Building a stroked ls1 for fuel mileage?
05-03-2011, 12:20 AM
#1
Building a stroked ls1 for fuel mileage? Was a funny idea I had. Wife is on my nutz about selling the ss due to insane fuel prices here and how much I drive ($100 every 4-5 days in fuel). Since I have a vette that successfully will be 4x as bad at eating gas I dont have much of an argument with the wife unless I try to find a way to make it more fuel efficient.
So, how small can we destroke an ls1?the idea of a 3-4L ls1 with good heads and. Baby cam with all the bolt ons makes me think a 300+ hp motor with a tiny appetite at cruising speeds in 6th can be much more fuel efficient no?
My camaro isn't very fast compared to the competition. Modern family cars can almost keep up and without destroying fuel mileage and building a 402 it can't keep up with vettes and modded 5ls anyways.
So, how small can we destroke an ls1?the idea of a 3-4L ls1 with good heads and. Baby cam with all the bolt ons makes me think a 300+ hp motor with a tiny appetite at cruising speeds in 6th can be much more fuel efficient no?
My camaro isn't very fast compared to the competition. Modern family cars can almost keep up and without destroying fuel mileage and building a 402 it can't keep up with vettes and modded 5ls anyways.
05-03-2011, 01:28 AM
#2
Displacement and fuel economy are nonlinear in relationship. With weight a constant, load will increase on the smaller engine causing fuel consumption to increase per a given RPM.
Not to say you cant get a little better mileage with a smaller LS engine, but it will be marginal at best. Factor in the cost of the build and amortize that over your usage of the engine.
Is it worth it? To go slower? Buy a used Cobalt Ecotec as a second car that has already depreciated if you want economy with minimal loss of value.
Not to say you cant get a little better mileage with a smaller LS engine, but it will be marginal at best. Factor in the cost of the build and amortize that over your usage of the engine.
Is it worth it? To go slower? Buy a used Cobalt Ecotec as a second car that has already depreciated if you want economy with minimal loss of value.
05-03-2011, 01:59 AM
#3
Yeah you're right about it all except for the cobalt. I'd rather wall naked to work than drive that car. Besides another car HAS to be 4 doors if I do add another. I like my ss. I should sell it and just make the wife happy and buy an m5 or s4 but I have visions of seeing my ss and vette side by side in the garage. Its definitely not a cost effective solution but I thought it was a fun idea to entertain at the least.
Last edited by Nastyc4; 05-03-2011 at 02:06 AM.
05-03-2011, 08:48 AM
#7
My stock 02 Formula gets 23-24 local driving 29 highway.......I think you woooood need to buy a really small car with a 4 cylinder to beat that mileage. Keep your foot out of it and you will see alot better mileage.
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05-03-2011, 09:55 AM
#10
I'm not going to do it but wouldn't it be possible to destroke to 5L and put on a small volume head that flows a ton and an appropriate cam and still make 350 hp with smaller displacement? At part throttle I would guess the fuel mileage would improve somewhat. At 5.7L making 345 hp that's pretty inefficient.
05-03-2011, 10:03 AM
#11
I'm not going to do it but wouldn't it be possible to destroke to 5L and put on a small volume head that flows a ton and an appropriate cam and still make 350 hp with smaller displacement?
At part throttle I would guess the fuel mileage would improve somewhat.
Your best bet for cheap fuel savings (what's the point of spending 3k on mods to save 10 bux a week on gas) is weight reduction, lower gearing, fuel efficient tires etc.
05-03-2011, 02:58 PM
#12
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A relatively easy destroking combination is throw in a 4.8 crank and rods. The combination will allow you to keep your stock LS1 pistons if the bore is within specs (3.897"-3.898" with a .0007" maximum thrust side bore taper). If the bore is in good shape, hone it and re-ring it with quality rings. Not to start a flame war but I'm partial to Total Seal Maxseal Gapless rings. I only use the the ones with the gapless ring on the top ringland. Part Number M7984 in your case. Ring seal is very important in your mpg goal. Either get your stock heads milled or even better, go with a ported 5.3 head at 59 cc. Compression is also important in trying to gain mpgs. That will put you roughly at 10.5:1. Long rod motors are a little less sensative to detonation so you still be able to run regular gas with a decent tune. Of course, do the usual inflation of tires to the maximum recommended, drive conservatively, blah...blah
I'm doing something similiar in a science fair experiment with my son. Same basic specs I just laid out but our goal is 300 rwhp and 30 mpgs. We built this motor with JE pop ups for 11:1 compression, ported 5.3 heads, the smaller LS6 cam. The trans is a T56 and it's in a Triumph TR7 with a Ford 8.8 and 3.0 gearing.
I'm doing something similiar in a science fair experiment with my son. Same basic specs I just laid out but our goal is 300 rwhp and 30 mpgs. We built this motor with JE pop ups for 11:1 compression, ported 5.3 heads, the smaller LS6 cam. The trans is a T56 and it's in a Triumph TR7 with a Ford 8.8 and 3.0 gearing.
Last edited by Bilster; 05-03-2011 at 03:04 PM.
05-03-2011, 04:14 PM
#13
Not necessarily because now you are adding more air through the heads and cam that will offset the savings you got by the smaller displacement engine. If you keep the entire thing stock except for the displacement then sure it will use less gas...but destroking it then adding a fuel hungry h/c setup makes no sense for gas savings.
Ignoring that this probably won't be cost effective in the short term whatsoever, there is room for improvement in efficiency... Here is my uninformed stab at it.
You need more static and dynamic compression to start with. The stock cam has pretty sad dynamic compression and because of the slow ramps also has little duration at 0.050". In fact, the LS6 cam has less duration at .006" lift than the stock cam.
You wouldn't need to go crazy on the duration with a nice ramp and you could get the intake valve closing earlier for higher DCR. Likewise, you would want to delay exhaust valve opening as long as possible to increase the length of the power stroke. You will end up probably with something that looks like it has "small" duration at 0.050", probably less than stock duration at .006" and what appears to be a mild lobe separation centered around TDC but without much overlap, if any (some at .006", not really any at .050")... because you have better ramps than stock on your lobes.
The heads would need to be quality, and in this case you need good static compression, a good combustion chamber design, and good flow throughout the lift of the valve, especially at mid-lift.
The stock 00+ exhaust manifolds would be the next thing to put on this car, predominantly so the O2 sensors stay nice and warm and give you an accurate fuel trim in closed loop. Somewhat related, you could skew the switch point slightly lower for your cruising airflow cells so that the car uses a slightly leaner point than stoich for cruise.
05-04-2011, 07:59 AM
#15
The throttle blade is what will control how much air goes into the motor at part throttle.
Besides, he is asking about the head and cam specs for fuel economy, not saying he is putting an MS4 on overly ported stock castings and expecting gas mileage.
05-04-2011, 09:01 PM
#17
05-05-2011, 04:12 PM
#20
What about getting a couple of wideband O2 sensors? Most of them will simulate a signal to the stock narrowband inputs, and are adjustable, so you can set them to switch at, say, 15.5:1 instead of 14.7:1. That way, you'd run leaner in closed-loop, but you could tune it to still give you enough fuel for WOT. That, coupled with either high compression or a smallish turbo, would increase your efficiency. The only down side would be you might get some detonation running lean like that; maybe water injection?