How much cylinder head flow is too much for turbo applications?

[dr_hunt]

Title says it all pretty much. In reading about turbocharging in general it is said you don't want any restrictions at all in the intake or exhaust to produce max HP.

 

Ok, with that I have a set of the AFR 220's set up for roller cam and I got a set of the competition cnc ported 227's. The 227's flow better from .500 lift on than do the 220's which are no slouch either. Question is then for the banks twin turbo motor (355) would the 227's work better or worse than the 220's? Is the port volume going to make it lazy on the low end? For those of you who dont' remember I'm building a new motor and the compression should be 8.5:1 TRW turbo pistons, 5.7 Eagle rods with L19 bolts, running solid roller turbo cam .575 lift 260 duration at .050, 114 LSA. I'm running a 4500 stall converter in a glide.

 

Comments would be appreciated. It is not big deal to switch heads off the 406 currently in the z and put the 220's on the turbo motor.

[Turbo Meister]

That converter will cover any thoughts of lazy airflow. That cam duration is much more than mine so the additional airflow from the ported heads should really help on the top end. This may be a good thing because you won't be able to hook up with that much torque at launch, anyway.

Hanns

[dr_hunt]

Kind of what I was thinking, but there is no real info avail that compares heads in a boosted application that I could find. Seems that the general concensus was that the boost overcomes intake obstacles, which kind of defeats the purpose IMO. All though in general the thought is more airflow the better in cylinder heads, but at what cost? I've seen some turbo applications that took forever to build boost even with a 5K stall, however I know nothing about the turbo(s) in use for those cars.

 

The glide softens the hit, we'll have to see what the turbo's can do and if I need to restall the converter to a lower stall to match the TQ curve to traction at the launch.

[grumpyvette]

Id seriuosly doubt that the differance in hp potential between the 210cc or 220 cc heads compared to the 227cc heads ON A TURBO APLICATION would be worth the costs involved in swapping cylinder heads altho theres bound to be at least some potental flow increase, the cam timing and compressor flow map, low restriction exhaust,and low restriction intake with intercooler, are going to be more critical

 

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some comon cross sectional port sizes

(measured at the smallest part of the ports)

...........................sq inches........port cc

edelbrock performer rpm ....1.43.............170

vortec......................1.66.............170

tfs195......................1.93.............195

afr 180.....................1.93.............180

afr 195.....................1.98.............195

afr 210.....................2.05.............210

dart pro 200................2.06.............200

dart pro 215................2.14.............215

brodix track 1 .............2.30.............221

dart pro 1 230..............2.40.............230

edelbrock 23 high port .....2.53.............238

edelbrock 18 deg............2.71.............266

tfs 18 deg..................2.80.............250

 

you may also want to keep in mind that having your ignition timing retarded as the boost pressure goes up is benificial, and the ignition timing, is critical to preventing detonation ,AND in some cases the octane of the fuel, and CAM TIMING needs to change, to make a combo perform correctly.....its also comon for the cooling system to need to be looked into as the heat levels rise under boost

 

http://www.chevytalk.org/threads/showfla...rue#Post1090850

 

 

before you ask about the toluene

 

http://www.team.net/sol/tech/octane_b.html

 

http://www.gnttype.org/techarea/misc/octanebooster.html

 

http://www.elektro.com/~audi/audi/toluene.html

 

http://www.turbofast.com.au/racefuel8.html

 

http://www.sdsefi.com/techocta.htm

 

you might want to think about that the boost pressure in the intake, manifold, shows the resistance to the airflow as much as anything, not necessarily the voluum of airflow actually filling the cylinders, larger ports may show a lower "BOOST" but perform noticably better, due to greater total air/fuel mix reaching and burning in those cylinders large port heads,that flow well tend to show boost pressures significantly lower in the intake manifold than the same engine with more restrictive heads,provided the cam used has the lift and durration to effectively use the greater flow potential

this is only comon sence, pressure or the boost is the measure of the resistance to flow , not the measure of flow voluum,larger heads being much less restrictive result in lower (resistance or boost)that DOES NOT mean that theres less power,infact frequently thers greater power produced due to the more efficient cylinder fill, and the resulting higher percentage of air/fuel mix that burns in the cylinders, provided the cam used has the lift and durration to effectively use the greater flow potential

look at it this way, your engines power is a dirrect result of how effectively it fills and burns each cylinders load of compressed fuel/air mix, as the engine rpms go up, the time available to fill those cylinders goes down fast.

at 1500 rpm theres about .02 seconds available per intake stroke if the valve was open the full 360 degrees, but since its rarely open for effective flow thru the ports more than 250 degrees thats really only .0139 seconds, spin the engine to 6500rpm and the time drops to only .00323 seconds, larger ports with higher flow rates allow the cylinders that are pressurized to still fill the cylinders, to a greater extent, yet that ability to allow flow into those cylindersalso reduces the back pressure in the intake manifold (boost!)but INCREASES the ability to fill and burn the mix in thoose cylinders, provided the cam used has the lift and durration to effectively use the greater flow potential

 

 

btw this may help

 

http://www.turbofast.com.au/TFmatch.html

 

http://www.turbofast.com.au/javacalc.html

 

http://www.blowerdriveservice.com/techcharts.php

[dr_hunt]

Yes, grumpy, this is what I was talking about and nobody seems to have really explored the relationship between higher flowing heads vs. boost pressure vs Hp/tq. I'm thinking that the boost will be lower all things considered for just the head change. Makes sense in that you will be lowering resistance on the intake side so I should see a corresponding boost drop. In addition I would think that the HP/TQ would rise, but it may have an expense, I don't know. The rationale is that most people tend to use ported intakes to gain power, which is basically the same thing.

 

Thanks, I'll do some more reading