Don Terrill’s Speed-Talk

Assuming all other things remain the same regarding engine combo and desired hp peak rpm, does a change from a say a 45* x 88% throat to a 50* x 91% throat configuration require more duration to keep your target peak rpm?

I know you can use more duration with 50s to get more lift but do you have to use more duration? If that's too vague, I can certainly add to it; I just didn't want to add just enough info to get out in the weeds.

I suppose we can at least assume a Gen 1, SBC with iron, Vortec heads and a hyd/roller.

When you use a steeper seat is making the throat bigger than 90% part of the trade off?? What angles and widths on your bottom cut or cuts into throat do you need, I am curious as well,

What I'm seeing is that if the different valve angle produces a seat that results in more flow (as in CD) as would be the case when going from a 2.02" valve to a 2.05" then yes, less duration is needed if peak HP RPM is to remain the same. That's given the same peak port CFM.
At least so says Torque Master.

steve cowan wrote: ↑Sun Feb 09, 2020 12:38 pm When you use a steeper seat is making the throat bigger than 90% part of the trade off?? What angles and widths on your bottom cut or cuts into throat do you need, I am curious as well,

with steeper seats it just happens to get the angles under the seat. throat will go up percentage.

as far as cam duration, steeper seats usually kills low flow, so adding duration or overlap helps get the air moving. and the cam doesnt really act as big.

skinny z wrote: ↑Sun Feb 09, 2020 3:40 pm What I'm seeing is that if the different valve angle produces a seat that results in more flow (as in CD) as would be the case when going from a 2.02" valve to a 2.05" then yes, less duration is needed if peak HP RPM is to remain the same. That's given the same peak port CFM.
At least so says Torque Master.

I don't think Torque Master is going to be useful here, at least not from what I've seen. A 2.02 valve with a 50* x .050" seat has about the same low-lift curtain area as a roughly 1.87 valve with a 45* seat.

I've never done 50* seats so when I start adding duration to what I think is right for 45s, my brain throws a flag on the play, "Over Cam Warning!" I just don't know if more duration is a luxury or a requirement to keep the same target rpm.

mt-engines wrote: ↑Sun Feb 09, 2020 11:50 pm... steeper seats usually kills low flow....

That would explain why TM is ineffective.

steve cowan wrote: ↑Sun Feb 09, 2020 12:38 pm When you use a steeper seat is making the throat bigger than 90% part of the trade off??

No, there is no set throat percentage that comes with the decision to use a steeper seat.
The throat percentage is just a result of the decisions on seat angles and widths you decide on that will fit the casting/application etc.
I've done 50* seats with the throat well under 90% of valve diameter.

steve cowan wrote: ↑Sun Feb 09, 2020 12:38 pm What angles and widths on your bottom cut or cuts into throat do you need, I am curious as well,

Whatever gives you a nice transition from bowl to chamber, and achieves the desired throat csa.

Randy

randy331 wrote: ↑Tue Feb 11, 2020 12:31 am

steve cowan wrote: ↑Sun Feb 09, 2020 12:38 pm When you use a steeper seat is making the throat bigger than 90% part of the trade off??

No, there is no set throat percentage that comes with the decision to use a steeper seat.
The throat percentage is just a result of the decisions on seat angles and widths you decide on that will fit the casting/application etc.
I've done 50* seats with the throat well under 90% of valve diameter.

steve cowan wrote: ↑Sun Feb 09, 2020 12:38 pm What angles and widths on your bottom cut or cuts into throat do you need, I am curious as well,

Whatever gives you a nice transition from bowl to chamber, and achieves the desired throat csa.

Randy

Thank you Randy for your response, I asked the question in jest as per our previous discussions, when talking to machine shop about a steeper valve job on my 1.94" dart 178cc heads I am still under 90% on the throat. If these heads respond how I think they will the dart 180cc heads will get a 50 or maybe a 52-55??
Can not answer about the cam question but I am looking at valve events that suits intake valve size, compression, rpm peak,
And application, as M-T says steeper seats kill low lift flow, fatter torque curve, and acts like smaller duration camshaft,
Steeper seat threads cause a lot of discussion

steve cowan wrote: ↑Tue Feb 11, 2020 2:42 am Steeper seat threads cause a lot of discussion

Yes. As do cam selection method threads, flowbench results vs Horsepower threads, dyno results threads, valve sizing threads, software prediction usefulness etc etc ...not sure how productive any of it is.

I just wonder...how many people walk away from any of those discussions on here with a different opinion or outlook than they had going in......I think virtually none. Not many are exempt from that.

I think a lot of it is an energy drain sometimes . Energy that could be used for doing something engine related rather than talking are arguing about faux engines. Its fun to bounce ideas around here and there for sure, but ultimately, at a point, you are on your own on certain things..got a little taste of that recently, when talking about cam testing, and thoughts on dynamics from my recent dyno tests on it.... with my contact at Bullet.

CGT wrote: ↑Tue Feb 11, 2020 9:38 am I just wonder...how many people walk away from any of those discussions on here with a different opinion or outlook than they had going in......I think virtually none. Not many are exempt from that.

I have. I just don't remember any of those long-winded threads being even fairly-conclusive on whether you simply can run more duration before you start getting the negative effects of reversion or if you have to to keep the same target rpm.

RevTheory wrote: ↑Tue Feb 11, 2020 9:49 am

CGT wrote: ↑Tue Feb 11, 2020 9:38 am I just wonder...how many people walk away from any of those discussions on here with a different opinion or outlook than they had going in......I think virtually none. Not many are exempt from that.

I have. I just don't remember any of those long-winded threads being even fairly-conclusive on whether you simply can run more duration before you start getting the negative effects of reversion or if you have to to keep the same target rpm.

I have learned a lot here, at the end of the day I think the opposing views shed more light on a subject then the old days when all we had were magazine articles and no way to question the info.

steve cowan wrote: ↑Tue Feb 11, 2020 2:42 am Can not answer about the cam question but I am looking at valve events that suits intake valve size, compression, rpm peak,
And application,

Those are some of the considerations. The application is a big part of it. Ex valve size/seat angles too. Rpm is up at the top of the list before comp for me. Cubes.

But application is a big one. Today I picked a couple lobes for the 454 lsx I'm working on. I like to run my pick by some others I value an opinion from before ordering the cam. I texted my choice to cgt and he thought a little bigger lobes, and maybe faster ones,....... but for him,.... all he wants to see is nice big fat power and power curve when I dyno it, .... Randy has to live with it down the road when it gets driven a lot on the street. LOL

So,.. see,... even the ones you take advise from may have a different "application" in mind. LOL

Randy

CGT wrote: ↑Tue Feb 11, 2020 9:38 am I just wonder...how many people walk away from any of those discussions on here with a different opinion or outlook than they had going in......I think virtually none. Not many are exempt from that.

I do. I learned long ago that a wise man can learn something from a fool, but a fool won’t learn anything from a wise man. Without an open mind no learning can take place. Many times a discussion about one topic opens my mind to an idea about something totally different. I figure anything that leads to my junk either making more power or lasting longer I need to be open to.

As far as 50* seats go, I look forward to trying them on a build some time, but the challenge will be finding out all the angles and such that will be best for the particular head and combo. I know like everything one size does not fit all. I don’t think the seats for my DRCE heads will be the best seats for my Tahoe. Then again, I could be wrong.

Paul

randy331 wrote: ↑Tue Feb 11, 2020 11:07 pm Today I picked a couple lobes for the 454 lsx I'm working on. I like to run my pick by some others I value an opinion from before ordering the cam.

Randy

Did you make a thread here asking for picks?

paulzig wrote: ↑Wed Feb 12, 2020 4:08 pm

randy331 wrote: ↑Tue Feb 11, 2020 11:07 pm Today I picked a couple lobes for the 454 lsx I'm working on. I like to run my pick by some others I value an opinion from before ordering the cam.

Randy

Did you make a thread here asking for picks?

Would that be time well spent ??

I decided to,...
Shut the valve sooner to trap more air!!
And calculate my "dynamic comp" to get it just right !!!
Run all the specs through a cranking comp calculator to make sure it is spot on !!!
Keep the ex valve shut later to help build more TQ !!!

There,.. did I leave anything out ??

Randy