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Old 01-10-2011, 09:47 PM
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Looking for help on 396 build

Hi , I've been reading forums on this site for quite a while, but first time posting anything. I'm deployed to Afghanistan right now and just looking for some ideas and/or help on this build. The block is out of a 1970 chevy pickup(2 bolt mains), and the heads are coded for 1969 SS Chevelle/Camaro(375hp rectangle port). I've had all the machining work done on the block(.060 over), and had hardened seats and everything else done to the heads. It came with a forged crankshaft and pistons(flat top). I bought some nice forged I-beam connecting rods for it. I have a hydraulic cam for COMP Cams rated for 1500-5500 rpm, switching this out for the Big Mutha Thumper Hydraulic Roller Cam from COMP Cams rated for 2500-6200 rpm if I remember correctly, with their steel roller rockers. I was looking at the Demon Carbs, but have read all sorts of forums on the right cfm rated carb for my size motor(any ideas?). I plan on puting the motor in either a chevelle or nova that came with the 396. I plan on using the car for the car shows, cruise nights, and some decent time spent on the drag strip. One thing dishearting about my motor though is I read a lot of people dissing it and saying "IF YOU ARE GOING TO BUILD A BIG BLOCK BUILD AS BIG AS YOU CAN." Something has just always caught my attention with the 396. One other radical idea I had was swaping out the rotating assembly and throwing in a 4.250 stroke crank with 6.385 rods. That would make it a 461" monster. I seen it on CarCraft's website. Although the guy kept complaining what he had to work with. Money isn't really a big problem for me so anything really goes, I just want to use the block and heads. I'm looking to keep a stock look under the hood too, make a "mega sleeper" out of it. Sorry for such a long post, but I figured I'd try and put as much info I could in hear so you don't have to ask a million questions to figure out what I'm aiming for.

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Old 01-10-2011, 09:53 PM
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welcome
theres nothing wrong with a 396 if you all ready own it
had one in high school
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Old 01-10-2011, 10:07 PM
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....

I agree Matt! I'm only 26, but when I was in high school I worked for a guy with a trucking business and he had a 69' SS Chevelle. That car just got me hooked.
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Old 01-11-2011, 03:53 AM
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Welcome to the site.


Cole
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Old 01-11-2011, 05:11 AM
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The way to even the playing field is to supercharge the lil 396.

if your 396 already has flat top pistons the cr is going to be low.

Supercharger friendly low.

For a maturely asphyxiated street/strip 396 that runs on pump gas you want the cr to be between 9.5 to 10.5. Requires a piston with a dome. The dome volume required will depend on the actual combustion chamber volume of your heads.
Its all in the details.
Are you sure your 396 pistons are flat top? What is the piston part number?

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Old 01-11-2011, 05:42 AM
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Quote:
Originally Posted by 396Rookie
Hi , I've been reading forums on this site for quite a while, but first time posting anything. I'm deployed to Afghanistan right now and just looking for some ideas and/or help on this build. The block is out of a 1970 chevy pickup(2 bolt mains), and the heads are coded for 1969 SS Chevelle/Camaro(375hp rectangle port). I've had all the machining work done on the block(.060 over), and had hardened seats and everything else done to the heads. It came with a forged crankshaft and pistons(flat top). I bought some nice forged I-beam connecting rods for it. I have a hydraulic cam for COMP Cams rated for 1500-5500 rpm, switching this out for the Big Mutha Thumper Hydraulic Roller Cam from COMP Cams rated for 2500-6200 rpm if I remember correctly, with their steel roller rockers. I was looking at the Demon Carbs, but have read all sorts of forums on the right cfm rated carb for my size motor(any ideas?). I plan on puting the motor in either a chevelle or nova that came with the 396. I plan on using the car for the car shows, cruise nights, and some decent time spent on the drag strip. One thing dishearting about my motor though is I read a lot of people dissing it and saying "IF YOU ARE GOING TO BUILD A BIG BLOCK BUILD AS BIG AS YOU CAN." Something has just always caught my attention with the 396. One other radical idea I had was swaping out the rotating assembly and throwing in a 4.250 stroke crank with 6.385 rods. That would make it a 461" monster. I seen it on CarCraft's website. Although the guy kept complaining what he had to work with. Money isn't really a big problem for me so anything really goes, I just want to use the block and heads. I'm looking to keep a stock look under the hood too, make a "mega sleeper" out of it. Sorry for such a long post, but I figured I'd try and put as much info I could in hear so you don't have to ask a million questions to figure out what I'm aiming for.
Thanks for your service to the country and welcome aboard.

The engine with flat tops and the closed chamber heads will be around 8:1 compression ratio. Fine for a mild camshaft or forced induction, but you'll need more CR to run a "choppy" cam w/a lot of duration/overlap.

Use that mother cam if you feel you must, but there are better cams for power out there- that sound less radical. Remember, the choppiness you get from a radical camshaft is a result of the inefficiency of the cam at low RPM. You will need more CR than FT pistons will give you to run that cam, I believe.

I'd rather see you use a set of pistons like the TRW L2240NF. They have a short dome and will get you about 9.5:1 CR, give or take, depending on the head gasket thickness, amount the head's been milled and deck height.

Before I would throw a 4-1/4" stroke crank into a 396 block, I would use the 4.250" nominal bore block from a 427/454 engine. At 0.060" over, a 427/454 block w/a 4-1/4" crank will get you almost 500 cid, plus even more gain from the valves not being shrouded by the small 396 bore.

AFA keeping it stock looking, a 454 looks like a 396 to many guys and the ones who are REALLY sharp won't be fooled anyway.

If you are sold on a 396 block, I'd keep it w/a 3.76" crank and live w/it.An engine in the 400 cid range will run fine w/a carb in the area of 750 CFM.
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Old 01-11-2011, 08:51 PM
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Thanks for the warm welcome ya'll!

F-BIRD'88- I would love to supercharge my 396 but I was wanting something that retains a stock look but still blows the doors off of fart can cars and later generation mustangs/camaros. Thanks for the suggestion though!

cobalt327- I'm very partial to the 396 even though I want to change it drastically. Trust me I'll be building a normal BB after this one, I just want this for street/sleeper car that will see decent drag strip time too. Thanks for the info on the CR for the FT pistons and cams. I was trying to figure out what the CR would be, but couldn't find the right info anywhere. I'll definitely be upgrading to a higher CR piston. I'm not completely set on what cam I'm going to get yet, just want a aggressive hydraulic roller cam.

I'm also waiting on dyno numbers from the shop that built that 461 in CarCraft magazine. I emailed CarCraft directly, but the guy told me he forwarded the email to the shop who built it. I plan on finishing this motor in April when I go on leave, after coming home from Afghanistan.
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Old 01-11-2011, 09:00 PM
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Sorry about that F-Bird I didn't see that part on if I was sure they are flat top pistons. The guy who did all my machine work said they were. I bought the motor about 6 years ago at a dumber more excited age and heard BB CHEVY for sale, and had the extra cash so bought is for $1200. I've learned my lesson, I PAID WAY TO MUCH! Although the heads are worth more than that to the right people. I was looking on Craigslist and finding complete 454 engines with 4 bolt mains for $400-500 all over my area in Nebraska.
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Old 01-11-2011, 09:08 PM
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If you go w/higher compression pistons, be sure to spec them for the closed chamber heads. The piston domes for an open chamber head will interfere w/the chamber of your heads. Open chamber domed pistons can sometimes be modified to work, but it's better to get the correct pistons to begin with, IMHO.

Good luck and have fun!
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Old 01-11-2011, 09:22 PM
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Thanks for the info again cobalt! I was wondering about that... I was looking on Jegs.com for the domed pistons. They had 3 different sizes all saying they were specifically for a 396. I guess I'll have to email them to be sure they have the right ones so I don't the valves with the piston...
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Old 01-11-2011, 10:07 PM
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Jegs shows what I consider to be an incorrect compression ratio estimate for the L2240NF pistons I mentioned above (Sealed Power now, not TRW).

Jegs list them as having a 21cc dome. If that's correct, with a bore of 4.124", a stroke of 3.76", a 101cc chamber, a gasket thickness of 0.041 and a zero deck height, I get over 10.2:1 CR. Actually too high for a mild cam on pump gas, IMO.

They say its about 8:1. So something is fishy.

In any case, you'll need to cc the heads and measure the deck height and know what the compressed head gasket thickness is to compute your CR. Start w/cc'ing the heads and measuring the deck height.

Then using a CR calculator, you can figure out what dome volume you need to get the CR you want.
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Old 01-11-2011, 10:18 PM
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cobalt327- Is there measurement tools I can buy to check the cc of the heads and the same for checking deck height... or will I be better of taking it to a shop? I was just checking a bunch of forums for the whole deck height/decking the block debate and if it's worth it. It's a good thing I joined this site and started popping off questions, because I was just planing on slapping it all together... that could've been a big disappointment, and costly!
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Old 01-11-2011, 11:39 PM
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To get a pretty good estimate of the deck height w/o using expensive tools, you can simply bridge across the bore of the cylinder you're measuring w/a straight edge or machinist rule on edge and use feeler gauges to measure the distance between the straight edge and the piston top, w/the piston at TDC. Measure over the axis of the wrist pin to eliminate the piston's rocking in the bore caused by the piston to wall clearance.

Measure the combustion chamber volume by using an old CD w/the plating scraped off w/a razor blade drawn across the plating backwards (opposite way than if you were going to "shave" it, if you follow me). This flakes off the plating so you can see through the CD to tell if there are bubbles. Or you can use a piece of plastic like plexiglass large enough to fully cover the chamber.

It has to have two holes- one for introducing the fluid, the other to allow the air to escape. Usually, the one hole in a CD is large enough to do both.

Then "glue" the CD or plexi onto the spotlessly clean head surface using vaseline or grease. Leave a spark plug in, and level the head evenly.

Then using a large syringe and rubbing alcohol (has low surface tension) dyed w/food coloring, fill the chamber until completely full, counting the amount of alcohol you used to fill it.
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Old 01-12-2011, 01:21 AM
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This sounds like something a little more advanced that I'm going to trust myself doing correctly... something I'm sure I could pick up if I watched it done first. You sure know your motors cobalt!
I was doing some more research around the web and I'm going to just keep the crank and rods that I already have, and use them. I'll definitely be looking at bumping up the CR to 9.5 or 10:1 with some domed pistons though. I'm going to have my Dad take the block back to the machinist and have them check the deck, as I read a lot of factory blocks are not true on both ends. I'm not expecting a big or even minimal gain out of this, I just like having everything the way it should be.
Also, do you or anyone else have suggestions on a good Hydraulic Roller Cam? I've been looking at Lunati Voodoo's... what RPM range should I looking to keep it under and still driveable?
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Old 01-12-2011, 02:01 AM
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Starting out with a "trued" block is an excellent idea, so you're definitely on the right track there.

I'm not the guy you want to get a cam recommendation from, but there are real sharp guys here who will be along to help, I'm sure.
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