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Ando81

Performance mods tips

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All the cams I have are stamped or engraved on the rear of the cam not the front face.But you could work it out with a degree wheel,dial gauge and some time.Or you could ring a Cam company like Camtech,Clive,Crow or who ever and ask them for a suggestion.Only once you have a feel of what certain cam specs do to a engine and how they perform/work in the real world do you get to decide what spec's you get.Remember they do it for a living so advice from a cam grinder is the best bet.

 

Just tell them all your engine specs so far and what you want form the car and they will do the rest.

 

My roller cam was designed with help from a US based Outlaw engine builder on a cam design program which took alot of work and within 2mins of talking to Clive at Clive cams he had a set of figures that was only a few th off what took us weeks to work out.Yes they know there stuff...but we did use the basic custom profile for my xflow with Clives touch.

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1. piss performance EFI cam off, if it doesn't  sound gassy and doesn't have a deep resonance...its too small!

 

2. Forget about porting it, Only makes a real difference in an engine with poor port design. Crossflow is quite efficient and big.

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there's a big difference between a major and minor port job. i'm literally talking about a port tidy up

smooth the airflow coming in, raise the air speed velocity and reducing turbulence apon entry to the cyl aiding swirl in the combustion chamber and atomisation while in the intake port, on the exhaust side the smoother the better, talking anyone out of that imo is not good advice.

 

of course if the OP only wants to turn it to 4000rpm, then i wouldn't see the benefit in doing it, but i'd do it anyway because i just about gaurentee a further upgrade would be had if performance was in mind and also for peace of mind, you know exactly whats in that head not what you have been told then, i don't believe on skimping minor details when it comes to performance, do it once do it right.

 

everyone has their own opinion but physics do come into it.

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General port work like mentioned above can make good gains, BUT if you bolt a stock intake and exhaust manifold to it you will not see the full gains. Port wall texture helps atomization, valve seat form is the biggest influence on low lift performance, you can only increase port velocity by decreasing the size of the port, to make a port work at it's best the minimum cross sectional area of the port has to match the cam and intended rpm range, the mcsa has to be far enough away from the short turn to allow sufficient time to slow the airspeed down at the short turn to allow it to turn the corner and not just tumble off the edge and crash into the opposite port wall, nearly every port has high and low airspeed sections, you want to fill in areas of low speed and remove material in high speeds, this is just a generalization as it is more technical than that, you have to work with we're the air naturally wants to flow in a port, to increase swirl normally means biassing a port to one side and create what is like a drain plug effect around the valve, after all this the most important thing is to match the cam to the flow figures of the head, there is no point in having 600 thou of lift if the port chokes at 500thou, there is no point in having a head that outflows the intake manifold also, so all these things need to be matched to get the most effective and efficient combination.

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agreed. i was reccomending the portwork on the basis of a cam being fitted, the port walls on the intake side i get done at 300# exhaust is as smooth as i can have it done, and as i said we are talking about tidying up the ports not massive amounts of port work just taking out casting marks and blending the bowl area if you can remove turbulence from the airflow you will see a substantial gain in both torque and hp.

 

as for velocity that can be increased by port work, by measuring the cc of the port compared to the cfm both before and after portwork, though this discussion is probably more suited to a tech thread, rather than this one, sorry for the hijack dude.

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The crossflow head has got a pretty uniform cross section and makes a pretty direct shot at the cylinder. All valid points but a crossflow wasn't built to rev over 5,000rpm.

I'm not here to start an argument but lets face it guys, the alloy crossflow head is alot more performance orientated then the rest of the motor will ever be. 

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I reckon someone should do up a detailed thread on porting a xflow head, would be interesting to see typical areas on the ports that need some work due to poor factory casting etc..

and clearly the idea of port work is too have the most flow and most direct shot to the cylinders so what is the most you can go? do they use an xray machine or something to check wall thickness?

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Well it has been done before and the arguments of what to and how to will live forever.Cam choice based on head flow is the general consensus of how to do it but often flow figures and cam choice don't match and the car performs better than it should? Even shown in the latest Street Machine when Bill Porker changed valve shape for a better flowing design and lost HP.Went back to the original design that flowed less and should not have worked and the car picked up HP again. 

 

Just shows there's more than 1 way to skin a cat really...

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Thanks for all of the shared knowledge fellas, I think we can all learn something from everyone's different opinions. Don't be sorry for getting into technical info or going off the thread topic,

I'm only too happy to learn and hopefully someone else can get some good tips from the discussion also:)

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Mcfly I will be doing exactly that in a couple of weeks when my flow bench is completed, also I will test and document every crossflow head in standard form giving valve sizes, chamber sizes and flow figures, the port castings are slightly different in the different heads so I'm interested which ones perform the best then I can get into mods I do and show the gains.

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Hey Sly I read that article also, I think the answer would be confirmed on a wet bench to see how fuel shear at the valve goes, it may be a case of too much flow or slower velocity past the valve or the larger port volume from the different shaped valve didn't match the combination, very interesting I find and your right sometimes a combination is so wrong it's right lol

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Someone on the old site reckons bolting a 4v intake to a 2v head gives bullshit torque, and makes no sense at all but Kostecki Engine Centre did it and got some rather unexpected results.

 

Maybe it's not bullshit torque, but bullshit talk. I dunno, plenty of myths out there but you can't go wrong with a cleanup of the plunge cut in the bowl and smooth the valve guide and match-port to the manifold.

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port and polish does jack all in the overall scheme of things..... Not even going to bother on my 408w because i know its gonna have more then me or the driveline can handle.

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Someone on the old site reckons bolting a 4v intake to a 2v head gives bullshit torque, and makes no sense at all but Kostecki Engine Centre did it and got some rather unexpected results.

 

Maybe it's not bullshit torque, but bullshit talk. I dunno, plenty of myths out there but you can't go wrong with a cleanup of the plunge cut in the bowl and smooth the valve guide and match-port to the manifold.

 

My guide bosses were removed and just the guide/valve sticks out.It has had a bowl job and shaped entry and valve job but exhaust is nothing with small exhaust valve size.Most of the work is on top of the head and the chambers not in the ports as such.

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