I've spent some time dreaming about my corvette and eventually I'd like to have it up to a supercharged 396ci. Doing this is going to take a lot of money so it must be done in steps. I'd like to do the 396 part first but if it takes me a year or two to get the super charger I want to have a great 396 with a decent compression ratio. Enought with the back ground, now for the question: Is there an easy way to lower the compression ratio without rebuilding the engine? Is there a way to put a "shim" under the head to raise it, or possibly making the chamber larger on a set of ported lt1 heads, or maybe something else.

I'm just trying to learn what can and can't be done, or what people have tried and had work or not work. Thanks for the info guys and gals.

 

You could change pistons once you add the supercharger. This is probably the best way to go for a long term type project. Have a strong running 396 until you can add the supercharger then do a piston swap and have an even better running 396. :cheers:

 

The easy way would be to shim the head. i.e. A thicker head gasket.
But this only solves one problem, and creates others. Thicker headgaskets are more prone to blow out. Even more so when you are talking about SC.

You could mill the chambers, but again you would have to make sure you don't have any thin or hot spots.

What you are really asking is, can I do great in both worlds. I suggest not.
A low compression 396 will do very well all by itself. Nothing beats cube's. If you still need more, then you can slap on the SC.

Hell, just build yourself a high compression 396, and ditch the SC. There is no great need for it, unless you have a fixation on being the baddest of the bad!

In the wrong hands, 600HP on the street is not a carefree toy.

 

Why not just go with the compression ratio you expect to have with the inevitable S/C. I had the same question in one of my posts.
http://forums.corvetteforum.com/zerothread?id=301041

Check out Jeb Burrnet's response towards the bottom. He builds these things for a living. I'll recap briefly, he says a 383 stroker with 8.5:1 was still putting out over 400 HP.

Do you really need more than this for the time being with the 396? If I were you I'd build it for the "eventual."

However, if you like tearing motors apart and plan on running just the 396 for a couple years without s/c, then maybe it's worth your time to downsize the compression ratio w/ new pistons when the time comes. ;)

 

Why else would you make your car faster??? :D

I only upgrade when someone beats me on the street. Right now there is a Supra running around towne, he beat me, I added nitrous, I beat him, he ordered bigger turbos, I'm waiting for him to get them installed to race again. :D Racing is an expensive hobby :lol:

 

I've got about 360 HP right now. After the heads and headers I should have over 400HP. The next step would be the 396ci giving me 500+ hopefully. Then slap a supercharger on it to get 650+ Maybe I'm just dreaming, but I've seen other people with these numbers and I'm hoping to do the same.

I don't really want to rebuild my engine and dump all the money into it for about the same horsepower, however it would allow me to run :crazy: INSANE :crazy: amounts of nitrous through it. I guess it's something I'll have to think about. The main reason I wanted to do a SC is so I don't have to keep filling the bottle. I've only had it for a little bit and it's left me haning in the wind with no juice in the bottle :rolleyes:


[Modified by mn_vette, 4:06 PM 5/22/2002]

 

Best solution would be to swap pistons to lower compression properly. You can add a thicker head gasket, but it won't lower it any more than 1/2 a point. Also, quench height is very important on high compression NA motors, shoot for .39-.45 don't know how it applies to boosted applications. Ring placement is also a big factor when supercharging, so piston selection is important.
Set the motor up for NA now with good heads 11.5:1, 235/242 cam and tuning you should hit 420-450 rwhp. Then when the time comes, change pistons and cam slap on the blower and your set.

 

High compression doesn't make as big a difference as many believe. Build it for the eventual use.

 

After seeing response about already having Nitrous, I think the answer is obvious. BUILD IT WITH LOWER COMPRESSION. You CAN run insane amounts until you get the S/C, or run both eventually. WOW you gotta gimme a ride when it's done!

Your main concern seems to be: If you're going to spend all this time building a 396 you want your time well spent, it will take more time in the long run though if you have to swap out parts. I know a lot of people though that take the 2 steps forward, 1 step back approach to adding HP. There's nothing wrong with that.
But, my example is an apples to oranges comparison w/ a 383 vs the 396 you want, give-or-take other mods. I just used it as an example of how much HP you can get with lower compression. Then, take in consideration all the other mods you did and I don't think you're only going to end up with the same amount of HP. (hint, hint NOS!)

You know what, listen to 95vettski, seems to know a quite bit, just keep in mind you'll have to change that CAM eventually too. ;) I still think you can get a CAM and pistons that you can run for eventual S/C and nitrous in the mean time.

It boils down to how much time you think it's going to take before you do in fact put an S/C on and if you can wait, but you already have the nitrous, so it's not like you're going to have to wait to feel the eventual power anyway, also the money issue, because you're going to have to buy 2 sets of pistons and possibly yet another cam,

I'd just save the money and time to get the S/C sooner :yesnod:

 

Bingo! You hit it, I only want to rebuild the engine once. This allows me to purchase the supercharger anytime I want as apposed to haveing to wait for the snow to fly to do it. It also saves me a lot of hassle. To many things to think about, but that's ok, I've got a few years before I actually get all of this done. Thanks for the advise guys.

 

I would just build a high compression 396. Then go to the junk yard and get an old 350 that need to be rebuilt. Set this motor on a stand in your garage and build the perfect supercharger motor while you run your 396 into the ground. By the time the 396 lets go you should have your other motor ready to drop in.


Besides I think a 355 can handle a bit more RPM than a 396 (especially supercharged). As much nitrous as you use you need to have a motor standing by to swap at all times. Unless you like to see your car not running!

 

Naaaaaah! If he builds the 396 strong it's not going to be easy to drop the bottom end out, even with an s/c. He's not going to save any time or money with a 350 swap either. Looks to me like he wants A LOT! of power, if he puts in a 350 s/c'd after he burns up his 396 w/ NOS, it'll just be a replacement, not an addition to. Even if it does typically rev higher. a 377 is the ultimate high-cube-high-rever.

If he doesn't use the NOS he's still looking at a possiblity of a 600 HP monster running high boost, that's the great thing about a PROPERLY rebuilt motor! They can take it!.......(there's always room for human error with every engine though) :yesnod:

Though, it is nice to know if you f ' something up seriously on your motor, that you have a nice motor in the waits, but MAN, that's a lot of time and money just for a standby. I'd rather just buy another vette to drive around in the mean time. :cheers:

 

The RPM thing is something to think about, but I'd rather just have enough torque down low so I don't have to rev it too high. With my 2.59's second gear gets me to 110 mph! I'm sure by the time I get the 396 done I'll have replaced the rear end because it broke, but I still want something close to what I have with the amount of highway driving i do. It's not uncommon for me to take atleast one 3-10 hour one way road trip a month. it's also nice to not have as many traction problems off the line :yesnod:


[Modified by mn_vette, 10:36 PM 5/22/2002]

 

Then Kieran's idea sounds better than anything considering what you're going to use the car for. 600 HP on a road trip will have you stopping at every gas station on the highway.

I'd be happy with 450HP right now. :yesnod:

 

Maybe but power always comes with a price, and if I have to pay it at the gas pump so be it.

I've learned that speed is a drug. It makes you high, but you also build up a tollerance to it. I remember when I thought 100mph was fast, now it's just like it was 60mph. And with more power comes more speed. There's nothing like the feeling of getting pushed back into your seat. My name is Brian, and I'm an addict, it all started when I was 10 years old and wanted my first vette........

 

So then what are you looking for out of your engine? Personally like I said before, after driving the car bone stock for 3 years and enjoying even 300HP, I'd be peeeeerfectly happy with 450 right now. Then in another season or too that might not be enough. don't get me wrong, I've been in some fast cars, my monza is faster than my vette, but I still want more power!!! I just don't want to get tooo ahead of myself.

Shifting into the wrong gear with a car that makes 600HP, well, you're looking for trouble. I'd concentrate on a brake upgrade before I'd look for that much power. maybe even a 5 point harness.

 

A 396 can rev just as high as a 383 if it is built tight. I have a friend who had a 401 (396 bored .060) rev to 7000. He put down 490 rwhp then added a 300 shot of nitrous and it survived.

You can build the engine with a 9:1 compression ratio using high quality pistons and still run a supercharger. The same setup NA will still produce plenty of power until it is time to add the boost. If you must get a supercharger (I am a NA guy) then just build it once with a supercharger in mind. If you want more power now, buy a cam optimized for your setup and then change it for the blower.