I'm taking an engine rebuild class at my community college.  This is my first engine I'll be rebuilding.  I'm building a chevrolet 350.  This semester I'm doing the heads and in the spring the shortblock.  I was wondering approxmately how much I'm going to have to put out to get 320-350 horsepower out of it and the types of parts I'll be needing to get what I'm aiming for such as: valves, valve springs, rocker arms, pistons, rods, crank, carb, intake, etc.  The engine will be put into my 71 nova when I'm done.

Stats come from Mortec.

Head info:  Casting #:  462624.....75-86...350/400......76cc chamber, 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves

Block info:  3970010....350...69-80...2 or 4 Bolt.

I know an important part of the process is getting parts that are going to match and work well together.  As of right now I've torn the heads down and they're sitting in the hot tank for a week.  This up and coming week I'll be checking for cracks and warpage and see if decking is needed.  Thnx for any info guys!

Those are some big chambered heads for any serious performance, but 320 horse is not out of the picture by any means.  I would stick some 1.94's or 2.02's in the heads, and do some porting on them.  Stick a cam in the .460 to .490 range in there, and add an aftermarket intake and carb.  Even with a stock bottom end you should meet your goal. Although with higher compression in the 9.5:1 to 10:1 range you'll pick up some torque. Making 300-400 horsepower out of a sbc is easy, it's the 500 mark that's tough to do and be streetable.

Although I agree with Mitch, I'm not a big fan of any more compression than what you need.  You could easily make the power you want on 9:1 with no drivability issues and use cheaper gas.  I might consider ditching those heads for some better quench, but if you have to use them, they'll do with some porting.

With some simple bolt-ons, 350 is very attainable.  Performer RPM intake, rejetted and epoxied Qjet, pocket ported and gasket matched heads, (shoot for about 250 cfms intake flow and 170 exhaust) small tube headers, and a cam on the order of 215/225 @ 50 on a 110 LSA.  That should peak you at 350hp @ about 5700-6000 and 375 torque at around 4000.

If you can swing it, swap up to better heads and you can get away with a little less cam duration; like Vortec 885s.  Out of the box with a 211/227 cam like Comp Cams #20-417-3 will get you easily to 350 hp and a touch more low end torque.  Torque would probably peak in the 3500 range now.

One, I can see your being smart about this. You know that not just one piece is the most important but a series of pieces must work together in a system to make power and you are setting a very reasonable goal, and I can tell you will not be dissapointed, just let me "correct" some things from previous posts and add to them.

Mitch is right, those open chamber heads aren't nearly as efficient as the closed chamber "camel back" style chamber or even better is the vortec or a aftermarket "heart-shaped" chamber. But if you are set on the heads, for these power levels thats fine. If the heads have a 1.72" valve put in a larger one, 2.02's probably won't be necessary, but new valves probably will be. The valve guide is extremely important to a long life and if the clearances are poor, can even sap up to as much as 20 peak Hp on some apps. So new valves are almost always a must since the stock valves probably have a lot of use on them and the stems are worn. With the new valves you will have to check the clearance in the stock guides, if the guides are worn significantly then new guides or at least liners should be put in. Knurling stock guides is worthless. Valve springs are a hard thing to choose for the enthusiast, so your best bet is to listen to the cam manufacturer on this one, all the major manufacturers have valve spring reccommendations in their catalogs, I suggest you follow them, if you disagree with them (very possible), I suggest contacting them. In your situation a set of stock stamped steel rockers will work fine, but the bad thing about that is factory machining tolerances can be so poor that some can be off by nearly a .5 a ratio. So a set of "stock replacement" rockers from a reputable company is the best, or if you want to upgrade later or want to spring for a better set the Comp Cam's "Magnum" style rockers are a great buy for *** On to cylinder head flow, I have no idea what Curtis is talking about, 250 CFM is hard to come by with a set of heads like this, especially at the lifts we are speaking of. I don't know if you've ported heads, but I have, I currently don't own a flowbench but have had my SBC heads flowed many times. And some serious porting with a 2.02 valve in a common SBC cylinder head like this got me about 240 CFM @.450 lift. So 250 @.500 is achievable but probably only with a flowbench and a 2.02" valve. So obviously this out of the range to someone who has never ported heads before. Oh yeah and 250/170 CFM, ???. That's a piss-poor 68% E/I Ratio, I prefer to see a 75% ratio at net valve lift.

Onto your cam reccomendation, a 110 LCA is too narrow, people will probably disagree with me on this as well, but there is no point on hurting your torque at low RPM's and even more so under part throttle just for some added torque at peak at WOT, this is a true street engine, so look for a LCA at 114 with a duration around 220* @.050 at most.

On to the buttom end. Well if the engine is apart and you are gonna rebuild it, there is no since in putting it back together near stock. Get a good set of rings and set of new hypereutectic pistons to start with, so you have a fresh ring land. Make sure you have a reputable machine shop bore and hone the engine, preferably with a torque plate and make sure it is honed for "moly" rings. I prefer speed pro rings and I'm not a fan of gapless, people could debate with me all day about it, but If I were I'd pick up a set of good file-fit Speed Pro moly rings and go with them. Reconditioned stock rods will hold fine on what your doing, as will a stock iron crankshaft. But depending on your machining prices sometimes getting new rods is a better idea, for this look into the "powder metal" rods, I remember Car Craft having engines on their website using these rods, but I can't remember the manufacturers, if you are gonna go this route, do some research.

The intake of choice these days is the edelbrock performer RPM, depending on your climate "air-gap" or not. As the air-gap will pick up power, it eliminates the exhaust heat crossover heating of the intake manifold, which makes cold starts a bear. So if the engine has to be started in the cold, consider the non air-gap variety. The carburation job could be given to anything from a re-done stock Q-Jet (very good choice for power and mileage if you know somebody that can tune one for you) a 600 Holley Vacuum Secondary, or a Edelbrock AFB are also good choics fopr budget stuff.

Speaking about decking, I really advise you to do it. Getting a good quench (.034-045 piston to head clearance) is great for added top end and low end torque and staving off detonation on pump fuel and increasing mileage. Even when "decking" increases compression ratio a engine with good quench can actually be more detonation resistant or use LESS octane if it is decked than not, so don't be scared

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I have no idea what Curtis is talking about, 250 CFM is hard to come by with a set of heads like this, especially at the lifts we are speaking of.

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I should have clarified.  I was using flow numbers @ 28" H2O.  I suggested Vortechs to him which flow 240 @ 28" at .5" lift out of the box and I was just giving him a ballpark.

As far as the LSA on the cam, you're right its a personal preference.  I was trying to maybe bleed off a touch of cylinder pressure so he didn't have as much trouble with tuning fuel and spark curves between 2000 and 4000.  Plus, he said this is going in a Nova, and he'll have enough trouble keeping the tires glued with the torque he'll have.  I certainly don't think a 110 LSA is out of the question, especially at the duration we're looking at and the light weight of the car.

As far as the I/E ratio, did you also notice that the cam pattern I recommended was 211/227.  That's a wide spread.  When you port, you have to take that into consideration.  I suggested that to broaden the torque curve above 3500.  That also means he can focus his porting on the intake and almost leave the exhaust side alone.  He's not going to be revving to 6500, so velocity in the exhaust port was my main idea there.  A little extreme, I know, but the Vortechs can take a good bit of flow in the exhuast before they reach max velocity.

I also respectfully disagree with listening to the cam manufacturer on spring recommendations.  I've received nothing but headaches when I've done that.  They typically offer three or four springs to cover all of their cams.  If you choose a cam on the mild or wild side of the spring rate they recommend, you won't be happy with their performance.   For instance, one manufacturer uses the same spring for everything from their 212/218 cam up to their 256/256 cam.  If you put those springs on the 212/218 cam, you'll be almost doubling the seat pressure you need for that cam.  Not wise.  Trust resources at your machine shop to determing spring pressures and let the dyno tell you how to fine tune things if you want to get that involved.

Again, no flames intended, just counterpoint.  I have little experience porting, but a good bit of time on flowbenches and other aspects of building and I think Gibs and I just differ on some opinions.  I just wanted to clarify my choices and let you know why I chose them

I once again have some "counterpoints" and even though I really don't think I need to reiterate, because I think you realize that debate is a great tool for learning I will anyway, incase I sound too high on myself.

Yes, I didn't realize you were talking about porting vortec heads, there is a big difference between starting with a cylinder head that flows 200 CFM than 235. I just assumed with the power levels he was expecting that he wouldn't change cylinder heads, but that is still up to him.

What do you mean by bleeding off cylinder pressure with a 110 LCA? Would'nt the 114 LCA bleed off significantly more cylinder pressure(duration staying the same of course)? The Intake valve closing point after all is the point that is taken into consideration for dynamic compression ratio calculations. Agreed with the light weight a narrower LCA than my spec may be considered, but I think that transmission choice/stall converter will also come into play for the LCA, not to mention if anything a wider LCA is gonna help traction by flattening the torque curve and not providing any "spikes" of power to the wheels, not to mention lower peak torque. Once again though, up to the builder, but I still see 114 LCA as more than likely the best choice.

By porting the exhaust you would not lower the velocity, almost always you will increase airflow in a percentage higher than the percentage increase in port volume, signifying a increase in average velocity. The larger the spread of a dual pattern cam the more overlap and thus "punchy" the torque curve can become and not to mention part throttle becoming less efficient, thus a drop in fuel efficiency. True it may broaden the curve up high, but is it worth it in this very mild build? I always think about part throttle being even worse than what could be shown by a flywheel dyno rapping the engine out even as low as 2000 RPM @ WOT. If your hurting torque there, how much are you losing at 1500 RPM part throttle?

Your are probably dead on about the valve springs, but I have never gotten anything together on how to choose a spring, for many of us a dyno is not a option and a valve spring is something that needs to be optimized. Have any info to give me here?

Good discussion going here

The 110 LSA would bleed off lower RPM cylinder pressure due to reversion.  The overlap is too great at lower RPMs and some of the pressure bleeds off.  It would however take advantage of the higher RPM scavenging.

On the exhaust porting topic (or any porting for that matter)... I thought that when you ported and increased the volume of the port, the velocity had to drop.  Of course you can still reach your peak velocity, but at a higher RPM.  I thought that was the whole point of how porting shifts the torque peak upward; the peak velocity (and therefore peak scavenging) moves up in the RPM band.

I don't think we are increasing the port volumes enough here to make that much of a difference. But I may be wrong, but I will speak for what I've read when I say that if you increase the airflow in percentage more so than the percentage increased in volume when porting you had to have increased the efficiency or velocity. But I do have a great idea for where this topic should go, please ask someone by the name of OldBogie on this topic... http://forums.chevyhiperformance.primediaautomotive.com/n/mb/message.asp?webtag=chevyhi&msg=1126.39&ctx=0

As you could tell from his previous posts Bog is a genius, and could teach us both a thing or two, if you want some more good disscussions, head there.

Oh yeah, and I almost forgot, how can cylinder pressure be bleed off if the engine is making no pressure? The overlap phase is between the exhaust and intake strokes, both of which have valves open. The Intake valve closing point "hangs" into the compression stroke of the engine, thus lowering dynamic compression ratio.

But I have always theorized that excessive overlap could infact indirectly lower cylinder pressure, since the exhaust gas reversion could contaminate the incoming mixture and once it ignites the burn would be less efficient and create less pressure. But directly the intake valve closing point is bleeding off cylinder pressure.

Overlap directly affects cylinder pressure because of how early the intake valve opens.  Ideally, the intake valve opens at a point at which the rapidly exiting exhaust vapors start to create scavenging (and begin intake of new gasses) before the piston even starts to drop.  With greater overlap (either by increasing duration on the same LSA, or by decreasing LSA on the same duration) you open the intake sooner.  At low RPMs this shows up as exhaust reversion into the intake.  At peak VE, what happens is that all of the factors come together in harmony and the intake valve opens at or about the perfect time for scavenging to start.  Anything above peak VE, the intake opens later than optimum and doesn't take full advantage of it.  Anything below peak VE, its opening sooner than optimum and a certain amount of exhaust reverts back into the intake.  This is the single most important factor in idle vacuum and the lopey idle that is exhibited with greater overlap.  With less overlap, the exposure to exhaust reversion is minimized meaning that almost all of the pulses in the intake are vacuum.  Increasing overlap tunes the scavenging for higher RPMs exposing more exhaust reversion to the intake; therefore lopey idle and less vacuum signal.

As RPMs increase, that increased overlap becomes less of a factor in drivability since the actual time its overlapped is less.  Hence why it favors higher RPM cylinder pressure and a shift in the torque curve.

I think its on comp cams website, but they have an excellent example of this in audio form.  They compared a small block chevy with a long-duration cam at 114 LSA and a relatively mild cam with a 108 LSA.  The 108 cam has a very lopey idle, while the wilder 114 cam has a silky smooth idle.  Both are variations on a theme.  The 108 cam gives up low-rpm cylinder pressure (and therefore torque) for higher RPM power.  The 114 is a good way of getting streetable torque out of a cam designed for higher RPM capability at the expense of a few peak HP.

I agree; the IVC point directly affects dynamic cylinder pressure, but its the overlap that has a more direct effect on where that dynamic pressure peaks.  More overlap, higher RPM peak.  So your theory is correct.  The excessive exhaust reversion exhibited at low RPMs with heavy overlaps lowers cylinder pressure because it pushes exhaust back up into the intake, then sucks it right back.  It drops the VE at low RPMs considerably.

I specifically chose a very mild cam (194/199 if I recall correctly) for an Olds 307 build that I was doing for a friend, but I specified a super tight 106 LSA because his big thing was that he wanted the "sound of power" as he put it.  I worked with Lunati to get a tight LSA for enough overlap to get a lopey idle and we also came up with a really fast EVO ramp to make a little "tat-tat" in the exhaust note.  He was happy, but the engine made about 230 hp and got about 8 mpgs   Talk about a nightmare to tune a fuel curve .  The igntion was easy.  I locked the mechanical at 36 and put a mild pull on the vac advance.

The heads aren't the best.  Smog era 76cc, if I'm not mistaken.

If you have to keep them (if it's a rule or whatever), consider an angle mill and some serious porting.  2.02/1.60 valves are a good thing too.

One of the first ones to reply to you gave you some good cam recommendations.  Look into a newer, computer-designed grind such as a Comp Xtreme Energy or Lunati Voodoo.  I've got  Crower Beast cam that I'm also very happy with.  These grinds have a wider operating range and better street manners than a lot of their predecessors of similiar size.

As for the bottom end, unless you're doing forced induction, a good hypereutectic piston from a known piston manufacturer will be a soild choice.  I personally prefer a flat-top piston over a dome because when coupled with a small chamber (64cc ideally), they make good compression and the force of the combustion is carried down the cylinder instead of being partially deflected by the dome of the piston. 

Unless the block is immaculate, a .030" over hone is a good idea in order to start with a like-new block.  Avoid turning the crank any more than absolutely necessary because thicker bearings spin easier than thin ones.  Also bite the bullet on some really good bearings.

Really concentrate on making those cylinder heads the best they can be (that or replace them with double-humps (041 castings) or Vortecs (906 castings), they have the best performance potential of GM iron heads).  A good set of cylinder heads can be the difference between a 275 HP engine and a 350 HP engine.  Also make sure your valvesprings are a good match to your cam; too light of springs can cause valve float (not good) and too heavy of springs rob power by putting the valvetrain under unneccesary resistance and can cause undue and premature valvetrain wear.

You do have a great point there that you also explained quite well, but the overlap may effect the dynamic compression (basically "cylinder pressure" peak) around peak VE and thus peak torque, but what are talking about with making a engine more detonation resistant on pump fuel? Would overly heating and diluting the intake charge be a more "in-efficient" way to lower pressure? Wouldn't  hanging the intake valve open slightly longer be better (even though it is also making the engine "in-efficient" at low revs) for making a engine more ping resistant? I really think you should talk with who I mentioned earlier at the CHP board. Disscussions between dedicated and knowledgeable people make great points to learn from. And I'm constantly searching for them.

Volumetrically speaking, yes it is inefficient, but it shows up as a very mild drop in the torque curve at certain points below VE.  BMEP drops predictably and that's what the narrower LSA is in effect achieving.

The dilution of the intake charge radically reduces combustion temps at those lower RPMs since it basically acts like an EGR; introducing exhaust gasses in with the charge.  At that point its also less of a factor of how much net cylinder pressure is present in the chamber, as much as its the amount of exhaust gas that is still there after the reversion.  If you've ever dealt with a car that had a stuck EGR valve, it idles a lot like it has a huge cam... if it idles at all   This is much the same way; the more reversion, its like the more EGR gasses you give to the combustion, which lowers combustion temps, and therefore octane tolerance.

There is the argument that lowering the pressures and temps at low RPMs with a narrow LSA, it also raises pressures at peak VE and therefore negates the octane tolerances you've created, but most cams where a narrower LSA is desired, there is enough duration that the peak VE is higher than needs to be dealt with.  By shifting the peak VE higher, you achieve greater piston speeds.  Any detonation that occurs in effect doesn't happen fast enough to cause dangerous spikes in cylinder pressure at those piston speeds.

I'm very interested in those other forums you mentioned... headed over now   Thanks for the discussion and keep it going if you wish.  Or you can email/PM me.  Great discussion, but we are sorta monopolizing someone else's thread

Don't forget to tell him to be very careful on the porting of the intake ports. Don't radically change the factory setp, open the throat, and blend the bowls, plus port match to the intake. On the exhaust work the short sode radius and work around the guide boss.  CC and HR have covered this fairly well, along with an excellent amount of measurements and tips. Search that and follow along, it will help.