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Old 07-25-2007, 12:21 PM
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Whats the difference 350 vs 355

What is the difference between a GM 350 and a 355. I see all the hoopla about building a 355 but unsure whats so great about it versus a 350. Just wondering.

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Old 07-25-2007, 12:40 PM
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A block that`s been overbored .030 adds 5 cubic inches, making it a 355. If both engines were built, one a 350 the other a 355 and used the exact same parts, they would likly be within 5 horses of each other or less.
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Old 07-25-2007, 01:19 PM
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So if I see an ad such as www.coasthigh.com/Assemblies/Chev/chev_355.htm they are selling a 350 base block that has been bored 30 over but adding different components to increase HP?

What got me curious was when I recently spoke to a guy at the strip, I commented "I have a 350 that I will be running in my 55"...he immediately corrected me and said it wasn't a 350, it was a 355.

So the 355 as I understand it is a base block 350 bored 30K adding 5 cu.in., but with similar components added to either, the hp should be pretty much the same?

Appreciate the info.
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Old 07-25-2007, 02:12 PM
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When you rebuild an engine the cylinders typically need to be bored out to make them round again. Not a big deal to bore out 0.030 or even 0.060". However, it does add more cubic inches and a little more power.

A 350 making 400hp could make 405hp if bored out to a 355. (Using the same parts). Not a big deal.
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Old 07-25-2007, 02:18 PM
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Quote:
Originally Posted by 454C10
A 350 making 400hp could make 405hp if bored out to a 355. (Using the same parts). Not a big deal.
BUT ...

If everything remains the same ... except for the .030 over bore ( same compression, and all other components the same ) ... the five extra cubic inches will not gain you anything you can feel " by the seat of the pants "


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Old 07-25-2007, 02:41 PM
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Quote:
Originally Posted by DoubleVision
A block that`s been overbored .030 adds 5 cubic inches, making it a 355. If both engines were built, one a 350 the other a 355 and used the exact same parts, they would likly be within 5 horses of each other or less.
Just to clarify, a 350 CHEVY that's been bored 0.030 over will be a 355. Other engines with different bore and stroke combinations will see different displacement increases from an 0.030 overbore.
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Old 07-25-2007, 02:44 PM
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355ci is just a 350 bored .030 over. Some truck motors came out with a 355 stock in them but as to my knolage there is no diffrence in the blocks.

Some big block truck motors were over stroked and the deck height raised to compensate, makeing them low compretion motors. Whitch = low power
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Old 07-25-2007, 02:53 PM
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454's can be bored 0.090" to make 473 cids. That is something you can start to feel.

A 402 bbc is just a 0.030" over 396. So a 402 is a 396 that came bored from the factory.
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Old 07-25-2007, 04:01 PM
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So could you have a 350 that's called a 400 simply based on bore?
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Old 07-25-2007, 04:17 PM
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Not possible to bore a 350 out that much. chevy made 400's with more stroke (3.48 vs. 3.75) and more bore (4.000 vs 4.125). 400 blocks are made with connected cylinder walls (Siamesed) to allow a bigger bore. Plus the 400's are externally balanced (weights on flywheel and balancer).

However, a 400 crank in a 350 bored 0.030" makes a 383. 17 little cids away from a 400.
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Old 07-25-2007, 06:41 PM
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Sorry; that's really what I was asking. What would be the maximum recommended bore (cu.in.) to still have a street driver on pump gas but still good for strip use. Cam and intake selection will be based on the gearing I have including 29-30x10x15 rear rubber.

I haven't built the 350 LT1 that I have to go in the 55 gasser yet. The information provided so far is very useful in planning for this.

I have a 370 posi gearing with a Muncie M21 close ratio and the origional bumper type traction bars from it's previous drag days.

Give me some ideas on how far I should go with a cu.in. goal for the setup.
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Old 07-26-2007, 07:47 AM
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Pump gas, street/strip setup with 3.70 gear, 29 to 30 inch tires, a close ratio 4 speed, and a 350. hmmm.....

You can bore a 350 +0.060" which makes a 360. However, not a good idea to go to the maximum bore if you can help it because it dosen't leave room for the next rebuild. If +0.030 or +0.040 is enough to clean up the cylinders then stop there. Boring with torque plates is also a good idea and worth the extra money.

I would use aftermarket heads. So much more power can be made. I like the small port Edlebrocks Performer heads. They come in 64cc and 70cc combustion chambers and have 170cc intake runners. Great street and strip power!

A set of flat tops (-5cc) and a set of 64cc heads with make 10:1 cr. This is a good compression ratio for a moderately sized cam, aluminum heads, and pump gas.

Those tires are pretty tall which reduces the gear ratio by quite a lot. Makes it equal to a 3.45:1 with 28 inch tires or a 3.33:1 with 27 inch tires. So, you shouldn't use to much cam shaft. I'm thinking you should use a Compcam 270H (224/224 at 0.050").

I don't like the new extreme series Compcams cams or most any new cam grinds. They are pushing the limits of the flat tappet cams which is causing cam lobes to go flat real fast. Especially with todays engine oils which have about half as much antiwear additives as they used to. Which brings me to the next point. Use diesel engine oil in your engine if you are using a non-stock cam.

Use the Edlebrock Performer RPM intake. I don't like the RPM air gap due to very slow warm ups. Also use the Performer heads, not Performer RPMs. You need the exhaust cross over feature if you are driving on the street.

I like holley 750 cfm 3310's. However, they don't get the best mpg. A Q-jet is a better carb if mpg is a concern. But a Q-jet must be setup to run a 270H cam. Jet Carbs can custom build you one. Also the Performer RPM intake can be purchased with a spread bore for the Q-jet.

Use full length headers (1-5/8 tube with 2-1/2 collectors) and 2-1/2 inch pipe, X-pipe, and Dynomax super turbo mufflers. Look at the 14 gauge doug thorley tri-Y's.

The above combo can easily make 420hp and 400 ftlbs. And move a 3500 pound car to a low 12 at 110 mph. And get about 12 mpg city and 16mpg highway.

A 383 stroker kit would also be a good idea. This will help pull a heavy car. However care must be taken to keep the compression ratio down. Dished pistons with a D-shape dishes are the best to use.
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Old 07-26-2007, 02:24 PM
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Good advise and info. 454. Really gives me something to think about. I'll probably shy away from the bigger crank setup and add solely to the 350 base with the suggested bore. Thanks.
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Old 07-26-2007, 02:35 PM
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A stock Pontiac 350 is really 354, but was also called a 355 for some reason, bore it out .030 and it's 359, .060 over and it's 365 which fits a 366 max cubes class I'm shooting for.

So a 350 is not always a 350, it's just what the factory called them.
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Old 07-26-2007, 04:01 PM
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428....That's interesting. That was my initial reason for the question as I wasn't sure if there was an "actual" 355 base block engine. I thought maybe Corvette (?) but wasn't sure.

Also, the earlier post regarding wheel size...I have an old school gasser with rear radius, so I have unlimited width possibilities. The radius looks like it is for a 29-30 tall tire, so the size will be determined by what best fits the radius and backset.

I may have to step up a bit on the gearing to offset this as mentioned by an earlier response. It's odd how so many things can affect torque and hp, including tire size .
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