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more gt40p info 

 

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 Post subject: more gt40p info
Posted: Sat Jun 30, 2007 1:15 pm 
Getting Side Ways
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as some may be aware i have recently purchased a set of these heads for my eb and on a quick visual inspection, there doesn't seem to be a whole lot of difference. i haven't got my e7's off yet but previous owner said they had been ported and having removed the lower intake manifold it does look to be the case. a quick rough measure of the size of the port openings shows them to be the same if not a touch bigger than the gt40p's. i was of the impression that even ported e7's were not as good as gt40p's. is this true. also the size of the vavle heads on the gtp's don't seem too much different to the specs i have for the e7's. once i get mine off i'll be able to compare directly. where is the benefit of the gtp's? is it to do more with the shape of the ports? i'm getting the feeling that i won't notice a whole lot of difference after bolting on these. is there any d.i.y. port work i can do on them. i don't really have the funds to do any more to the heads although that would be the smart thing to do while they're off. i guess they won't be any worse and have much more room for improvement down the track although hopefully i don't have to pull them off again in a hurry as its proving to be not quite as straight forward as i imagined.

has anyone got the specs for each for a side by side comparison? not sure what year the gt40p's are but they are not off an xr if that makes any difference.

 

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Posted: Sat Jun 30, 2007 1:29 pm 
Getting Side Ways
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search the forums i think someone put a porting post up all you need is a dremale and a steady hand.

 

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Posted: Sat Jun 30, 2007 3:09 pm 
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The intake port (GT40P) is marginally bigger than in volume than the E7s...I can't remember the quoted figures but I think its 145cc vs 140cc.

However the real difference in flow comes from better shaped ports in the P's. I think the exh valve is even smaller on the GT40P's but they still move more air.

If they are very well ported E7's, then the std GT40P's may not be significantly better.
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Posted: Sat Jun 30, 2007 3:13 pm 
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prydy, youll see a difference when vavles removed. I had my gt40ps improved by Mclarens (just off port road) had bigger exhaust valves fitted, valve chambers back cut with CNC machine, short term radius' taken out as much as you can, a clean up of casting imperfections and heads shaved 10 thou to square them up and raise the compression slightly.
With this work done i got a 25rwkw improvement up from 196rwkw with stock gt40p heads. work done to heads cost me $1500. People will prob say should have got alloys instead. I had these heads allready , and if i do or did purchase alloys i would spend the same sort of money on them before they go on anyway.

 

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Posted: Sun Jul 01, 2007 3:41 am 
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Froudey wrote:
search the forums i think someone put a porting post up all you need is a dremale and a steady hand.
search about 6 months back there was afew threads on the heads,flow charts and stuff,also intake charts--mouses diy porting is good,also links to others.

 

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Posted: Sun Jul 01, 2007 11:34 am 
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Head porting has become a science in it's own since Engine Masters started their competitions.

Old theory was to make the ports and valves as big as you could.

These days flow is gained throughout the rev range by making the ports the same cross sectional area from manifold to valve. You see ports advertised as runner volume which relates to rev range. That's why putting tongues in clevelands actually improves the flow, especially bottom end. Think of it this way, any restriction creates backpressure and any opening of the runner creates it's own turbulence and backpressure.

Polishing runners is counter productive as it makes the slug of air stick to the walls of the runners creating a drag on the inlet/exhaust slug. Want to polish something then polish the chamber to reduce hot spots and chance of detonation.

Bigger valves do not always work as the bigger you go the more shrouding (blocking) of the valve area is created, both by the head/cylinder walls and the piston.

That's why smaller inlet opening at manifold and/or smaller valves could actually increase flow.

Hope this helps.

Grumbles

 

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Posted: Sun Jul 01, 2007 3:33 pm 
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cheers guys. because i got the heads from a wrecker with no km history attached i'm going to spend a bit more (hopefully not much) and run them down to a head place so they can give them a look over. everything looks pretty good to me except one of the inlet ports was obviously open to the weather (engine had no intake manifold on it but was under a tarp) as it is all rusty looking in the port.

with regard to porting the intake side is pretty much the same as the gasket and matches pretty well with the already ported intake manifold. looks like the old heads and intake were ported to match the gaskets and the gt40p's are already that size so the intake is of little concern. the area that is of concern is the exhaust ports. the old heads were squared up to match the extractors whereas the gt40p's are still a rounder opening. should i get the heads matched to the extractors or the does the fact that the head ports are smaller than the extractor openings mean that no flow is lost or interupted?

bear in mind that i'm not looking to do any more modifications except for the explorer type intake manifold or similar so the heads left in their stock form may be ok.

i am running a cam and with the old ported e7's made 158rwkw. i was hoping to nudge the 170 region with the p's but after seeing the similarity in port and valve size between e7's and p's i'm not so sure.

 

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Posted: Sun Jul 01, 2007 6:41 pm 
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be careful porting the thermactor hump in the exhaust port as theres a waterjacket hiding in there ...if you go into www.stangpro.com theres a heaps of info on gt40p,s also DIY porting
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