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Old 10-10-2009, 02:08 PM
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Mild build chevy 350 guts question

I have a 74 2 bolt main chevy 350 out of a impala. I have torn it down for a rebuild. I have a 79/80 2brl aluminum intake and 883 heads that will get ported to match. I will probably stay with stock valve springs and not turn anything into a roller. I do a little racing and that is what this engion will be for. Fuel econ is not something I will be interested in. I am trying to find a cam that will work with the carb/intake/heads, but still be in the power range of 1200-5800. Personally I want a good low to upper torque along with good mid to upper HP. I was looking at several cams that tend run generally around that rpm range and the lifts run between 442 and 480 ish. I run probably around 12 times for roughly 10-25 mins each time. I am looking for something that will stay as cool as possible, probably stay around the 9:1-10:1 comp range. Any help in this decission making process would be greatly apreciated. Mainly looking to bounce some ideas off of people.

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Old 10-10-2009, 07:01 PM
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You already have the cam`s realistic goals in mind with the powerband so you don`t need anyone`s help. Look into all the cam company`s out there web sites and it will tell you the RPM band that is realistic for the given cam.
If you plan to do some dragging then know the gears play a far bigger role then the engine ever will. When you gear it, think of weight, drag times and street cruise RPM and pick something that will work with all.
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Old 10-11-2009, 09:50 PM
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thanks for the help. I am definatly a student when it comes to building a great motor. Heres another question. The heads are 76cc, dont know the dish of the pistons, but if I replace the stock ones with flat tops what would the compression normally jump?
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Old 10-12-2009, 02:57 AM
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It depends. Some of the cheaper rebuilder pistons have .020 off the compression height, even so the head has a flat top, with .020 off the comp height the piston doesn`t come up as far in the bore so in effect it really doesn`t help compression any. A piston with the correct compression height and a flat top would likely make the compression jump by half a point or slightly more.
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Old 10-12-2009, 10:14 AM
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Like DV said careful on the compression distance. Stock i believe for a sbc is 1.560" and many cheap rebuilders are 1.540" that way if u cut the deck you can still run stock gaskets.

Here is a calculator from KB: http://kb-silvolite.com/calc.php?action=comp

Do some reading on "quench". It tells you that the total distance from the bottom of the head to the top of the piston. So this value will include your deck clearance and the thickness of the gasket.

So if its a stock rebuild with a 3.48" Stroke 5.7" rods and a compression height of 1.560" Your stack should come in at 9.000" Now from the factory the deck height of SBCs are "supposed" to be 9.025" I say supposed because they can vary and are sometime tipped from corner to corner. But on a mild build i wouldn't worry about it. So as of now we know the piston should be about .025" in the hole so add a gasket that is .015" thick and your quench will be at .040". This is how i built my 350 with 6cc flat tops, 76cc heads, and .040" quench and my cr is about 9:1, which would probably be okay from a mild cam. Hope this helps just my .02
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Old 10-12-2009, 10:43 AM
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look for a piston that has 1.565" compression height, 2VR's, and run a Mr. Gasket steel gasket, you'll be a hair under 9.5:1 depending on your heads final volume. I'd run an Elgin cam (they are cheap and work well) and file fit rings, make sure you run good bearings and everything is in pristine cleanliness when you put it together.
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Old 10-12-2009, 10:45 AM
How fast is fast enough?
 
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a intake would do woners for you, you can get some used off of craigslist or ebay or local for under $50. the stock 2bbl is very restrictive.
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Old 10-12-2009, 05:41 PM
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I dont know much about the intake that I have other than what year it came off the line. I dont have a clue what rpm range it is set to run and top out at. I would like to stay with a good 2brl intake if I can just because I have had some bad luck with adapters and if I could cut out that process all together I would. Thanks for the tips on the flat tops, it helps me out a lot. I was thinking of getting the intake I have ported along with the heads, but dont know if that is very cost effective. I have been thinking of getting a slightly larger cam than before and going with new 600 lift valve springs and roller rockers. If I do that than should I just do an entire new top end? I would really like to try to keep the cost down if I could, but get the most for my buck. Will stock valves work together with the springs, rockers, pushrods, and lifters?
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Old 10-13-2009, 11:05 AM
How fast is fast enough?
 
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why would you need an adapter? a 600cfm holley and a good 4bbl intake should be on the top of yuour list, and they can both be had cheap.
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Old 10-13-2009, 02:29 PM
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Following zildjian4life218's correct line of thinking, a 0.030"-over 350 with 76cc heads, 5cc piston deck height, 6cc piston eyebrows and 3cc gasket will have a 9.07:1 static compression ratio. If I were to choose a cam to this SCR, I'd use a CompCams 265DEH, 1500-5750 rpms, 211/221 @0.050, 0.442"/0.465", 110 LSA. The shorter intake duration will allow an acceptable intake closing point for the 9.07 SCR and the longer exhaust duration will help to crutch up those awful exhaust ports in the heads.

Use a 2-bbl carb/intake only if you have to according to the rules. Forget about port matching, you'll hurt the motor more than you'll help it. If you don't understand this last statement, do some studying on fluid dynamics.

This appears to be a budget build, so I would try to get the best 1.560" compression height piston I could for the money. A hypereutectic piston will last just fine if you keep the motor out of detonation and don't overheat it....
http://www.summitracing.com/parts/STL-H345NCP30/

One other thing, using stock, worn-out valve springs on a healthy cam is playing a fool's game. Scoggin-Dickey offers some affordable springs, retainers and locks that will drop right in your heads with no machine work and provide the pressure required to control the valve without excess pressure that may result in a pooched lifter/lobe...
Order 32 of part number SD1132 @ 55 cents each.....
http://www.sdparts.com/product/SD113...alveLocks.aspx
Order 1 of part number SD364 (pkg of 16) for $29.95....
http://www.sdparts.com/product/SD364...gRetainer.aspx
Order 1 of part number SD1004 (pkg of 16) for $25.95....
http://www.sdparts.com/product/SD100...lveSpring.aspx

Last edited by techinspector1; 10-13-2009 at 03:26 PM.
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Old 10-14-2009, 12:36 PM
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I don't really want to buy a new carb and I already have 3 very nice rochester 2brl carbs which are easier to work with and cheaper. I have run 4brls before and have a problem with either to much fuel or stalling out. I have had good luck with the rochesters and would like to stay with them. I have done some looking into intakes and it looks like I can get one for around 100-150 that would work with the rpm range that I am looking for. will it be worth it to buy a intake if the heads will not flow good enough to make it matter? Got a set of roller rockers, and tall valve covers picked out. I do get these engions hot every now and then. They can get up to the 280 range and still have some run time left on them. Thats another reason for the budget build. I will end up rebuilding it every 3-5 summers anyway. This engine has been run before, but in its stock form. I don't know if I am forgetting anything. Not going to do a valve job because I don't think it would be worth it with these heads.

Last edited by dadicted; 10-14-2009 at 12:42 PM.
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Old 10-15-2009, 03:50 PM
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these are the rockers that I am looking into buying. Anyone have much experience with these in particular?

http://www.speedwaymotors.com/Sports...Arms,6562.html
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Old 10-16-2009, 06:59 AM
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Quote:
Originally Posted by dadicted
I don't really want to buy a new carb and I already have 3 very nice rochester 2brl carbs which are easier to work with and cheaper. I have run 4brls before and have a problem with either to much fuel or stalling out. I have had good luck with the rochesters and would like to stay with them. I have done some looking into intakes and it looks like I can get one for around 100-150 that would work with the rpm range that I am looking for. will it be worth it to buy a intake if the heads will not flow good enough to make it matter? Got a set of roller rockers, and tall valve covers picked out. I do get these engions hot every now and then. They can get up to the 280 range and still have some run time left on them. Thats another reason for the budget build. I will end up rebuilding it every 3-5 summers anyway. This engine has been run before, but in its stock form. I don't know if I am forgetting anything. Not going to do a valve job because I don't think it would be worth it with these heads.
A valve job- especially on SBC heads that tend to wallow out the valve guides- would be near the top of my "to do" list.

Be aware that the Rochester DualJet 2-bbl. carbs are nothing more than the primary side of a Q-Jet. Just the swap to a Q-Jet carb and OEM alum. intake will be more than worth the effort, IMHO.

AFA using an aftermarket 2-bbl intake, save your money. There's nothing of any substance to be gained by using an aftermarket intake unless you were also going to change carbs to, say, a Holley Mod 2300-type carb (350 or 500 cfm), or a 2-Jet Rochester done up by Jet or someone. I know of no intakes besides OEM that will take the Rochester DualJet (1/2 of a Q-Jet, mentioned above). I know of no adapters, either.

Do not run excessive valve spring pressure- it isn't needed, just match the springs to the cam, using the manufacturer's recommendations. I'd suggest doing a search on cam break-in procedures and lubes that have become necessary since the motor oil formulations have changed, if you're not up to speed on that front.

You need to do whatever it takes to bring the temp down from 280 degrees. This leaves nothing in reserve if there are problems.

Just what type of competition are you into?
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Old 10-16-2009, 10:28 AM
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I do some figure 8 shows that you tend to run on some pretty wet tracks and are all throttle in the corner sometimes. You do hit other cars while doing this and for the most part the 650el 4brl that I have stalls out when that happens which ends up making me lose position pretty quick. I don't want to run a stall converter and still want the power when I touch the gas. The times that you hit someone in the middle or have to slow down to let someone pass in front of you is where you lose position and I would like the engine to just keep up and when those times happen to be able to not stall out, and get a jump off the start. If the heads wont breath any better than what the valves can produce then does a valve job matter? I guess what I am saying isn't a valve job only as good as the heads can breath? Which OEM intake would you guys suggest? Any 4brl with a rpm range in what I am looking for or is it worth it with these heads to spend the extra money for a high rise or something more?
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