Thread: Questions regarding an engine build I'm doing. I am new and learning as I go. 355 SBC

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Originally Posted by Steves1968

I would like to know how much horsepower I will expect to have after this engine is complete. 350 sbc .30 over, flat top hypereutectic pistons, HYD Voodoo 504/525 lift cam and lifters, new steel crank, flow tek aluminum heads. If there is more information needed just let me know, just a ball park would be great. Also I had a 700r4 built for a mild performance engine, was wondering the best rear end ratio to have. This is going in a 68 GMC step side for a street rod. Thanks

Hello Steve and welcome to the forum. My best advise is to STOP where you are and figure out your combination based on math and science. I'll pitch in to help you with my 60 years of hot rod experience and I'm certain the rest of the fellows on this board will do the same.

For starters, let's look at flow numbers for the heads....

Valve Lift .400" .500" .600"
Intake 206 237 244
Exhaust 165 177 187

If these numbers are valid, these look like decent heads for a 355 street driver, although I might expect them to stall at around 5500 rpm's. In other words, the heads will probably lay down before the cam will.


Let's look at the cam you have chosen....
10120704 60104 2200 - 6400 .504"/.525" 233/241 276/284 110/106 Hyd/Hyd
Hot street cam, likes 2800 converter, hirise
type dual plane intake with 750 CFM
carb, headers, 10:1 compression and
3.73 gears. Likes up to 200 HP nitrous
LSA/ICL: 110/106
This cam will want more head than you have chosen. You will want to make arrangements for a way to provide more manifold vacuum than this cam will provide, for power brakes, like an electric pump or vacuum reservoir. If you have manual brakes, never mind.

The 64cc combustion chambers and flat-top pistons will generate an approximate 10:1 static compression ratio, so you'll be OK there as far as matching the cam to the static compression ratio. Choose straight spark plugs in the heads for ease of fitting headers. Angle plug heads will make you tear your hair out trying to make headers fit properly.

Now, here's the problem....
Aluminum heads will not tolerate a steel shim head gasket, you must use a composition gasket such as a Fel-Pro 1003.
When the block was produced at the Chevrolet plant, the block deck height was set at 9.025". That's the measurement from the centerline of the main bearing bore to the flat part of the deck where the heads bolt on. The block may be a little shorter or a little taller due to factory tolerances. Your job is to fit a stack of parts into the block that will result in the proper piston to deck height so that you can use a composition gasket and still maintain a tight squish/quench of 0.035" to 0.045".
If the block is 9.025", you must choose a stack of parts (piston compression height, rod length and crank radius added together) that will fit into the block with the piston deck height (distance from the piston crown to the block deck with the piston at top dead center) equal to zero in order to use the composition gasket and create a tight squish/quench.
Here's an illustration that shows piston deck height as "deck clearance".....
http://www.matrixgarage.com/sites/de...s_image002.gif

If the block is 9.025" and you choose a stack of parts that equals, for instance, 9.000", then the piston will be 0.025" down in the bore with the piston at top dead center. Then, when you use your 0.041" composition gasket, the squish/quench will be 0.066", too wide to be effective in preventing detonation. We need a squish/quench of 0.035" to 0.045" in order to prevent detonation on pump gas.

Your crank radius is 1.740", your rod length is 5.700", so you will want to choose a piston with at least a 1.560" compression height to make your stack measure at least 9.000". A taller piston is even better and will allow you to cut the block less to get to zero piston deck height. Bottom line, you will have to have a machine shop cut the block decks to zero-deck whatever stack you end up with.

I'm not being as fluent this morning as I usually am and hope that I have done more than just confuse you. This is where you make or break a motor build, so please ask questions until you fully understand what I'm saying here.

You'll make more power with a high-rise, dual-plane intake manifold than any other type of manifold, although there are other members of this board who have found that they like a different type of manifold. It's just that I have seen too many dyno tests that show the high-rise, dual-plane type to make the most power. The manifold of choice is the Edelbrock Performer RPM. Not the Air Gap, which may present driveability problems in cooler weather, just the plain old RPM. This is a take-off from the design that Chevrolet used on the '67 to '69 Z-28 motor. Aftermarket companies such as Edelbrock, Holley and Weiand have copied that design and you may be able to find one of them used on craigslist, ebay or racing junk. Look for Edelbrock 7101, Holley 300-36 or Weiand 8016. If you want to buy new for a little less money than the 7101, Weiand has a current production model intake under part number 8150 that will do a good job.

If I can find the time, I will run the combination on my Dyno-Sim and determine the power the motor will make, but in the meantime, you need to be addressing the zero-deck aspect of your build.

Now, as far as rear gearing, you want to pay attention to the cruise rpm's of the cam. The cam you have chosen will want to cruise at over 3000 rpm's, so you will not be able to use an overdrive transmission with it for gas mileage. Install a set of 3.73 gears with 27"/28" tires, no overdrive and you're good to go. The idea of an overdrive transmission works great with the weenie factory cams, but when you install a hot cam like you're going to do, you have to make concessions on the gears or the truck will disappoint you. Not only will you not get any mileage with an overdrive trans, you will not make any power either because the cam is not ground to make power down low in the rpm range. Again, if you are looking for fuel mileage, drop the static compression ratio down to 8.5:1 to 9.0:1 and use a cam that has closer to 200 degrees intake duration, rather than the 233 degrees of intake duration with the cam you're planning on using.
Here, for instance, are some different cruise rpm's for different intake duration cams, according to Crane Cams engineers....
192 1600-2200
204 2200-2600
210 2400-2800
216 2600-3000
222 2700-3200
226 3000-3400
230 3400-3800
234 3800-4200
238 4200-4600

If you're looking for power plus fuel mileage, then you need to be putting together a turbocharged or supercharged engine package using a mild cam. You cannot have both power and mileage in a naturally-aspirated package. Everything is a trade-off.

And finally, flat tappet cams are ancient technology from the previous century. Metallurgy has changed as well as lubricating oil formulas, none of which is geared to allowing a flat tappet cam to work in today's environment. Please bring yourself up to speed with this tutorial....
http://www.crankshaftcoalition.com/w...ips_and_tricks

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