compression
 

what's the best compession ratio for a bbc 632 that would make the best power? I'm looking to purchase a short block, my heads are dart 360 cnc.

Most of my racing is done at 4800 ft. not ajusted.Average ajust is around 7500 ft.

Depends on the gas your going to be using. We typically do 15 or 16:1

I currently use 114, I can go up if i need to. my comp now is 14.5 to 1. I wouldn,t mind going hirer if it will produce more power without problems.

Who's 114 octane, there is a huge difference between fuels brands. Adding Compression alwasy increases power.

The higher the compression, the better the parts need to be.

---

I think those heads will be what limits your hp unless they've had some hand work done to them.

OK, at the average corrected altitude of 7500 ft. a 15.5/1 comp ratio would work with 116 oct. and 37-8° of lead, what's the hot tip on going to, say Topeka where you're going to be looking at 800 Actual, probably 3700 corrected and twice to three times the water grains? Are we going to have to step down with a thicker head gasket? If so, how thick? I'm under the impression that .060 is our thickest option.

Or do we just bump the timing a couple and suffer on the top end?

Coming from Bear's dumbassed old crew chief . . . .

Yep, not enough head.

:shock: :shock: :shock: :shock: :shock: :shock: :shock: :shock:

Racers rule of thumba.."Heads equal HORSEPOWER!!!"

The heads were cnc'd by a steve schmidt program. Not sure of the flow rate.

Lessee, the question was about compression ratios with a BBC . . Then I added more to the same question . .

Is there anyone looking at this that has a clue? Not being a wiseass, but there is no such thing as "More heads" . . it's what you do to the heads and the corresponding valve train that improves your E.T.s . . Also compression has a hell of a lot to do with both 60' time and top end MPH . .

Currently, math and competiton tells us we're building somewhere between 650 to 690 HP. At this point, the heads are fine, but we're putting together a "Back up Bullet" which is the reason for the query . . We would like to know what the compression ratio should be ideally for a high altitude engine that can be taken to near sea level without changing pistons or heads . . and without beating hell out of it on top end . .

I'm a novice on Chevy Truck motors, although back aways I tuned and was crew chief to several Blown Alky cars . . Just never screwed with anything with doors or a carburetor on it . . Just thought some old hands that know some of the short answers might have something for us . .

Guess not . . .

Yep, guess not. You seem to have all the answers. What do you need from any of us? :roll:

Good luck on your backup "Bullet"

More head would be a head that flows more. :shock:

If you're not even going to make 700hp with a 632, why not just run it on pump gas? Just curious. I'm sure I'm not the only one wondering that.

I asked what I thought was a simple question for someone with experience on a 632 cubic in motor. I currently run a 496 and am looking to upgrade to a 632. I assumed I could get some advice here, but only got aswers about the heads I have. I realy don't get the sarcasm about making 700 hp with a 496 at 5000 ft.

X2....You try and give people advise to make thier set-up more efficient and optimize horsepower, ( and some appreciate the advise ) but others don't want to hear that it could be better.

TS1955

Send us an e-mail [email protected]

We will be more than happy to answer any question you have about building the 632.

We have built 4 in the last 6 weeks for customers.

Lessee, What the initial question concerned was "Were Bear to buy a 632 BBC, what compression ratio would be a good one for high altitude racing?"

Answer, 14 to 15 . . Then I asked for more particulars concerning the same issue.

I never said we had or were using a 632, nor did I bring up any HP facts . . I did note that "More Head(s)" weren't an answer because there's no such thing. What you do (or might do) to a head might be a factual answer, but more head is just a pornographic request . . While it might be a good idea, it won't make you go any faster . . In the second post, I did mention an estimated HP figure(s) from the current engine we are racing, but never connected that to any 632 statements, nor did I give the CI . . Thus, any answer to that specifically, would have been less than a partial answer (had one been given) because you didn't have enough facts to build on . .

Apparently my critic is better at jumping to conclusions than giving specific and factual advice or answers . .

As I said, I've done this before, but not with the engines, tuning or modifications that a BBC responds to or likes . . I don't have all the answers but apparently enough to understand that specific heads and the way you use them require more than grabbing a roto rooter and making them "Bigger" . . Flow is very dependent upon the combustion chamber size, RPM range you intend to operate in and Valve sizes, duration etc . . Thus, "More head" is like saying "More Gear" or More Driver" . . Exactly "How much More" becomes the question . . and specifics becomes the answer . . :roll:

And thanks, CNC for your specific answers . . . They're appreciated.

Nowhere was anything mentioned about a 496BBC making the 700hp.

Sorry for the misunderstanding. I'm done.

Re: compression
 

I swear that says 632bbc dart 360s :wink: followed up with :P

Back to the questions on compression 15.5 on gas and 114 octane isnt enough... if alky 14.5 is enough. The dart 360s will be a major hold back unless you get one of the TPS guys to work on them.

Thanks Guys, we're just trying to see what our options are before getting froggy and buying this coming year's backup short block, which, will end up being next year's Bullet if all goes well this coming season . . As I said, I'm not closely familiar with Big Inch BBCs and the Boss was just getting his feet wet this last year . . We ask questions because we want the shortest learning curve available and it's a hell of a lot easier (and cheaper) to get answers from those of you who might have them, than to learn them the hard way . .

Not that we're lost, as we've been in the money twice last year . . We just wanna do it as easily as possible . . Hell, I'm an old guy, I'm tired of climbing mountains and fighting thunderstorms . . There's a bunch of know how here and I'd love to share what I've learned about other classes of drag racing with guys who're successful in the brackets . .

Bracket racing is a whole hell of a lot different than either heads up or index racing . . But most of you know that . .

On the Headwork, they've been massaged by Steve Schmidt (former Pro Stocker and engine builder) and are all CNC . . At this point the heads aren't close to their potential, I believe, as we've had other glitches. Those, as far as we can tell, have been cured and we're just waiting to get the car to a race and see what the results on the present setup will be . .

Thanx again to both CNCMotorsport and Hammertime . . serious discussion with factual info . .

Not sure how far the 360 heads have been taken, but they are capable of making 950+ Horsepower on the 632.

Not sure where you want to be at for over all horsepower, but this will give you a basic idea of what you can look for.

Good luck

?
 

This Kind of Gives me a bit of Info?
I have a 634 that little by little I'm peicing back together?Had a few Main bearings Spin,so I ended yup with it?
Callies Ultra Crank& Rods,2-Sets of Pistons,set of 18*,and a set of 23*,and Just figured I put my Dart CNC Pro-1 355's on with the 23* pistons,and it will be 16.1,dont have a Cam,but would get something in the Range NEEDED?
Was REALY Hoping to make 1050??But,after reading the about post?You got me THINKING>?Although I know thw 355's are a Much better Flowing Head than the 360!
I'll just keep Plugging along and see what Happens,.............?
Later
G 8)

Thanx again . . As far as horsepower ratings, real or imagined, go, neither I nor the Boss are particularily concerned about them. That's a subject you BS about at the bar . .

Bottom of the timeslip is the intent for all the money being spent and questions being asked/answered. We're just looking to get consistent 9.50s (or close) at 4800-5000 feet . . and when we get to that point, then we'll try to step up. That's the reason for the 632 (or whatever we end up with) We've run high 9.80s with a tired 468, so 9.50s are a relatively reachable goal . . a little at a time . . .

We do use mathematical formula to establish a HP rating for each run, from the 60' time, the ET and quartermile MPH, but it's expressly for data base and not necessarily for bench racing . . Just another set of numbers to look at and compare actuals (Leakdown, Trans pressure, etc) to . .

The more data you have on hand, the better the decisions you can make both on race day and in the shop . . .

What I gather, is, they are Dart 360's, that were ported by Steve Shmidt. Meaning, they are likely MUCH larger than 360. Likely 380ish cc+? Dart 360's with what I would consider fairly basic porting, meaning, not moving anything, just grinding metal out, with a larger intake, say 2.350, will make easily over 1000 hp.

As far as compression, due to the altitude, as much as possible. 15:1+, which, is fairly easy to achieve in a 632. The one thing I wouldn't do, is use a mega huge dome to just achieve a number. I would mill the heads and use a moderate dome, vs a huge dome, and more chamber. The engine will make more power at say 15:1 than to 16:1 with the huge dome. There is also a point of diminishing returns on cr.

Frank

Thanx . . . Good to know . . . Appreciate it . . .

Re: compression
 

First are you ever going to run any power adders. if not, how often do who want to go into the motor, With nos we run 118 or even 123 and limit our c ratio to 14.2 If a straight motor deal would can go up to 16.5 to 17.1 but you will have to watch the timing, Now in bad air, or high altitudes you can run more timing, but if you are just going to bracket race, then build it with 14.5 and just have fun. Q-8 stuff is a whole different process, and your cost in the end will be higher. At 14.5 you can always add nos, now don't get me wrong you can add nos to about any motor, but nos works better at a lower CR, this is what we have found out on the motors we have and we do have 486 cubic smallblocks and three BB over 800 inches, and I do build motors for a living even though I'm retired. Hope this Helps

Results . . .
 

OK, just to let you contributors know how and what. Yesterday, at Bandimere Raceways, in 7600' air, 49° and one of the first down the track, the 496 ran a 9.843, 139+, 1.44 60' . . . with a little wheelspin. (we were screwing with the wheelie bars) . .

Track and air went away from there, But the next three corresponding trips were, 9.849, 9.859 and a 9.915 with hard tire spin out past the tree . . Not to mention 9600' air . . And . . the MPH never got below 139 . . That's why we call it the "Grape Ape", it's an "Animal" on the top . .

Put it in the box and went home . . Couldn't ask for a better day than that!

Can't wait to see what it'll do with a little good air . . !

Thanks for all the help and conversation, you guys are great!

Happy Easter!

From Bear4333 and crew (Roadkill2, the crewchief)