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Old 05-28-2009, 08:32 PM
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Well guys I just found out that my recently aquired 396, is the 396/425hp version, it came out of a 1968 corvette. Its an old motor and needs to be completely overhauled. Im going to be getting around $1500 and I was wanting to ask all the things I could do to overhaul the motor cheaply but quality and efficiency in mind. In the long run I would like to maybe get around 550hp-600hp, with a small shot of nitrous. I actually have alot of plans for this engine and I have a wonderful website to plan out my plans if you will. Anyways back to subject, I want to cheaply but with quality rebuild this motor, can anyone suggest to me some reliable effiecent rebuild kits ?, or anything really, I was thinking about just rering/gasket overhaul maybe even having the heads done for now and once I got more money start replacing some of the internal parts. Speaking about cylinder heads, The compression is 11.:1 on this motor, instead of paying thousands for some heads could I just port/polish the heads and throw in some bigger valves ?. Anyone know a really good but cheap way of getting all of the oil/grease/sludge off of the outsid off the motor ?, some kind of degreaser that works well ?
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Old 05-28-2009, 09:56 PM
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Anyone know a really good but cheap way of getting all of the oil/grease/sludge off of the outsid off the motor ?, some kind of degreaser that works well ?
fuel oil, it has a wonderful odor too. Once you get worked thru the crud n grease good just use regular cleaner, or some that purple stuff.
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Im going to be getting around $1500 and I was wanting to ask all the things I could do to overhaul the motor cheaply but quality and efficiency in mind. In the long run I would like to maybe get around 550hp-600hp, with a small shot of nitrous
Well, your numbers seem quite high for the dollar amount. HP costs money. Your goals are like 1.4 - 1.5 HP/CI. Doable but not on $1500, not even with nitrous time you buy a kit and parts for your '96. Best thing to do is come up with a total budget and then work from there. How much is HP per dollar, do you figure? You will see that budget get eaten away quite soon by the time you start doing things.

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The compression is 11.:1 on this motor, instead of paying thousands for some heads could I just port/polish the heads and throw in some bigger valves ?
NO. Do not think you are going to just grab a set of heads and come up with a port and polish that will lower your compression??? Bigger valves will not lower your compression either. No sense in attempting to 'port and polish' a set of heads if you have no experience as you could flat out ruin them. The polish part... you might polish the exhaust runners, but don't go to polishing anything else 'ceptin yer boots.
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Old 05-29-2009, 05:25 AM
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With your goals a rebuild to the stock specs and a 150 shot will do what you want.Upgrade the cam to a more modern solid and you pass your goals.A good valve job 3 angle min. will help a good bit.As far as porting just clean the casting flash under the valve seats and call it good.
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Old 05-29-2009, 06:48 AM
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it will take more than a 150 shot to get you to 600 hp on a stock rebuild. If you double your budget and settle for 550 hp you can probably make it. Clean up your heads and especially under the valve and SSR. A more modern cam, an intake, headers, and a 150 shot could get you some where close to your goals.
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Old 05-29-2009, 06:58 AM
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I'd be tempted to do a nice overhaul on it, and leave it alone. Or even put it in Hemmings and see if someone's looking for a classic original engine for their Vette.

You might come out with enough money to build what you're looking for, and not have to do shortcuts. This is a rare piece, all things considered.
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Old 05-29-2009, 07:00 AM
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The CR needs to be lower to run on the swill available from the pump. What's the casting number on the heads?

Once you get an idea of the cam you want to run, tailor the CR to the cam by choosing pistons w/less crown. Or, looking at it from another angle- choose the cam by determining what the max CR you can get away with, w/o retarding the ignition timing.

The valve sizes in the heads is sufficient, if the heads are original. As said, some bowl work (pocket porting) will be enough for what you want to achieve.

IIRC, the correct "425 HP" (L78) heads should be rectangle port, 2.19" intake x 1.88" exhaust valves and 109 cc closed chamber if they're the right heads that came on the engine.

Even if they have the smaller valves (oval ports), they'll work- actually, IMHO, an open-chamber oval port head would make more sense in some cases.

But because you are down on cubes, you will be spinning this engine high enough (in order to make your power goals) to maybe justify the rectangle ports, but in a larger engine- or one that was built to make power below 6000 RPM- I'd use the oval-port heads, w/the larger valves.

You might consider selling this engine if it has the proper markings for a 'Vette, and if the heads match AFA dates and numbers go. IMO, the original heads are worth more to a restorer than they'd be worth to actually build an engine with.
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Old 05-29-2009, 08:33 AM
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If she's 425 stock 150 will put it at 575 which is in the range asked about.A cam change to a more modern design will give even larger gains.
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Old 05-29-2009, 09:41 AM
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Im sorry I didnt mean I wanted to get the 600hp out of 1500, no no no, I meant I wanted to get a complete (stock) rebuild out of the $1500 and once I gained more money then I would begin looking for more parts. On the heasd I was wondering why I couldnt have a machinist port/polish the heads for another 10-25 hp. ??
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Old 05-29-2009, 09:43 AM
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Quote:
Originally Posted by 396flyby
have a machinist port/polish the heads for another 10-25 hp. ??
What's the casting number of the heads?

What are the numbers from the front of the engine, on the pad, passenger side?
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Old 05-29-2009, 09:53 AM
How fast is fast enough?
 
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Quote:
Originally Posted by barnym17
If she's 425 stock 150 will put it at 575 which is in the range asked about.A cam change to a more modern design will give even larger gains.

It would not make 425hp as a stock rebuild.

I do agree that it can benefit from a more modern cam profile though.
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Old 05-29-2009, 11:10 AM
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Why not? if it was 425 when it came out freshening it shouldn't decrease horsepower.Also just as many engines in the 60's were overrated many more were underated for insurance purposes.
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Old 05-29-2009, 11:26 AM
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IIRC, this same basic engine was also rated as 375 HP when installed into anything other than a 'Vette, with a few possible exceptions.

I don't know what the actual HP of the engine was back in the day- some certainly were underrated. Was this one that was? Personally, I don't know the answer to that.
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Old 05-29-2009, 12:07 PM
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Quote:
Originally Posted by barnym17
Why not? if it was 425 when it came out freshening it shouldn't decrease horsepower.Also just as many engines in the 60's were overrated many more were underated for insurance purposes.

This is one of the "over rated" ones if you want to call it that. It was just tested under different circumstances than todays enignes. 425 factory hp from 2009 is a lot more power than 425 factory hp from '68 primarily due to testing procedures.

It wasn't a bad combo back in the day, just realize that its not the fastest thing on the street any more.
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Old 05-29-2009, 12:43 PM
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I understand they were rated at sae gross hp. but so are most hotrod builds, crate motors etc.The new vehicles being rated as installed with all accessories and exhaust systems will naturally show lower output. The reason the engines were 375 hp in all cars but vettes is they were derated and different exhausts were used .No one allowed to dethrone king vette.One popular way to do it was publish numbers from a few hundred rpm under peak in the lower level models.
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Old 05-29-2009, 02:41 PM
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Quote:
Originally Posted by ap72
its not the fastest thing on the street any more.
It wasn't back then, either. lol

But yeah, they had some balls.
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