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Old 04-27-2011, 08:32 PM
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Recommend SBC Cam for torque & fuel mileage

I have a GMC 3/4 ton 4WD truck with the GMPP 350/290hp. However, the 222/222 @.050 cam in this engine is not very well matched to my driving needs. I have a TH350, Edelbrock Performer EPS intake, Edelbrock 1406, 4.10 gears and 31" tires. I am using stock exhaust manifolds and full duals, but plan to switch to headers in the future.

I want to switch to a cam that provides a wide torque band from idle to about 4000 rpm, and I'd like to also get a little improvement in gas mileage.

The most commonly recommended cam is an RV grind in the range of 204/214, but I think I may be better off with something even milder. Two of the cams I'm considering are:
Summit 1101 - 194/204 @ .050, .398/.420 lift, LSA 112
Summit K00032 - 204/204 @ 050, .427/.427 lift, LSA 110
I'm also looking at the various Comp Cams products - XE250H (206/212 LSA 110), 246PE (203/212 LSA 110) , and 252H (206/206, LSA 110).

I've read a lot of articles on how to select a cam, but most are focused on achieving max horsepower. As I said, I'm looking for a flat torque curve that starts at a low RPM, and the best gas mileage possible. I'm also not sure how the single vs. dual pattern cam question applies, since I assume the relatively weak SBC exhaust flow is not be as significant at lower RPM.

Any suggestions on what would work best for my application? Does anyone have experience with the Summit K00032 or the similar Crane cam?

Thanks,

Bruce

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Old 04-27-2011, 09:20 PM
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that 290hp GM crate engine has probably the absolute worst cam/ compression relationship of any engine out there. Unbelievable GM does this.
Don't get me wrong, good engine but WRONG cam.

With a 3/4 ton truck, 8.5:1 compression, I would be looking at nothing bigger than stock. (The first Summit cam you listed is really close to the GM stock 350 cam or a '929' cam, which you should seriously consider).

If it was my truck, I would opt for this Elgin unit...
.368/.398 194/203 on a 109LC. It's really small and probably all done by 3,500 but you have a less than stellar compression ratio, heavy truck, and wanting torque and milage to boot... the smaller the better in my opinion. The 109 CL will help out moving the big vehicle.

http://www.competitionproducts.com/E...uctinfo/E1100/

Also, an exact blue print of the GM 929 cam is here... for $34!!!
http://www.competitionproducts.com/T...ductinfo/E274/

(Also, because Elgin cam prices seem sooo cheap, many people take them as off shore stuff... they are not, made is America)

Last edited by GenYnNC; 04-27-2011 at 09:30 PM. Reason: wrong link
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Old 04-28-2011, 04:22 AM
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I agree with the above small cam recommendations.

If you want to take it a bit further find some small chamber heads like the #4416 305 HO heads and give them a bit of a home port job and some new valve seals.

More compression ratio and more flow once ported a bit.

Install with a felpro 1094 gasket for max effect and efficiency (fuel mileage)..

Often you can find these 305 heads in good condition on running 305's.
Needing only new valve seals.

The edelbrock carb will need fine tuning for good fuel mileage.

I'd use a Qjet and tune that.. A afr gauge makes the job a lot easier.

Your crate motor large chamber heads and the big cam would be good for someone building a low budget blower motor.

This same 350 crate motor is offered in a "260 Horsepower" version.
It uses a small "stock cam".
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Old 04-28-2011, 06:36 AM
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I second the recommended Elgin cam, its a good cam for a daily driver with low RPM torque. I would also run it with 1.6:1 rockers, but it isn't necessary if you don't want to spend the money, you'd probably only pick up about 10-15 ftlb with 1.6 rockers, to some people that's not enough to worry about.
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Old 04-28-2011, 07:51 PM
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Quote:
Originally Posted by 75gmck25
I have a GMC 3/4 ton 4WD truck with the GMPP 350/290hp. However, the 222/222 @.050 cam in this engine is not very well matched to my driving needs. I have a TH350, Edelbrock Performer EPS intake, Edelbrock 1406, 4.10 gears and 31" tires. I am using stock exhaust manifolds and full duals, but plan to switch to headers in the future.

I want to switch to a cam that provides a wide torque band from idle to about 4000 rpm, and I'd like to also get a little improvement in gas mileage.

The most commonly recommended cam is an RV grind in the range of 204/214, but I think I may be better off with something even milder. Two of the cams I'm considering are:
Summit 1101 - 194/204 @ .050, .398/.420 lift, LSA 112
Summit K00032 - 204/204 @ 050, .427/.427 lift, LSA 110
I'm also looking at the various Comp Cams products - XE250H (206/212 LSA 110), 246PE (203/212 LSA 110) , and 252H (206/206, LSA 110).

I've read a lot of articles on how to select a cam, but most are focused on achieving max horsepower. As I said, I'm looking for a flat torque curve that starts at a low RPM, and the best gas mileage possible. I'm also not sure how the single vs. dual pattern cam question applies, since I assume the relatively weak SBC exhaust flow is not be as significant at lower RPM.

Any suggestions on what would work best for my application? Does anyone have experience with the Summit K00032 or the similar Crane cam?

Thanks,

Bruce
The basic problem with the 290 horse goodwrench is too little compression for too big a cam. This is kind of a case of using a balsa wood club to beat a bear to death with.

You can keep the cam you have and go to a better head. The compression increase of a small chamber head would with the cam you have would build up the bottom end torque a lot and leave the engine with a good top end. It might actually improve mileage enough to measure because the greater amount of torque would net using less throttle to get moving and to cruise on once moving.

Or you can lower your expectations of a cam and stay with the existng heads. This will probably help mileage in cruise but won't offer any improvement in bottom end torque because the compression still isn't there even for a milder cam. But the direction to go in would be the Summit Summit 1101 - 194/204 @ .050, .398/.420 lift, LSA 112. The additional LSA would reduce overlap which is a place where considerable fuel gets wasted right out the exhaust without contributing anything toward motion. this cam is pretty simialr to the old 300 horse 327 cam and nobody threw rocks at that engine.

A very basic problem this engine has is the wrong pistons, they have a deep circular dish which just nullifies much needed squish and quench. Certainly a change to D dish pistons along with a more modern head would be a big across the board improvement in mileage and torque. But let's get real, you're probably not inclined to do that in-spite of the fact that this engine is almost the epitome of 1970's smog design thinking. By that I mean everything they could do wrong, they put into one motor. I guess they're just using up parts to get rid of the stuff. I mean everything about this engine's working end configuration of cam, heads and pistons is wrong. Franky I'd be pretty POed over what it costs to fix this thing. you might be better off to find a sucker to sell it to and start over, we'll help with the design if you want to go that way.

Probably the best way out for the least cost would be small chambered heads, Vortecs come to mind but that means an intake as well, though the Chinese have gotten into that market and are offering intakes for substantially less than GMPP, though Edlebrock seems to have cut the cost of their's, but GM is still in fantasy land. 305 heads can be made to work but the effort of large valves and mild porting hardly makes them a bargain. Plus the remoteness of thier spark plug makes these heads kind of ping prone with a 4 inch bore because it takes to damn long for the flame front to get across the chamber so the far side mixture tends to go bang before the fire line gets there. Better piston shape helps eliminate this but we're trying not to change pistons, remember?.

For heads beside the ubiquitous Vortec are the castings 14096217 and 14101083 these are essentially cast iron versions of the aluminum Corvette L98 head. They're actually a pretty decent head but not well known so don't demand big costs. There are two part numbers that derive from these one has the center intake manifold bolts at the 1987 up 72 degree angle and the other with the older version at 90 degrees to the head's intake port line. Another inexpensive and very common head is the Swirl Port. These will work well with your RPM range of up to 4000 and they do better with a long cam as they choke up pretty early but a long cam gives them some staying power. The swirl feature does a lot to improve combustion in slower turning higher loaded engines.

Bogie
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Old 04-29-2011, 05:34 AM
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I appreciate the input. I realize a change of heads would help a lot, but for budget reasons I'm sticking with only the cam for now, and headers as the next addition. I have an wideband AFR already and I used it to tune the 1406. I also have my original Quadrajet, but would have to see whether its in good enough shape to use without rebuilding. 1.6 rockers are also a consideration, but might not quite fit within the budget.

These three cams seem very similar. Is there anything that is significantly different that I should be aware of? The GM 929 is often called an "old", design, but I'm not sure what its missing when compared to newer cams. The wider LSA of the first two would seem to have a low to mid range torque advantage over the Elgin cam.
Summit 1101 - 194/204 @ .050, .398/.420 lift, 112 LSA
GM 929 195/202 @ .050" .390/410 lift, 112 LSA
Elgin 194/203 @ .050, .368/.398 lift, 109 LSA

Bruce
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Old 04-29-2011, 06:40 AM
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Quote:
Originally Posted by 75gmck25
The wider LSA of the first two would seem to have a low to mid range torque advantage over the Elgin cam.
Where did you get that from? With a decent set of headers the TIGHTER LSA gives you an advantage at lower/mid RPM.
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Old 04-30-2011, 04:48 PM
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Do you have a reference that gives a better explanation of the relationship between LSA and the torque at various RPM?

Every article I've found says that with a smaller LSA you will get an overall higher peak torque, but it will be at the peak only over a short RPM range. With a higher LSA the peak will be lower, but you will have a more even torque curve over a wider RPM. Since I'm looking for good torque from idle to about 4k RPM, the wider LSA with a broad torque curve seems like it would be an advantage. Am I missing some part of this explanation?

Bruce
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Old 05-01-2011, 12:21 AM
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Bruce, I think what you have read and are saying are correct but (there's always a 'but', right?) in your questioning, you have already answered you own question... I'll try to explain.

Your words...
"with a smaller LSA you will get an overall higher peak torque, but it will be at the peak only over a short RPM range"

In all forms of racing, you'll see common LSA of 106-108 etc... These cams are ground to get maximum torque at X rpm... so let's say a circle track car. The driver comes off the corner at 5,600rpm... that's where he needs the torque, not 3/4 of the way down the straight. Right?

Your words...
"With a higher LSA the peak will be lower, but you will have a more even torque curve over a wider RPM"

Now, look at the OEM cams today. Most on ground on 115-118 LSA. For good reason. They have to operate over a huge rpm range 0-5,000 at least. Have good vacuum and to a lesser degree, a smooth idle. So they don't need 'peaky' torque like the racer or necessarily 'targeted torque' like the racer. And they don't need the absolute most torque the engine could make with the ideal cam, they need the best torque average (or torque curve) they can make over the operating rpm. So, in essence they sacrifice the best torque at whatever rpm that may be for a good curve.

Those description may not be totally accurate (I think pro-mods and pro-stock have 115LSA and such ground on their cams) but I did my best and there are always exceptions.

However, I think you fall in to the 'racer' category. You have a relatively small rpm range and it's targeted. And I don't think you'll mind if torque falls off at say, 3,000 rpm and if it did, I don't think if would be that drastic of a cliff.
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Old 05-01-2011, 05:01 PM
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Quote:
Originally Posted by 75gmck25
Do you have a reference that gives a better explanation of the relationship between LSA and the torque at various RPM?

Every article I've found says that with a smaller LSA you will get an overall higher peak torque, but it will be at the peak only over a short RPM range. With a higher LSA the peak will be lower, but you will have a more even torque curve over a wider RPM. Since I'm looking for good torque from idle to about 4k RPM, the wider LSA with a broad torque curve seems like it would be an advantage. Am I missing some part of this explanation?

Bruce
This just isn't quite as simple as the popular press and even many camshaft manufacturer's web sites would lead you to believe.

Before you get to a discussion of LSA you need to know the Lobe Center Angle (LCA) of both lobes. This describes in crankshaft position degrees where the mid point at maximum lift occurs.

Now the LSA describes in crankshaft degrees the angle between the LCAs of the intake and exhaust lobes. This usually lands somewhere between 106 and 115 degrees. Now most everybody reads and talks about tighter LSA's increasing the overlap of both lobes where as the piston transitions from the exhaust stroke to the intake both valves are open as the exhaust is closing and the intake opening. Where wider LSA angles tend to eliminate the overlap period. Overlap is used to take advantage of the mass flow of the exiting exhaust to initiate the intake flow while the piston is barely physically moving through the many crank rotational degrees of the TDC event. While an effective way to start filling the cylinder, overlap is very wasteful of fuel and some fresh mixture will be drawn out the exhaust unburnt. I'm kissing highlights here there is a whole other conversation to be discussed about the extent of exhaust dilution having somewhat the effect on the engine as EGR. But this will be long enough without that.

As I said, the popular press greatly simplifies and provides a set of LSA rules that have a for a set of underlying assumptions that moving the LSA also moves the intake and exhaust such that one the other or both are significantly altered so as to cause readily definable changes in engine behavior. Simply put they say that wider LSAs loose low end torque and gain top end horsepower because the intake lobe is advanced which means the LCA happens latter, therefore the intake valve closes later which is of itself a condition that favors top end power against bottom end torque and the converse is therefore true that a tighter LSA changes retards the LCA favoring an earlier closing intake thus more bottom end torque and less top end power. This however is a gross oversimplification; as to change the LSA one can more the intake or exhaust LCAs to and fro independently of each other and still change the LSA without necessarily making a change in engine operation as is commonly thought. The intake LCA can be held steady and the exhaust moved to change the LSA. Or the exhaust LCA can be held steady and the intake's moved. Or both LCAs can be moved. In each case the operating characteristics of the engine will be different from the simplified versions you read about.

Generally it is thought that the intake closing point is the most influential characteristic of the cam. This is what the computation of the Dynamic Compression Ratio is all about. The DCA is computed against the previously calculated Static Compression Ratio (SCR) for the engine by the effective stroke lost to the point in crankshaft degrees where the intake valve closes and compression begins to build. This is a lower side of the torque peak effect where the mixture velocity within the intake system lacks the inertia to fill into the cylinder against the effect of the rising piston. The sooner the intake is closed the less this effect at RPMS under the torque peak and the lower the specific RPM where the torque peak occurs, good for mild engines. The later closing intake favors higher engine RPM power because the mixture velocity at high engine RPMs can ram mixture into the cylinder against the force of the rising piston. This is because much of the pistons movement around the points of TDC and BDC use a lot of degrees but present little movement within the bore. This is to say that the piston does not linearly move in direct proportion to the degrees of crankshaft rotation. We are in the area of sine and cosine motions where the vertical movement of the piston is governed by the type of triangle formed by the position of the connecting rod, it's length and the effective stroke which is not the stroke of the engine. The effective stroke is pair of vertical lines top to bottom through a rod journal and the main journal. At the TDC and BDC points these lines lay on top of each other and the effective stroke is zero dimensionally. As the crankshaft turns these lines begin separate and the effective stroke is the distance between them. The only times the effective stroke is equal to the measured stroke is when the rod journal is a 90 degrees to the vertical plane. Then the rod sees the full stroke dimension of the crankshaft and maximum leverage can be applied to the crankshaft. These are also the places on either side of this point where maximum piston speed is being achieved where there is a lot of movement of the piston for the degrees the crankshaft is turning through.

This is a lot to digest so let me link you to a picture:
http://www.youtube.com/watch?v=VHvBW2DXONY

This is aimed at the question of balance which in terms of secondary balance the causes of what is or is not ideal cam timing and the problems of secondary balance arise from the same source.

Way back when I aimed you at the short duration long LSA cam was for a couple reasons, One, you said good gas mileage was important so such a cam eliminates overlap which is a source of considerable fuel wastage. Secondly, the cam's duration is pretty moderate such that the LCA even with the big LSA number isn't going to occur late in the intake cycle. Therefore, the intake closing point wouldn't be late after BDC, thus it will hold up pretty good bottom end torque. Without a head charge to get the compression and combustion efficiency up, you're quite limited in what can be done to improve the bottom end and mileage at the same time. Also 1.6 rockers would be a step in the wrong direction, the faster lift exposes more valve area sooner which slows port velocities at low speeds and will enhance the effects of overlap and low RPM reverse pumping making the engine act like the intake is closing later than it does.

In the camshaft numbers game you need the intake closing degrees whether you get that off a timing card or calculate it from the LCA and duration figures, that is the cam's single largest effect on torque and power and where it occurs in the RPM band. Overlap has a big effect on idle quality and fuel mileage, but it's hard to take the whole concept apart and say this affect is bigger or more important, the whole thing has to work as a system. While the one affect of intake closing is important and influential, several of the lesser affects can augment or negate the intake timing's impact on the total design.

Bogie
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Old 05-01-2011, 06:52 PM
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Bogie,

Thanks for the additional explanation. I'm still looking at these three cams, and they seem to be very close to the same. However, its hard to compare the specs of the GM cam, since the duration seems to be based on an old method of calculation. The Crane equivalent to the GM cam shows a total duration of 319/320, which must be calculated a different way.
Summit 1101 - 194/204 @ .050, .398/.420 lift, 112 LSA
GM 929 195/202 @ .050" .390/410 lift, 112 LSA
Elgin 194/203 @ .050, .368/.398 lift, 109 LSA? (online specs say 112)

For now I favor the Summit cam because the price is right and its easy to buy online as a package with lifters.

Now a follow-on question. I plan to buy new lifters (of course) and put in a new double-roller timing set. The engine has about 30k miles on it, and I'm switching to a milder cam, so I would think I can reuse the springs, pushrods and other pieces. Other than lubricant and various gaskets, is there anything else I should buy or replace?

Thanks,

Bruce
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Old 05-02-2011, 08:51 PM
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416's 305 heads work good

Really if you can find the 416's 305 heads
U can use ur same cam u have in motor now.
I had these heads on my truck motor and it was torquey
And good fuel mileage
I never needed to rev past 4500 Rpms
Look for 416 heads on eBay
Were talking 300.00 bucks
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Old 05-03-2011, 06:48 AM
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Look at your overlap with the 3 different cams. your duration is so short even with the 109 LSA your overlap is nonexistent, what a tighter LSA will do is delay the exhaust valve opening so you get the most of the burning fuel before you send it out the exhaust.

On a cam with that little duration the ONLY advantage of a wider LSA is emissions- would you rather have more power and better mileage or lower NOx?
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