DEEP THROAT... The Discusion!

[GARY C]

Just curious what you guy's have found for throat size on 23* SBC heads vs something like an 18* or 14* head?

From my research on it some feel a 90ish throat but this seems to be shallower angles and some feel on a 23* head it can be bigger and others feel the 23* should be smaller.

Would you size the throat different for say a 2500 to 6500 RPM range verses say a 6000 to 8000 range and if so what can you share on this.

[ClassAct]

Just curious what you guy's have found for throat size on 23* SBC heads vs something like an 18* or 14* head?

From my research on it some feel a 90ish throat but this seems to be shallower angles and some feel on a 23* head it can be bigger and others feel the 23* should be smaller.

Would you size the throat different for say a 2500 to 6500 RPM range verses say a 6000 to 8000 range and if so what can you share on this.

IMO (take it for what it's worth as it's worth exactly what you're paying for it) when you get to 90% throat you need a steeper than 45 degree seat. I had cutters that were 88% and if I thought I needed more throat than that I used a 50. And then, I realized I could use a 2.02 valve instead of say...a 2.055 valve and get the same sized bowl with the 2.02 valve as I had with the 2.055 and a 45 and I didn't have to worry about getting the CSA to feed a bigger valve/bowl with a 45. If that makes everything any sense.

[GARY C]

Just curious what you guy's have found for throat size on 23* SBC heads vs something like an 18* or 14* head?

From my research on it some feel a 90ish throat but this seems to be shallower angles and some feel on a 23* head it can be bigger and others feel the 23* should be smaller.

Would you size the throat different for say a 2500 to 6500 RPM range verses say a 6000 to 8000 range and if so what can you share on this.

IMO (take it for what it's worth as it's worth exactly what you're paying for it) when you get to 90% throat you need a steeper than 45 degree seat. I had cutters that were 88% and if I thought I needed more throat than that I used a 50. And then, I realized I could use a 2.02 valve instead of say...a 2.055 valve and get the same sized bowl with the 2.02 valve as I had with the 2.055 and a 45 and I didn't have to worry about getting the CSA to feed a bigger valve/bowl with a 45. If that makes everything any sense.

The head I am working with is a ProTopline 200cc runner 2.02 valve, 45* seat and recently discovered they are cast with a 1.81 to 1.83 throat so I am trying to epoxy them down a touch but not sure what I should look for or shoot for.

If I need to look at air speed then what is the best way to probe it and what speed would I look for?

If it's just cfm then so far reducing both runner and throat has virtually no effect.

Here is the thread to the heads... https://www.speed-talk.com/forum/viewtopic.php?f=1&t=55982

[Stan Weiss]

Gary,
I done know what your flow numbers are. These numbers I believe are from a 220 cc ProTopLine head with 2.02" intake. The 4 pictures show the average throat velocity for 1.77 1.79 1.81 1.83 throat size.

Stan

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[GARY C]

Stan, thanks for posting those, would that still be relevant if the MCS/Pinch is smaller than the throat?

[Stan Weiss]

Gary,
Yes, All I am doing is calculating the average velocity based on the given CSA at different areas. As you know when you probe the 9 sectors of a given CSA the velocity will not be the same in all 9 sectors. What I calculate is what the average should be. That being said. If you head has the Min CSA at the pinch that velocity will be higher than the throat.

Stan

Code: Select all

Intake_Valve_Size_=_2.02___________________Exhaust_Valve_Size_=_1.6
Intake_Valve_/_Bore_Ratio_=_0.505__________Exhaust_Valve_/_Bore_Ratio_=_0.4
Intake_Valve_Area_=_3.204739_sq._in._______Exhaust_Valve_Area_=_2.010619_sq._in.
Intake_Valve_Stem_Size_=_0.3415____________Exhaust_Valve_Stem_Size_=_0.3415
Intake_Valve_Stem_Area_=_0.091595_sq._in.__Exhaust_Valve_Stem_Area_=_0.091595_sq._in.
Valve_Lift_at_which_the_Valve_Area_and_Window_/_Curtain_Area_are_the_SAME_SIZE
At_that_point_the_velocity_will_be_the_same_in_both_areas
Intake_Valve_Lift_=_0.505_Inches___________Exhaust_Valve_Lift_=_0.4_Inches
Throat_CSA_(0.89604)_Intake_=_2.4814_sq._in.Throat_CSA_(0.56875)_Exhaust_=_0.5588_sq._in.
Effective_Throat_CSA_=_0.87995_____________Effective_Throat_CSA_=_0.52718
Valve_Lift_at_which_the_Throat_Area_and_Window_/_Curtain_Area_are_the_SAME_SIZE
At_that_point_the_velocity_will_be_the_same_in_both_areas
Intake_Valve_Lift_=_0.39102_Inches_________Exhaust_Valve_Lift_=_0.11117_Inches
Intake_Valve_Seat_Angle_=_45.0_____________Intake_Valve_Seat_Width_=_0.055
Exhaust_Valve_Seat_Angle_=_45.0____________Exhaust_Valve_Seat_Width_=_0.08
User_-_Intake_MCSA_=_2.43__________________User_-_Exhaust_MCSA_=_1.583673


_____Intake________------_Curtain_-----___Effective__---_Throat_--____----_Valve_---____----_MCSA_----
_Lift______CFM_____fps_______DC_____Area____Area______fps_______DC______fps_______DC______fps_______DC
_.2000__126.000__238.260___0.6802___1.269____.863__121.864___0.3479___94.360___0.2694__124.444___0.3553
_.3000__184.000__231.957___0.6622___1.904___1.261__177.961___0.5080__137.796___0.3934__181.728___0.5188
_.4000__233.000__220.296___0.6289___2.538___1.596__225.352___0.6433__174.492___0.4981__230.123___0.6569
_.5000__265.000__200.441___0.5722___3.173___1.816__256.302___0.7317__198.456___0.5665__261.728___0.7472
_.6000__287.000__180.901___0.5164___3.808___1.966__277.580___0.7924__214.932___0.6136__283.457___0.8092
Avg_____219.000__214.371___0.6120___2.538___1.500__211.812___0.6047__164.007___0.4682__216.296___0.6175


_____Intake_______%_Step___--------_CFM_per_Sq._In._-------____L/D___Lift___________Sq_In
_Lift______CFM__Increase___Throat____Valve__Curtain_____MCSA__Ratio___mm____M^3/s____Area____fps
_.2000__126.000____________50.777___39.317___99.275___51.852__.099___5.08__0.0595___1.032__293.160
_.3000__184.000____46.03___74.150___57.415___96.649___75.720__.149___7.62__0.0868___1.643__268.772
_.4000__233.000____26.63___93.897___72.705___91.790___95.885__.198__10.16__0.1100___2.260__247.381
_.5000__265.000____13.73__106.792___82.690___83.517__109.053__.248__12.70__0.1251___2.481__256.302
_.6000__287.000_____8.30__115.658___89.555___75.375__118.107__.297__15.24__0.1354___2.481__277.580
Avg_____219.000____________88.255___68.336___89.321___90.123

[GARY C]

Thank you sir, that will give me some idea of what to look for, the flow #'s and throat are very close to mine so that helps a bunch.

I guess the next question is... does anyone know what speed would be ideal for a given application?

[RevTheory]

Gary,
I done know what your flow numbers are. These numbers I believe are from a 220 cc ProTopLine head with 2.02" intake. The 4 pictures show the average throat velocity for 1.77 1.79 1.81 1.83 throat size.

Stan

Gary_177.gif

Gary_179.gif

Gary_181.gif

Gary_183.gif

What program did this come from, Stan? It's prettier than my scribbled, unorganized notes

[Joe-71]

What I found on my flow bench was that when the throat diameter was increased from 88% to 89%, the flow came up several cfm. Just did that on a 2.300 intake that was flowing 352 cfm with 1.97 throat which was .857%. Went to 2.02 throat and flow came up to 394 cfm with same valve job. I am going to take it out to 2.085" throat, and see how that does next. I don't understand how the flow can stay the same on your chart with decreases in velocity.

[Stan Weiss]

Shawn,
Those are some screen captures and also the data from a text report from my program. Here is a link to the latest User's Manual which is in PDF format http://www.magneticlynx.com/carfor/carfor.pdf

Stan

[GARY C]

What I found on my flow bench was that when the throat diameter was increased from 88% to 89%, the flow came up several cfm. Just did that on a 2.300 intake that was flowing 352 cfm with 1.97 throat which was .857%. Went to 2.02 throat and flow came up to 394 cfm with same valve job. I am going to take it out to 2.085" throat, and see how that does next. I don't understand how the flow can stay the same on your chart with decreases in velocity.

I may be wrong but I don't think it was to show the CFM change in relation to throat size but was to show the change in velocity and DC due to throat size at a given CFM.

On my application reducing throat diameter did not decrease flow so it would increase the DC... I think.

[racin69z]

I have a similar issue I am working on now. I am doing a set of 862 ls heads that are factory with a 1.89 valve. The throat is 92.6% from GM. I read that people have gain good flow by going to the 2.00 valve with these heads. But I'm not sure if that will help what I'm trying to achieve in my scenario.

I am running these on a 6.0 with a 208 218 cam. Going into a 6k 3/4 ton 2500hd. My intention with running these heads was to increase intake velocity at 2500-3000 rpm. Thats my interstate towing rpm. I am going to run a tbss intake which I believe has longer runners which should boost low rpm torque and intake velocity.

Would I be better at 93% throat and a smaller valve, or take some 2.00 valves and cut them down to 1.94 which puts me at 89%?

Lynn

[GARY C]

I have a similar issue I am working on now. I am doing a set of 862 ls heads that are factory with a 1.89 valve. The throat is 92.6% from GM. I read that people have gain good flow by going to the 2.00 valve with these heads. But I'm not sure if that will help what I'm trying to achieve in my scenario.

I am running these on a 6.0 with a 208 218 cam. Going into a 6k 3/4 ton 2500hd. My intention with running these heads was to increase intake velocity at 2500-3000 rpm. Thats my interstate towing rpm. I am going to run a tbss intake which I believe has longer runners which should boost low rpm torque and intake velocity.

Would I be better at 93% throat and a smaller valve, or take some 2.00 valves and cut them down to 1.94 which puts me at 89%?

Lynn

If you increase the throat size without gaining flow then you loose velocity and DC, If you gain flow while maintain the smaller throat size then you gain velocity and DC which I believe would favor low end tq.

Without having a head to test on I would opt for bigger valve and maintain the smaller throat.

My thought is that if you go 2" valve and set the throat at 87 to 89% of that then you will increase flow and velocity not only at the throat but in the complete intake runner, it's hard to say without testing.