A head that is not streetable.

[babyviper]

I always wondered what shops meant by stating a head was not streetable. For example slowboy's stage 6 head and jacksonautomachine.com stage 4 CNC head. Just to give you an example to what I call streetable, I drive a 98 talon with a journal bearing sc61, no cat, kaaz lsd that locks up all the dam time, 1g throttle body with the bottom half blocked off and no A/C. If the problem is that I don't have any low end, then that's not a problem I don't mid waiting for the power to kick in.
Slowboy Racing, Inc. :: Mitsubishi :: DSM :: Engine :: Heads :: 1G :: SBR Stage VI 4G63 2.0L 6-bolt Head
Stage 4 CNC Race Ported Pkg,+1000whp

 

[DSM_PWR]

Its definetly not because of the 1mm over valves...

IMO, i believe its mainly the fact that the ports are ported to an extensive level that they have a higher rate of cracking

People DD plenty of ported heads out there... but when it comes to Race ports... shops will port the head even more than is what's recommended (taking the risk of hitting coolant passages) which is why they use them on strictly race cars

 

[babyviper]

That makes sense I'll buy that. I remember from the sexy grandma build thread, that guy hit a coolant passage.

 

[TSIfreek]

Save your money and buy a stage 1 or 2 head with new guides and valves. Stock size valves are fine as well. Put your money twards a bigger turbo or transmission.

 

[twicks69]

Also when you start modifying the ports on the cylinder head you will be changing the powerband structure as you are modifying the volume and flow velocity of the air coming in and out. By increasing the CFM of the head you effectively can flow more air volume, but it takes more air to fill up as well, resulting in potentially slower spoolup, shorter powerband for street cars, and powerband shift toward higher RPM. Ways to maximize a heavily modified ported head is by using a larger displacement and a LARGE turbo, or sticking with a better rod-stroke ratio (2.0L, 2.1L, 2.2L setups) and revving out over 9000rpm+ while sacrificing your lower rpm powerband (1000-6000+rpm of little or no boost on larger turbos).

With that said, I am still running a 1G turbo 60mm throttle body and a stock-port 1G head, with only 1mm oversize valves, Supertech dual springs, big cams, and 3G lifters. And I am shooting for 900+AWHP.

In my opinion, it is better to spend the money elsewhere and run a normal head with maybe slight portwork and port cleanup, stock size valves, bronze valve guides, good springs and good cams.

Good luck,

 

[SBR Joe]

To be totally honest, the stage 2 and 3 port work is the most important part of the port work. By taking out the lips behind the seats and radius-ing the floor to flow better into the combustion chamber, and just smoothing all the casting imperfections out..is where all the gains come from.

I did extensive testing on a flow bench in school with a head to see where the gains were made and how much. JUST by taking the lips out in the casting behind the seats on the intake yielded 25CFM gains on the intake side at .400 lift. I got to a certain point where the more material i took out, the less gains i was seeing. Unless youre only concerned about how much air can FIT and flow into each cylinder and making un godly HP numbers, keep the port work to stage 2 or 3, with STD valves and good springs/retainers, and bronze guides.

It will maintain great street manners and make the power youre looking for on pretty much any setup. Like twick said, you COULD do it with 100% stock casting head. Ive seen 9 sec cars with unported heads...but it will help.


Joe
SBR

 

[joe sobo]

i also have one question about a ported head. i have seen a ported head the when they port it, they also cut the valve guide to be level with their port work. doe this help in any way? ordoes it hurt anything? if NEED be , ill try to get a pic from him.

 

[TSIfreek]

i also have one question about a ported head. i have seen a ported head the when they port it, they also cut the valve guide to be level with their port work. doe this help in any way? ordoes it hurt anything? if NEED be , ill try to get a pic from him.

I dont like cuttting down. Reason its not a good Idea is the valve guide supports the valve to keep it straight threw out its motion. Cutting it down removes some of this suport causing the guide to wear out faster and allowing the valve to wable in the seat.
Its just not a good idea
Keeping the guides stock length also prolongs the valve, valve seat and the valve job that was done.

 

[SBR Joe]

i also have one question about a ported head. i have seen a ported head the when they port it, they also cut the valve guide to be level with their port work. doe this help in any way? ordoes it hurt anything? if NEED be , ill try to get a pic from him.

On a straight race head, absolutely. I have seen a good bit of gain from it...but on a car that you drive on the street alot....no. Like stated above, it will help longevity having them in there at normal length.