10caipirinhas

Simple question.......no ?

I know what it is and how/why it works, but at what RPM level does a raised cam position become directly beneficial to the overall build ? Talking about a standard deck (9.80) BBC here with a 4.60 x 3.76 rotator assy.

Obviously on a street car, if you're staying under 6,000 it doesn't matter unless you are going to be spinning over that speed for an hour + nonstop........but is it a "must do" when you plan to hit 7,500 +/- on a regular basis for short periods such as WOT acceleration ?

From the perspective of my wallet, it is roughly a $3K question.........

SteveG75

Raised cam position has nothing to do with RPM. Raising the position of the cam in the block allows a bigger stroke. That is all.

10caipirinhas

You can also buy a regular deck block with a .400 raised cam position that allows you to use shorter and thicker pushrods for stock throw cranks.

bashcraft

And you would gain what?

You'd be better off spending your money somewhere else.

10caipirinhas

Hi Bob.....

Better (more stable) valve train dynamics at higher rpms.......hopefully improved longevity and reliability (in relative terms while still budgeting for a teardown every 3rd year).

Is it worth the $3K ? Trying to figure that out right now.......FWIW it also means going from a steel to an aluminum block. And that is not something that particularily matters to me nor is it worth it. I'm not going to be drag racing here.......just wanted to build an as reliable as possible high rpm BBC for $15-17K.......and the extra $3K moves me a little over that level.

bashcraft

You're joking, right?

.400" shorter pushrods isn't going to make enough difference you you to even notice.

billla

If you think you're going to be turning over 6,500 RPM you should be far more concerned about the balance of the rotating ***'y, the straightness of the main bore and valvetrain configuration/weight than moving the cam up.

Why do you think you need a teardown every 3rd year for a street engine?

10caipirinhas

Hi Bob......

Nope, it was a serious question.

Then why do they produce such a block in a standard deck height ? Solely for stroker crank clearance ? If a reduction of .400 in pushrod travel really doesn't matter to the valvetrain that's one thing, and I am not an engineer, just some guy about to open his chequebook, so I am deferring to the experts here. But.......I can understand when you have a tall deck block, as it's common to put the stroker crank in those and you need the raised cam to create the clearance when building a big cube engine (589 - 632). Seems pointless to me to either make and then buy a regular deck block and do the same otherwise for the same $$ amount and fewer cubes, so just wondering if there was more to it than the crank clearance angle. And I think there is.....but don't know for sure as I've been out of American iron for 2 decades.

Billa.......

I know that......

"Hopefully".......there's a difference between just budgeting for a teardown every 3rd year assuming 10K miles a year, and actually doing it. I am not expecting Honda durability out of something, just being pragmatic if it happens to be called for. Spent much more money on Ferraris and Porsches than I ever will on a C3.......but just in case, I'd rather plan for it.

MotorHead

As far as I know the main reason for a raised cam position is more clearance for the rotating assembly so you can build a bigger motor.

Usually you will see them at the track more than on the street, I personally don't get where you would benefit in valve train reliability / stability but there might be marginal gains there

bashcraft

Yes.

Not everyone can or is willing to run a tall deck block.

10caipirinhas

Bob......

It's a real PITA to make a tall deck fit in a C3 so I understand that aspect........but pretty much every other piece of GM iron out there has lot of clearance for one AFAIK......that's why I was wondering. If I would enjoy driving it and could fit it easily (and cheaply) in a C3 I'd love to have a 5,500 RPM tall deck 632....the thing would live forever. Seems like such a waste of money to buy the block just for that reason alone though. Cheaper to notch and overbore a 454 block IMHO and live with what you've got.

Motorhead......

Every engine I have ever had built was measured to 3 spaces right of the decimal point and has the rotator balanced to within a fraction of less than a gram of tolerance......so, to me anyways, 4/10 ths of an inch really seems like "a lot" of space, when you are talking about a valvetrain moving about at 7,500 + RPM. Is it worth $3K in the aluminium block and does it really matter that much ? Maybe, maybe not......

Jim (427Hotrod) however did talk me into shortening the stroke from 4.00 to 3.76 if I wanted to spin it up there..........so potentially having .400 shorter pushrods is reason enough to ask if it is worth it. May very well be a waste of money for marginal return in my application.......don"t really care about the aluminum block, so having a hard time with the $3K figure......but always better off to ask around.

Thanks to everyone so far..........appreciate the input.

billla

There are a bunch of comments here that don't make sense to me...

"Cheaper to notch an[d] overbore a 454 block" - you're clear that we're talking about cam-to-rod clearance here and not block-to-rod clearance for the raised cam, correct?

I don't understand your focus on the length of the pushrods. A hardcore BBC pushrod ain't gonna flex, and the weight of .400 of pushrod is negligible at best.

Why in the world would you go to a 427 vs. a 454 stroke? You're giving up 27 CID right out of the gate. Stock 454's were externally balananced and so not good high RPM candidates...but you'll have a balanced assembly and you're giving up significant torque and HP gains by going with a shorter stroke.

10caipirinhas

Hi Billa......

Yes, I am.......

Just saying that I'd rather not buy an expensive "standard deck block" for a few more cubes if that (clearance) was the only benefit of the raised cam. Cheaper to make an overbore 454 into a 496 stroker combo like Vortecpro does. Now, a lot more cubes (in the case of the tall deck), a more stable valvetrain, aluminium weight savings and heat transfer.....those are all good reasons, and is another story entirely, but again, only if it is worth it. Like was earlier said, $3K goes along way, it's a TKO600, or an Autogear M22, or a Duntov HD diff for example.

Insofar as the push rod focus goes, first, they make this block, so there must be another reason why they do besides clearance (see my first comment about cost). If not, then I'll have to make up a "head scratch" icon.

Now, to continue with the answer, my problem is that I come from owning and driving 20 years worth of high performance, small displacement, multiple everything, aluminium engined cars that spin all day long at 8,500 rpm, without pushrods. So, inquiring minds wanna know..........I hope that explains the use of a shorter stroke as well, since I wanna play in the same sandbox.

Big learning curve here for me right now...........sure appreciate all the feedback. Maybe it is all in vain on this topic.

MotorHead

You say it's a big learning curve, then you seem to question or even dispute what some knowledgeable people are telling you ?

If your motors are built 3 spaces to the left of the decimal place I would be looking into buying mics that measure 1 / 10,000 of an inch for your current build if you want to rev a big block to 7500RPM's

10caipirinhas

Motorhead.......

Don't understand why my questions are a problem.

Not disputing anything or arguing with anyone, just trying to understand why Dart builds this block, and if there is any benefit to the specific aspects of it based on the cost and my own automotive background. Please don't take it any other way. Maybe if we were sitting across from each other it might be interpreted differently.......the internet is a hassle that way.

billla

The background helps. If I may, I'd like to suggest that a mindset adjustment is required.

There are two aspects that you need to embrace to build an effective BBC. First, as you note there's a world of difference between a SOHC/DOHC engine and an in-block cam engine such as the BBC. We do spend a lot of money on valvetrain components to get acceptable dynamics, especially at high RPM. Heavy springs, light valves, sewer-pipe billet pushrods - every crazy thing you can think of. In the end, this means we tend to design peak power at lower RPMs than SOHC/DOHC engines. Doesn't mean you can't build an 8,500 RPM BBC...but you should bring lots of money

Second, consider how the bore/stroke ratio plays into this as well.

Rather than trying to make a BBC something that it's inherently not, consider designing to the strengths of the engine design to make power.

gkull

Yes, there is a big relationship to the raised cam blocks and higher RPM potential.

Some guys mentioned clearance, but not exactly what. The answer is that the raised cam allows for: Larger diameter cam bearings or even roller bearing races. Larger diameter cam shafts for higher strength when compressing very high pound triple springs. Larger lobe lifts to get those valves lifted up in the .800 - 1.000 inch range. The additional clearance allows room for big rods. Especially Aluminum which are massive is size compared to titanium or the billet steel.


IMO - rpm kills motors. I work on v-8 motors that can exceed 10,000 rpm. They make lot's of power per ci. But they don't last very long

MotorHead

So all that cam stuff doesn't matter then, they blow up anyway ?

I think the OP is worried about pushrod deflection, which is going to happen with any size pushrod. 400 thou longer ? Or in his case he is looking at shortening the pushrod by less than 1/2 inch. If it's a good pushrod then it's really a non issue IMHO

And no your questions are just fine and I hope you build yourself a killer motor

gkull

You solve pushrod deflection with bigger diameter and thicker wall push rods. Minor length changes are a non issue.

MotorHead - the raised cam small blocks actually use big block diameter cam bearings and they can be machined out for actual roller bearings. The big block raised cams can even go bigger. Comp cams has the big diameter cams right in their cat.

MotorHead

10caipirinhas - Get ahold of 427Hotrod he'll give you the lowdown on big blocks and what is and what isn't needed for your particular application