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Head to exhaust match 

 

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 Post subject: Head to exhaust match
Posted: Sat Jul 02, 2005 7:44 pm 
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I've been thinking recently about my Pacemaker headers which have a primary size of 1 5/8" ( 44mm ) and what the exhaust port size of the GT40P is and whether they will match properly. Does anyone know? Will the exhaust port be smaller than the header primary?

 

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Posted: Sat Jul 02, 2005 8:32 pm 
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The exhaust ports will be a fair bit smaller, and thats the way it is suppose to be, you dont match the port sizes on the exhaust.
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Posted: Sat Jul 02, 2005 9:18 pm 
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But doesn't going from a smaller exhaust port into a larger diammeter primary give some torque loss? That the suddenly larger opening robs the engine of torque?

 

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Posted: Sat Jul 02, 2005 9:59 pm 
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Yes going too large will reduce torque but the design of the tri-y pacemakers maintains the low down torque while giving plenty of flow.
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Posted: Sat Jul 02, 2005 10:17 pm 
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The reason I ask is that when I had Mick Webb look at my car briefly previously, we got to talking about exhausts and GT40P heads and he was saying that the primaries of my headers are too large for the heads and that it robs it of torque. The thing is I cannot remember if he was talking about my E7's or the GT40P's which was the main discussion, hence my curiosity. I was trying to learn just what exhaust port size would be too small for the Pacemaker headers I have and how to know when it is okay or a problem or even if porting would help out.
Feel free to educate me.

 

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Posted: Sat Jul 02, 2005 10:56 pm 
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What headers are you running Vic?
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Posted: Sat Jul 02, 2005 11:08 pm 
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PH 4000.

 

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Posted: Sun Jul 03, 2005 6:22 am 
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The PH4000's are an excellent match IMO, they don't seem to loose low down torque at all. The pacemaker tri-y design probably helps the greatest here, maintaining enough backpressure to keep the low down torque but also flow enough to produce good peak power.

I will get the actual measurements of the GT40P vs Pacemaker PH4000's tomorrow as my heads are off at the moment. There is still plenty of room in the GT40P's for porting while still keeping enough exhaust port to header difference to aid in the scavenging process but IMO the PH4000 headers aren't too big and porting or smaller primaries are not needed.
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Posted: Sun Jul 03, 2005 1:27 pm 
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Appreciated.
I was certainly wondering how precise Mick Webb prefers to match headers to heads and if he was referring to my E7's or the GT40P's. I'd always assumed that GT40P's might be harder to port for matching to headers because maybe there wouldn't be enough meat on the bone so to speak to safely shave off - if I was to worry about it.

 

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Posted: Sun Jul 03, 2005 9:49 pm 
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there is more to it then just the size of the port and size of the header.

things like the length of the primary and secondary pipe.

the shape of the pipe as it come off the head.

and the miss match of port to header is also a very critical part of the deal.

the wrong miss match can be the down fall of even an otherwise perfect header

 

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Posted: Mon Jul 11, 2005 2:11 am 
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EDXR8, did you have a chance to measure the exhaust ports on your GT40P's?

 

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Posted: Mon Jul 11, 2005 2:47 am 
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Nope I forgot, I am working on them tomorrow so will do it then and post the measurements.
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Posted: Wed Jul 13, 2005 12:46 am 
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My GT40P's and Paceys matched up perfectly.
Across the port was a good match. I was checking it out with calipers a while back.
The stock E7 heads would do better with 1 1/2" primaries I think.

 

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