Hope the HAMB can help. I'm building a 350 for the first time and have got together my parts list (I think), and need some advice. I'm not looking for a race motor as this is going into a 1939 Pickup... just need a decent 350 with a nice sound. What I currently have: Fresh machined 350 SBC Chevy with stock bore - 1974 (based on casting date), new bearings, rings, freeze plugs, etc. 1976 Corvette crank, rods, and what I believe are the stock pistons (pic attached) What I'm looking to get 64cc/190cc aluminum heads Comp Mutha Thumpr cam (more for the sound) Intake and Carb TBD Based off my calculations, I'd be around 9.5:1 compression ratio... I think. 4" cylinder bore; 3.5" piston, -13cc for stock dished pistons????, 64cc combustion chamber. Is this correct? My biggest issue is if the stock pistons are -13cc or not? and are they ok for this setup? Thanks for your help in advance. This is a pic of the pistons that are in there now.
From the pic, it looks like those pistons are not dished......they do have reliefs for the valves though. Seems like you can easily measure the volume of the reliefs and then recalculate your compression ratio.....add that volume to the combustion chamber volume, and the volume between the deck and the piston at TDC. Divide this total into the cylinder volume.
You will use the Thumper and lose some power. Those are flat top pistons. With an aluminum head and good turning your fine. A thick blue FELPRO head gasket (I used on a sbc non alum head) will help too. A .450 intake .460 exhaust lift cam will be more everything for the street. Your choice, good luck.
Figure the pistons at 7cc's. Those valve reliefs are very shallow. You can figure the piston deck height by bringing any piston to top dead center. Stand a steel rule on edge and extend it out over the bore by an inch or so, then use the blades of a feeler gauge to determine how far down in the bore the crown of the piston is. Most of these motors will be around 0.035" if the builder used premium pistons with a 1.560" compression height and the block has never been cut. If the builder used a "rebuilder" piston, then the piston will be 0.020" shorter in compression height, at 1.540", and the piston deck height will be closer to 0.055". Let's go through an exercise of finding the static compression ratio and then you'll know how to do it...... Block (standard bore) at 4.000" and standard crank at 3.480". (.7854) x 4. x 4. x 3.48 x 16.387 = 716.62 cc's in the cylinder. 64 cc's in the chamber 7 cc's in the piston crown For now, we'll use a piston deck height of 0.035" (.7854) x 4. x 4. x .035 x 16.387 = 7.2 cc's Now, depending on the piston deck height, you'll want to use a head gasket that when added to the gasket thickness, will come closer to the desired 0.035" to 0.045" squish. Squish is the mating of the piston crown with the underside of the cylinder head. When the piston comes to TDC in the bore, we want it to "squish" fuel/air mixture out from the area above the piston and below the head surface. This squishing creates turbulence and "jets" the mixture which would be stagnant there, across the chamber toward the spark plug just as the plug fires. This turbulence homogenizes the mixture in the chamber and contributes to the elimination of lean and rich pocket of mixture, giving a cleaner burn and more power. A tight squish will also allow the motor to operate on a lesser grade of fuel with no detonation than a wider squish or no squish would. With a piston deck height of 0.035", there will be no way to arrive at a 0.035" to 0.045" squish because the thinnest gasket you will find for a SBC (that will not Brinell an aluminum head) is about 0.039". So, if we have a piston deck height of 0.035" and a gasket thickness of 0.039", then we have a squish (or the lack of squish) of 0.074". Since you must use gaskets that are specified for aluminum heads, there is no chance of using a thinner gasket. If you want to improve the squish, you must cut the block decks for a shorter block deck height. In this case, you might cut the block decks to "zero", meaning that the crown of the piston is even with the block deck when the piston is at top dead center. This is usually done when you are planning the build and haven't bought any parts yet or done any ***embly. Anyway, I got off subject, as I tend to do sometimes. You can find the cc's of the gasket by looking at the specs of it or you can calculate it yourself the same way we did piston deck height above..... (.7854 X 4. x 4. x .039" x 16.387 = 8.03 cc's. I used 4" just to keep it simple. Now, let's add up all the values.....we'll drop off the decimals.... 716 + 64 + 7 + 7 + 8 = 802 cc's Now we'll drop out the cylinder and add all the rest..... 64 + 7 + 7 + 8 = 86 cc's Now, divide 802 by 86 and find 9.325:1 static compression ratio. Now, use the calculator on the Keith Black piston site to find the proper cam to work with this SCR. I'll show you how if you don't know. Richard
Thanks for all the help. I got the edelbrock performer rpm heads, ARP bolt kit, comp cams aluminum 1.5 roller rockers, billet alum. tall valve covers and went with the thumpr cam instead, comp cams lifters and timing chain. Edelbrock performer eps intake manifold. Put it on for a quick picture since I can't wait to get it done! Next up is deciding on the carb and distributor, etc. any recommendations?
Pertronix Flame thrower distributor. An Edelbrock 600/650 cfm carb. Electric choke. Stainless return spring kit & kick down linkage if a 350 trans is your choice.
ah we have some good people here (fridaynitedrags) reminds me ... (docholiday) of me ... lol heres a nother one borexborexstrokex8x.7854=(ci's) u do the math
If you are looking for a nice choppy idle, the thumpr cam is all you need. Here is a video of mine to listen to, keep in mind that I am running a hydraulic roller set up though. Its a 98 350 with vortec cast iron heads, stock lower end, aluminum intake, Holley 670 carb, and some free flowing exhaust... I am more than happy with the set up, after all its just a street motor, and it works pretty good too... http://www.youtube.com/watch?v=kpypBWBOCo8
Your parts list indicates better than a "Decent 350"............so why not have a cam to match its potential? After you get your 9.5:1 compression ratio, ditch the Thumpr and get a CC's Xtreme Energy cam (#12-246-3) that will make some power, have better vacuum and shake at the stop lights as well.
I don't want to put too much power in to it because it is a 73 year old frame. While I have boxed it some, I don't really want to box the whole thing. The truck is going to be more of a show truck. I will never take it out on a track. Here's a pic of how it was when I got it and how it sits now. Its come a long way but still more to go!
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