Thread: Chevy 350 rebuilding tips

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Ok so I am new to this website but always get great information from it so I was wondering if someone could help me out. I go to a school for mechanics and I am in a class right now where we build stock chevy 350 motors and put them in T-Buckets and run them on the dyno. Now the point is, is to get the most horsepower out of them over all the other groups. So far the highest HP from previous classes has been 185.5 on the Dyno. Sooo, if anyone has any little tricks or litlle things to do to up our HP on our Dyno run I would greatly appreciate it. Also the next class is where we get to put mods on it like headers, intakes, heads, etc. I will keep you updated on our progress.
Thanks to everyone in advance who reply's I really appreciate it!

If you have to use stock internals, zero deck the block and mill the heads to bring the compression ratios up. Then, port the heads. Depending on how high you can get the compression ratio, you might be able to get the engine well over 185 hp. If you're allowed, you can use 1.6 rockers to make that stock cam seem a little bigger. Do some tweaking on your ignition timing, factory curves are probably far from ideal.

Originally posted by 76GMC1500
If you have to use stock internals, zero deck the block and mill the heads to bring the compression ratios up. Then, port the heads. Depending on how high you can get the compression ratio, you might be able to get the engine well over 185 hp. If you're allowed, you can use 1.6 rockers to make that stock cam seem a little bigger. Do some tweaking on your ignition timing, factory curves are probably far from ideal.

they arn't letting us mill the heads unfortunatly but I can ask if we can use the 1.6 rockerse. As far as the ignition timing, I wast it to peak out at around 3500 RPM, what would be a good starting base timing for that?
Thanks!

Every engine has it's own timing requirements and there is no way to predict what an engine will require. Around 30 degrees total is a standard number. You will just need to put the car on a dyno to figure out what its timing requirements are. I do recommend disconnecting your vacuum advance as it has no effect on the timing at full throttle and will help simplify the process of adjusting. Also, if you do get a lot of dyno time, play with your cam timing. You'll likely loose a lot of power in the lower rpms, but you can get a sharp peak in the upper rpm range and you're only looking at peak power, right? Anything you do to move your peak power output up in the rpm range will increase peak power.
You will also need to adjust your carburetor based on the same trial and error basis.

Also, don't ignore the oiling system. There are very large losses in the oiling system and there are certain things you can do to minimize these losses. Don't use high volume, high pressure, or hv/hp pumps because they all require more hp to turn than a stock pump. Aim for 30 psi oil pressure at 3500 rpm. 5-10 at idle. Windage trays and crankshaft scrapers to keep the oil in the sump and off the crankshaft will give you large gains in the higher rpms. Light weight oils like 5w20 or 0w20 will also reduce power lost to friction and windage. Don't use oil coolers because cool oil has more viscosity and will create more friction.

Porting the heads will give you your biggest gains. I wouldn't polish the combustion chambers, cut the valve seats, or do anything that might increase the volume of the combustion chamber because the stock 350 chevy is compression ratio deficient enough as it is.

Wrapping the exhaust will increase the velocity of exhaust through the system and increase the scavenging effect (fast moving gasses have a lower pressure than slow moving gasses so it creates a kind of a vacuum in your exhaust system to help pull air into the cylinder during the period between the intake and exhaust stroke when both valves are open at the same time). Also, every engine has an overall ideal length of its exhaust system. This can be calculated using engine rpm and exhaust tubing, but the calculations are very complicated and I don't know any of the formulae. I do believe the length will be something between 36 and 60 inches from the exhaust port to the end of the pipe. The more rpm you turn, the shorter the length.

Carburetor spacers can help. An open spacer vs the one with 4 holes will turn your stock dual plane intake manifold into a single plane manifold which will build more power in the high rpms at a cost to your low rpm power. But, we are only looking at peak power, right?

Wow that's a lot of really good information! Thank you for that. Well we put on the heads today and will finish up doing the piston to valve clearances on Monday but as for the stock engine building part we are pretty much done. I was a little dissapointed that our spring tention on the Intakes where 100lbs and the exhaust springs where around 80lbs. Another group had 151lb springs so we'll see if that effects anything at all. now that the engine is almost all assembled we need to paint it and put it in the T-bucket and get it ready for next week on the dyno. As we get farther into that area i will post the optional upgrades we can use to see what matches best with what parts. I was told today we need to run our peak horsepower at around 3500-4000 RPM. A friend from another class ahead of me said to use dry ice in the intake to boost about 15HP out to the rear wheels/ i don't know abotu that but I guess it's another idea I can jot down. Again thanks for the ideas and if you have anything else I would love to hear it!

If the light springs are enough to close the valves at your target rpm, you will have no deficet in power.

Since you've got the engine assembled, now you need to focus on the things on the outside, like spark plugs. Don't worry about running any fancy platinum plugs or anything. Try and get a stock type non-resistor plug. File back the tip until it covers only half of the center electrode, and then round the corners off. Open up the gaps on the plugs until the engine starts to misfire under full power close them up a little. Stock gaps are too conservative. If you open them up too far, though, t's harder to light a cylinder under higher pressure and pressures increase as you open the throttle so you may be ok with a big gap at idle but it will hurt you under power.

Find yourself a vacuum guage. In order to hold a certain rpm, you have to open the butterflies on the carburetor to a certain opening. The more you open the butterflies, the less vacuum you make. So, if you increase the efficiency of the engine, you don't have to open the butterflies as much to make the power required to run a certain rpm and you'll pull more vacuum at that rpm. Tune the engine to make as much vacuum as possible under light load at the rpm near where you expect peak power to be.

hotrodgal
i would like to know what you get after mods.
i run a 350 4 bolt mild crane cam edelbrock
performer intake 600cfm edelbrock carb hypereuteck pistons
9.5 to1 compression and a ballanced engine and malory
electronic ignition the engine runs and revs fast and smooth
its the best i have run ever in a small block,i run pump gas
a get 240 hp.

Originally posted by dotgone
hotrodgal
i would like to know what you get after mods.
i run a 350 4 bolt mild crane cam edelbrock
performer intake 600cfm edelbrock carb hypereuteck pistons
9.5 to1 compression and a ballanced engine and malory
electronic ignition the engine runs and revs fast and smooth
its the best i have run ever in a small block,i run pump gas
a get 240 hp.

I found out today what mods we get to run next week.From stock we can replace the:

Heads: Bow Tie cast irons
Edelbrock Vic. Jr.s 66cc's Aluminum,
or another Edelbrock, but forgot which kind it was.

Valve Sizes

Compression ratio changes due to different gasket thicknesses and heads.

Intake System:
Edelbrock RPM new and old models,
Single plane manifolds, and a holly dual plane manifold.

Carbs:
Edelbrock carbs with a CFM ratings of 600, 650, 700, 733, & 1100.
As well as Holley Demons in those CFM ratings.

Exhaust System:
Small tube headers, large tube headers, with or without Flowmaster Mufflers on them.

Camshafts:
Hydraulic or Solid lifter CAMs with different types of lift and duration.

Rockers:
Aluminum roller rockers, stock 1.5:1 rockers, or stock 1.6:1 rockers.

So there is the list of things we can replace and do to the engine to get it's optimum Hp on the dyno. The goal is to get over 335Hp which has not been done at our school for about 4 months now. I would like to be the group that does it! With all the great tips I get from this forum and all the hard work we are putting into this engine hopefully we will surpass the mark.
thanks again to everybody who has responded.

Also one more thing. I heard from a friend of mine today that if you put dry ice on the intake manifold for a couple hours before you get on the dyno it will make the air going into the cylinders denser so that your Hp's will go up by about 15. Do you think that this will really work? We are allowed to do it and are also allowed to use velocity stacks with our air filter. Also does the engine oil eat the Hp if we are using 20w-50?

Thanks!

The 20w50 will eat hp. Icing the intake does work.

I use 20W50 what kind of h.p. decrease are we talking? I'd hate to use something lighter and loose a lot of oil pressure.

Ok we put our stock 350 in the T-Bucket yesterday and today we are putting it on the dyno.
Other than the mods I was told we get to switch out with I was also told we can use whatever spark plugs we wanted. Would this make a difference from the autolites we are using? Don't ask me why we are using Autolites in a Chevy but the schools cheap. Anyways and suggestions on good cam/intake/carb combo's? Everyone has been saying to go with a 600-700cfm demon.
I will let you know how we did in a post tomorrow!
Thanks again

Originally posted by 76GMC1500
The 20w50 will eat hp. Icing the intake does work.

I don't thinks we have a choice when it comes to the oil we use, unfortunatly. Any additives for the oil that would help?
Also we arnt going to get dry ice for the intake because it is really expensive. Is there any other method of cooling down the incomming air?

regular ice works just fine, too, it just makes puddles

try a cold air intake or an intercooler. Just cause a car is intercooled doesn't mean it has to be turbo charged

Originally posted by firebird45331
try a cold air intake or an intercooler. Just cause a car is intercooled doesn't mean it has to be turbo charged

How do I use a cold air intake when the Dyno temps are around 80 degrees inside the room? Should I rout it towards the ground since heat rises? Or towards a bucket of ice or something?