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| XR 1992 |
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i gots a a stage 5 JMM cam and a similar motor to the JMM dev 5 package except i only have a mild port. just wondering if the loss in tourque from porting is worth the outright power. Anything in particular i should look out for or have done and who have some people used in sydney area!
_________________ XR 1992 161 RWKW 14 sec 1/4s |
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| cjh |
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Porting is done to give air speed to increase torque. Also with that, if the cam has a decent duration, then you will need a rise in compression to compensate.
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| stockstandard |
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cjh wrote: Porting is done to give air speed to increase torque. Also with that, if the cam has a decent duration, then you will need a rise in compression to compensate.
I think he is referring to enlarging the ports to increase flow/hp which usually decreases airspeed/torque.
_________________ Stoke me a clipper, I'll be back for Christmas |
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| cjh |
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stockstandard wrote: cjh wrote: Porting is done to give air speed to increase torque. Also with that, if the cam has a decent duration, then you will need a rise in compression to compensate. I think he is referring to enlarging the ports to increase flow/hp which usually decreases airspeed/torque. That comes back to where you take it off, and how much.
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| fastleno |
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i remember a favorite FM quote, "pissing in the dark" LOL
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| cjh |
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fastleno wrote: i remember a favorite FM quote, "pissing in the dark" LOL
Yeah, yeah, but If you have half a clue, then its got to be better, eh? I have only ever 1 set of heads flowed,( as in checked on a flow bench, after I did them ) I ported & polished them. They were Red 308 pre-pollution heads with L34 valves. The guy I did them for paid for them to be tested on a flow bench. He came back and told me that they flowed 480 HP ( he didn't tell me at what lift). This was before it became popular to fit VN 5.0L heads, and before you could get a carby manifold to suit VN heads. Anyway, turns out that that p!ss in the dark turned out well. Oh yeah, the engine was a Red 308 with a stroker crank, which took it to 367 cubes, had a turbo 400 auto, 3.36 Sals LSD, running 275/60R15 Yoky's 352's and was punching out 320 HP at the wheels using 95 RON fuel, and would get over 500k's on a tank ( 75 HJ Holden ute ) with half a ton of plumbing gear in the back around town. He was very happy with it. Its been over 10yrs since I did that. The last time I it was about 2yrs ago, has same engine in it, but now has a 9" diff.
_________________ http://youtu.be/jJTh9F3Vgg0 Last edited by cjh on Thu Sep 06, 2007 11:52 pm, edited 1 time in total. |
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| fastleno |
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i guess thats why its called pissing in the dark, there are times when the piss makes it in the bowl first up other times it takes adjustment to miss the seat
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| Slick |
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XR 1992 wrote: i gots a a stage 5 JMM cam and a similar motor to the JMM dev 5 package except i only have a mild port. just wondering if the loss in tourque from porting is worth the outright power. Anything in particular i should look out for or have done and who have some people used in sydney area! stick with the mild port. no point go pissing in dark unless theres room to adjust & funds to play with. 
In my opinion, torque is more important then absolute power. that is, if you're going out to break the land speed record. what I mean is, a well balanced all rounder is what you should aim for! 
_________________ Mind f**k!!! it works on feeble minded ignorant sheeples... there's plenty of em on this site... some are very intelligent but by god they are so thick!!! Pakrat wrote: You can buy them seppertly
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| cjh |
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Here's some in the dark porting.
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| Johnson stroker |
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Who cares, your off topic anyway.. try and help the guy not show us your handy work with a dremel.
XR 1992, get intouch with Joe from Crescent Motorsports at liverpool, or Jaysen from Jays RPD, these guys have done alot of porting stuff and would be able to give you pretty direct answers as to what port sizes would suit your application. if you need some contact numbers, Joe is a sponsor here you can get his info from the various banner adds round the place, Or PM me, I can put you in touch with Jays RPD. Cheers mate, hope that was a little more helpful. Also where are you based? what part of Sydney? Might also influence where you go as well.
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| tickford_6 |
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Posts: 6449 Joined: 11th Nov 2004 |
this surly is some pissing in the dark. the swirl ridge is still there you polished the the intake ports and seem to have left out the pics of the most important part of the ports. No pics of bowl at all??
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| turbotrana |
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most of the gains are in deshrouding the chamber ,bowel and short side radius work. There are a few pictures of JMM chamber work on this forum which shows what is needed to be done for chamber. Also there is an Autospeed article on AU head porting which is of help.
It takes a while work out what is really needed. Try reading some books like "How to build, Modify and power tune Cylinder Heads" by Peter Burgess and David Gollan/ How to build and modify Chevrolet small block V-8 cylinder heads. There are a few others and quite a few articles on the net. You DONT need a flow bench to port (although it helps) and there are alot of porters who dont fully rely on flow bench figures for their porting. Airspeed is a big factor. Pictures of professionally ported heads are a big help. For starters smoothing the bowel transitions is a good place to start.
_________________ Turbo 6s rule |
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| XR 1992 |
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Thanks for your replies (the ones that helped) all i was trying to establish was that if there was a loss in tourque due to the bigger port, and if there was is it worth the gain in outright power as tourque is what makes it fun. Ill get on 2 crescent i think thanks
_________________ XR 1992 161 RWKW 14 sec 1/4s |
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| efmarek |
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whats with the mirror finish??? Your living in the 70's man! Your not meant to Polish......u lose power.
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| cjh |
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efmarek wrote: whats with the mirror finish??? Your living in the 70's man! Your not meant to Polish......u lose power.
Yeah, and I was there, and you weren't even an itch in your dadys pants. The mirror finish is to help eleviate the carbon build up, which can cause pre-ignition in hi-comp ratio engines. Here's one for you, your 21, yes???, take a step back and have a look at all of whats going on in the performance stakes/gains.
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