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Old 01-15-2005, 05:18 PM
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how strong is a 350 small block

Hi,

Iím a student from Belgium. I have a 1981 Chevy sportsvan. It has a 350 ci 4 bolt stock small block. 2 years ago I did a school project. I installed a turbo on it with 7 psi boost.
I runís great. My best time an the ľ mile was 15.8.
Now the engine is broken. I open it and found the first piston broken.
I want to rebuild the engine. World heads, JE pistons, steel crank 383 strokerÖ
I want to run 14 psi boost. Can anyone tell me if my stock small block can handle this?
On 14psi it could have about 400-500 hp and a lot of torque.
Can the cast iron engine handle this kind of power?
I use the van daily, and ones a month I go to the strip.
How many horsepower can a stock Chevy small block handle, without breaking it?
Thanks for the info!

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Old 01-15-2005, 05:30 PM
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block strength

The block will weaken with bore size. The more boost the better the parts you have to install. Opinions will vary on which parts.

I would install steel crank, forged rods, and forged dished pistons.
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Old 01-15-2005, 05:34 PM
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The block can handle 500 HP, but any more than this you might want to consider going to an aftermarket block. The reason you broke the piston is because stock cast pistons are not meant for the high cylinder pressures of running boost. It is also possible that you were detonating running 7psi on a totally stock setup, which usually is around 8.5:1 to 9.0:1. With 7 psi boost it is like having over 12:1 which calls for high octane fuel and/or an efficient combustion chamber.

Make sure you use forged pistons with the turbo, strong forged H beam rods and at least a 4340 forged crank when running 14 psi boost. Aim for a static compression ratio of 8.0:1 or so unless you plan on running race gas. I would recommend an aftermarket race block, because you may easily surpass 500 HP with that much boost on a 383. Also consider water injection if you have detonation problems.

Just some suggestions, I'm sure the blower guys on this site may answer your questions better.
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Old 01-16-2005, 12:37 AM
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if you have a good machine shop check for cracks and especially sonic tested for core shift and such first you won't have any trouble with 500-600 h.p..the key for that much power is finding a good block thru testing and building a bullet proof bottom end.it sounds like you had something other than forged pistons.you'd be surprised at what uesd to be done back before we had 4 bolt mains in the day of the 327.they used to routinely get 700 h.p. at the strip.
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Old 01-16-2005, 04:44 AM
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Thanks for the info.
I did run it on LPG, so it has a octane rating of 104.
The water injection is a good idea.
To be save, I think Iím forced to use an aftermarket engine.
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Old 01-16-2005, 08:13 AM
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I don't think you need an aftermarket block, and its a valuable determination to make, considering they run upwords of 1500 bucks (more like 2500 3000 USD). If you use good equipment in your motor, you should have no problems with afactory block. .030 over is no problem, .060 would be pushing it. Keep in mind your turbo size, is it big enough to go from 7psi on a 350 to 14 on a 383? 14 is a pretty stiff amount of boost to run on a daily motor. I would run 9 or 10 to be honest.

Forged slugs, steel crank and some good rods and you'll be fine. Don't bore the hell out of the block and it won't break-

K
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Old 01-16-2005, 04:14 PM
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I donít now anybody who has a sonic tester.
I bought my Van 7 years ago here in Belgium. The last owner did put a brand new stock 350 ci.
When I bought the van, the engine had about 6250 miles.
I donít want to bore the block. Only install a steel crank so I get a 383ci and more torque.
On the dyno, the stock engine had about 177 hp ( without the turbo, 8.5:1 compression ).
I installed a small turbo with 7 psi boost.
Now I want to rebuild the engine with strong internals ( steel crank, good pistonsÖ ) and ad a bigger turbo so I can give 14 psi boost.
If the basic is a 383 ( 8:1 Ė 8.5:1 compression ) with good heads, a turbo camshaft, better pistons Ö I would have more than 177 hp. I donít now, maybe 200 hp. Add a turbo that can give 14 psi, I would have 400 hp.
I want to use the engine without being afraid it will break.
I drive the van every day. With a bigger turbo, I only will give it 14 psi at the track, so on day a month.
So you think the stock engine is strong enough for my plan?
Thanks for the response!
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Old 01-18-2005, 01:14 PM
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If you're only aiming for 400 HP you don't need a blower at all with a 383. In fact a relatively mild buildup of a naturally aspirated 383 will get 400 HP. Unless you are after earth twisting torque at low RPMs you are wasting the effect of the turbo using stock induction components and the tiny stock cam. For the money you are going to spend on the turbo, you could buy a set of AFR heads, a more aggressive camshaft, a better intake and a bigger carb and have the potential to make 500 HP depending on which parts you pick. If you are really ambitious and want to start breaking parts or twisting your van in half, you could add the turbo on top of this when you get more money. The point is, you should concentrate on building the motor to perform well naturally aspirated (albeit with low compression in case you want the turbo after), that way the effect of adding the turbo will be well worth the money. Don't worry about a turbo camshaft unless you have a poor flowing exhaust port or a restrictive exhaust system, most good aftermarket heads have overkill flow numbers on the exhaust anyhow.

my $0.02
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Old 01-18-2005, 03:59 PM
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Hi,
The only stock element I want to use is the engine-block. I want to install performance heads ( world ) performance pistons ( JE ), performance rods ( Manley ) , a steel crank that make a 383 ci from my 350 without to bore the block and a turbo camshaft.
Iím aiming at 500 hp, because I think a 383 with low compression ( 8:1 Ė 8.5:1 ) has about 250 hp at 5000 rpm without turbo. With a boost of 14 psi, I think I make about 500 hp ( 250 x 2 ).
Because the engine be installed in a Van, I need a lot of torque to get the thing going.
Thanks for the info
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Old 01-18-2005, 06:32 PM
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HI,
What was being said is that you can make 500HP from a 383 without the turbo.
Your after TQ for the van which is a good idea to want a 383. I would suggest you talk to a machine shop about your parts combo because while it will work you want to make sure everything fit together as it should. (always check)

I would say go and get a full rotating assembly from one of the good companies out their (Scat, Eagle) that will have the correct pistons for the rods and the correct crank for given purpose.
The reason why I say this is that having all your parts made by a good company (ones you listed are good as well) but having them all made by the same places gives you a slightly higher chance that everything will go together well (again always check)

Go HERE and look for your assembly you can see the price and they come with JE or SRP pistons also KB hypers

If you really plan on pounding this thing get the forged parts both make them if not you can easily use on of their "lesser" units.

I would save the money on the turbo and buy either Dart or AFR heads World is good too.
Here is a good way to think about it.
You can have the best turbo you can get but if you can't get the chamber to mix well and flow correctly you just have an expensive whistle.


Also a 383 with low comp. can still make way more power then 250 given the cam is limited due to the comp. but the added cubes allows for a bigger one to begin with. If you want to stay safe for the future turbo you can always buy the lower comp pistons and then add the blower (as was said)

The cam should be a product of the rest of the combo. Once you know what is going in the engine call the cam company.
In other words if you do this now and the turbo later (a few years) it would be better to buy the correct cam now and replace it when you are freshening up the engine for the turbo with the correct cam then.

One thing you must think about is when picking heads is to pick ones that can work with your given rage and that means cam.

Don't go out and buy huge cc heads and put a small cam in instead pick out heads that work in your range (lower for van) and then you can match a cam to that to make that range work the best for you.

Sorry for the long post hope that helps

Chris

Last edited by strikingthematch; 01-18-2005 at 06:38 PM.
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Old 01-18-2005, 07:00 PM
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I agree that a 383 can make way more than 250HP even with 8:1 compression, given the upgrades you have listed. Which world heads are you planning on getting?

-- also, which intake and carb are going on this motor? For the intake I recommend a dual plane like the Edelbrock Performer EPS for low end torque or the Performer RPM air gap for a little more high end power. For the carb, it's not so simple. Given this is a turbo application, you will need a carb with special modifications for a blow-through setup. For 14lbs of boost things like a third metering circuit and boost referenced power valves are often needed, among a bunch of other things. Make sure you got your bases covered for this one, it can get quite complicated. Running too lean on a blown motor can be disastrous, regardless of what pistons etc. you have.

Last edited by Mad Maggot; 01-18-2005 at 07:00 PM.
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Old 01-19-2005, 04:14 PM
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Iím going to install a turbo cam right away. Max rpm at about 5000-5500.
When the engine is ready, I want to ďdrive the engine inĒ ( i donít now the right english word for it ) with a holley carburettor. Then, I want to install a Impco LPG system with the turbo.( like my previous setup, but bigger )
I want to use an edelbrock, but donít now which ( thanks for the tip on the performer EPS ).
I also install a data logger with lambda sensor to be sure the engine donít go lean.
I think Iím going to use my stock 4 bolt and put new performance parts into it.
Before installing the turbo, I going to test the Van on a dyno.
If the 383 will give more the 250 Hp ( without the turbo ), I will set less boost. ( if it will give 250 hp, I will give it 14 psi, if it will give 300 hp, I will set it at 10 psi )
You guys said that the max power of the stock block is about 500hp, I donít want to go higher than this.
Again, thanks everybody for the info!
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Old 01-19-2005, 05:31 PM
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Lots of non turbo guys getting off subject here, so I will disagree with most. For those, turbos are not the devil

Chevyvan, you are on the right track. Dont doubt your knowledge based on what you get here.

Your block should be fine with what you are wanting to do. From what I gather you want low RPM torque to pull that heavy beast around, which a long stroke, low rpm turbo engine will do. If you plan on going over 500HP it gets a little less predictable on breakage, but at 500 low RPM HP you should be fine.

While it may be possible to make the same power NA, but it is certainly not cheaper. You can get any number of turbos that will make 500HP at 5000RPM for around $200. He already has all the other equipment needed. So $200 for a turbo and a few odds and ins or $1200 for a set of heads.

Also, you definately DONT want a dual plane intake. If you read just a little you will find that turbo engines should always use a single plane intake. A turbo cam is also a very good idea. The idea is not to increase exhaust duration as in NA or blown stuff, but to reduce it. This increases EGT and velocity to aid in spooling of the turbo.

I say get you a larger turbo, decent bottom end and bolt it together. Stock iron heads will support 450-500HP on boost easily. With the propane, you are good to go in the detonation department. Just needs a little tuning when you up the boost.

From what I remember of your setup, you are just running the turbo on one manifold. You will need to tie the two together for sure if you have not, but I might be mistaken on your setup. If you are running on only one side, it could explain your breakage.

Chris

Last edited by TurboS10; 01-19-2005 at 05:42 PM.
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Old 01-20-2005, 10:47 AM
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You also need to make sure you have the vent on your vaporizer tied into the compressor side of the turbo or it will go lean under boost and burn up pistons too.

John
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Old 01-20-2005, 11:53 AM
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http://www.cardomain.com/memberpage/343766

Pics from the past set-up.

Yes, the plan was low rpm, lotís of torque to get the heavy beast around.
On my previous set-up I had a small turbo, a T3. But this turbo did spool up very quickly, so it did give boost very quickly and a lot of boost at low rpm. My time on the 1/ 8 mile was 10 sec. On the ľ mile it was 15.8. So at high speed I had not enough horsepower to get the thing going.
I used on my previous set-up a dual plane intake. Thanks for the tip, I now getting me a single plane intake.
My stock heads where damaged, so I get me some brand new iron world heads.
I calculated a Garrett T04B-60-1 ( flow rate 65lbs/min).
The exhaust manifolds are put together before going to the turbo.
The LPG set-up works great on my previous set-up. I could only drive on LPG with the turbo, because I didnít adjust the carburettor to work under boost.
Thanks for the info Chris, if you get other tips, please let me now.

I did connect the vent of the vaporiser to the boost side. Itís a ďbalance lineĒ. The impco mixer is made with this connection.
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