This cam should work similar to the crower level 2 , http://www.competitionproducts.com/...5-050-443_475-112-LS/productinfo/CL540011-12/ The crower level 3 would probably be good too. Straight up or even advanced 4 degrees. Proven combo with the level 3. I do think your going to need a bump in compression over the 8.1 that you may have. Your going to need plenty of consistent low end torque. a good dynamic compression will be needed to. The biggest killer is those giant tires on the lesabre. . Considering others getting up to 20 mpg with 3.42/3.73 gearing and bigger tires . So you should not have a problem getting similar and built for torque you might even see more but I would at least consider 3.23 gears.and around 9 to 1 compression. Estimates if you shave heads to bump compression are .030 off head nets about 50 cc chamber and 8.75 to1 .060 off head is about 42 cc chamber and 9.45 to 1. These are possible ratios if specs are.058 piston depth with.043 gasket 24 cc piston.
....The biggest killer is those giant tires on the lesabre. . Considering others getting up to 20 mpg with 3.42/3.73 gearing and bigger tires . So you should not have a problem getting similar and built for torque you might even see more but I would at least consider 3.23 gears....[/QUOTE] I have 235/70/15 on there now. Ive considered 275/60/15. This is a gear ratio calculator that i made a while back. Its nice for comparing tire sizes and gear ratios. check it out let me know what you think. http://ackermana.com/gearhead
It's pretty good. I do hope your understanding my comments about the tire size . Big tires are fine but from a performance standpoint in 1/4 mile times it does slow you down. I forget not everyone wants to race 1/4 mile. Alitte more rpm at 70 isn't going to be that bad though. 2700 would put you in a higher peak of torque curve. .
I think 2700 at 70 is not desireable for my goals. steady speed cruising doesnt require much hp or torque so I dont see why I would have to be in my peak torque rpm range for cruising.
OEM engineering will show that best mileage IS near the torque peak, even if they don't set up the cars that way. Don't assume that 2700 rpm is detrimental to anything. It's not that big of a deal.
That's exactly my point and where mpg will come in as you can lean out more when you have more torque. You don't need hp to cruise but you do need enough torque to maintain a big car at that speed. 455 cars could have been a 2.56 geared and some Cadillac 500 cars had a 2.08 gear because they have more torque to carry at speeds
Running lightly loaded at higher RPM with part throttle, an engine draws lower vacuum (i.e. less air flow). The carburetor responds to lower vacuum by supplying less fuel. At 1800 RPM, the engine doesn't run as efficiently so the effective load on the engine is higher, causing it to have much higher vacuum (i.e. drawing in more air and fuel). You have to open the throttle more to compensate than you would at higher RPM.
Yes, this is true... I have done testing with my truck at the same speeds in 3rd gear vs 4th gear and he is right the low RPM does not always help the MPG as if the engine is in too low of a RPM it requires lots of throttle to keep it at that speed. Of course down a hill or in a super light car with lots of power the lower the RPM the better the mileage... But up a hill, you will get better mileage being close to the torque peak of the engine, which is not 1500 RPM in most engines.
1800 rpm is still on idle circuit in carb and not atomizing fuel distribution as effective as main circuit would. So cruise at 1800 rpm is inefficient and will have much less available power under load. You could try fuel injection but if you don't have enough power at 1800 rpm it's going to need more . When throttle blades are closed during engine braking do you think it's using less fuel? No it's using more due to higher vacuum.
I'm not so sure about that. Fuel use through the venturis is determined by ported vacuum, or the flow of air through the venturis. High manifold vacuum with the throttle blades closed won't draw a lot of air through the venturis so you won't get any extra fuel flow there. Though it may pull a little harder through the idle circuit.
Don't forget everyone that we have actual engineers here on this board, so factual information is appreciated. Yes, with the combination I suggested earlier, a (consistent) cruising RPM needs to be between 2400-2800 RPM, where the torque is at its highest, for optimal fuel economy. With such a wide powerband--and literally flat--torque band between those RPMs, you'll have more leeway on where the RPMs can be kept for optimal efficiency. This is with the stock cam. My scale for low, med, and high RPM on a street engine are 1500-3000=low; 3000-4500=med; 4500-6000=high, using 1500 RPM increments. The (large) 2 barrel setup will have excellent torque at 1500 RPM all the way to 4000 RPM using the stock cam, which is what I mean when I say low-mid RPM torque. Lower RPM band would be the best place to keep it for best mileage, I.E., 1500-3000 RPM. Getting back to aftermarket cams, one (such as the Crower level 2 cam) with an earlier intake valve closing raises dynamic compression with your same pistons, increases dynamic stroke and displacement, and with more intense lobe profiles, is where your extra low-mid range would come from with this cam. You keep low-mid range with the Crower level 2, and sacrifice upper end where the 2 barrel tends to restrict the engine anyway, so the level 2 cam is much better suited for a 2 barrel setup than the level 3 cam is, though would still work if you just had to use it. The level 2 is a better match for your application needs. You won't need to do a bunch of extra machine work either with the level 2. You can pretty much keep a basic rebuild to minimal cost with the use of this cam, and let compression end up being wherever it comes to, using tuning techniques and extra octane pump gas for optimal power. For a general purpose application, I'll always recommend the stock cam. In this case, however, you wish to maximize low-mid grunt, and the Crower level 2 cam is your cam. The cam trades torque for hp vs the stock cam, which is what the 2 barrel setup does innately as well, so it's a perfect match. Use the scavenging methods described earlier, and you have a 1,2,3 punch to victory (Crower level 2, large 2 barrel, low-mid RPM scavenging exhaust). The torque band is similar on the Crower level 2 vs the stock cam with the 2 barrel setup, though the stock cam's band is a bit wider, just not quite as strong, so using the previous advice is still applicable for use with the Crower level 2 cam. Gary
The theory is there, but the terminology is a bit off. You'll want to run higher vacuum to use less fuel. Vacuum is a measure of load on a engine, the higher the load the less vacuum. At WOT vacuum will be near 0 and be very inefficient as far as fuel mileage is concerned. The higher the vacuum, the less load on the engine and the higher the volumetric efficency, which means that more of the cylinder is filled and the fuel that is introduced is atomized better by the stronger draw and burned more completely in the chamber. There's 2 camps of thought on getting good fuel mileage while cruising: Driving at lowest possible rpm. Advantages: less wear on engine, easy with overdrive transmissions and EFI, easy to understand, quieter exhaust noise. Disadvantages: Lugging of engine up slight grades reduces mileage, not as fun Running at highest vacuum possible. Advantages: Better mileage in hilly terrain, fun, works well with non overdrive transmission. Disadvantages: Engine wear, exhaust noise, counterintuitive, easy to blip throttle for fun and reduce mileage.
Good post Keith! Thank you for your contribution. Did some number crunching with the 1,2,3 punch combo a bit modified for max effort, to show everyone what the potential is. This is within the Dyno program simulator, so take it for what you will. I've (and others) found it gives a pretty decent general idea. I took the Crower level 2 cam, put it at 110 ICL (this will be 2* retard for those using a typical timing gear, since 4* advance is incorporated into the cam by default), or 2* advance using a wheel. This location helps to raise the powerband slightly over the default 4* advance position, which seems to work best even with the 2 barrel, and puts it closer to the OEM cam's powerband. I then used a static compression of 9 1/3 :1 (9.33:1) to put dynamic at almost 7 3/4 :1 (7.73:1) for optimal use with 93 octane pump gas, leaving a margin of error and safety based on elevation, atmospheric changes, fuel quality, etc. using the now 60* intake valve closing point (up from 58* at default location of 4* advance). One main advantage of this is being able to use stock cast "10:1" pistons (the 10cc dish) without having to do much (if any) machine work to the engine, permitting the pistons to sit in the default location below deck. Cam can be positioned to suit the actual compression the build comes out to, to compensate if it comes out to be too high or low above target goal. A 500 CFM 2 barrel is used (@3.00" vacuum) with the 'high torque' dual plane intake setting (which it is). Small tube headers (1 5/8" for the Buick 350) with open exhaust is assumed for this measurement. Heads are stock iron with stock valve size and mild port/bowl cleanup flowing slightly better than untouched heads. VE is between 80-83% between 2000-4000 RPM. Power figures will be flywheel. Average torque output is 421 ft. lbs. between 2000-3500 RPM, peaking at 2500 RPM @428 ft. lbs. Average hp output is 283 between 3500-5000 RPM, peaking at 4500 RPM @293 hp. Power figures will be less without headers, but will exist closer to these numbers than an exhaust system without any scavenging effect. This is what a large 2 barrel with good scavenging and a cam specialized (and installed specifically for) low-mid range power can do. This is an effective and usable powerband between 2000-5000 RPM. The stock cam won't perform quite as well as this, but it's not too far behind and trades hp for tq. Gary
so if the stock cam trades hp for tq, are you saying that everything else equal the stock cam would make even more torque than 428 ft/lb? also how much different would the numbers be with a full exhaust of the type described vs the open exhaust ? what change for manifolds instead of headers?
Main difference between headers and manifolds is exhaust note pulses and how they are pulled away from the engine, which the manifolds aren't as efficient at, which is why some form of scavenging merger pipe is needed. It won't make as much power with manifolds and scavenger merge pipe, but it will be closer to the headers than it will be with a separate dual pipe on manifolds setup. Full exhaust and mufflers will reduce the figures as well, but depends on the type of mufflers and exhaust used. I tried describing this a bit earlier on and the exhaust's effect on performance. The stock cam would produce less torque and make more hp vs the Crower level 2 cam, by about 10-15 numbers, making the Crower level 2 cam even better for low-mid range grunt like you need. This simulation shows off the potential of the Crower level 2 cam when set up in an optimal environment using a large 2 barrel. Other things besides exhaust and cam will affect usable power, including the accessories (alternator, AC, water pump, etc.), transmission used, rear end rotating mass, tire weight (bigger isn't always better, and as with everything else, depends). There has to be a balance between durability and power/weight savings, whether acceleration, linear or rotating mass momentum to minimize energy loss and increase efficiency. You're burning gasoline. You have to make it work best for you. The cast iron air pump of choice needs a lot of things considered to make this happen, as well as the environment within which it exists. Torque is moved down further to be better used with highway gearing and a heavier mass to lug around vs a sequentially opening 4 barrel carb, a cam better suited for maximizing power in this range, along with scavenging exhaust to help pull it through even more, all work together to maximize your efforts, whether you use headers or an exhaust described earlier in this thread, though obviously headers would make the most power (but then there's other things to consider, such as hassle, maintenance, cost, ground clearance, etc. but to many, this is worth it). You could also use the headers with your existing exhaust. TA sells a nice set of 1 5/8" primary headers that will fit your car. I think they're $425 last I checked? If you go this path, make sure you coat them for reasons I described earlier in this thread on exhaust scavenging. Even if you don't swap to a 2 barrel, small tube primary headers will help produce more torque at all RPMs, even lower, though a large 2 barrel will maximize your efforts, even if you don't rebuild or use the Crower level 2 cam. Remember that with headers, a crossover merger pipe is less needed... If you get a square bore carb with a secondary accelerator pump, such as the Holley 650 'double pumper', or "DP", or even a 750...your primary sizes will be increased and improve low-end over the Qjet at partial and full throttle, and will maximize your upper end powerband as well, though the large 2 barrel will maximize low-mid range even vs these 4 barrels. How much money do you wish to spend? Which results would you be happiest with? Which sacrifices are you willing to make and which end results are you willing to live with? Lots of stuff to think about huh? Gary
It's a matter of when to use which schools of thought on mileage. The rpms aren't so important to the equation as much as what's happening at that rpm. Is there adequate vaporization? Higher vacuum is a major helper. Plenty of SAE test papers and decades of proof on that. Is there enough torque to maintain vehicle speed without constant throttle opening? The ones that deliver good mileage at lower rpms have significant strategies to them, like long intake runners that assist in vaporization and cylinder filling (tuning) at low rpms as well as ports and chambers conducive to high mixture motion (prior to combustion), assisting vaporization when the low rpm itself or piston speeds are counterproductive. They also have to have enough torque at a light throttle setting or this strategy is wasted. [Basically... if you have a heavy, brick-shaped car you need to have enough torque AT PART THROTTLE to attempt to use low rpms as a mileage strategy. Part throttle torque curves and performance data is very hard to find and have less to do with full throttle than appears. This is a shining example of WHEN bigger engines get better mileage than smaller ones, or longer stroke than shorter.] The strategies then shift to "If you are going to.....(try this) , then do .......(that)". Once you figure out how to achieve that with your engine, then you see that there's more variables to the vehicle and how it's going to be used, as your strategies would change accordingly. Therefore...it's unlikely that an engine can be designed for best mileage when it's installed into several different vehicles used for different applications. The best that can be done his try to hit a broad range of applications. Rpm's aren't necessarily what's wearing an engine out. Piston speeds are more important than rpms (stroke, rod length/peak piston speeds) Ring width, tension and materials have a strong influence on life. Examples include import engines that prove long life while buzzing pretty good as well as light duty diesels spinning 3000-4000rpms for 700k+ miles. Inconel exhaust valves will see 500k++ miles under boost, then have the valve faces touched up and go back down the road for another lifetime at heavy load/rpms as long as they pass initial inspection. How about this one...the highest vacuum you see on the gauge at the lowest rpm possible, or throttles open but increased mixture motion in that rpm range to make up for the natural loss in vaporization (in the combustion chamber rather than the intake tract)as well as methods of reducing pumping losses... etc., etc., so on... Those all work well. Like anything it's better to use the castings' natural strengths (and architecture) to the purpose of the application. Kung fu is about when to use it :Brow: .
all this talk about vacuum and rpms made me think about this 65 impala ss convertible I had many years ago. (it had a bad frame, bodyshop seller ripped me off as a teen), anyway, it had a factory tach and factory vacuum gage. I think they were for maximizing economy somehow am i right?
Driving with a vac gauge staring at you is quite the education on driving style. They were at least making you aware of YOUR contribution to that formula.
