Healthy 355

[c1500sbc]

I have a fairly recently rebuilt 355. Stock rotating assembly with some hypertuectic pistons. Promaxx maxx series as cast 190cc 64cc chamber CR at about 10.3:1, Lunati bare bones flat tappet 224/234 Duration at .050". 112 Degree Lobe Separation Angle. 0.465"/0.488. Running a dual plane edelbrock rpm intake (not air gap) with a 650 avs2 carb, HEI distributor and 1.6 roller rockers (so cam lift is a little higher than advertised). 34-36 degrees of timing all in by 2800 rpm. All running through a 5 speed NV3500 and a GM 10 bolt rear end with a Yukon 3.73 limited slip.

For you engine gurus. What HP/TQ would yall expect from a set up like this? I know there's some variation but a general guess. I'm not happy with what it put down to the wheels.

With that being said a 383 is in mind but I hate to toss out a perfectly good running 355. Any suggestions on improvements to the current set up and still keep it streetable? Custom carb is an option but i'm not sure how much it would help considering I feel like the AVS2 is fairly dialed in. I'm okay with a little driveability loss to gain a little power. Right now its pulled 16 in of vacuum at idle. Power brakes are a must and while not ideal, hydro boost is an option or even a vacuum pump.

[FC-Pilot]

What gear and trans does it have? Auto or manual? I would say gear and converter (if an auto) would be A good bang for the buck. Nothing strangles a good engine like a bad converter and too tall of a gear.

Paul

[c1500sbc]

Thank you for the reply. Sorry I should have clarified, its a 5 speed NV3500. 3.73 gears. I fixed the original post!

[Monza355]

My guess would be somewhere around 375 hp / 400 tq.
Should be a fun street combo. How’s the timing curve in the distributor ?

[c1500sbc]

Its a fun little truck for sure, just didn't put the power down to the wheels I was expecting. I know dyno numbers aren't the end all be all but none the less I was a little disappointed. It put down a little over 300 hp and a hair more torque.

I'll be honest and say I'm not sure how to check the timing curve? I know that it is all in by 2800 rpm. 18-19 initial and the rest is mechanical.

[rebelrouser]

for what my opinion is worth, I would advance the cam 4 degrees and see if that does not improve it a bunch.
And on the timing curve have a buddy help you get a timing light that has an adjustable advance built into it. Get a piece of graph paper, and have your buddy rev the engine about 100 rpm increments from idle, until the advance is all in. note the amount of advance on the graph paper at every 100 rpm, and draw a line to connect the points, instant timing curve.
And you might try changing the springs under the rod pistons. Start it up and let idle, carefully take the screw loose that holds the plate where you access the piston, and slide it over so you can see the piston work. tap the throttle while you watch the piston move up and down, careful, if you rev it too quick the piston will shoot out. Stretch the spring or buy some stiffer springs until you get the piston to start moving the instant you touch the throttle.

And play with the secondary air door yours if it is an AVS is a simple screw type adjuster, lossen spring tension until the secondaries come in as early as possible with out a bog.

[c1500sbc]

The cam is supposed to have 5 degrees advance, if I remember right, "built" into the cam, but i've heard varying opinions on what that really means. It seems like some think that is just a marketing tool and it's not necessarily advanced in the way it would be upon in stall with a degree wheel.

I'll do that this weekend! Thanks for the tip. I've heard people mention timing curve but wasn't sure how to graph is correctly.

As far as tweaking on the piston spring, i'm assuming that you're meaning the needle spring on the carb for the primaries? If not, can you explain that more? If so, then I have a Edelbrock tuning kit that i've played around with the needles/seats and springs. I feel like its dialed in pretty good in that regard.

Playing around with the secondaries is not something I have done. I'll look into that also.

[F-BIRD'88]

Forced induction was certainly a thought, but the engine wasn't built for it at all. 10.3:1 compression and rings weren't gapped for it. The thing would grenade on pump gas before I got out of the neighborhood! lol

Is the CR really 10.3:1 or ???

Unless the block has been decked etc I bet the real cr is
lower than...
If the pistons are 1.54" CH vs 1.56" it can be a good bit lower .

(assuming non-intercooled supercharging)→
You have the choice of lowering the cr or using water methanol injection . Its very effective.

What is the current vehicle performance?
What is the performance target?

[c1500sbc]

Yea, flat top pistons with -5cc valve relief and 64cc heads.

I’ve thought of methanol injection but I’ve never used it. Definitely something to look into.

I’ve never had it on the track, and probably never will, but I want something that’ll feel pretty strong/quick on the street. About 300 whp is where it’s at now and little more torque. I’d love to get they number to 350-375 but that seems like a lofty goal with this engine.

383 I’d like to get 475-500 crank power and 400-425 wheel if I end up going that route. Honestly, though, if I could get another 50-100 hp out of this one I’d be happy.

I’m not sure what my drivetrain loss percentage is. All synthetic fluids and a 5 speed should keep that minimal. 28” tire and 15” wheels.

[rfoll]

It's a truck, and it's heavy. They have the aerodynamics of a brick. I see them at the strip all the time and unless the have a power adder and more cubes they are not very fast. They have huge engine compartments and usually a 3.73 gear or lower, but it takes a lot to overcome the simple physics of the package. I remember a night late in September that had outstanding atmospheric conditions. 60 degree dry air and a barometer 30' below sea level. One of the participants was ecstatic because his 71 C10 was running record times in the high 11s. The truck had a well sorted out 406 with slicks.

[vortecpro]

It's a truck, and it's heavy. They have the aerodynamics of a brick. I see them at the strip all the time and unless the have a power adder and more cubes they are not very fast. They have huge engine compartments and usually a 3.73 gear or lower, but it takes a lot to overcome the simple physics of the package. I remember a night late in September that had outstanding atmospheric conditions. 60 degree dry air and a barometer 30' below sea level. One of the participants was ecstatic because his 71 C10 was running record times in the high 11s. The truck had a well sorted out 406 with slicks.

I think its possible to run high 11s in my 1979 NA 327 powered C-10 in those conditions, if not 11s it would be close. I do agree these trucks are HP bandits, heavy brakes, 2 piece drive shafts, horrible arrow dynamics.

[Roadknee]

I have a 79 C30 with about a 520 HP 496. Truck is 5600 Lbs. Has the huge 14 bolt full float rear end with 13” by about 3” wide drum brakes. It has thick, heavy 1 ton aluminum wheels with 265/75-16 10 ply tires. 3.73 gears, TH400 with stock stall converter. It will light the right rear at will and run right past 100 mph. However, performance isn’t awe inspiring. We figure the easiest way to increase performance is to swap the engine into my Dad’s 67 C-10.

[c1500sbc]

Deck height is .025. I built the motor myself. Measured before assembled. I’m running a .028 head gasket. So quench isn’t ideal but I couldn’t get a .015 shim to seal up.

[travis]

I’m not familiar with the NV3500. Is that the late 80’s-mid 90’s truck 5 speed? Any idea what it’s gear ratios are?

For a heavy truck, 2 things that stand out to me are the heads (a bit big for a truck IMO), and the old school lazy cam with a bunch of seat duration, big I/E spread, and wide lobe centers. It’s the same cam as the Summit 1105. IMO, torque is what makes a heavy vehicle fun to drive while remaining streetable and still functional as a truck.
I’m guessing your setup doesn’t really start coming on strong until 3000 rpms or so?

I would suggest hitting up Camking on here and have him whip you up a cam, hydraulic roller preferably if the budget is there for it.

[c1500sbc]

I’m not familiar with the NV3500. Is that the late 80’s-mid 90’s truck 5 speed? Any idea what it’s gear ratios are?

For a heavy truck, 2 things that stand out to me are the heads (a bit big for a truck IMO), and the old school lazy cam with a bunch of seat duration, big I/E spread, and wide lobe centers. It’s the same cam as the Summit 1105. IMO, torque is what makes a heavy vehicle fun to drive while remaining streetable and still functional as a truck.
I’m guessing your setup doesn’t really start coming on strong until 3000 rpms or so?

I would suggest hitting up Camking on here and have him whip you up a cam, hydraulic roller preferably if the budget is there for it.

Power band seems decent but it certainly picks up in the higher RPM range. Do you mind explaining a little more on the "old school lazy cam with a bunch of seat duration" to me? I don't use the truck to haul/tow anything. It's just a fun street truck. I went ahead and sent Camking a message as well.