F-Body_Fetish

iTrader: (1)

Alright, there seem to be alot of people who are in the same boat as me. so I feel sort of bad asking this same thing again. anyways, heres the situation.

This is my first car, and my first time rebuilding an engine. I'm 19 and have already rebuilt the motor, with background help from my dad of course. anyways, at the end of the summer we tried to drop it in without using a clutch tool (3 weeks to ship the 6 dollar tool in, but i had to move out for university). needless to say it didnt fit. now while i'm at school and away from my car I've found myself wanting to change the entire valvetrain combo.

At the moment, I've got a rebuilt '69 010 block, 2 bolt mains punched .060 over. it has if i recall correctly 883 casting '72 heads. anyways, I was reading an article by a member of this site as well as his home page, he wrote the article on camshafts in the tech articles section. it helped a bit but I went on the internet to find more information on how to calculate runner size, lift, duration, and so on to optimize a given rpm.

First off, if any of you have any links to good articles to help me calculate my requirements, it would be a great help to me, and probably save you time explaining it to me (if you were so kind).

Anyways, the situation as it currently sits is as such; i've got an edelbrock rpm air-gap intake, I would like to keep it unless another combo will make much better use of another intake (yes, i know, pick heads first. but i've already got the intake). I plan to drive the car around the city, but i want it to have some descent punch. its a 5-speed, so some low end would be nice.

From what i've read, revving a stock internal 2bolt main past 6000 is dangerous, is it true? Also, alot of items, esp on summit will give you an operating range, but how do you know when its optimized? if i have a target rpm of 5500, will buying heads that go to 6000 or 6500 be useless? this is why i need calculations, so i can calculate the specs i need and buy the closes matching parts.

I want to get a set of aluminium heads, probably going to be aftermarket. from what I understand, for a target of 5500 rpm (sounds reasonable right?) i'll need about 175 cc's of runner volume (to keep power "up to" 5500-6000)-do i want it to give power only up to the rpm to optimize it? or go past slightly? also, 2.02/1.6 valves would work well, esp since its punched out it should reduce some shrouding. I plan to go with 1.6 roller rockers, i feel its better to raise a bit with 1.6's because this way you don't run into duration/lift limitations inherent to flat tappet lifters as quickly. I'm going to guess i want around .500" lift? and acccording to the rpm's i'm shooting for, around 220 deg duration. another question comes up here, if one degree value is calculated as optimal for a given rpm, how come cams are given different durations for intake/exhaust?

Anyways, i'm going to attempt to sum it up here into several straightforeward questions.
-is 5500 a good target, or should i go up to 6000-6500?
-What size runners should I have?
-How much duration should I have?
-How much overlap should I have?
-How much lift should I have?
-I need to learn about head flow.
-How can I calculate any of the above?
-Any suggestions on aftermarket heads?
-Do you have any links which could help me?

I know it seems like i'm being lazy and don't want to figure this out on my own; however, this whole car/project i took on because I want to learn as much as I can about cars, (would help, I'm in automotive engineering) and honestly if you can tell me HOW its worth more than the answer. I want to know how to calculate everything and why it is how it is.

Anyways, my greatest thanks to those of you who can help me out. it means alot. even reading this whole thing is a mission in itself.

Atilla the Fun

You're where I was about 15 years ago.
First, I'd say that unless your heads have truly excellent exhaust port flow, a dual-pattern cam will broaden the powerband somewhat. Intake closing has alot to do with cylinder fill time, but exhaust duration will limit or extend the powerband. More duration gives more RPM.
Most stock Chevy small-block heads, except swirl-ports, have poor exhaust flow, and they typically give better results when you have an extra 10-14 degrees exhaust duration at fifty.
If you ran AFR 180s, then adding an extra 10 degrees to the exhaust could hurt, especially with well-tuned long-tube headers, because of scavenging. Some say over-scavenging. It's not a dramatic thing, but a cam like that with heads like those is better suited to nitrous or a supercharger, depending on overlap.
I think that'll get you started on the why of dual pattern cams. Write a letter to Billy Godbold at COMP CAMS. He's friendly and knowledgeable. So is Scooter Brothers, his boss.
As to overlap, this depends on a few things. You seem to want a small-block equivalent of an LS1; good low rpm torque and good power to 6000. The LS1 does it with about 20 degrees of non-overlap at fifty. It gets to 6000 by virtue of good flowing heads and a late intake closing.
David Vizard would tell you to lock in a 108 degree lobe sep for a 350, and choose duration according to your heads and rpm range. My own experiences tell me he's not entirely wrong, but not entirely correct. He's written a few books.
For a stock headed 350 to pull well to 6000, it would want about 10 degrees of overlap at fifty, and an intake closing point of around 40 degrees ABDC.
With this, it'd like an exhaust opening of around 50 degrees BBDC.
Plug that into a desktop dyno program and see what it shows.
I feel there is only one perfect resource for you, the School of Automotive Machinists run by Mr. Jud Massengill. Try sending him a letter.

F-Body_Fetish

iTrader: (1)

wow, that was pretty helpful. I'm going to see if I can get a hold of those guys. I find it odd that they'll be so willing to randomly help me, but it would be pretty sweet if they did. Also, I believe the cam companies catalogs have some information on how to choose a cam and heads and whatnot in there, so once i read it tonight, it might proove to be a valuable resource.

I was on the net last night looking at heads, I went over to trick flow and AFR's websites. They have some really nice heads, but then i found they cost around 1300 USD for a pair, I don't have that kind of money, unless I can find a used pair. would going with iron heads net me similar performance? Or maybe some aluminium corvette heads?

Atilla the Fun

Going iron, like DART IRON EAGLE PLATINUM, would only save you like $300/pr. If you're okay with $540/pr plus shipping, it's tough to beat the Vortec heads. Nothing cheaper is even close in performance.
Billy Godbold is a top guy at COMP, and once he called me to answer my letter, which I had addressed to Scooter Brothers.
No idea about Mr.Massengill, but he should at least know the best resources for you.

F-Body_Fetish

iTrader: (1)

Arent vortec heads even cheaper since theres so many around? How do you think a vortec head would compare to aftermarket ones for my application? do they fit into the rpm range i'm shooting for? or would i be better off with some dart heads or something.

hereinmissoula

im looking at the patriot vortec heads... have heard that they have the same "fast burn" comb. chamber as the vortec heads (one of the main reasons they are so good for what they are..) and are about the same price with alittle better flow, esp on the exhaust...

Stekman

First and foremost figure out what you're able to spend. Go from there. That said..

Calculations are only as good as the information being put into them. Give a simulator false info, it will give false results.

Give a look at RHS heads. Pretty good flow numbers, price for price, comparing to Dart, World, etc. Obviously they're not going to be a Trick Flow, Brodix, or AFR caliber head, but, you get what you pay for. I like RHS's assembled options (If you're not one to try assembling heads) as they come with all the quality Comp Cam hardware - springs, retainers, locks, etc. I think my last look was running them at about 1k per set, fully assembled.

Start with the heads. Figure out what you can afford and what you want. I agree that 180cc's is a good target number. Lower CC's for a little more torque at the expense of top end. Vice versa is also true.

Cam: Assembled heads always have a "max lift." Say, common case for RHS, is .590 or .600". As above, good idea to drop a line to a cam manufacturer and talk with someone. They know best. As you will inevitably browse pages looking at various cams, look at the powerband. Find a powerband that suits your likings. A cam with a lower powerband (idle to 5k) will have lower duration, lower lift. Raise the powerband, and you're going to have a cam that has higher duration, higher lift. Air is required to make RPM. More duration and more lift is the door for that air. Overlap usually isn't listed on a common cam card. Can be calculated, but usually not listed. As for the lift, if max lift is .600, once I find the powerband I like, I make sure that advertised lift (lift on a cam card is always at "factory" rocker ratio, 1.5), is under the "max lift" of heads. Bad juju otherwise.

Rocker arms: Kind of like a poor mans cam swap to some. I put them in the fine tuning category. By the cam first, get the rocker arm later. If your cam has x lift, and your heads that you chose have x+y = max lift, find out if 1.6 rockers would fit (lift on card / 1.5 = ...mulitply that times 1.6 to get the lift with a 1.6 rocker. I.e. cam has .400" lift on card. .400/1.5=.26666. .26666*1.6=.426".) So in that example swapping rockers to a 1.6 adds .026" lift at the valve. If, after calculations ( you wanted to calculate...), you find that 1.6 rockers still leaves adequate lift under the heads max lift, then go with 1.6's. Increasing rocker ratio will have a greater effect on more mild cams than it will on the real aggressive, high RPM moon spinners.

To kind of answer the questions:
-is 5500 a good target, or should i go up to 6000-6500?
I like 6grand for a street motor. 2k to 6k powerband is a lot of fun.

-What size runners should I have?
answered above.

-How much duration should I have?
220intake/230exhaust-ish @ .050. (Look at the Comp XE274HR or 276HR, whatever it is I forget - great all purpose street cam, hydraulic roller -there's a similar flat tappet version)

-How much overlap should I have?
Figure out lobe seperation angle, if carb, 110 is a very common LSA. Overlap will then fall into place.

-How much lift should I have?
mid .550's on an aftermarket head, stock castings would require machine work to be usable above .480ish.

-I need to learn about head flow.
High flow at low lift is great for a street head. More racing-type heads skip the low lift (kill velocity by using a massive intake runner), to allow for huge amounts of air at high lift, high RPM. Smaller intake runners allow for higher velocity at low lift. Think of it like sucking air through both a coffee stir straw and a slurpee straw. Low RPM's equals not really trying to drink but still doing something. You will get decent velocity through the stir straw, but not a lot of much through the slurpee straw. But suck the life out of something (high RPM) and the slurpee straw is large enough to suffice, whereas the stir straw pretty much chokes out. It's a lot like that with engines and intake runner sizes.

-How can I calculate any of the above?
What are you trying to calculate?

-Any suggestions on aftermarket heads?
Dart, World, RHS. I stated my preference. All are better than stock castings, though.

-Do you have any links which could help me?
At the moment, no.

About Vortecs: My take, having done the Vortec 383 once upon a time: Great heads for someone who has to buy an intake anyway. With a little casting clean up, they can be great heads. Somewhere there's flow data to compare to aftermarket castings. However, they do require machine work to make any reasonable cam work, which = $$. Add that to the list of things needing to be done to make them work. Then you look at what cam. General consensus is to run the springs the cam recommends. Any hyd. roller cam from Comp, that's probably going to be 986. That means spring pockets get cut larger diameter = more invested (there are decent hyd. roller springs not requiring cutting, though). Long story short, by time you have the Vortecs where they need to be to support a real decent street motor, plus the cost of the special vortec intake, you're pretty close to a entry level aftermarket casting that doesn't require a new intake. And you already have a really good intake, so rule out Vortecs, but that's my opinion.

Sorry about the essay.

Oh, yea, go out and buy a few of the how to make horsepower type books. Good investments for the learning ones.

hereinmissoula

i still think the patriot vortec's deserve a look from you... they are 185cc and are drilled for both intake patterns....

F-Body_Fetish

iTrader: (1)

I like essays, I get more info from them. my block has flat tappet hydraulic lifters (i wish i had rollers, they've got wicked cam lobes). I'm probably going to throw some 1.6's on to help increase lift, but more importantly they increase "lift rate" or whatever and i can keep a certain duration with more lift since the increased ratio increased lift without the lifters running into design problems with the lobes (theres only a certain ramp angle or whatever that flat tappets are capable of handling).

Important question; I would like to get the band up to 6k, however, I was reading an article that said if I push my motor past 6000rpm its going to fall apart since i've got stock internals and only 2bolt mains. (obviously not instantly, but it cant be good for it)

Also, since I've got a manual, I think my torque curve should be a little but "peakier" since I have more gears to shift through i can take advantage of it. if so, then where do I peak it? around 5500 so i can shift at 6k and pick up at 4k the next gear?

As for calculations, given an rpm target or whatever I was going to say how to I calculate duration,LSA,runner size and all that for a given rpm, but after reading the cam companies websites, theres ALOT of factors which affect the specs you need.

As for the duration statement, 220/230 seems about right from what i've heard so far, i'm guessing the 230 is for restrictive flow exhaust chambers, however these numbers would be dependant on the heads you have and their flow. but is there a way I can actually calculate the optimal duration for a lobe if I know my rpm range and my approx flow numbers?

so then i guess it comes down to the following:
-Can I run safely past 6k rpm on a regular basis? when does it become dangerous?
-can i calculate optimal duration? what do I need to know to do so?
-can i calculate optimal runner cc volume?
-can I calculate overlap? i thought 112 was supposed to be what I needed, and yes I'm going carb.

paul_huryk

Heads, camshaft, and the rest of the valve train need to work together in perfect synergy to get the maximum power output. You also need to heavily consider intake manifold, ignition, and exhaust system as past of that equation too.

While 2 bolts are weaker bottom ends, it can be strengthened with ARP main bolts and good bearings. Obviously a stock crank and rods are going to be weak points. Pistons are typically ok at 6000+ rpm unless they start to detonate under high dynamic timing conditions.

Heads are the key to both total power and your power curve. Sure you could put 165cc stock heads on, but they will F you at the top end. Same goes for 225cc heads that are great at 7000rpm - they will have no low end. I like dual pattern cams, even with excellent flowing heads as no heads flow as much on the exhaust side as intake side, regardless of the exhaust velocity.

Atilla the Fun

Due to the dynamics of scavenging and thermodynamics, the exhaust port flowing 75% of the intake port has proven to be best, far better than if they flowed equal.
AFR has the best exhaust port flow, engine for engine, of any heads on earth. When they recommend a single pattern cam for a given combo, they speak from testing.
Those patriots are great compared to 882s or 624s or 993s, but compared to any other same-cc aftermarket heads, they suck, except for price, and they are aluminum.
They are great for some applications. But if these are in your budget, then get a bare pair of Brodix IK180s for $700/pr.and a set of valves from www.competitionproducts.com, as they have the valves for $80 per 16. These are excellent valves, and noone else has them for less than $120.
These IKs flow comparable to the vortecs on the intake side, and better on the exhaust side.