268 has less lift, is asymmetric and a 110 LSA. The only time you know anything about the output of horsepower is after lots and lots of math or looking at a dyno chart that displays that math in a linear visual. You can't see it, you can't feel it, you can't touch it, you can't hear it. What you feel it torque, what you hear is compression, what moves the car is torque. What makes torque is cylinder pressure. What gets good mileage is staying in that torque window of most torque for lowest rpm. 500 ft lbs at 2800 Rpms is a way different animal than 500 ft lbs at 7000 Rpms. Want to win races? You need torque on the high end of the RPM range. Launch at 4000 + in the torque band and build more from there. Make cylinder pressure at high Rpms.. Want a fun street car? Build torque or cylinder pressure right off idle. If motor is done or running out at 5000-6000 so be it. What's actually happening is the air flow and mechanics aren't keeping up with each other at those engine speeds. Want to drive your street car like a race car? Put a highend rpm cam in it, manual trans or 3000 stall converter in it, put high 3:xx or low 4:xx gears in it, build the rest to take high rpm abuse and tourture, and drive it in the high rpm range. At low Rpms the mechanics and air flow aren't working together. They work much better and keep up only at higher rpm speeds. These mechanical happenings and air flow take time. One has to lead the other to be in the right place before the piston gets there.
As they said, that 106 lobe separation will be miserable. I put a 233/241 on 106 cam in a mild 9.7:1 455 olds, it ran mid 11s but its idle was a train wreck. Around 3000rpm, it came on like a sonofabitch and sounded like a serious engine.
Just to confirm, I am not looking for a race motor, I am not looking to drive my car on the street like a race car. I am wanting a good running motor with close to 350 hp. I am currently running a bone stock mid 80's chevy 350 (around 180-200hp). I want something with more power. The power down low is not bad on the stock motor, but want more. The real issue is the mid range to high RPM (around 5000) really is lacking. So I thought a little more compression and better heads with bigger valves would be good. I was given the 355 as a fresh rebuild with the SR heads. So all I am looking to do is replace the cam. The cam in it now is a Crower 234/244 @0.50 and a 112 LSA. Which I know is way too big for my application. The truck this was in has 2400 stall 3.73 gears and 28" tall tires. We thought this cam would be good for that application, but it is pretty lazy until about 4 grand. My original thought was that the 112 LSA moved the power band higher in the RPM range. The cam we had in it before the Crower was a 232 with a 110 LSA and it had a lot more power down low. So am I wrong about the lower LSA (112 to a 110 or 108) bringing the power band tighter and lower in the RPM range?
That sounds like fun but like you said you'd need a 3500 stall I'd think (I'm generalizing bigtime here). The 106 vs 110, the 106 would have a lot more overlap, be much more lopey, and it would have stronger midrange and less peak hp. I'm not sure what's in my Merc's 350, but it idles like it's more like a 108 than a 110 or 112. I like the idea of staying around a 110. Split duration is good. I like the idea of 225/230 that's still pretty mild for me. My last late model OT setup was a LS with 240/244 @ 50, 112 with a 4800 stall, and 4.10's, 28 slick and at 330 raceweight, 10.9@123 a dog below 4500.
You have some first hand experience right there that a wider LSA cut your lowend torque. Your own back to back test. Did you degree the cam, advance or retard or straight up out of the box. All things equal you lost lowend. Here is some discussion on it with back to back test of peak tq & HP #s http://speedtalk.com/forum/viewtopic.php?f=1&t=15475&sid=fb26eb620c55d3980ebc447591f1d8a0 You are really not concerned with peak #s on your street car but theres lots to see there. Based on your theory of wider = less so narrow should = more I think you should try it. Some place there is a wall that starts to negatively impact performance. Run a desk top dyno comparison . Keep in mind that if you want to compare LSA, all things should be equal . These two have Identical LSA but are very different. You could very easily slew your comparison by adding a few degrees of duration or couple points of lift or intake closing angle. your change could have only widened the LSA or it could have been very different. Next is if you have it set up to overlap evenly over TDC ( 360) . That could differ from manufacures, production quality or your choosing to advance or retard it. Easy to see how durations change will change overlap even if LSA stays the same. Ramp shape has plenty to do with it too. Just for grins what kind of results do you get from cranking compression ?
If you could get that grind with a 112* lobe center,it will work well in a light car with a stock Vega torque converter. (1800ish stall) I've run as much as 290*/high 490's on 112cen. with a Vega converter no probs.
I don't think that rpm is realistic, I have an 1840 lb car with L78's and 3.25 gears, th350 and a cam that mic's out at a 496. The cam was used so I don't have any other stats other tham what I measured. I know that I'm out of your "normal" operating rpm all the time.
Where the L78s 15 or 14. If 15 then they were only a little shorter than my 8.20 x 15. I don't have a tach so I am using an rpm calculator to estimate the rpms. How far out were you from what i quoted?
The L78's are 15's and I'm around 2300-2500 on the thruway with people still passing me. Around town with all the stoplights I'm going through the gears pretty good and it still has plenty take off speed. I'm at least hitting 3 grand if there is enough room, 1500 just seems like idleing to me and you'd get run over trying to hold that.
.495 is too much lift for a street stocker motor. Really anything you put in the rpu is gonna be fast because of weight. Maybe this; http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=156&sb=2
My estimate is normal street driving I am going around 40-50 and that puts me in the 1500-1850 range. On the freeway I am usually doing 70-75 which is 2500-2750. Again I am using a rpm calculator to figure this out. Maybe the best thing for me to do to ensure I am looking at this correctly is to put in a cheap tach and watch what my cruising spot is. I am sure I do not want to be in the fat part of the torque curve when I am doing 40-50 in third gear. Shouldn't I be in the fat part of the torque curve when cruising on the freeway? Yes you said that. I have also moved around on my choice since I talked to you as well. I moved to a smaller cam and will probably move to a smaller cam than that. My choice is not final yet.
Seek and find Paul, here's the specs. in the 56. Lift -.447, Adv. Dur. -280*, Dur @.050 -230*, Lope seperation - 111*, 1800-5800 range.
I used what Summit sells as a K-1106 cheap ass cam. I didn't get mine from Summit, but I'm pretty sure it's of the same "Blue Racer" variety. It has 234 degrees duration at .050" lift, .488 lift, 114 degree lobe separation. I have a Model A with a 5 speed and 3.50 gears. Reality street camshaft specs? If you study a cam catalog like I did and compare street fuel injection/4x4/boat/all the others, you will make observations about what cam specs work with what, if vacuum is needed, vehicle weight, MANY VARIABLES. Reality street cam? At .050" lift, the duration shouldn't be over 215 to 225 degrees, vehicle weight and converter stuff can change how high a number you go. 110 degrees lobe separation will make less vacuum than having 112 degrees LSA, if that matters. LSA affects idle sound, lumpy or smooth. Lift is determined by what's available with the above duration choices in a street cam, generally. Comp's boat cams have decent duration numbers, with more lift than their 4x4 or street cam selection. Valve/piston clearance would need to be looked at along with valvespring and rocker choices with the choice of a boat cam. Grab a catalog, or look at one on line, with all the duration and LSA numbers, and the description of RPMs and needed _________ that are required too. That's how I learned.
Funny how everybody's setup reacts differently. One of my OT rides has a .060" over 327, flat tops, early 2.02 heads, Edelbrock dual quads, headers, etc. 4 speed, 3.55 gear. I put a Isky 280 mega in it last spring. Great lopey idle and awesome performance after 2500, but totally dead below that. In city driving I have to bring up the rpm and slip the clutch for half a block to get going or it will fall on it's face.
Exactly the point. It appears everyone's experience is a little different. I am currently thinking a cam around the 220 degree area or a little less would be the best. I plan on calling back the cam companies I talked to originally and asking for a suggestions again, but with specific emphasis on street performance. and make sure they understand what I want and not assume they did. They may not have paid much attention to the fact that I have high gears and stock converter.
Hope someone is still out there. I have a 37 Chevy business coupe with ford 9", 3:70 gears and a Turbo 350 ... Don't know what the converter is as it was in the car when I bought it. 350 w/ TRW forged flat top, trick flow twisted wedge, 67 cc heads, 2.02 and 1.6 valves with a Comp Magnum 292 cam(It had a Weiand Team G tunnel ram with 2 Holley 650 dbl pumpers) and a MSD billet distributor. Anyhoo, the distributor gear fractured and took the cam gear with it. I am rebuilding it now and thinking about replacing the cam. Comp says that the more modern SE274H would be a better choice but the 292 is a good choice as well BUT.....(hang on all you naysayers!!) I LIKE THE SOUND OF THE 292Magnum!! I don't want to pull into a cruise sounding like a citation. I will be going with a Team G or possibly Hurricane intake with a Holley 650 or 750 and just wanted some feedback on the cam choice.
The 106 LSA will INCREASE cylinder pressure as compared to a wider LSA, NOT bleed it off. Narrower LSA closes intake valve earlier, wider later. Contrary to the bullshit in the magazines, overlap plays no role in reducing cylinder pressure, delaying the intake closing point through longer duration or WIDER LSA does. Run through the four cylces in you mind, thinking about the valve events as you do. it will become clear that increasing or decreasing overlap has no direct bearing on cylinder pressure.
Thanks for the update. My understanding is that with a wider LSA the power band gets wider and moves up higher in the RPM band. Is that true? My thought was going to a smaller duration cam of about 220 @0.050 and a 110ish LSA. Thoughts?
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