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increasing compression 

 

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 Post subject: increasing compression
Posted: Sun May 28, 2006 8:30 pm 
Tyre Shredder
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has anyone planed there gt40p heads to increase compression ratio ive read in usa mags if you take 30 thou off ups C R from 9.0:1 to9.5:1 approx thinkin bout takeing mine off and ccing etc they reckon any more than 30 thou and you runinto probs with intake manifold ports not lining up and have to skim manifold etc .Anybody had any experience with this cheers
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 Post subject: Re: increasing compression
Posted: Sun May 28, 2006 8:54 pm 
Getting Side Ways
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fairy v8 wrote:
has anyone planed there gt40p heads to increase compression ratio ive read in usa mags if you take 30 thou off ups C R from 9.0:1 to9.5:1 approx thinkin bout takeing mine off and ccing etc they reckon any more than 30 thou and you runinto probs with intake manifold ports not lining up and have to skim manifold etc .Anybody had any experience with this cheers.

You have to consider what octane you want to run, 9.0 is almost 96 oct.-9.5 will be 96-98 oct..

When you cc the heads you have to work on the largest of both heads and bring the rest to it, shaving the heads changes the width across the heads [narrower] so a stock intake wont fit in to the gap with gaskets, you have to machine the intake on both sides evenly may be only a few thou to fit.

I done it to a vn v6 but 3mm off each bank, raised compression to 10.6 to 1, then matched ports, they will change slightly, also the heads and manifold are now a set, if you replace any parts it has to be all 3 together. good power, cheers. :roll: :roll:

 

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Posted: Sun May 28, 2006 10:01 pm 
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hey good points Hans,yer i didnt think would be a prob i think ts 50s are 9.6 and i read somewhere that the 5.4 290kw is 10.5 sounds pretty high? did the one you did go much better? :D
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Posted: Sun May 28, 2006 10:53 pm 
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fairy v8 wrote:
hey good points Hans,yer i didnt think would be a prob i think ts 50s are 9.6 and i read somewhere that the 5.4 290kw is 10.5 sounds pretty high? did the one you did go much better? :D
just got back,yes,i went from 124kw to 175-190kw,with cam change and chip,revs 5200rpm-auto and fast launch, fast 0-139ks but i beefed it up for hills,around here its all hills on the coast.on the flat it drives well,its on lpg\petrol,i didnt want to over power the body,brakes vt ss twin piston fronts-stock 270mm disks,vt 310mm disks,stop real well.

 

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Posted: Mon May 29, 2006 10:06 am 
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sounds good just not to sure how far you cango cam im thinkin of .544 lift which is quite high, dont want valves hittin pistons etc and i dont want to pull pistons out i thought someone might have done similar with gt40ps
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Posted: Thu Jun 01, 2006 11:53 pm 
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fairy v8 wrote:
sounds good just not to sure how far you cango cam im thinkin of .544 lift which is quite high, dont want valves hittin pistons etc and i dont want to pull pistons out i thought someone might have done similar with gt40ps
i dont know if pistons are flush with deck or below, have to ask a engine builder -if so you may have some clearance if not may be close,crow cams have computer build check,for free.i faxed my specs on motor with a cam spec. and what i wanted from motor -rev.range and and torque range,if lift issue, they should advise what type pistons,flat,crown,machined relief valve,etc

 

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Posted: Fri Jun 02, 2006 9:00 am 
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sounds like a good idea cheers hans ill get on to it
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Posted: Sat Jun 03, 2006 9:54 am 
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Felpro do a set of super thin head gaskets for the 5L. .039"

I used them and had my heads overhauled and I'm up round the 9.5:1 from 9.0:1
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Posted: Sat Jun 03, 2006 10:34 am 
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Be real careful upping compression ratios by shaving heads on v8s. As mentioned valley covers can be real problem. Also conrod bearings can suffer premature wear and the rev range of the engine can be reduced. Detonation can also become a huge problem. CCing works but only if you are real serious about chasing quarter mile times other wise not really worth the extra expense. As for the cam, anyhting up to 560 thou should be alright. Am unaware as to the design of the pistons' if they have cutouts etc (have a feeling they do). It would be more the duration that will cause valves to hit pistons. And yes I am an engine reconditioner.
Bundy up! 8-) :twisted:

 

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Posted: Sat Jun 03, 2006 1:52 pm 
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yer u read these articles but dont know if the same pistons etc ,does that thin gasket seal as well as a thicker one sylox,cause thats about the figure i was wanting 9.5 ,i was gonna cc the heads mainly to confirm C R and tidy up while porting the rest in 1 article i read they reckon you can take off up to 24 thou b 4 u have probs with the manifold ports not lining up/sealing etc .Be good to get organised b 4 i do it because of the time off the road cheers guys :D
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Posted: Sat Jun 17, 2006 8:52 am 
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Yep seals up fine no seapage that i have spotted anyways. And the ute now since tune is going very very well. TFS1 gets the thumbs up.
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 Post subject: Re: increasing compression
Posted: Sat Jun 17, 2006 10:05 am 
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hans hartman wrote:
shaving the heads changes the width across the heads [narrower] so a stock intake wont fit in to the gap with gaskets, you have to machine the intake on both sides evenly may be only a few thou to fit.

shaving the heads lowers the height of the intake ports in relation to the head gasket surface, and as such, will require port matching of both the intake manifold and the heads, but it wont bring the heads any closer together....

shaving the block *will* bring the heads closer together making extra machining of the intake manifold lower half necesary

 

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Posted: Sat Jun 17, 2006 7:12 pm 
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yer thats true what you say interceptor but it does bring the bottom of the inlrt manifold closer to the block which shouldnt be to hard to fix hey sylox what is the thickness of the standard head gasket compared to your thin one
cheers guys :D
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Posted: Sat Jun 17, 2006 8:45 pm 
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Standard head gaskets have a compressed thickness of 0.040". Most aftermarket gaskets are in the range of 0.039 to 0.044"

SCE and Cometic do some really thin gaskets, but it sounds like most of those require loc-wire to seal properly.

The other important thing to look at, with respect to affect on compression ratio, is the bore size of the gasket. Most aftermarket head gaskets have a bore size between 4.060" and 4.100". The standard head gasket I pulled off my AU has a bore size of 4.080".
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Posted: Sun Jun 18, 2006 7:35 pm 
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ok thats interesting that would counter the affect of the thinner gasket the larger bore size ill check into that thanks xr8 ute :D
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