Camshaft/ intake/ HEI upgrade questions!

[81_Chevy]

i know there has been alot of cam questions posted on here alot, but i didnt find alot relating to my specific set up 

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!

[rich weyand]

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.

[Fairlane514]

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. 

[81_Chevy]

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!  so looks like ill just put an advance kit in it and call it good! 

-Nic

[81_Chevy]

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

[rich weyand]

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.

[81_Chevy]

thanks again rich!! that explains everything! 

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!
 
-Nic

[rich weyand]

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.

[gildardo01]

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...

[rich weyand]

That's very close to the 12-306-4, which was one of my contenders. 

[81_Chevy]

thanks rich! 

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!  just for the heck of it lol

[rich weyand]

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.

[81_Chevy]

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!  the fact that i can barely break them loose while im power breaking it, this make it much more worth my wild! 

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

[rich weyand]

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.

[Fairlane514]

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.