We are currently running on the new domain and server: www.Speed-Talk.com

IMPORTANT: Update your bookmarks to https://www.speed-talk.com/forum/
(Right-click the URL and select "Bookmark this link")

Minimum Cross Sectional Area: Question

General engine tech -- Drag Racing to Circle Track

Moderator: Team

gmrocket
HotPass
HotPass
Posts: 5981
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Minimum Cross Sectional Area: Question

Post by gmrocket » Sun Feb 09, 2020 3:29 pm

skinny z wrote:
Sun Feb 09, 2020 3:10 pm
gmrocket wrote:
Sun Feb 09, 2020 1:40 pm

Are the advertised ratings for the 274 and 283 taken at same lift?

You may better off with something like 275 and 235 or more...with 1.6 on intake only.They are out there.
The 274/224 w/.575" is right out of COMP's profile catalogue and is based on a 1.6 RR. That's an XFI intake lobe. The 283/231 was spec'd by Torque Master but there's no XFI lobe with that duration. 280/230 and 286/236 is as close as it gets with lifts around .575". My job will be to find a cam supplier that can deliver that duration with similar lifts of .575". There are two lobes in the Xtreme Energy category at 282/230. One with .544" and the other with .622". The .622" is too much IMO. The .544"....maybe.
Like you said, they are out there.
I have to get back into Jones' catalogue as I believe he has lobes that fit that bill.
Ok, but you didn't answer my question.. are you talking the same adv rating specs?

Is tq master giving you the 283 number at the same starting lift point?

skinny z
HotPass
HotPass
Posts: 285
Joined: Tue Mar 11, 2008 8:42 am
Location: Canada

Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 3:47 pm

gmrocket wrote:
Sun Feb 09, 2020 3:29 pm


Ok, but you didn't answer my question.. are you talking the same adv rating specs?

Is tq master giving you the 283 number at the same starting lift point?
Oh. I see what you're asking. Good question. Well, there's no way I can tell if Torque Master is giving the advertised rating at the same lift (.006" or .004" or whatever) as COMP's which is specified as .006".
Plenty of folks use .050" values as the go to spec and the "advertised" spec means little to them. Seems to me though that's going to be lacking in some way information-wise.

GARY C
HotPass
HotPass
Posts: 5913
Joined: Tue May 14, 2013 10:58 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by GARY C » Sun Feb 09, 2020 4:19 pm

skinny z wrote:
Sun Feb 09, 2020 3:47 pm
gmrocket wrote:
Sun Feb 09, 2020 3:29 pm


Ok, but you didn't answer my question.. are you talking the same adv rating specs?

Is tq master giving you the 283 number at the same starting lift point?
Oh. I see what you're asking. Good question. Well, there's no way I can tell if Torque Master is giving the advertised rating at the same lift (.006" or .004" or whatever) as COMP's which is specified as .006".
Plenty of folks use .050" values as the go to spec and the "advertised" spec means little to them. Seems to me though that's going to be lacking in some way information-wise.
I have not really messed with TM but most of DV's programs focus on what needs to happen at the valve as opposed to what the cam is doing unless he is specking a specific cam then his hyd cam stuff has always been at .006, you may want to PM Stan to get a clarification on this.

In order to compare lobes you probably need to look at advertised/seat numbers, .020 .050 and .0200 as well as total lobe lift.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

skinny z
HotPass
HotPass
Posts: 285
Joined: Tue Mar 11, 2008 8:42 am
Location: Canada

Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 4:33 pm

GARY C wrote:
Sun Feb 09, 2020 4:19 pm
you may want to PM Stan to get a clarification on this.
That is an excellent idea.

gmrocket
HotPass
HotPass
Posts: 5981
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Minimum Cross Sectional Area: Question

Post by gmrocket » Sun Feb 09, 2020 4:56 pm

skinny z wrote:
Sat Feb 08, 2020 1:30 pm
raynorshine wrote:
Wed Feb 05, 2020 11:24 pm
Skinny: what do your computer sims recommend for duration at .050"...6000 RPM redline...3.75" stroke...? (intake specifically)
-i feel 240 degrees is excessive :shock: not many small-block tow-trucks have 240 intake degrees duration.. :P
As far as the cam recommendations go, as well as the computer simulations, almost all peak at 6000 RPM. Makes perfect sense in that the CID, heads (in particular)and compression ratio are the same across the board. That said, I place my red line about 500 RPM beyond the peak HP RPM.
Professional picks ranged from 232 to 242 @ .050" on the intake. All peak at 6000 (so a 6500 red line shift). The lower duration tends to be flatter at peak. Essentially flat from 5500-6000. Then they all fall off the map after that as, I assume, the heads run out of steam.
My latest experiments use Torque Master as a guide and moving the inputs around to see the trends that develop. As an example, all else being equal, at 9.8:1, duration at .050" is 231. LSA 106, ICL 102. Push that compression up to 10.4 and suggested duration is 224 with 107/103.
There's one more iteration I want to study and that's the "too big a cam" in DV's write-up on a small headed 383. That particular combination used a small head (Edelbrock Performer RPM 170 cc) but the cam spec was 288/293, 236/242 (no spec on the LSA although given that is was described as Comps so I'd guess a 110 LSA). Plenty of low end torque which was attributed to the higher port velocity while the longer duration helped the top end.
I'm less enthusiastic than I was about the approach though.
Something's not right here

9.8 requires a 231 in at 102 with a 106 split

Yet with 10.4 it says you need a 224 in at 103 with a 107 split?

Don't make sense needing less .050 with more comp

skinny z
HotPass
HotPass
Posts: 285
Joined: Tue Mar 11, 2008 8:42 am
Location: Canada

Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 5:31 pm

gmrocket wrote:
Sun Feb 09, 2020 4:56 pm
Something's not right here
9.8 requires a 231 in at 102 with a 106 split
Yet with 10.4 it says you need a 224 in at 103 with a 107 split?
Don't make sense needing less .050 with more comp
Keeping the minimum required flow at 250 CFM (as an input selection) regardless of the compression gets that result yes. Peak HP RPM drops by about 200 RPM with the higher CR but the DCR goes through the roof as you'd expect.
If I shift the target data point spec from max CFM available to a given HP RPM peak (5500 in this case) then the spread is less between the two CRs but the higher CR asks for more port flow than I can deliver. So what's being said here is the engine is certainly under-supplied and I have to limit my target peak HP RPM accordingly. At it looks like 5500-5600 is about the most I can expect. And that fits in the 9.8 CR as well.
Some screen shots of four different selection specs.

9.8 250 CFM.jpg
10.4 250 CFM.jpg
9.8 5500.jpg
10.4 5500.jpg
You do not have the required permissions to view the files attached to this post.

gmrocket
HotPass
HotPass
Posts: 5981
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Minimum Cross Sectional Area: Question

Post by gmrocket » Sun Feb 09, 2020 7:08 pm

In the real world do you really think if you added more than half a point of compression, you would REDUCE the .050" numbers?

Effectively, put in a smaller cam? That's what I'm asking because you said the program suggested a much shorter cam

Sure don't sound right to me

GARY C
HotPass
HotPass
Posts: 5913
Joined: Tue May 14, 2013 10:58 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by GARY C » Sun Feb 09, 2020 7:30 pm

gmrocket wrote:
Sun Feb 09, 2020 7:08 pm
In the real world do you really think if you added more than half a point of compression, you would REDUCE the .050" numbers?

Effectively, put in a smaller cam? That's what I'm asking because you said the program suggested a much shorter cam

Sure don't sound right to me
Oddly enough back when NASCAR ran 9.5:1 Bush engines it was said that they ran a bigger cc head and a larger cam than their higher compression Cup engines and the claim was because they didn't have the compression to run the rpm that they needed to run?

I could never confirm the cam #'s but the heads listed showed the Bush head to be bigger than the Cup head in the few examples I could find.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

skinny z
HotPass
HotPass
Posts: 285
Joined: Tue Mar 11, 2008 8:42 am
Location: Canada

Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 7:43 pm

gmrocket wrote:
Sun Feb 09, 2020 7:08 pm
In the real world do you really think if you added more than half a point of compression, you would REDUCE the .050" numbers?

Effectively, put in a smaller cam? That's what I'm asking because you said the program suggested a much shorter cam

Sure don't sound right to me
I'd suppose that if the port flow was higher then the "real world" result would prevail.
Last edited by skinny z on Sun Feb 09, 2020 8:27 pm, edited 1 time in total.

Orr89rocz
HotPass
HotPass
Posts: 1907
Joined: Sun Sep 28, 2008 9:25 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by Orr89rocz » Sun Feb 09, 2020 8:14 pm

gmrocket wrote:
Sun Feb 09, 2020 7:08 pm
In the real world do you really think if you added more than half a point of compression, you would REDUCE the .050" numbers?

Effectively, put in a smaller cam? That's what I'm asking because you said the program suggested a much shorter cam

Sure don't sound right to me
Doesnt make much sense to me either

skinny z
HotPass
HotPass
Posts: 285
Joined: Tue Mar 11, 2008 8:42 am
Location: Canada

Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 8:45 pm

Is it an effective practice to over-cam an engine relative to the MCA? That's the question in the 1st post.
What happens with this higher CR and lower duration (call it under-cam) is that torque goes through the roof. There's only a 2 degree less difference on the intake but the DCR sits at 8.2 and estimated cranking compression is 211 PSI. 20 ft lbs more torque as an estimate over the 9.8:1 spec.
It's more like questioning why is 9.8 duration what it is and not the other way around.

GARY C
HotPass
HotPass
Posts: 5913
Joined: Tue May 14, 2013 10:58 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by GARY C » Sun Feb 09, 2020 9:00 pm

Another thought on duration, compression and rpm is that Pro Stock now uses 10 + less total degrees of duration but turns more rpm than what they were doing in the past.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

raynorshine
Expert
Expert
Posts: 933
Joined: Tue Mar 06, 2007 1:59 pm
Location: BC, Canada

Re: Minimum Cross Sectional Area: Question

Post by raynorshine » Sun Feb 09, 2020 10:47 pm

GARY C wrote:
Sun Feb 09, 2020 9:00 pm
Another thought on duration, compression and rpm is that Pro Stock now uses 10 + less total degrees of duration but turns more rpm than what they were doing in the past.
-my basic physics/ math sez it's hard to build compression when the valves are open, off the seats... :lol:
Use it up
Wear it out
Eat it all!

-the greatest..."Dale Armstrong"

GARY C
HotPass
HotPass
Posts: 5913
Joined: Tue May 14, 2013 10:58 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by GARY C » Sun Feb 09, 2020 11:00 pm

raynorshine wrote:
Sun Feb 09, 2020 10:47 pm
GARY C wrote:
Sun Feb 09, 2020 9:00 pm
Another thought on duration, compression and rpm is that Pro Stock now uses 10 + less total degrees of duration but turns more rpm than what they were doing in the past.
-my basic physics/ math sez it's hard to build compression when the valves are open, off the seats... :lol:
I just thought it was interesting that their reduction in duration has not effected their increasing rpm although most people equate duration with rpm.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

mt-engines
Member
Member
Posts: 59
Joined: Fri Sep 27, 2019 12:35 pm
Location:

Re: Minimum Cross Sectional Area: Question

Post by mt-engines » Sun Feb 09, 2020 11:18 pm

GARY C wrote:
Sun Feb 09, 2020 9:00 pm
Another thought on duration, compression and rpm is that Pro Stock now uses 10 + less total degrees of duration but turns more rpm than what they were doing in the past.
you want to hold onto as much torque as possible.. you want to run the least amount of cam to hit that target rpm, especially when nhra decides to rpm limit you.

with induction that exceeds what the engine is capable of consuming, valve events can change drastically and pick up.. look at modern ls engines. 200 degree cams making 450hp. 23 degree chevys need cams in the 227-230 duration to make that kind of steam

Post Reply