bbc cams (throttle stop/ reliability)

airflowdevelop · Post by **airflowdevelop** » Mon Jul 18, 2005 10:09 am

Does anybody understand the market "throttle stop" lobes some of the cam companies are grinding? It seems that the RPM range they are shooting for, far exceeds the valve curtain area availible, does keeping the port in choke make it a "throttle stop cam".

Also, has anyone run a larger stick(+.900") in a 300+ run application? How is the realiability? VE makes consistency....I can't have a tight motor if it is always paralysed!

I have a 11-736-9 in a 470" BBC, 2.300 intake valve (415 @ 800). from 7200 - 8600 it picks up 18 horsepower, I am sure with another .100" lift, that would become 118 horsepower....

sorry for rambling...I am going back to beating my head against the wall!
Dennis

airflowdevelop · Post by **airflowdevelop** » Tue Jul 19, 2005 10:32 am

oh yeah, any help would be greatly appreciated. Don't feel like you have to answer all the questions

SStrokerAce · Post by **SStrokerAce** » Wed Jul 20, 2005 12:56 pm

I like the sarcasim Dennis

I don't understand the "throttle stop cam" meaning that they are squared off at the nose?

It's hard to say what lobes they are using on this cam...

The exhaust looks like a High RPM Exhaust Lobe while the intake could either be a HXL or a High RPM Intake Lobe... my guess is it's both of the High RPM series which is a pretty tame series of lobes but the HXL lobes on the other hand are pretty square nosed lobes. Any idea what the .200 duration is on the lobes you are using? That would give me a better idea as to the shape of the lobes.

You are using a 1.8:1 rocker now and thinking of going to a 2.0:1 rocker? I don't know if those lobes are going to like more rocker arm or not, certianly they are going to beat on the pushrods a lot more.

Bret

airflowdevelop · Post by **airflowdevelop** » Wed Jul 20, 2005 2:15 pm

203 I and 198 E as messured. I Don't understand the cam at all. How they can come up with the revs, without opening the valve is beyond me!

I would think something a little softer, like the low 190's @ 200 , with .850 over the nose, even a 510 lobe.

I am more confused what this has to do with it being a "throttle stop cam"?

Thanks
Dennis

k-star · Post by **k-star** » Wed Jul 20, 2005 3:10 pm

Not a answer but another question...

Would the cam grind reflect what the engine needs to recover after it's been "shut-off" for x amount of time?????

keith

airflowdevelop · Post by **airflowdevelop** » Wed Jul 20, 2005 3:12 pm

you are asking my question in another way ...

This is the reason they are calling it a "t-stop cam" but what does having the ca in choke have to do with recovery at a low RPM? specifically with a fairly wide lobe?

Thats the part I dont understand

SStrokerAce · Post by **SStrokerAce** » Wed Jul 20, 2005 9:45 pm

airflowdevelop wrote:203 I and 198 E as messured. I Don't understand the cam at all. How they can come up with the revs, without opening the valve is beyond me!

I would think something a little softer, like the low 190's @ 200 , with .850 over the nose, even a 510 lobe.

I am more confused what this has to do with it being a "throttle stop cam"?

Thanks
Dennis

Are you sure it's the cam that causes this? Yes the valve curtain is lower than what should be put in this thing and the cam is only listed for 7800rpm so the lobes are probably not made for 8600rpm hell it just says it's good for that RPM range not that it's going to peak any higher.

I realize you are the head porter here but what are we looking at in terms of CSA, port volume and length? I know how you guys like small ports to get the job done but that might be a variable in this... hell going tamer on the lobes is only going to like more area since it's going to have less lobe area in the upper 15% of the lift curve.

It would be hard to get a lobe with .510 lift softer than about 200-202 @ .200.... with lift comes area, adding lift to the lobe here is actually a good idea even if the .050 and .200 numbers stay around the same you will gain stability.

For example the Comp CE Drag Race Intake 1272 lobe in place of what you have now for a intake lobe .... 322 @ .020, 286 @ .050 and 198 @ .200 with .478 lift. That is about as tame as you can get. Couple that with a 1.8 and you would have a pretty stable setup with the lift you are looking for. Bad thing is that the lobe would throw off the intake to exhaust ratio you have now and probably would hurt the upper RPM where you are having problems so you have to look at both sides of this.

With something like that you are going to need one hell of a valve spring. What's on there now in terms of rate, installed pressure?

Bret

Jay Allen · Post by **Jay Allen** » Thu Jul 21, 2005 3:18 pm

I am having trouble understanding the question, I think.

It sounds to me like you are attempting to get an engine to recover during low piston speeds. A tall(er) lobe [short(er)@.050 with a high(er) lobe lift] will accomplish this.

Let's assume a 1.8 rocker arm.

262 at .050
185 at .200
.466 lobe lift
.839 lift
.021" lash HOT

OR

267 at .050
188 at .200
.475 lobe lift
.855 lift
.016" lash HOT

Either of these would make for nice intake lobes in an application such as this. The *Lobe Area* is what needs to be paid attention to IMHO. The L/A of a 280+ at .050 and 470+ lobe lift is HUGE! That type of cam *may* (but probably not)make a few more HP at the top of the RPM range, but average power and the engine's ability to recover will be poor. The engine will appear to be lazy. I would try to concentrate on Average Power and tq. Not a top end number.

Good Luck.

dbusch · Post by **dbusch** » Thu Jul 21, 2005 9:14 pm

Jay and I know of a lobe that has only 189* at .200 but has .511 lobe lift

Jay Allen · Post by **Jay Allen** » Fri Jul 22, 2005 9:11 am

dbusch wrote:Jay and I know of a lobe that has only 189* at .200 but has .511 lobe lift

But it'll NEVER work!
It'll eat valve springs!

What do ya know. It is bad ass just like I said. Has power EVERYWHERE!And a full season on valve springs at 9000 RPM ain't too bad.

Good Job Duane!

airflowdevelop · Post by **airflowdevelop** » Mon Jul 25, 2005 9:48 am

we are not really concerned with power period, we are concerned with VE.

My question is this... Is their an industry traight to a t-stop cam or is it marketing B-S?