71 SBC 350 build question/opinions - also new - Hi
First off let me say hi - new to the forum.
I have a question or more like seeking opinions on my build. Bear in mind that this truck is almost a daily driver and occasionally tows a bass boat. Doing this on a semi budget, currently the heads and carb I am flexible on as I will buy a set - and maybe a new carb.
Let me list as much of the details as possible - Curious as to what kind of horse power I can expect and if you all think it's a decent package.
Vehicle: 1971 Chevy Cheyenne C10, 1/2 ton 2 wheel drive
Transmission: TH350 with 2000-2200 stall.
motor: 71 350 4 bolt main - .20 bore
Crank/Rods - stock .10 over
Cam - Comp Hi Energy 268/268 454/454 - 110 deg lobe separation
Pistons: Flat Top, 4 valve relief, Hypereutectic Aluminum, 5cc
Intake: Edelbrock Perform
Carb: 650 Holley
Exhaust: Headers, duals, 40 series flow masters.
Heads: 72cc Chamber heads, cast iron, 165cc intake runner volume, 2.02 intake, 1.60 exhaust. (Summit)
Ok, that should cover it.. Do you think these heads will be decent for what I have bearing in mind - daily driver. Is there anything that doesn’t go well here? Intake? Carb? Etc…
Thank you in advance.
I am guessing that the truck has 3.08 gears. If so then the cam is a little too big. The 260. h would be a better choice.
The heads are fine but I would recommend you take them apart and perform some bowl smoothing and get a quality valve job.
The rest of the build is good. However power and MPG could be down if the Carb and timing isn't tuned correctly.
Your build seems on tack for a daily driver/tow. Make sure your carb is a vacuum secondary carb NOT a double pumper. Also I would just like to up the compression as it always increases power. Maybe a set of 62cc flow-tek heads from speedway motors which are also aluminum for $740 assembled. But all in all your heads and cam should make enough torque to make you happy. Good luck
First the heads.....
The Summit tech guy only has flow at 0.500" valve lift, 210 intake/138 exhaust. That's about the same flow as production 434 or 462 Chevy heads and should work fine for your application.
I think in this case, I would opt for a stock cast iron intake manifold and mount a rebuilt Quadrajet on it. The stock manifold will max out the low end torque that you will need for towing and the tiny little primaries of the Q-jet will maximize your fuel mileage. Plus, when you get down on the loud pedal, the huge secondaries (BUHWAAAAAAAA) will be music to your ears.
Here's how I see the head flow....
0.100" 57 54
0.200" 123 97
0.300" 171 123
0.400" 203 133
0.500" 210 138
0.600" 217 140
These numbers were arrived at by playing with the numbers posted on the Stan Weiss site for production 434 and 462 heads and are the best SWAG I can come up with.
If you have a virgin cylinder block and don't do any decking to it, the block deck height will be 9.025". (If the stamped suffix numbers are still legible on the passenger side of the block deck at the front of the block, it's probably virgin). If you choose pistons with a compression height of 1.560" (choosing a piston with a compression height of less than 1.560" will be a mistake), the stack of parts you will be using will be 9.000". Deduct the stack from the block deck height and find a piston deck height of 0.025". If you use a shim steel head gasket (0.015" thickness), that will put the squish at 0.040" and will make the motor nearly detonation-proof on pump gas with a reasonable static compression ratio and cam to match. Here's the gasket.....
Wipe down the block and heads with a good solvent to make sure they are clean of any oil or other material and install the heads dry.
With a cylinder volume of 724.63cc's, heads with 72cc chambers, pistons with ~5cc eyebrows, piston deck height volume of 5.2cc's and gasket volume of 3.25cc's, I calculate the static compression ratio at 9.48:1. Absolutely perfect for a pump gas motor with iron heads. :thumbup:
Here's the cam you have chosen....
12-210-2 - HIGH Energy
Install it 2 degrees retarded on these 0.050" tappet lift numbers for a Dynamic Compression Ratio of 8.26:1.......an excellent pump gas number for use with iron heads.
IO (1) BTDC
IC (37) ABDC
EO (41) BBDC
EC (-3) ATDC
Here's a DynoSim of this very affordable and common sense build.....Look at that torque curve....flat as a pool table.
Max volumetric efficiency 83.5% @4000 rpm's
Max BMEP 169.9 lbs @4000 rpm's
The slightly looser torque converter should put you right on the numbers from the git-go. Well done.
Thank you for the replies.
454C10 - I am assuming so too on the rear end being the one in there is stock. But in my shed, I have the factory posi that off the truck, the old clutch type - I am thinking it is geared different and that is what will go back on it. Of course, once I get a good look at everything inside is started to develope bearing noise, so I did a quick change out from another truck.
1BadLeman - I had considered the 64CC head route, but think I'll stick with the cast and the stock valve train for now. I can always upgrade later.
Techinspector1 - I wouldn't figure many would recommend the old cast iron intake over an aluminum one with the holley. On a side note - the aluminum intake may be a performer RPM, if that makes a difference. I happen to have the original intake for this motor still. Towing is very minimal on this truck - it will mainly be driven on the street and to work most of the time. Still go with the cast iron intake?
I'll have to pick up a new Carb - any suggestion on CFM's?
I too like the sound of a quad opening up. I've had my fair share of them over the years.
Your Question about it being a virgin block and the deck heigth - I am the 2nd owner on this truck and I know for a fact that the drive train is all original, down to the transmission. This is the first rebuild on this motor and after getting the machining done - no deck heigth was shaved.
In questioning the pistons and head gaskets - They are also from summit
The pistons are ZH345ACP20 - I was limited due to .20 bore and didn't drop the extra $$ for forged. It looks like it's slighty below your 1.560" recommendation - looks like it's @ 1.548"
Based off this added information, using those pistons mentioned - would you change to a different head gasket then what comes in that kit? any recommendations or opinions for everything said above?
The gasket set with the heads gaskets I have already puchased also are: Z2601000 - also from summit.
Send the pistons back and get these.....less than a hundred bucks for the set.....
Use the shim gasket I suggested. That's why I spent all the time that I did for you.....to get you the best possible combination. If you want to build it differently, go for it.
I appreciate your reply techinspector1 - that's why I came here and asked. To get some opinoins/ideas before I assembled this motor together. I have built a few in the past, but it's been many years and I am not "up" on some of the finer qualities of matching to get peak performance.
I will take you advise on the pistons and gasket as well as the prior advise. Thanks.
welcome to the forum.enjoy the group and post some pictures
Will post some pics when I get back home and get the build going. And thank you for the welcome aboard.
I don't recommend using a higher than stock stall converter if you plan to tow a boat. A 2400 stall converter will stall around 3000 pulling a trailer which isn't good for the transmission.
Thanks, I will definately keep that in mind about the converter. I have a stock one and a 2000-2200 stall. I can use either.
Good point 454C10, with 402 ft/lbs of torque at 2000 rpm's, this rig won't need much converter.
I have run the 268H cam in other engines (SBC and BBC) and it seem a little too much for a truck with a 3.08 gear. And a little too much for a stock converter, even through Compcam says it is the biggest cam that can be used with a stock converter. That is why I think the 260H would be better (212/212 duration at 0.050), as I have run that cam with a stock converter with a 3.08 in a 1/2 ton truck and it works nicely.
However, I would limit compression ratio to 9.0:1 with the 260H if you want to use cheap gas, and 9.5:1 for high octane. The 268h can tolerate a little more compression, say 9.25 to 9.75:1 with 87 to 91/93 octane fuel
The 268H does better with a little more gear, especially in a truck since truck tires tend to be taller. I do like 3.08 gears, as they are a good compromise between city and highway gearing, but the 268h would like 3.40-3.55 gears.
454C10 - The posi unit I have - I believe is geared more towards 3.40-3.55 range. This is the unit I am going to rebuild and remove the current 3.08. I am not at home right now and don't remember the exact ratio - but do know it's not the same as what is in the the truck currently.
As for tires - 275/60/15's are on it right now.
The cam(268H) is bought/paid for alread and with posi unit and the low stall converter - from your opinion, sounds like it should work fine.
I am taking all of the opinions expressed above into consideration. I have already replaced the pistons and headgaskets as I agree with techinspector1's breakdown of things.
Sound like I am still on the right track for a succesful combo?
during a few trial fits of pistons and gapping rings etc,ask Tech where the cam is best degreed?perhaps between him and 454 they might consider plus 3 or 4º for the cam?
ask this question after you confirm gear ratio.
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