header size question 1 5/8 or 1 3/4 pipe diameter
#51
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
I will never understand why anyone would go to the trouble of installing heads with 1 5/8 valves and then use a header that has in inside diameter of 1 1/2".
Surely you must realize 1 5/8 is 1.625 and has an inside diameter of 1.500
1 3/4 is 1.750 and has an inside diameter of 1.625 like the valves.
It doesn't matter how well you have run with 1 5/8" headers, you probably could have done better with 1 3/4" headers.
Just my $.02
Surely you must realize 1 5/8 is 1.625 and has an inside diameter of 1.500
1 3/4 is 1.750 and has an inside diameter of 1.625 like the valves.
It doesn't matter how well you have run with 1 5/8" headers, you probably could have done better with 1 3/4" headers.
Just my $.02
Years ago I ran the same Hedman 1 5/8 headers, and I swapped them out for 1 3/4 headers mid season and the car still trapped 120mph and still ran the same ETs. The bottleneck was the exhaust runner on the sportsman-II heads.
He's running ported 305 heads with a .479 lift cam. His exhaust flow is going to be around 150cfm max. When you calculate out the duration of the cam and that exhaust flow, it calls for a primary diameter around 1.4"
-- Joe
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
While I believe in absolute truth, not in this instance.
I have LT's and am lowered. In this pic, the pass side was just a little low - you can barely see it. In the second, you can see what I did to get 3" inters (w/2" primaries) around an 4L65e and is much better, now. It always seems to come down to how much money your willing to spend, and what your own skill level is.
I have LT's and am lowered. In this pic, the pass side was just a little low - you can barely see it. In the second, you can see what I did to get 3" inters (w/2" primaries) around an 4L65e and is much better, now. It always seems to come down to how much money your willing to spend, and what your own skill level is.
#53
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Engine: 355 w/AFR 195's Elem. 400/430 HP/TQ
Transmission: Tremec T-56
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
Because the diameter of the valve has absolutely nothing to do with the flow capability of the port.
Years ago I ran the same Hedman 1 5/8 headers, and I swapped them out for 1 3/4 headers mid season and the car still trapped 120mph and still ran the same ETs. The bottleneck was the exhaust runner on the sportsman-II heads.
He's running ported 305 heads with a .479 lift cam. His exhaust flow is going to be around 150cfm max. When you calculate out the duration of the cam and that exhaust flow, it calls for a primary diameter around 1.4"
-- Joe
Years ago I ran the same Hedman 1 5/8 headers, and I swapped them out for 1 3/4 headers mid season and the car still trapped 120mph and still ran the same ETs. The bottleneck was the exhaust runner on the sportsman-II heads.
He's running ported 305 heads with a .479 lift cam. His exhaust flow is going to be around 150cfm max. When you calculate out the duration of the cam and that exhaust flow, it calls for a primary diameter around 1.4"
-- Joe
Be my guest
But, nothing could be further from the truth!
#54
Senior Member
Re: header size question 1 5/8 or 1 3/4 pipe diameter
While I believe in absolute truth, not in this instance.
I have LT's and am lowered. In this pic, the pass side was just a little low - you can barely see it. In the second, you can see what I did to get 3" inters (w/2" primaries) around an 4L65e and is much better, now. It always seems to come down to how much money your willing to spend, and what your own skill level is.
I have LT's and am lowered. In this pic, the pass side was just a little low - you can barely see it. In the second, you can see what I did to get 3" inters (w/2" primaries) around an 4L65e and is much better, now. It always seems to come down to how much money your willing to spend, and what your own skill level is.
#56
Re: header size question 1 5/8 or 1 3/4 pipe diameter
While in some cases an 1 3/4" primary tube would work well on a 350, that isn't the case on this build. Stay with 1 5/8" primary and 2 1/2" secondary.
That is what I used on my solid roller 355, which was in my 67 Chevelle. It's been 91 mph. in the 1/8 th. on motor., with 3.89 gears. I shift at 6700.
That is what I used on my solid roller 355, which was in my 67 Chevelle. It's been 91 mph. in the 1/8 th. on motor., with 3.89 gears. I shift at 6700.
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
^^ this lol. when we ran the numbers and after I talked to a couple of exhaust shops I told them my build and what I was aiming for. both shops told me the same thing going up to 1 3/4 inch headers wouldn't do me any better the 1 5/8 same thing with exhaust size that if I wanted to run duals stick with 2 1/2 inch piping I could go bigger but it would just be spending more money for no reason.
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
I used the wallace header calculator and came up with the following for his cam/displacement/valve size:
Your Primary Tube Length is 38.89
Your Primary Tube Diameter is 1.58 inches
Your Collector Diameter is 2.75 inches Two Collectors
This assumes I used the right cam card. He didn't specify exactly which part number cam he was running so I picked the first one with similar specs.
-- Joe
Your Primary Tube Length is 38.89
Your Primary Tube Diameter is 1.58 inches
Your Collector Diameter is 2.75 inches Two Collectors
This assumes I used the right cam card. He didn't specify exactly which part number cam he was running so I picked the first one with similar specs.
-- Joe
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
I used the wallace header calculator and came up with the following for his cam/displacement/valve size:
Your Primary Tube Length is 38.89
Your Primary Tube Diameter is 1.58 inches
Your Collector Diameter is 2.75 inches Two Collectors
This assumes I used the right cam card. He didn't specify exactly which part number cam he was running so I picked the first one with similar specs.
-- Joe
Your Primary Tube Length is 38.89
Your Primary Tube Diameter is 1.58 inches
Your Collector Diameter is 2.75 inches Two Collectors
This assumes I used the right cam card. He didn't specify exactly which part number cam he was running so I picked the first one with similar specs.
-- Joe
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
The problem with most 1 5/8th headers, (or smaller)they block about 20% of the port
at the head. The flange opening is not large enough for most Hi performance heads.
That is a restriction you don't want if you are trying to make power.
at the head. The flange opening is not large enough for most Hi performance heads.
That is a restriction you don't want if you are trying to make power.
#61
Re: header size question 1 5/8 or 1 3/4 pipe diameter
AFR reccomends a PN. 1405 exhaust gasket for their 195cc heads. That gasket has a 1.5"x1.5" opening. At 16 ga. primary, 1 5/8" tube the inside of the tube will measure 1.5" across.
They, AFR also say their Eliminator exhaust ports are raised .150", which tells me off the shelf headers will more than likely wont fit. Because, like you said the pipe will cover the port.
But, when you look at the largest exhaust valve generally associated with a SBC. It falls in at 1.625 on the face. Now, you can put a 1.74 Pontiac valve in the head but it requires the intake to shrink, to allow clearance.
Back to the subject. A 1.60 exhaust vale requires an 80-85 percent seat diameter for excelent flow. That number is 1.280". Now with a 1.625" valve the seat dia. should be 1.300".
You see, the port is the restriction, not the header tube.
As long as the tube does not cover the port, its size is fine. Even a 1.500" tube would work.
And smaller tubes increase velosity while larger ones decrease it, and affect reversion in the exhaust.
#62
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
Ok, you guys win, I was just using a little common sense.
That seems to be a lost cause in todays world.
BTW AFR 195 ports are larger than 1 1/2"
I wouldn't want mine that way, suit yourself.
I guess you will have to ask them why they recommend a gasket smaller than their ports.
That seems to be a lost cause in todays world.
BTW AFR 195 ports are larger than 1 1/2"
I wouldn't want mine that way, suit yourself.
I guess you will have to ask them why they recommend a gasket smaller than their ports.
Last edited by Dyno Don; 07-15-2015 at 02:09 PM.
#63
Re: header size question 1 5/8 or 1 3/4 pipe diameter
Ok, you guys win, I was just using a little common sense.
That seems to be a lost cause in todays world.
BTW AFR 195 ports are larger than 1 1/2"
I wouldn't want mine that way, suit yourself.
I guess you will have to ask them why they recommend a gasket smaller than their ports.
That seems to be a lost cause in todays world.
BTW AFR 195 ports are larger than 1 1/2"
I wouldn't want mine that way, suit yourself.
I guess you will have to ask them why they recommend a gasket smaller than their ports.
Only thing I wanted to express is that the throat of the bowl before the valve face, is the real restriction. Not the header primary tube. And you cant open up that area over a certain percentage or there wont be any place for the valve to seat.
#65
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
I totally disagree.
AFR reccomends a PN. 1405 exhaust gasket for their 195cc heads. That gasket has a 1.5"x1.5" opening. At 16 ga. primary, 1 5/8" tube the inside of the tube will measure 1.5" across.
They, AFR also say their Eliminator exhaust ports are raised .150", which tells me off the shelf headers will more than likely wont fit. Because, like you said the pipe will cover the port.
AFR reccomends a PN. 1405 exhaust gasket for their 195cc heads. That gasket has a 1.5"x1.5" opening. At 16 ga. primary, 1 5/8" tube the inside of the tube will measure 1.5" across.
They, AFR also say their Eliminator exhaust ports are raised .150", which tells me off the shelf headers will more than likely wont fit. Because, like you said the pipe will cover the port.
The AFR 195 exhaust port is 1.450" H x 1.550" W, and yes they recommend a 1404 which is 1.5 x 1.5.
I do find it kind of funny that guys are buying expensive 1 3/4" headers just to stick them on TPI motors and run 12s.
-- Joe
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
Really?
Does that look like 12's to you?
Best of 11.57 and 115.73 mph(1811DA).
Motor: Dart SHP block 368ci, AFR Comp 195cc heads, 11.1:1 comp,
highly modified TPI 1st style SLP runners, moded GM plenum
and First Injection TPI intake manifold, Mike Jones cam,
Yank PT4000 converter, Dyno Don 1 3/4" shorty headers,
Dyno Don custom exhaust, custom cold air intake,
Kevin91Z Tune. 4L60E installed. Now 420RWHP, 417RWTQ with new motor.
Does that look like 12's to you?
Best of 11.57 and 115.73 mph(1811DA).
Motor: Dart SHP block 368ci, AFR Comp 195cc heads, 11.1:1 comp,
highly modified TPI 1st style SLP runners, moded GM plenum
and First Injection TPI intake manifold, Mike Jones cam,
Yank PT4000 converter, Dyno Don 1 3/4" shorty headers,
Dyno Don custom exhaust, custom cold air intake,
Kevin91Z Tune. 4L60E installed. Now 420RWHP, 417RWTQ with new motor.
#67
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Car: '88 Formula, '94 Corvette, '95 Bird
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Re: header size question 1 5/8 or 1 3/4 pipe diameter
Really?
Does that look like 12's to you?
Best of 11.57 and 115.73 mph(1811DA).
Motor: Dart SHP block 368ci, AFR Comp 195cc heads, 11.1:1 comp,
highly modified TPI 1st style SLP runners, moded GM plenum
and First Injection TPI intake manifold, Mike Jones cam,
Yank PT4000 converter, Dyno Don 1 3/4" shorty headers,
Dyno Don custom exhaust, custom cold air intake,
Kevin91Z Tune. 4L60E installed. Now 420RWHP, 417RWTQ with new motor.
Does that look like 12's to you?
Best of 11.57 and 115.73 mph(1811DA).
Motor: Dart SHP block 368ci, AFR Comp 195cc heads, 11.1:1 comp,
highly modified TPI 1st style SLP runners, moded GM plenum
and First Injection TPI intake manifold, Mike Jones cam,
Yank PT4000 converter, Dyno Don 1 3/4" shorty headers,
Dyno Don custom exhaust, custom cold air intake,
Kevin91Z Tune. 4L60E installed. Now 420RWHP, 417RWTQ with new motor.
Send him this way and we will fix it.
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