350z_SA

Sorry have looked around for this topic but i'm lost.. can anyone point me in the right direction, or if not will i gain hp on gas flowing ?? Thanks.

overZealous1

iTrader: (27)

you won't make much power at all if the "gas is NOT flowing"

350z_SA

they will be going on a flow bench and a reputable tuning shop will be doing the mod, so what are you saying ? does the VQ de motor gain much on this mod or not ? answers in english would be appreciated..

__jb

iTrader: (3)

Not sure I actually understand your question.

Are you asking if porting your heads based on flow bench data will be a good mod?

If that's what you're asking, I would ask the tuning shop that's doing the work for you. If they don't know, I might look somewhere else.

Changing the air/fuel flow through cylinder heads is a tremendous overtaking. I wouldn't call it a mod. It will change the design/build characteristics of your entire engine.

I'm not sure what your horsepower goals are, but I suspect your goals might be reached by spending your money on something other than flow bench time and cylinder head porting. If, on the other hand, you are building an unlimited budget race car, go for it.

350z_SA

Thanks , i am planning on doing bolt on eg 5/16 MD spacer, full exhaust, spec 3+ clutch and flywheel and just thought porting the heads would see gains ??? the cost of this would be approx R4000 ($533) a fairly inexpensive mod..

Z1 Performance

iTrader: (564)

$530 aint going to get you any meaningful port work, that's for sure. - perhaps they will clean the heads up a bit and port match things, but that's the bare minimum, and not where the big gains are had. Not to mentuon, taking the heads off to do the port work, disassembling them, reassembling them, and reinstalling them in the car is ALOT more than $533 worth of labor in and of itself

350z_SA

thats the price of loose heads for porting only.. a shop in my area will strip etc.. I stay in durban and the head shop is in Jhb about 600k's away.. Thanks for the feedback Z1

Q45tech

Tuliping the intake valves often generates more volume [flow] than the best head work................assumming near stock rpm range. Since the CNC machines at factory are spot on but they must consider MPG cruise efficiency [BSFC].

OCG35

iTrader: (2)

is this the same as 5 angle or radius valve job?... also, your mention of factor MPG at cruise - does this mean a valve job would drastically negatively effect mpg?

OCG35

iTrader: (2)

Q45tech... you often provide info in existing threads - but rarely (in fact I dont remember ever) respond to questions about your post

go-fast

stock heads flow excellent,4 valve heads have totally different porting requirements from conventional 2 valve heads,be carefull who you hand them to.5 angle and radiused valves usually leave a smaller seat area and are reserved for race apps due to shorter service life....be carefull what you ask for.imho if you are n/a you are wasting time and money.what are your hp goals?

Z1 Performance

iTrader: (564)

no, they are not the same thing. Valves can be cut in several different methods. This is something only an experienced engine builder can do..it's not a DIY

Z1 Performance

iTrader: (564)

Stock heads flow excellent for what they are - stock heads. They leave alot on the table though that can only be extracted via an experienced machinist. Especially around the valve area. Any engine work not done by someone who knows their sauce is a waste of money. Any engine work done by someone with the experience and equipment to make it a success becomes the difference between mediocre and exceptional

Z1 Performance

iTrader: (564)

Also it's important to point out that different machinists have their own methods and preferences. This is why they are the most important ingredient of the build process. As far as whatQ45 tech said, I've got no idea what technique this is, as any time I've heard tuliping of a valve described, it was not a good thing as it can prevent proper seating. It is essentially making the top of the valve concave. Volume is not the only thing to be concerned about - as important as volume is velocity. Good porting, a better valvejob, and variouos other tricks that an experienced machinist can employ, improves both

go-fast

+1,you don't want someone "learning vq heads" on your build.there are comonalities to all heads but learning the nuance of the vq is critical.if he just hogs em' or uses traditional techniques you will most likely lose power.especially for n/a these heads want a "soft touch",that's why i asked your desired hp level.

OCG35

iTrader: (2)

lol! I'm very aware it’s not a DIY... I've talked with very experienced machinists locally and was considering valve job when I do cams & springs (figured a might be a ood time to do valve job too)... I fully understand 5 angle and radius and the benefits - I'm not all together familiar with tulip... clearly it’s a type of cut/grind, but I don’t know the benefits over 5 angle...

My primary concern is Q45techs mention of mpg degrades... I'm already at 15 mpg avg - but I don’t drive the car much so its not an issue... but I can get almost back to stock for resell and gain a good amount of mpg back... however I wont swap valves when it comes time to sell... so I'm curious about the negative mpg from valve job and more details on "tulip".

Thanks to those of you that have responded.

Z1 Performance

iTrader: (564)

15 mpg avg I'd recommend having the car checked, dyno'd, etc. That is much lower than a stock car gets and much lower than what one should reasonable expect unless they are beating the snot out of the car at every moment. I avg the same exact mileage post build as I did pre build - 320 miles per tank, which works out to me 20 mpg (car always takes right at 16 gallons when I refill, which is just when the light goes on, at least on my car)

OCG35

iTrader: (2)

It’s due to almost all spirited street driving... AT... 3.7 vs 3.3 FD... and almost always in aggressive performance map of Osiris.

I am going on a road trip this weekend.. I plan to go up in econo mode and back in performance and determine a good highway mpg in each map.

BTW, with much fewer mods than I have now (more than I mentioned in this post), I only got 18.5ish regularly - 80% fwy driving. This car has always got sh!tty mpg.

BTW its' been dyno'd once or twice (actual about 3 dozen times)