000+ rpm. torque at 2500 rpm was 477 on the first one.
 
Common factors I see that result in poor fuel efficiency:

Aftermarket carburetors that are taken out of the box and bolted on. They are almost always a super simple design (which is bad for fuel economy) and they are sent completely generic, you can't bolt a carburetor on and expect it to run right unless it's built for your truck/motor/location/altitude etc.

Out of tune or poorly rebuilt stock carburetors. The stock Quadrajet carburetors that came on most of the K-series trucks are some of the best and most underrated carburetors ever made. They are very fuel efficient because they use small primaries, they are as good at angle as anything (I walked the carwash on Hell's Revenge with a Q-jet, search youtube and you'll see how steep that one is) and they have huge primaries and can feed anything through at least 500 hp.

Obviously driving habits, weight, tire size/width etc are a factor but the above two are the reasons most have issues with fuel economy.
 
COCHEV said:
The question was both for me and theoretical- at what point does economy drop as performance increases? What is the sweet spot for max torque and max economy and at what rpm does that happen?
Click to expand...

That is going to be very specific to each truck and driver.

You just need to go through and optimize all the systems. If you are going to stay carbed, a quadrajet is the only way to go but make sure it is a good one, no leaky throttle bushings or anything.

Then move onto ignition. Then exhaust. Just make sure everything is optimized.

Economy is just about as much about what its in and what it is. Buddys 455 olds got about 8 mpg in a truck with 40s and a t400 but in his 50 buick with a richmond 5 speed in it he gets 19 out of it, no motor changes at all but the circumstance changed

To really optimize an engine you need alot of street time and better still some dyno time.
 
CGT80 said:
I have wondered the same thing about economy and power. My truck with a cheap rebuilt 350 and stock parts, 5200 lbs and only a th400 at the time, got 7-8 mpg. With my 383 (edelbrock heads, cam and intake, good headers, and a Gearvendors overdrive) I got 8-10 mpg and the truck weighed 6500lbs with tool boxes and a ladder rack added to it.

My new engine is a 406sbc with a comp cams 270 magnum cam that is installed 4 degrees advanced. The edelbrock heads and intake have had a ton of work done to them including anti-reversion work done to the intake valves to make the cam sound a bit smaller and to keep it burning cleanly for smog, valves and intake manifold have been thermal barrier coated. CR is 10:1 and the squish quench is about 30-35 thousandths. The flat top pistons stick out of the hole about 5 thousandths. The cylinder pressure should be in the low 200's. And the VE could be at 100% or more, based on similar engines from the same head porter. I am running a 600 cfm edelbrock 1400 carb and get 10mpg, and I don't drive it nicely. This engine is a night and day difference to my 383 as far as torque goes. I think the high torque/lower hp numbers help with fuel efficiency.

My manifold vacuum doesn't drop below 5 inches at 5500 rpm. This shows that I need a bigger carb. I am going to try a holley 750 vac secondaries. I may gain the bit of power that is lacking due to the small carb, but I wouldn't be surprised to see my fuel mileage drop.

This engine hasn't been on a dyno. Very similar engines (impersonator 406 I and II) made 525 ft. pounds of torque at 3500 rpm and 420-498 hp at 5000+ rpm. torque at 2500 rpm was 477 on the first one.
Click to expand...


so does advancing the cam like that help you run higher compression without detonation and/or the need for high octain gas? How low rpm wise does this motor start making torque? does it have a nice flat torque curve?
 
38377k5 said:
Common factors I see that result in poor fuel efficiency:

Aftermarket carburetors that are taken out of the box and bolted on. They are almost always a super simple design (which is bad for fuel economy) and they are sent completely generic, you can't bolt a carburetor on and expect it to run right unless it's built for your truck/motor/location/altitude etc.

Out of tune or poorly rebuilt stock carburetors. The stock Quadrajet carburetors that came on most of the K-series trucks are some of the best and most underrated carburetors ever made. They are very fuel efficient because they use small primaries, they are as good at angle as anything (I walked the carwash on Hell's Revenge with a Q-jet, search youtube and you'll see how steep that one is) and they have huge primaries and can feed anything through at least 500 hp.

Obviously driving habits, weight, tire size/width etc are a factor but the above two are the reasons most have issues with fuel economy.
Click to expand...

A good rebuild is all i've ever done to my q jets. and making sure you get the float set properlly too. most of em seem to be out of wack when i pull em apart.
 
So about the whole q jet/ small primary thing... my 1406 has the same size primaries...

2011-06-18_08-03-01_106.jpg
 
I've had em both apart. Just thought it was interesting. I know the q jet will out perform off road. I will be doing a mileage test to see real world economy for purely DD operation
 
how well do you keep track of your mileage? do you check it or do you resist the urge to know how bad it really is? is your speedo corrected? not that it matters too much as you can just keep track of mileage per tank and compare the two.
 
I keep track of my mileage for work. But when I want to get my actual mpgs I use my garmin gps. I checked it a few months ago- mostly highway, got 11.

The ugly is plenty evident in my $600+ per month gas tab

Got the q jet on today. It was a rebuilt one I got from a K5 member here. After some minor idle screw adjusting, it runs great! Smoother tip in idle response. Better hot starts. I'll have to throw the garmin in this week and see it it helped. Then i'll start tweaking the timing like you suggested

2011-06-18_08-32-59_835.jpg

2011-06-18_12-35-21_880.jpg
 
COCHEV said:
currently its a a crate 350, performer rpm (po installed, don't know why), edelpuke 1406. stock everything else...
Click to expand...

Part of your lack of torque is that manifold. We must have had the same previous owners. LOL Mine was exactly the same when i got it. Crate engine 350, edelbrock 1406, edelbrock performer rpm, HEI, and edelbrock smog legal headers. I first changed to a quadrajet and that helped a lot. But the bottom end was lacking a bit. After tuning with a A/F tool i found a regular spread bore performer manifold and swapped it on. That got back what i lost and made the engine perform to the level that i knew it should be at.
 
scottsdale86 said:
Part of your lack of torque is that manifold. We must have had the same previous owners. LOL Mine was exactly the same when i got it. Crate engine 350, edelbrock 1406, edelbrock performer rpm, HEI, and edelbrock smog legal headers. I first changed to a quadrajet and that helped a lot. But the bottom end was lacking a bit. After tuning with a A/F tool i found a regular spread bore performer manifold and swapped it on. That got back what i lost and made the engine perform to the level that i knew it should be at.
Click to expand...

Trust me, a regular performer is on the to do list.
 
You must log in or register to reply here.

Latest Posts

Top Bottom