Personally I think your ports are too big for the stock valve size. The port velocity will drop and take the efficency with it....

the optimum port diameter for stock valve size is... drumroll please... 27mm, or a standard port

 

just the shitty standard short radius restricts flow, so even a stock bigport is better than a stock standard head. i don't think a tosco port with stock valves would do that much harm, just be a restriction, and you might get intake reversion if you had a crap exhaust. or does xany mean he used the valves that were already in the head, and they are already oversize?

K guy some questions i wanna find out

 

(q1)does anyone know if i do or don't need to get my rolla engineered for a 5k

or what i need to get it past?

 

(q2)what sort of work should i do to the 5k ( the main use for my roll is burnout comps)what going to give me the best result ?

 

(q3)will i need to upgrade the brakes to get it pastfor rejo?

 

another thing yas have confused me on the flywheel issue will the 4k

flywheel bolt up to the 5k and not through anything else out ?

 

I'm all confused i was talking to an engineer today and i didnt understand a word he said

 

just give me the tools and parts and i can do it

;)

the 4k flywheel WILL fit on the 5K engine.....

 

hope you're not confused now.

^^^^^^^^^^^ thanks nick.......least now i know my car has at least some class....hehehehehe.....

Nah you gotta go 3K...that way you can see the stunned faces on people when you tell them its "only 1200cc"

OK Quoting from Bill Sherwoods page *bows down*

 

"Quite often you can make some improvements by making the area just above the valve (including the exhaust) 90% the size of the valve head, ie, if the valve is 30mm diameter, then about 3mm above the valve seat should be 27mm in size. This is the optimum for the venturi effect the inlet port needs."

 

so yes...having oversized ports IS detrimental. But I havent seen Xanys head with the valves out so I can't really say for sure with his head...

 

What I am 99% sure about is that his port velocity will be down. This IS bad. High velocity creates turbulance, which influences the air flow. Think about it. If the airs all rushing in it will have momentum as opposed to just lingering on in and the engine having to suck it in. When the piston gets to BDC and begins the compression stroke (providing the cam timing is right) the air will still have some momentum (provided the intake runner is a nice length and nice and straight too) and try to push its way into the cylinder. Not a huge power gain but a gain none the less.

 

Thoughts? Comments? (be gentle ;))

irokin = Superjamie Mk 2

 

;) :D

that comment from bill's page is a bit of a general rule on venturi porting, which is different to actual port size, its a whole different area of the head. port size is based on more than just the size of the inlet valves. you have to take into account valve shrouding and volumetric efficiency. read a few david vizard books (email me if you want some good titles to look for) and get back to us

 

yes, the ports on xany's bigport head are a bit too big for the stock valves, so are mine, and really a stock bigport is too big for the stock valves. but if that is indeed a tosco spec head, then f@$k it's going to be heaps better than a stock head, or even a stock bigport. there's more than just port size to consider when comparing head potential. i would say the bowl area and combustion chamber are more important than anything else. which is why doug's motor is better than mine

almost all head porting is basically theory. you can have an "educated guess" at how it all goes, but unless you have done the research (ie: multiple port jobs and a flowbench) then there's nothing 100%

 

different head designs require slightly different porting, what works well for a crossflow 16v might not be the best for a non-crossflow 8v. you also port different heads for different applications. a venturi port is going to be great for street response and keeping the air velocity up during all sorts of throttle and rpm conditions. if you're building an all out race or drag motor that gets held tapped all the time it's running, then i would think a venturi port would be a restriction. if i was going to get another head done up, i'd get a bigvalve race port, it would run "well enough" down low, and crack up high

 

that's the best thing about internal combustion engines, you can throw all sorts of shithouse conditions at them - oversized or restrictive ports, undersized valves, crappy air-fuel ratio, totally off ignition timing - and they will still RUN! not to their full potential, and sometimes not very well, but they will still move your car with decent speed

grim sorry dude v8 ? all noise like ya said 5k has class y not use it

thax for the help Xany

lol thanks for the emails ;)

If you are in Queensland, you will need an LA1 blue plate. What sort of KE is it going into? (Sorry, too lazy to trawl back 3 pages...) Shouldn't think you'd need a brake upgrade.If you want to do one, though, talk to me in about 3 months, and I'll tell you what I've done to the TE55. ;)

Edited July 29, 200422 yr by Redwarf

where'd you get the blueplate info?? i need some

I know a couple of people who do them. What do you require?