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Old 02-12-2020, 01:27 AM
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What HP is my 350

Hi, I had an engine built and trying to find out my hp.
I am wanting 400hp but I don't think this is close. I haven't been around this stuff for years.
Any help will be greatly appreciated.
- It is a 350 block 0.030 over
- World Torquer heads
- there were to be roller rockers
but just regular ones
- GEH-270S cam, specs are
204/214 @ .050
.420/.442 valve lift
270/280 @ the seat LSA 112
- Edelbrock Performer RPM intake
- Holley 670 street avenger

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Old 02-12-2020, 02:41 AM
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Quote:
Originally Posted by Willy1950 View Post
Hi, I had an engine built and trying to find out my hp.
I am wanting 400hp but I don't think this is close. I haven't been around this stuff for years.
Any help will be greatly appreciated.
- It is a 350 block 0.030 over
- World Torquer heads
- there were to be roller rockers
but just regular ones
- GEH-270S cam, specs are
204/214 @ .050
.420/.442 valve lift
270/280 @ the seat LSA 112
- Edelbrock Performer RPM intake
- Holley 670 street avenger
A pretty old fashion build with really obsolete components except for the intake, probably in the range of 300 maybe 310 depending on physical details of the pistons, deck clearance, head gasket.

Carb is adaquate, cam is a totally geriatric design, heads are 25 years obsolete.

400 horse 355 takes modern heads the L31 Vortec being the minimum, aluminum aftermarkets way mo-better.

Cam is out of synch with modern fuels, too little lift, waaay toooo much ramp between zero lift duration and oh-fifty duration. Look at the Comp XE268H, not the only solution, but the duration and lift characteristics represent where your thinking needs to go. Springs need to be compatible with cam and head constraints, beehive springs are a nice way to go but you gotta watch the details as most retainers are for 8mm valves not std Gen I 11/32 stems.

Valve train would need 1.6 ratio rockers preferably full rollers on 7/16th screw in studs. This could get by with 3/8ths studs and a stud girdle, that will eliminate using center bolt rocker covers. Power is not simply about big valves any more but better shaped ports and heart shaped combustion chambers.

Modern pump fuel octane limits dictate a shorter overall duration featuring much less ramp higher lift and a faster rate of lift, less overlap, and earlier in the compression stroke closing of the intake valves. Modern oil and higher lifter to lobe forces drive a more carefull spring selection, smart over stiff, as too much stiffness kills lifters and lobes hence beehives and conicals deliver more control with less force. Getting the intake closed early builds more cylinder pressure for the ratio used, its pretty important these days.

Shape of the piston and dimensions are big time important. Piston compression height needs to be monitored, there are 1.54 tall pistons, pin to crown, called rebuilder pistons these are .02 inch short of the stock 1.56 piston. Put these into an engine that wasn't decked and the compression ratio is out to lunch. To the other side there are .015 taller pistons that let you run an aluminum head with a thicker gasket without unecessarily removing deck material.

Ideal squish/quench clearance for the street is .035 to .040 inch piston crown edge to chamber step; deck clearance and gasket thickness is summed. For an aluminum head this mostly means the block needs to be zero decked with a standard compression height (1.56 inch) piston. Flat top is ideal but if you need to control compression the D dish not circular is the way to go. An option with a flat top piston is to use an aftermarket head with a modern heart shape chamber at 74-76ccs. Aluminum at the least lets you use another point of compression, often more which more than offsets the faster heat dissipation compared to iron so there is a significant net torque and power gain.

These days you need to do a lot of reading, prior planning and a fair amount of math if your not familiar with where engine technology has gone over the last three decades.

So what you have would be a great 350 if this was 1970, but not today. Without significant changes 400 hp on this combination of parts without some form of boost being added is simply out of reach for this motor as it stands.

Bogie

Last edited by BogiesAnnex1; 02-12-2020 at 02:47 AM.
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Old 02-13-2020, 12:29 AM
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Hi Bogie thank you very much for the info. There is alot there. What I do remember is that the pistons are flat tops. What I get from this is to get alum/heads, change cam, 1:6 roller rockers and carb? The guy that built this was a circle track racer also.
Am I just better off selling this and build a 383 setup? I found some aluminum heads but 200cc runners. I haven't tried to see if they have smaller, yet.
I'm not into racing. Just a street hotrod. But I like hp.
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Old 02-13-2020, 02:31 AM
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Quote:
Originally Posted by Willy1950 View Post
Hi Bogie thank you very much for the info. There is alot there. What I do remember is that the pistons are flat tops. What I get from this is to get alum/heads, change cam, 1:6 roller rockers and carb? The guy that built this was a circle track racer also.
Am I just better off selling this and build a 383 setup? I found some aluminum heads but 200cc runners. I haven't tried to see if they have smaller, yet.
I'm not into racing. Just a street hotrod. But I like hp.
Not surprised to hear the builder is a circle track racer, the engine sounds like it's built to a class rule.

The cam is pretty mild it is about the same timing and lift as the old 300 horse 327 and 350 cam. 327 used nearly 11 to one to get there, the 350 did it on 9.5.

A reasonable 380 hp can be done on just about anybody's iron or aluminum version of the L31 Vortec head. They are all over the place from inexpensive Ebay imports to costly Dart, AFR, World, etc. and a huge range inbetween. Your budget and dreams of race level reliability are our guide, they all are pretty darn good. A cam that well supports this is anybody's reasonable version of the Comp XE268H or for a little softer treatment of the valve train through a little less lift rate is the simple 268H both for flat tappet hydraulics. This cam timing is the upper limit of stock stall converters not that you can't go bigger but then replacing the converter gets in the picture and maybe gears.

To tweek into the 400 bracket requires either cleaning up cast ports or slipping into heads with 190 to 200cc intake ports, 1.6 rockers, roller better as they don't fry the fulcrum bearing as ball and socket types do. Self guiding rockers are fine for a street build especially if you step up to a 7/16ths stud. If you go with pushrod guiding then be sure to get a stud with a base thread of .75 inch to accomodate the guide thickness and still have plenty of thread engagement in the head, especially critical with aluminum. Most aluminum heads with the exception of some GM production heads use valve stems .1 inch longer so if you buy the heads bare be aware that both the required stem length and a starting point for the pushrod must be .1 inch over the stock length. You should also note that it is recommended to use a slightly longer head bolt to accomodate a ground washer used with aluminum heads. Frankly, I like studs.

Your intake is an excellent choice for getting a 355 into 400 hp, even the 650 carb will work at that level, the 750 makes tuning for that power easier, but a 650 will get there as well.

Long tube headers with 1-5/8ths primarys are almost a must as long tube tri-Y's also work this magic.

Aluminum heads almost always use a fairly thick gasket which kills squish/quench assuming the piston is .025 in the bore at TDC and you have flat tops you are going to have to do some compression ratio math which might lead you to a 74cc chamber to get the compression where detonation is avoided. I'm talking a moden heart shape chamber not an old fashion open SMOG chamber. To get the squish/quench down around .040 might take the FelPro 1094 coated .019 thick shim. You just have to play with this stuff on paper, and with us, before committing hard earned dollars.

Some people will suggest porting the heads you have and upping the cam timing and lift, that works to get the power your looking for by a somewhat more brutal process that for sure will require a stall converter if an automatic and likely stiffer gearing to chase the RPMs where the power goes to. So there are different ways to skin this cat.

Bogie

Last edited by BogiesAnnex1; 02-13-2020 at 02:37 AM.
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Old 02-13-2020, 04:47 PM
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Quote:
Originally Posted by Willy1950 View Post
But I like hp.
Well then, stop dinkin' around with tiny little small block motors and step up to a man-sized motor, either a 383 or a big block. And for heaven's sake, stop dinkin' around with second-rate cylinder heads. Any cylinder head manufacturer who is worth his salt will publish the head's flow rates right up front, for everyone to see. But if you're lookin' at some Fosdick manufacturer whose heads don't flow well, then he may hide the flow rates or not publish them at all, or he'll publish one example at maximum valve lift. There will always be second-rate manufacturers who produce a second-rate product for a lower price. It is generally agreed among savvy hot rodders that when shopping for cylinder heads, you should compare flow at 0.400" valve lift, not max lift.

Aluminum or cast iron? There are pros and cons to each choice. Aluminum takes some weight off the front end of the car, which seems like a good thing. It's also pretty to look at, but generally costs more to produce than a cast iron head. Aluminum will also shed heat quicker than cast iron. At first glance, this would seem like a good thing, but bear in mind that an internal combustion engine is a heat machine. It has to run hot to produce power, so the sloughing off of heat is actually not such a good thing. Using aluminum heads, you should build the motor with a higher static compression ratio than you would build one using cast iron heads. Using today's junk pump fuels, an aluminum-headed motor can be built to a max static compression ratio of about 10.5:1, or a little more or less depending on squish/quench, chamber design and spark lead. On the other hand, a cast iron headed motor, because it retains more heat than an aluminum-headed motor, needs to be limited to about 9.5:1 SCR to prevent detonation.

When using an aluminum head on a cast iron block, the head has a tendency to move around more than a cast iron head will, due to the difference in the rate of growth and shrinkage of the aluminum as the motor heats and cools. This movement mandates that a composition head gasket should be used because it is thick enough to comply with the movement of the head and will prevent it being abraded against he much harder cast iron material of the block. Every aluminum cylinder head manufacturer specifies the use of a thicker (0.039" to 0.041") head gasket with their heads to prevent this "fretting" or abrading of the softer aluminum material. In other words, it is not a good idea to use a steel shim (0.015" to 0.020") head gasket with aluminum heads to arrive at a squish/quench clearance that the motor will need to prevent detonation on pump gas.

Squish/quench. This describes the clearance from the squish pad on the piston crown to the squish pad on the underside of the cylinder head when the piston is at top dead center. This very close "near collision" of the piston with the cylinder head squishes the air/fuel that is in that area, over and across the combustion chamber at a very high rate of speed. This "jetting" of the mixture across the chamber helps to homogenize the mixture and break up large clumps of raw fuel that might otherwise go unburned. This action maximizes the BANG and contributes to maximum power and mileage from the fuel. Optimal squish clearance between the piston and cylinder head is generally agreed to be between 0.035" and 0.045" (the thickness of 10 to 15 sheets of copy paper). Make certain that the pistons you use have a squish pad on the crown that will mate up with the underside of the cylinder head. Some pistons have only a raised ring around the top of the piston. This will do NOTHING for squish/quench. Engineering a 0.035" to 0.045" squish/quench into the build will be one of the most important parts of the build, practically insuring that the motor will not experience "knock", better known as DETONATION.

Now on to the "quench" part of squish/quench. Bogie had explained this before, but not to my satisfaction or that I can understand completely. As related in the dictionary, quench means "the act of quenching, or cooling, something that is very hot". I would take this as removing heat from the piston and transferring it to the water jacket of the motor. Now, since the piston is in close proximity to the underside of the cylinder head, with the piston at top dead center, it would make sense to me that the act of quenching would mean transferring heat from the crown of the piston to the underside of the cylinder head, where the water jacket is only a thin slab of material from the piston crown. This makes sense to me.

Let's move on to how we are able to engineer a good, tight squish/quench into the motor. First, let's understand a few things...…

BLOCK DECK HEIGHT: The measurement from the centerline of the crankshaft bore in the bottom of the block up to the flat surface of the block where you bolt the heads on.

PISTON DECK HEIGHT: The measurement from the flat crown of the piston to the top of the block where the heads bolt on, with the piston at top dead center (TDC).

ROD LENGTH: The length of the connecting rod as measured from the centerline of the wrist pin hole to the centerline of the big end of the rod.

STROKE: The travel of the piston in its bore, from top to bottom of the bore as dictated by the offset of the crankshaft rod journals. If a crankshaft rod journal centerline is offset by 2 inches from the centerline of the crankshaft main journals, then the crankshaft will move the piston up and down by 4 inches. If another crankshaft to fit the same motor is offset by 2 1/8 inches from the centerline of the crankshaft main bearing journals, then doubling this number, which is called the radius of the crankshaft, would reveal a stroke of 4 1/4 inches.

PISTON COMPRESSION HEIGHT: The height of the piston as measured from the centerline of the wrist pin bore to the flat crown of the piston. Design measurement of a 350 motor piston, using a 5.7" center to center rod and a stroke of 3.480" is 1.560". Design measurement of a 383 motor piston, using a 5.7" center to center rod and 3.750" stroke is 1.425". Design measurement of a 383 motor piston, using a 6.000" center to center rod and 3.750 stroke is 1.125". When you use pistons that are very short on the piston compression height, the bottom oil rings will encroach on the wrist pin bore and a special spacer ring will have to be used in the oil ring groove to prevent the oil ring grooves from catching in the pin bore and breaking or bending. Some piston are manufactured with an altered piston compression height. They can be shorter to allow the piston to remain at the same piston deck height after the block has been decked or they can be taller to help prevent cutting the block decks so far to clean them up. These taller pistons are what us hotrodders are interested in, because they will reduce the approximately 0.025" piston deck height that is built into the motor from the factory. You will remember that we need to use a composition head gasket with aluminum heads, well if we have a piston deck height of 0.025" and a composition gasket thickness of 0.040", this results in a squish/quench of 0.065", too wide to be effective in preventing detonation or quenching the piston effectively. We need to keep the block as close to stock as we can to keep the integrity of the casting, so using a taller piston will keep the amount that we cut off the surfaces of the block to clean them up and make the measurement from the block deck to the centerline of the crank the same at all 4 corners of the block. And by the way, stock block deck height of a Gen I small block 350 is 9.025".

STACK: The measurement of the sum of all reciprocating parts of the motor.
Crankshaft: Here we need to use the RADIUS of the stroke. For instance, the
radius of a 350 crankshaft is 1.740", or half the 3.480" stroke.
Connecting rod: Measure from centerline of the wrist pin bore to the
centerline of the big end of the rod.
Piston: The measurement from the centerline of the wrist pin to the flat part
of the piston crown.
Add these 3 values together and you will find the STACK measurement of the parts that you intend to fit into the block. If you measure all these parts as STOCK parts for a 350 Chevy, you will measure out to 9.000". Fitting them into a block that has a BLOCK DECK HEIGHT of 9.025" (stock) will leave the crown of the piston down in the bore by 0.025". Now, using iron heads and a steel shim head gasket (0.015" compressed thickness) will result in a squish/quench of 0.040", perfect for maximum detonation resistance and fuel mileage.

However, if you are using aluminum heads and have a need to use thicker composition gaskets to prevent fretting the heads, you need to either use a piston with a taller compression height to bring the crown of the piston closer to the block deck to keep the integrity of the block casting in place, or cut the block decks on a milling machine so that the block deck height is shorter. It will be to your advantage to take as little off the block as possible, because of block/manifold fitment.

The machinists at the Chevrolet factory are no more than human, so they make mistakes sometimes. They will clean out the register of their milling and cutting machines after every block is machined, but once in a while, they will miss removing a little chip from the register. Now, when they lower the next block deck into the mill, the block decks may be cut a little off kilter. You may have a tall #8 cylinder deck and a low #2 cylinder deck. On the other side of the block, you may have a tall #1 cylinder deck and a low deck at #7. This block will be lolly-gagged for the rest of its life, or until another machinist sets the block up in another mill and cuts the decks correctly.

So, this is the first thing that I do in an engine build, I measure the block decks on all four corners and determine whether or not I will use taller pistons and/or will cut the block decks to parallel so that the manifold fits without allowing oily vapors from the crankcase to be sucked into the intake ports through the bottom of the ports because the head ports are not parallel with the manifold ports as viewed from the front or back of the motor.

I have spoken of taller pistons. Two suppliers that I have used over and over are Keith Black Pistons and the special Wiseco forged pistons from Skip White Enterprises. For small block Chevies, the Wiseco pistons are 0.015" taller than stock. If the block is 9.025", this will allow you to go to ZERO DECK by removing only 0.010" from the block decks, retaining block integrity.

And as far as aluminum cylinder heads, there are only two suppliers I would use, ProFiler and Airflow Research. Either one with 195cc intake runners will make 500/500 on a 383.

I will continue this on another post at another time, when I am less tired. Carry on.
.

Last edited by techinspector1; 02-13-2020 at 05:02 PM.
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