I'm looking for a quick way to get a little more bottom end through the center and off the corner without sacrificing upper end. Would using 1.6 rockers on the exhaust and or intake help out with this?
Thanks!!!!!
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I'm looking for a quick way to get a little more bottom end through the center and off the corner without sacrificing upper end. Would using 1.6 rockers on the exhaust and or intake help out with this?
Thanks!!!!!
I doubt it.
Loosen your lash some, it will make the cam seem smaller.
On the chassis dyno a few years ago I started checking lash and 1.6 rockers vs 1.5 on my motors and they all benefited from looser lash and 1.5 on intake and exh.
These were 400 plus cube motors with 350cfm and or 500 cfm carbs.
I dont bother to try 1.6 anymore when I go down with a motor. Ive also gone smaller and smaller on cam.
What cam are you running?....I'm thinking I may have gone to big with my flat tappet motor. I'm pushing the envelope on flat tappet cams, valve springs, etc..almost to roller level...Looking for ideas as I'm redoing the motor this winter....Thanks!
This is on a Northern SportMod claimer motor. Been trying to come up with something to keep up with the 4bbl crates without having to go up in gear ratio. I dont think the motor I have now will take the extra RPM with Hyper. pistons. I'm running a 5.43 and turning 6400-6500. With the crates only turning 6200 and a 5.29, I think the speed at the end of the straight aways is the same but they can get up in the RPM much quicker with the bigger carb. There are only 2 or 3 of us claimer motors out there all running about the same. I don't really care to be a sheep and run out to buy crate nor will my budget allow me to fork out $4000 with all the goodies.
PS...my lash is allready at .024 on both sides. Do I dare go much more? Its what the cam card says to set them at but seams a little loose considering my last one was at .014 and .016
thanks!!!
BBC cam core............Bigger cam core and larger diameter lifters.
The 2 barrel limited engine is a beast of its own. Depression under the carb at WOT is KING>
Has to be stock diameter lifters..
You should be able to go .006 looser from recomended specs fine.
.030 is about the loosest Ive seen for a lash spec
Quote:
Originally Posted by bmodracer
Different cam lobes may use different ramps and require different lash amounts. Just because one lobe design uses .014 lash and another uses .024 doesnt mean you can compare them.
If your cam card says to set them at .024, are you setting them hot or cold? IF you are setting them to .024 cold, then they will tighten up .002-.003 when it gets hot, so you may be able to back them off a little there anyway. If you want to know for sure, when your engine is hot, set the valves for one cylinder, then let it cool down and recheck it, then set the rest of the vavles to that cold number. I usually go .002 looser on the intakes and .003-.004 on the exhaust cold to get to the correct hot number on an all steel motor.
Also I would think you could go .005 or so looser than spec (hot) and not tear anything up. But if you go to loose you lose the take up ramp on the lobe and hits hard on the lobe and lfiter.
Question. No i have never claimed to be much of an engine guru but let me see if i understand this/ talk through it. It sounds like you had too much cam(so you loosened lash and went to 1.5 rockers). Obviously your motors are very limited by the carb. You have gone smaller and smaller on cam and say you are getting better. Not sure if thats driveablility or HP. None the less from my understanding you should go even smaller yet and use a 1.6 rocker arm. Can someone explain to me why my thinking is flawed or not flawed.Quote:
Originally Posted by stock car driver
From what i remember of what bill was talking about he always used the largest rocker ratio he could get and smaller cams.
thanks guys
higher ratio rockers increase the area under the curve and make the lobe act larger. i've read 1 point increase in rocker ratio you should reduce the duration 2 degrees. this is assuming you pick a lobe that keeps the lift the same on both cams.
yep many say always run highest ratio possible, that said Im just posting the factual data that I have seen with the 11 different motors Ive built and chassis dynoed over the last few years.Quote:
Originally Posted by powerslide
Since Im running a off the shelf cheap cam now. Im NOT going to have a custom grind done to try and use higher ratio rockers on it. I have one more cam option that is smaller yet to try eventually here.
My understanding of higher ratio is they lift the valve off the head FASTER... I am guessing with a 350cfm or 500cfm carb LIFTING the valve faster isnt mattering because of the carbs limited air intake...
of course this could be wrong
Try 1.3 break in rockers.. on the exhaust side. Just to muddle the mix... Just one of those things if it ain't broke why change it.
.333x1.3=.433 adjust lash from there... bottom end- top end
Let the pissin match begin.
Can you get a bigger carb? Sounds like your on a 2bbl. If tech dont have a go no go gauge,There is some big carbs out there.
I was told a roller cam / makes 40 to 50 more hp because of fricktion ? Im not sure thats true but it would be ez to do. costly about 800 bucks.
Theres a cam we used to run till or engines went nuts.Some of you will laugh. Elgin #2 cam,I see they make it still. Its a solid and they used to be $69. We tryed all kinds of cams,And we always went back to the cheap elgin #2. Now we were running 461 stock heads,that we ported as big as we could. even poked thru a few.lol
One more thing put it on alky. That will pick up tork. Good luck!
The reduction in duration for rocker changes is pretty accurate about 2* per .1 of ratio. You should also increase the lash by .001-.002 for every .1 of ratio. Higher ratios and less lobe is also easier on the valve train as a whole. If your gaining power with smaller cams you where to big to start and most shelf cams for 2bbl engines are just that, too big. Should be around 250/248*@.050 with 1.5 rockers for an engine that will see about 7000rpm. And again less duration if using higher rockers. We are using 1.7/1.5 on a 248/248*@.050, This thing just keeps pulling down the straights.
fyi- My cams that you guys want to call TOO big because they made more power with more lash were all SMALLER already than 250 on both intake and exh duration @50.Quote:
Originally Posted by fast_crew
Theories on camshafts can be very confusing but what people don't know is that their still to big on duration for the restriction of carb!! Even 248* is to big. It all depends on fuel system and head/intake. If using stock type head w/ 2 bbl carb I've found that going down to a 230-238* is best for restricted engine! The larger camshafts slow intake air speed WAY down thus feeling "boggy" off corner then feels like a 2 stroke powerband in the middle of the straights.
I'm an engine builder/cam grinder w/ an in-house dyno. I race a sportmod locally every week. Last year I had a 251-255 w/ .540 lift and ran good but off corners was just so doggy (Great traction control). I spent months R&D ing on making different profiles and dynoing them and I went down to a 238*-243* w/ .530 lift. And to tell you the truth, I'm running more RPM then last year and plenty of spunk out of the corners. I'm actually having problems w/ forward bite because of power on a dry track. For the hobby stock classes I'm down to a 230*-237* w/ .530 lift. If any of you know Devon Smith (National points champion) races locally here and I have a customer that can race door to door with him with that little cam! I think we're on to something :)
youre on the right track. i havent had a cam over 250 duration for at least 8 years. i've gone as low as 234/234 on my stockcar. my current favorite is a 244/242.
Powerslide,your thinking is not flawed.
Sounds about right to me, stay at or less than 250 @ .050 on 2bl stuff.
Another reason not mentioned for the gain from going back to 1.5 rockers, is the heads might choke at the higher lift the 1.6 's gave the engine.
It's all about the combination, plain and simple.TB