73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: 81_Chevy on May 16, 2013, 09:12:39 PM
-
i know there has been alot of cam questions posted on here alot, but i didnt find alot relating to my specific set up :P
im looking at upgrading my stock cam to something different. im mostly looking for low to mid range torque, while still mainting "decent" fuel mileage and economy, also having a great idle sound and maybe a little bit of a lope. im open to any options. ive got a 350 goodwrench in my truck, its 4wd, turbo 400 tranny, 4.11 (or 10 cant remember) rear end gear, headers with a free flowing exhaust with some glass packs. everything is bone stock. also with the new cam im not looking to do anything with the heads at all, just gunna leave them stock. so would i need to get new lifters as well? then engine only has 50-60k on it so its fairly new!
money wise, i will be willing to spend some decent money on the different parts, not crazy, but decent. my dad will be helping me out alot on the upgrades so im not too worried on price. but i dont want to buy like the crazy expensive stuff, but i dont want to buy the "el-cheapo" parts either! if that makes sense lol
ive got a Holley 4 barrel on my shelf right now waiting to be installed. so that will be going on soon. me and my dad will also be putting on a new intake because we dont want to put an adapter plate on. im looking at the Edelbrock performer, or rpm intake, but am open to other options as well.
what do you guy think i should go with? some summit cams? what ha y'all had experience with and what do you guys like the best?
since we will be doing all this i figured i might as well upgrade the distributor as well, were gunna go a HEI but not sure what one to get. what are the advantages of a HEI over stock? is it worth the money to buy one?
i figured id ask y'all because everybody on the forums is very helpful and knowledgeable! ive got a couple week before were gunna start tearing into everything so ive got time yet. if i missed any details let me know! thanks in advance!
-Nic
edit: i found these cams: http://www.summitracing.com/parts/sum-1101/overview/make/chevrolet and http://www.summitracing.com/parts/sum-1100/overview/make/chevrolet whats the difference? and which is better? lol sorry for all the questions!
-
First and foremost, ALWAYS replace lifters when replacing a cam. They bed into each other really quickly, like in the first hour.
Repeat: ALWAYS. A-L-W-A-Y-S.
Both of those Summit cams will have a smooth idle, i.e., no lope. Basically the lope at idle indicates that the cam is not optimized for low rpm running, but higher rpm horsepower. A cam that gives you really solid low-end torque will idle smoothly. It will also give you a hotter hole shot, so think of it as a sleeper. The 1101 cam has higher duration and lift, and will give you more horsepower at peak, but the 1100 will beat it on low-end torque and gas mileage with its lower lobe separation angle. So the 1100 has more power to, say, 3000 rpm, and above that the 1101 cam will have more power. Most of your driving will be in the 1000-3000 rpm range, so the 1100 cam will feel more powerful than the 1101 in normal driving. Wind it up, and the 1101 will beat it up top.
I made a similar decision between the Comp 12-300-4 and the Comp 12-306-4. The dyno curves are shown here: http://users.rcn.com/weyand/smalls/300-306.jpg. The 12-306-4 has later peaks.
One thing to note when you compare the Comp cams to the Summit cams. The Summit cams have a difference of about 75* between the .050 durations and the "advertised" (seat-to-seat) durations, while the Comp cams have a difference of about 48*. The critical timing events (particularly with the stock heads) are the intake closure (earlier gives higher dynamic compression) and the exhaust opening (later gives better mileage). The greater difference between the .050 and advertised durations in the Summit cams means you have either 1) more overlap or 2) later intake closure and earlier exhaust opening than the Comp Cams for the same .050 duration, which governs your flow rates. Basically, they are opening and closing the valves more slowly. Actually, they sound to me like older grinds. Modern grinds tend to be more aggressive on getting valves open and shut, which is better. Opening and closing the valves more slowly makes it harder to optimize the other numbers, faster allows greater flow without compromising mileage and dynamic compression.
I decided on the Comp 12-300-4 for myself, which is the torquier of the two Comp cams, sort of like the 1100 compared to the 1101. The Comp cams are an extra $100, but it's a lot of work, and a set of lifters, to change cams, so the $100 shouldn't be a big deal. It will pay for itself in better mileage with the later dump of the exhaust valves.
On the intake manifold, I went with the Edelbrock Performer Air-Gap manifold #2601 (not the RPM Air-Gap, which is a higher rise manifold intended for higher RPMs and will reduce low-end torque). A word of warning: do not use an air-gap manifold unless you are going to keep the thermostatic air cleaner. You need the hot air to warm up the carb. I rigged a heat riser tube from the headers for that, and ran the cold-air induction tube to the knockout on the radiator bulkhead. Pic here: http://users.rcn.com/weyand/smalls/dsc03923small.jpg I've since put a chrome lid on the air cleaner to clean up the look. Result: I get warm air when the engine is cold and cold air when the engine is hot. Those two-chrome-pie-plate air cleaner things are OK for looks, but you get cold air when the engine is cold and hot air when it's hot. Not good. If you don't want to use the thermostatic air cleaner, then go with a low-rise manifold like the Edelbrock Performer #2701.
On distributors, I'm less informed, and will let others help you out there.
I am getting the truck back tomorrow with the Comp 12-300-4 cam in it. I'll report back.
-
The Goodwrench heads are terrible, so you can get a nice cam and not see the full potential because of the poor flowing heads. You may consider some vortec heads since you are getting an intake anyway. The HEI is a good upgrade, electronic vs. points is a big difference. Like Rich is saying, a lopey cam will not get you the desired results, stay in the low 200's at .050 in duration and mid 400's for lift on a 112 or so lobe separation and you should have torque coming in at low rpms and done around 5200-5500.
-
Rich, wow! thanks for the great information! and fast reply! i will defiantly look at that comp cams, cam that you suggested! i dont think we will be keeping the thermostatic air cleaners so i will defiantly look at the performer 2701! thanks!
Fairlane, well it actually turns out that i already have a HEI from the factory! ;D so looks like ill just put an advance kit in it and call it good!
-Nic
-
here are the specs of my stock cam that i have now: .383''/.401'' and 112° lobe separation, 76cc chambers and 8.5:1 compression.
these are the specs of the comp cams 12-300-4: Lift .390"/.390" Duration 240/248
im a bit confused, what are the differences between my stock cam and the comp cam? im clueless when it comes to cam specs lol
thanks
-Nic
-
The things that you want to look at are the exhaust open angle (in degrees before bottom dead center, BBDC), the intake closure angle (in degrees after bottom dead center, ABDC), the overlap in degrees (the angle during which both exhaust and intake are open), and the lobe separation angle (the angle between the centerlines of the lobes on the cam).
See the cam timings on this page. http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=70&sb=2
Later exhaust opening will give you better mileage. 50* BBDC is about as late as it gets.
Earlier intake closure will give you higher dynamic compression ratio, which is really important with those stock heads. 50* ABDC is about as early as it gets.
Smaller overlap angle will increase torque in the bottom and move the torque and horsepower curves to the left. 10*-40* is the range for bottom end torque.
Smaller lobe separation angle will increase torque in the bottom and move the torque and horsepower curves to the left. 108* or even 104* is about as small as it goes.
Here's a good article on all this stuff. http://www.crankshaftcoalition.com/wiki/How_to_choose_a_camshaft
Some additional info. Older grinds and stock factory grinds have slow opening and closing of the valves. This makes all the numbers above harder to optimize for your application without giving up a lot of flow with low lift. Higher speed ramps on the cams allow higher lift while keeping timings tight. You can take this to extremes, and then the ramp speeds are harder on the cam lobes and valve train. The engine also sounds like a sewing machine with a bunch of ball bearings in it, because they will clatter like heck.
I did a lot of research and studying and reading every user recommendation I could find and talking to some people I know who know what they are talking about. A buddy who was a GM mechanic for a long time, who has a tremendous '32 deuce, and whose kid worked for a Chicago engine builder and drag races semi-pro, recommended a marine cam, which is what he has in the deuce. My brother taught aircraft engine design for 30 years and helped a lot on the theory and the trade-offs. Sean Murphy (of Jet Carburetor and Sean Murphy Induction) recommended the Comp 12-235-2. The Comp 12-231-2 would be the torquier equivalent. Others recommended the 252/260 cams, like the Comp 12-306-4. The 12-300-4 is the torquier equivalent.
I then ran all of these cams through a dyno simulator. You enter the engine (cylinders, displacement, static compression ratio), the induction system (cfm of the carb, type of manifold, type of exhaust manifold pipes), and the cam numbers, and it gives you torque and horsepower curves.
I have a stock 350 with stock heads, a 600 cfm Edelbrock (which is enough for this motor; increasing the cfms didn't touch the curves in the simulator), a dual-plane high-performance manifold, headers, and duals all the way back. In other words, almost exactly the setup you are aiming at. My goal was a good hole shot, good street driveability around town, and decent mileage, while holding down stresses on the valve train. So I looked for a cam with an exhaust valve opening around 50* BBDC, low lobe separation angle, low overlap, and an early intake valve closure around 50* ABDC to help out those anemic heads. I just wasn't into replacing the heads and all, because I kinda like the stock look of the engine and you can get talking some real money. And you don't need to replace the heads if what you want is torque in the 1000-3000 rpm range where you spend all your time in daily driving. If you want more horsepower in the upper half of the rpm range, then you need to go with more overlap, and earlier exhaust opening, and later intake closure, and higher lift, and then you really want some higher compression heads, which gets you into higher octane gas, etc.
My truck is back from the garage from putting in the Comp 12-300-4. I just drove it home today, so this is just first impressions.
Idle is very smooth. It has the normal V8 sound, but no idle "lope" per se like it had with the other cam. Pull from stop is *very* strong, and I haven't even hit the secondaries yet. The other cam would drop a gear at the twitch of the throttle, but this cam just pulls hard enough, and has enough vacuum, that it takes more throttle to trigger a downshift. Of course, the carb has been off and on, so I will readjust the TH350 throttle-sense cable to make sure it's correct. Haven't put the A/F ratio meter on to check if the carburetion needs adjustment yet, either.
Anyway, my first impressions are very good. More info in a couple days.
-
thanks again rich!! that explains everything! 8)
since you have almost the same setup me i will definitely be going with the Comp 12-300-4! it sounds like a great cam just for what i want! thanks again!! and ill be going with the edlebrock performer intake as well!
8) ;D
-Nic
-
I think you'll be happy. I would advise you wait a couple days to order it, though. Give me a chance to drive it around a bit and post my further thoughts on the matter here. I'll do it in this thread so you don't have to hunt for it.
But I think all of these four cams -- 12-235-2, 12-231-2, 12-306-4, and 12-300-4 -- are pretty close to what you want. I think the most 1000-3000 rpm torque and best mileage will be from the 12-300-4, which is why I chose it, but a couple of days won't slow your project much and you'll benefit from my further experience with it.
BTW, Comp sells it as a kit that includes appropriate lifters, which is what I did, so that's my recommendation as well.
When you do the new cam, make sure you coat the surfaces when assembling with the Comp assembly lube, then use the Comp break-in oil additive in an oil that includes ZDDP. My shop used Valvoline VR1 racing oil at my request. Better to use an oil with the ZDDP distributed throughout rather than add ZDDP in an additive that may not be well mixed in at the start. Change the oil when you put the cam and lifters in, and fill the oil filter with oil before you put it on. I used the GM PF1218 filter. After the run-in per the instructions, and the initial test driving, dump the oil and reload with VR1 and a new oil filter. Change oil and filter again after 500 miles, again with VR1. Then change oil and filter once more after another 1000 miles, with Mobil 1 with ZDDPPlus additive. Mobil 1 with ZDDPPlus every 3000 after that is probably the best lubrication possible for these engines.
-
hey there... personally the cam in my truck has 204 intake duration and 214 exhaust at 0.05 with .420 intake and .442 exhaust valve opening... i really like it, great torque for passing at highway speeds...
-
That's very close to the 12-306-4, which was one of my contenders.
-
thanks rich! 8)
ya we will be waiting for a bit anyway, ive got finals in school >:(
im also gunna put a clear distributor cap and clear rotor on too! ;D just for the heck of it lol
-
A little more feedback on the 12-300-4 cam.
I've advanced the timing to 16* BTDC at idle (36* total timing) with no knocking issues. I put the NGK A/F ratio meter on it today, and I do have to lean out the cruise circuit on the carb a bit, and richen up the power circuit a bit. It's because the vacuum signal from this cam is so much stronger than the GM 350/290 12499529 engine. New metering rods are on the way from JEGS.
The difference in the vacuum signal also means that the shift points have moved down in rpm. I need to get into the pedal deeper to drop second where the 350/290 engine would drop a gear at the drop of a hat. Also, when accelerating hard, the transmission shifts earlier than it did before; with the 350/290 it held gears way too long IMO. So the shift points adjusted themselves to the higher-torque-at-lower-rpm engine.
I have noticed much more power when cracking the throttle around town. You slow down for somebody making a turn, and then they turn and you hit the gas and it has a lot more power on tap than the other cam, which you would have to give it enough throttle to force a downshift so it could get some rpms under it. I had the stock engine in the truck for the first two years, before I replaced it with the GM 350/290 engine a bit over a year ago. The 12-300-4 cam also has more punch than the stock cam did.
Here's one data point on that. I have a 3.42:1 axle ratio with a 12-bolt posi in the back and 31X10.50R-15 BFGoodrich All-Terrain T/A KO tires. Those 31-inch tires mean I have an effective 3.10:1 axle ratio. Yet if I WOT it from stop at the light, on cold, clean, dry pavement, I will now break both of those big BFGs loose in the rear. Neither of the previous cams, given that axle ratio and tire size, would do that. With a 3.78:1 axle ratio or stock tires, this cam should really light 'em up. With a 4.11:1 and 35s, 81_Chevy, you have like a 3.41:1 rear-end ratio, so with this cam you should spin 'em off the stop even on clean, dry pavement if you don't modulate a bit. You can always get deeper into the pedal once you're rolling. ;-)
Anyway, that's what I have so far. No mileage numbers yet, but I did fill the tanks yesterday so I have a point to measure from.
-
With a 4.11:1 and 35s, 81_Chevy, you have like a 3.41:1 rear-end ratio, so with this cam you should spin 'em off the stop even on clean, dry pavement if you don't modulate a bit. You can always get deeper into the pedal once you're rolling. ;-)
man do i like the sound of this! 8) the fact that i can barely break them loose while im power breaking it, this make it much more worth my wild! ;D
thanks for the feedback rich! i really appreciate it! im interested to see what your getting for mileage.
also i was at a grad party this weekend, and some guy was talking to me about my truck and he said if i put a fuel regulator on the like between my fuel pump (mechanical) and carb that i will get better gas mileage. not sure if this is true or not?
-Nic
-
The carburetor already has one of these. It's called a float bowl valve. It only lets the gas in until it's at the required level.
Someone may correct me, but I don't think a fuel regulator would buy you anything.
-
Only if your pump was putting out too much pressure and overriding your needle and seat causing it to flood, would you need a regulator on a mechanical pump.
-
thats what i was thinking as well... i think the guy may have had a little to much to drink! ::)
-
what do y'all think of this cap? http://www.summitracing.com/parts/SUM-G5236/
i think its pretty cool. i know it will yellow over time but im not concerned about that really, just kind of a show thing for the summer time.
would be kinda cool having your own little light show under your hood ;D
-Nic
-
Rich- did you ever get numbers on fuel mileage?
-
Yeah, I'm getting between 10 and 10.5 on the driving I do, which is all around town and up and down the 13* hills on the two-mile-long, 25 mph lane I live on. Unless I run up to Indy, I hardly ever get over 50!
I am now hyper-tuning the Edelbrock. I tuned it to perform just fine with stock parts. Then I had a new exhaust (duals with H-pipe and Flowmaster 40s) put on. Now I am tweaking the Edelbrock with such tricks as stretching step-up springs. There is so much vaccum with this cam that even the 8" springs are stepping up the mixture too deep into the throttle for me. Per Edelbrock, 8" springs are for engines with 16" of idle vacuum, and I must be pulling 18-20, so I stretched the 8" springs by 1/5 of their length to get about 9.5", which gives me a much better step-up spot. No more balking lean on cracking the throttle, which showed up again after I went to the H-pipe and Flowmasters.
I'm also burnishing metering rods to sizes you can't get from Edelbrock. .065/.052 is OK, leanish cruise, rich power; .062/.052 is OK, richish cruise, rich power. I am now taking some .065/.057s down to .064/.055, which is not a stock size, but will be dialed in very close. Just waiting for replacement batteries for my electronic dial calipers to get here.
Mileage should be close to 11 mpg when I get it dialed in, even with the slow and hilly and stop & go driving I do.
Some things about the long-term impressions on this cam. First, I like it a lot and it's perfect for the driving I do. Driveable, excellent out of the hole, very responsive generally. Also starts really easily, and idles well. Pulls like anything. Fantastic around town. Runs great on the highway at speed.
All that being said, if I drove open-country two-lane highways to work every day, I would probably go with the 12-235-2 or 12-306-4, both of which were recommended to me, the first by Sean Murphy at SMI, and the second by people who really like the 252/260 cams.
The issue here is the 50-90 passing shot. One thing I can say for the cam that GM puts in the 350/290 engine. It's anemic as heck off the line, no balls in the bottom, but the 50-90 time makes it a two-lane terror. The 12-300-4 cam does nicely 50-90, but that other cam was hellish! When you stomped it and it dropped second, it exploded around slower traffic.
So if you do a lot of two-lane highway driving, the 12-235-2 or 12-306-4 would perhaps be better choices, giving up some oomph in the low end for a bit better passing times on the two-lanes. Interstate stuff wouldn't matter, because you are not doing the passing thing. If you mostly do around town, and some off-road and such, and Interstate driving, with less two-lane highway driving, then the 12-300-4 remains the right choice IMO.
-
Rich... Ditch the eddybroke for a qjet. I've got the 260h cam 9.5 comp... Via flat tops a/valve reliefs, th350 and 3:42 gears. Get 15Mpgs on the highway
What's under the hood??? If you have to ask maybe we shouldn't race...
-
Well, I don't know what I get on the highway. I should probably fill a tank, run up to Indy and back, and then see what I used. Big difference between C and K as well, even with the t-case disengaged.
When I talked to Sean Murphy at SMI, though, he thought I was doing good for mileage with the setup I had at the time, and that a Qjet wouldn't help much over what I had. He was curious about how I got the Edelbrock dialed in so well, and once I said I had an NGK A/FR meter, he said, "That would do it."
Once I get everything else done, though (and I'm very close), I may do a Qjet. No sense doing it before I have everything else done, because Sean needs to know what setup he is tuning for.
Or maybe not. I don't really care about mileage much.
-
Dude I had an Eddy... recall kit and all.hit tired of it and went to the junk yard.scored a qjet off a 305 rebuilt it
And been happy ever since :-)
What's under the hood??? If you have to ask maybe we shouldn't race...
-
So I took the NGK A/FR meter off the truck tonight. It's dialed in where I want it.
When I put the Flowmaster 40s on, the tune changed, so the prior mufflers were holding back pressure.
With this tune, I tried the .062/.052 needles, and the .065/.057 needles. Ran them for a while and got some readings. I decided what I really needed was .064/.055 needles. Which they don't make. So I used some jeweler's files to file down the .065/.057 needles to .064/.055. I also figured I needed about a 9.5" (of Hg) step-up springs, which they also don't make, so I stretched the 8" springs by 20%.
Tune now is pretty spot on by the meter, and it drives great.
Next up, I think I'm gonna get that bumper with the fog lights built in and a fold-a-way bumper step for the front.
-
Hey rich, what do you think of the Lunati 10120700 vs the comp cams 12-300-4?
-
Lunati 10120700 looks more like the equivalent to the Comp cams 12-231-2. Specs are almost the same. So you could dyno-sim it on camquest.com and see how the 12-231-2 does against the 12-300-4, and the 12-231-2 results should be spot on the Lunati 10120700.
The 12-231-2 was one of the ones I looked at. Google that number and my last name and you should see some discussion of it and some dyno charts of the various cams I looked at.
The 12-300-4 has shorter LSA, shorter durations and lower lift than either the Lunati 10120700 or the Comp 12-231-2.
-
what do you think would work better with a holley 600cfm and aluminum intake?
-
That doesn't matter. What matters is what you want to do, how you want it to drive. I got a real stump puller cam, the Comp 12-300-4, which I like for the driving I do. The 12-231-2 (which is near-the-same-as the Lunati) will have a little more top and a little less on the bottom, and the 12-235-2 will be a little more so yet.
Any of these are good cams for our trucks. They are all pretty torquey. What you want to stay away from are the winders, with a lot of horsepower and nothing in the bottom. The trucks are just too heavy for that. You don't have enough giddyup off the stoplight, though they make for a two-lane terror with astonishing 50-90 times.
Here are the cam diagrams on the 12-300-4, the 12-231-2 (and pretty much that Lunati) and the 12-235-2. Open all three in separate windows and switch windows back and forth to see the differences really easily. These were done with my setup, but should be about the same for yours as long as it is a dual-plane manifold.
Note how they progress from the 12-300-4 to the 12-231-2 to the 12-235-2. 12-300-4 has the most torque in the bottom, but runs out of breath soonest, with the hp rolling over at 4000 rpm at 274 hp. 12-235-2 gives up a bit of torque in the bottom, but the horsepower doesn't roll over until 4500 rpm at 300 hp. 12-231-2, and the Lunati, lie in between.
So here they are in increasing order of top-end horsepower, and decreasing order of low-end torque.
http://users.rcn.com/weyand/smalls/12-300-4small.jpg
http://users.rcn.com/weyand/smalls/12-231-2small.jpg
http://users.rcn.com/weyand/smalls/12-235-2small.jpg
-
Rich, How would that cam do with 4.10s and 31" tires?
-
I have 3.42 and 31s, and full-on starts make the tires complain in RWD. With 4.10 and 31s, any of these torquey cams (12-300-4, 12-231-2, 12-235-2, 12-238-2) ought to smoke 'em pretty good off the line. For all-around driving, 12-235-2 is probably best.
-
how about 12-234-2 xe256h? I noticed 12-235-2 is 4x4, mine is 2wd, 12-234-2 shows slightly more torque, will it make any noticeable difference?
-
Very slightly more torque, slightly more horsepower, mostly in the 4000-5000 rpm range. Very minor twiddles to the cam timing numbers. Lift is the same, so no difference in valve train wear. These cams are very close to each other, dang near the same, truth be told.
I'm not sure you would notice the difference. Either would be about the same IMO. Especially in normal driving (i.e. in the lower half of the rpm range).
Much bigger differences would be involved with things like headers, muffler choice, H-pipe or not, carb tuning, manifold selection, etc.
-
Hey rich do you know of any good rollers that are good for 383. With a nice lope do it at idle and that would work good off road to?
-
in a way that contradicts itself, because a cam with a lopey idle is for top end horsepower, where as a cam for off roading will have a smooth idle and more bottom end torque
-
in a way that contradicts itself, because a cam with a lopey idle is for top end horsepower, where as a cam for off roading will have a smooth idle and more bottom end torque
Ok he said when he built the motor had a aftermarket cam in it already this my first 4x4. I had 89 5.0 mustang E303 cam in it was nasty sounding with dual 40's dumped i was just hoping to get the cam sound to. But what you are saying makes since. Thanks for the info
-
Yup, like he said. A torquey motor will idle very smooth.
As for the roller stuff, I have no experience with it. Someone else here will know.
-
Rich, I would like to thank you for the help and the insight. You are a knowledgeable person and quite generous to share what you know. I'll argue with my dad some more and try to get him to give me a few good reasons why I should use stock instead of the comp.
-
De nada.
Biggest reason to go stock is reliability. Lower lift and slower ramps mean less wear and tear on the valve train. But you can step up to something like the 12-235-2 or 12-234-2 and they aren't real hard on things because they aren't that radical. And you get a lot in return.
GM sold 9 MILLION of these trucks during this 15 year period. They had to make them something everyone would be happy with, including the EPA. They were pretty de-tuned as delivered.