Staggered Head Work

[DaleH]

I know this subject has been beaten to death several times over, but I have yet to find the answer I am looking for. Upon searching SM and SF I have come to the conclusion that the stock head flows enough for close to 600 RWHP. However, I am currently Over-Building a 7M for a daily 600 RWHP and currently working on the head. Also stated, the main bottle neck is our Exhaust side, flowing some 6Xish percent of the Intake side.

Would there be any ill-effects of having 1mm Over-sized Exhaust Valves combined with Standard-Sized Intake Valves to try and bring the exhaust flow closer to that magical 90%? Of course, necessary bowl and Seat/Port work. Thanks again and sorry to bring up yet another "Head" thread. :icon_bigg

-Dale

 

[Nomad707]

ok well the exhuast valve is always about 75% the size of the intake valve, thus about 75% flow.

Putting a 1mm oversized valve in the engine is like putting a bigger bottle cap on a soda... its not going to do much unless you port and polish the hell out of it, its just going to allow more flow through, but you have to port/polish to compensate for flow, otherwise performance gains will be minimal.

in performance applications, exhuast valves are about 90% of intake size.

it shouldnt be an issue. With 1mm oversized, severe port work, you should be looking at very respectable gains in my opinion

 

[starscream5000]

Try port and polishing the entire head. With at least a 1mm reversion dam between the exhaust ports and the exhaust manifold, with the manifold having the larger opening, 1mm OS exhaust valves, with standard sized intake, along with a 3 angle valve job and see what happens .

 

[DaleH]

Try port and polishing the entire head. With at least a 1mm reversion dam between the exhaust ports and the exhaust manifold, with the manifold having the larger opening, 1mm OS exhaust valves, with standard sized intake, along with a 3 angle valve job and see what happens .

Exactly what I have in mind! I was just wondering if there were any issues with only the exhaust valves being oversized.... I guess not :evil2: .

 

[IJ.]

+1mm valves here

Works well once the seats are opened up, I also opened up the ports 2>3mm to suit.

I wouldn't do just the exhausts though.

 

[starscream5000]

What type of negative side effects would there be Ian? None? Is it a, "since you've got the other valves and a head sitting here, might as well do it all at the same time." type of thing?

 

[IJ.]

SS5k: There's a % relationship between the Intake and Exhaust valves due to incoming charge being much denser than the outgoing.

I like to think a couple of hundred years of engine development has this right so I leave it be.

If someone had done some back to back testing and had proof that going bigger on the exhausts made more power I'd do it

 

[starscream5000]

Say Dale.... You wouldn't mind being a test mule to do this, would you? :naughty:

 

[DaleH]

Sure! I'm still searching around to see what would be better, increased flow all across the head with 7X% Exhaust->Intake. Or, try and bring that closer to the 90% with a little less flow from the intake side overall. Choices...:1zhelp:


Edit: I have yet to find some really indepth information regarding the 90% ratio with boosted setups. The majority of hits on my searches always end up with some kind of domestic NA application where you want a lower ratio. If anyone knows a link to some good reads on Intake/Exhaust Ratios for a Turbo'd engine please share .

 

[starscream5000]

More air/fuel in the mixture= more power. The engine will make more power if it can ingest more fuel and air. Wether doing both at the same time, or doing just one or the other at a time is more economical, has yet to be proven.

 

[DaleH]

I'm heading to the local Machine Shop today, going to see if they have a flow bench and talk to them about my plans. If anything, I may just go with all oversized valves and see how close I can get the exhaust with porting/polishing, but only port the intake enough for the new valves.

 

[starscream5000]

Doesn't hurt to at least gasket match...

 

[DaleH]

Well, machine shop said they wouldn't touch it! Heh, they don't mess with "Imports". That is THE only machine shop in this local area. Looks like I'll have to find a reputable shop to ship this off to : /.

Yea Star, funny thing; when I put my intake gasket against the intake ports they were already the same size.... This head was on a parts car and seriously doubt it had been worked on.

 

[Nomad707]

"Heh, they don't mess with "Imports" " = We are ignorant domestic lovers and we only know how to work on the chevy 350!!!

a real machine shop works on anything. i say you demolish their building in the middle of the night with a D8 catipillar.

or take them a ford probe engine (which is import, made by mazda) trick those fuckers!

 

[DaleH]

"Heh, they don't mess with "Imports" " = We are ignorant domestic lovers and we only know how to work on the chevy 350!!!

a real machine shop works on anything. i say you demolish their building in the middle of the night with a D8 catipillar.

or take them a ford probe engine (which is import, made by mazda) trick those fuckers!

:rofl:

 

[jdub]

Yeah...Del Rio is out in the sticks (I was stationed at Laughlin many years ago). Why don't you check over in San Antonio? Or, you could PM Suprarich and see what he'll do it for you...he knows what he doing on a 7M

 

[DaleH]

Yeah...Del Rio is out in the sticks (I was stationed at Laughlin many years ago). Why don't you check over in San Antonio? Or, you could PM Suprarich and see what he'll do it for you...he knows what he doing on a 7M

Nice, hard to find people who have been out this way . I didn't even bother to look for a machine shop in Del Rio , I was in College Station at the time of that post. I'm now in Oregon visiting relatives.

I take it Suprarich can do machine work? Searching username. Thanks!