Ok heres the deal: If anyone has desktop dyno, please use it, if not, give me your best experienced guess.

355 c.i. 4 bolt block

10-1 compression ( 9.35 C.R. pistons, 56 cc heads)

Vortec heads- 56cc- High lift springs, 3 angle valve job.

Edelbrock Performer intake/ Performer Rpm ( I'd like to know the difference in dyno sheets between the two)

Road Demon 625 cfm center hung floats Carb / possibly a Demon or Holley 750

What cam do I need for 400 horsepower and at least 380 lb feet of torque?, I'd like to make the peak HP at about 5700-5900 RPM ( Fun to shift at 6000! )
I will also be using 1.6 roller rockers.

I know that I'm gonna need a 750 cfm carb, but I'd like to know how I would do for the time being so I can save up for a Demon instead of a Holley. I have tha Performer Intake now ( Summit had neither one and Jegs only had the Performer, couldn't wait, there you go) But am planning on getting a RPM or Air Gap later.

Also will be using a old style HEI ( obviously ) re-curved and total timing will be 36-38 degrees.

THANKS !!!

 

Lt4 hotcam is on sale at sdpc2000.com
That'll give you ~412hp with an RPM intake, ~422 with the super victor. That's a roller cam, not sure about flat tap. I wouldn't try making that much power without a roller if you want to keep the peak power below 6000.

 

Don't forget, along with those "high lift springs", to get the valve guides cut down so the retainers won't hit them.

The Comp XE cams match the flow characteristics of those heads well. The XE268 with 1.5s gives about 420 HP with those heads and a RPM manifold. If you want to get rowdy, use a XE274; or one of the solids in that series in the 225°-230° range. People usually don't find that going to 1.6 rockers, or really high lifts, makes much difference with those heads.

 

Going from stamped steel rockers to 1.6 rollers will make a big difference. Going from 1.5 roller rockers to 1.6 roller rockers will only gain 5-10HP at the most.

The amount of HP an engine can produce is based on the amount of air that can flow through them. Since a naturally asperated engine is just an air pump, there's only so much air that can be pulled into the cylinders.

Max HP = .2575 x CFM (@ 28" of water) x number of cylinders

Stock L31 Vortec heads flow only 239 @ .500 lift. Bigger valves will help a bit and porting only increases airflow a small amount. Since they're truck heads they're not designed to flow big numbers above .500" lift.

Theoretically stock Vortecs should be able to flow enough air for up to 492 hp. Fast Burn heads are better and so are most Dart heads. It just comes down to how much you can afford.

 

The cam needs to be hydraulic.

I don't want to run a roller valvetrain. ( costly )

I don't mind producing my peak above 6000 rpm, I just want to be able to reach 6k no prob.

Can someone give me approximate lift #'s???? Duration #'s to get my peak power around 6k rpm??

I am planning on working the heads a bit, doing whatever is neccessary to optimze the setup.

How much horsepower is it gonna cost me with the performer intake as opposed to the performer RPM?, I'm not gonna run a Super Victor. I was thinking about 15 horse.

 

I gave you the cam part #s. I don't know how to get much more specific. Here's that page of the Comp catalog.

http://www.compcams.com/catalog/056_057.html

The RPM is a far larger intake than the Performer. The Performer is a copy of a moderate stock intake like the old "184" that came on lots of motors with double-hump heads and Q-Jet carbs. It's less intake than the ZZ4 one for example. The RPM is just altogether larger. I can see how on some motors it might make only 15 HP difference; on others it might make more like 50 difference. The Performer will make your motor nose over long before it reaches any 6000 RPM. My guess would be that peak HP on a Vortec-head 350 would occur somewhere around 4800-5200 using the Performer, and would be about 340-350. The RPM would bump that up closer to where you want it.

 

The XE268, rpm manifold and your list of heads,CR,etc is a proven 400 HP combo.

Lonnie

 

First question I have is how in hades are you getting a Vortec head down to 56cc? You're using the 305 heads aren't you. :nono: I know you are because by the time you shave L31 (062) heads down that far, you'll be kissing antifreeze.

I don't know what kind of money you're paying for those Vortecs even if they are 305 heads, but I can tell you that the money is better spent at www.sdpc2000.com for a set of new ones which are modified for cams up to .550" lift for ~$650. IIRC, they're also warranteed.

Here's an article where CHP made 390HP at 6000RPM on 87 octane using Vortec heads, the XE268 cam, Performer RPM, and a Road Demon 625cfm.
http://www.chevyhiperformance.com/ed...0viewtype=text

Follow the links near the bottom and you'll see they ran a best time of (corrected) 13.07 ET @ 102.11 MPH in a '65 El Camino. There's also a link down there "Parts List"

 

I am definately not stupid, I would never take 305 heads off to replace them with another set of 305 heads.

YES you can mill them to 56cc and they run fine. I built this motor off of a car craft article called "305, build it or scrap it" in which they used the same Vortec L31 heads and milled them to 56cc like I did and used the same super thin gaskets to retain the correct compression.

THANKS ALOT FOR THE ARTICLE BY THE WAY!!!!

 

I never said you were stupid nor did I intend to imply it.

Even though they run fine (I never said they wouldn't) you are jeopardizing the thickness of the deck mating surface making them more prone to crack if the engine gets a little too warm. Plus you’re decreasing the area for the great swirl characteristics for which the Vortecs are so well known.

For the life of me, I can’t figure out why you’d do that anyway? Why would you put 56cc heads on just because you read that Car Craft put them on a 305? You’re contradicting yourself by saying your building a 355, then come back with “a car craft article called ‘305, build it or scrap it’”. So which are you building? A 305 or a 355?

And you’re welcome for the article, but you should figure out what size engine you’re building before you read it.

Again, I’m not TRYING to imply that you’re stupid.

 

I had them shaved because I'm runnig them on a 305 now....

Look in sig.

Now I've decided to build a 355 bottom end. I got a 4 bolt block and I'm gonna do it here in about a month or so.

Edit: oh yea, I've decided that the Comp Cams XE268 is my best bet for the cam, thanks!

 

For my rod and main bearings, what sizes should I get????

I'm going for the least costly setup here, I don't want to do anymore than the basics for the machine work. Do I just get standard sizes or .010 or what???

 

O...... I C NOW!!!!!

You want to use the heads that you ALREADY have? I understand now.

I still don't think a 355 would be very happy with 56 cc heads, unless you guys have high octane pineapple juice there...... LOL!!!

Seriously, you're looking at ~10.5:1 with .040" gaskets and flat top slugs. Not good for iron heads. 12cc dish would put you right ~9.25:1

Just making you aware of what you're gonna need to do.

Oh yea...... and the bearings will depend on what machining needs to be done. Only the machine shop will be able to tell you that.

 

Right, you match your bearing sizes to the crank, the rings to the bore, etc. If you've had routine maintenance done (boring, crank turning, etc.) you'll need to know what size it was cut to, or measure it all with a micrometer to see what sizes of things to get.

 

I need to wait till the block gets over to the machine shop before I can order my parts huh.... bummer. Hassle. Wanted to order now, I have a time limit here.

Thanks guys..

About the compression thing. With stock style .040 thick gaskets and the 56cc head I'm looking at 10.5-1 with flat tops??? I did my math and decided that If I get a kit that makes for a 9.3-9.4 C.R. w/64cc heads, then I'll end up right around 10-1 which is where I wanna be. Should I run less than that, like get pistons that are like 8.75-1 or so, to get approx. 9.5???? That would probably be best huh???? In that article they ran 8.75-1 compression and got 390 horse, I'm gonna shoot for 425 horse, (Probably end up with 400, what I really want) so I figured that If I build the motor to the same specs as they did, but with a bit more compression, .75-1 point, I can get at least 10 more ponies to get that 400 mark.

What do you guys think 10.0-1 or 9.4 - 9.5-1???

EDIT: The heads are close to 56cc, when I had them milled I told them to get it under 58cc for the 305, and they gave them back and said that they were a bit under 57cc. I figure I'll call it 56cc to be on the safe side and not get a detonation prone setup.

 

4.030 bore
3.48 stroke
56cc chambers
.025 piston to deck clearance
.038 gasket
12cc dished pistons

This will give you a 9.9:1 CR


Lonnie