BigRich954RR

iTrader: (1)

Ok not sure how to word this

On a 427 engine in the perfect world how much would the heads need to flow so at 6k rpms and 7 rpms to fill the cylinders 100 percent?

SO X (maybe 350) cfm of head flow fills the cylinders 100% now put 15 psi of boost on that in perfect world would fill it to 200 %

Now a engine should make more power at a higher boost pressure cause the starting point of the cylinder pressure will be higher at what point is added head flow not worth its and just adding more psi benfits the hp goals more?

I keep hearing how boost means nothing its just a restriction which i agree to a point. But wouldnt a 427 with 350 cfm head at 30 psi make alot more power then a 427 with 700cfm heads at 15 psi?

Sorry about how badly worded this is. ill edit it if i can figure out how to ask the question more clearly.

sultan(ZR-1)KSA

more flow = more horse power

more boost = more torqe

ChevyChad

iTrader: (50)

Basically, all that matters is cfm. Boost is a measurement of how much restriction the heads are. Regardless if its 20psi, or 10psi of boost, if your blower is outputting 1500cfm, your engine has no choice but to consume all that 1500cfm of air thats being forced into it. The boost is just a measure of head flow efficiency so thats why people say not to worry about it so much.

ummmm no.

LS1Silverado05

iTrader: (41)

**From page 57 of the April 09 GMHTP**

According to the findings of Jason Haines from Lingenfelter Performance Engineering: "Cylinder head flow is not as critical on turbo applications as Jason has found that LS1, C5R, and LS7 heads make nearly the same power".... Thats pretty interesting stuff in itself...

sultan(ZR-1)KSA

??????????????????????????????????

can you send me that artical?
please

Beaflag VonRathburg

iTrader: (176)

Head flow is head flow. The more you can use the more power you will make. Take heead y that flows 270cfm and put it on an engine. You may make 500 hp at 7lbs of boost. Take head x that flows 340cfm and put it on the same engine. It may still make 500hp, but at 4psi. This argument has been covered a lot on here if you search for any of the ls6, vic jr, fast, ls2 intake manifold comparisons.

ss_girl

iTrader: (9)

In english....a head that flows better will make the same power with less boost.

BigRich954RR

iTrader: (1)

But there has to be a point where head flow doesn't matter as much as the boost psi.

If a engine is at 100 percent VE with a 350 cfm head and make 500hp. Then 700hp at 7 psi

It should make more power at 15psi with a 350cfm head then a 700 cfm head at 7 psi
Cause you have a more dense mixture of a/f at 15 psi in the cylinder.

Cfm flow is only good to a point then the compressed amount should come in to play

H21surfer

iTrader: (2)

I think that point is when you actually get into boost. Read what chevyChad posted and think about it. If your heads naturally flow 350cfm, and your FI system puts out more than 350cfm you get boost. You engine is forced to consume that amount of air. I do not believe there is a tradeoff... Limiting factor would be space and money.

BigRich954RR

iTrader: (1)

True to a point but there has to be a point where flow though a port means nothing and base boost psi is better then flow.

If cylinder holds 1 cbf of air then it means nothing if the head flows 300 cfm at 7 psi. Cause engine will still make a lot more power with a head that flows 100 cfm at 15 psi cause the cylinder will have twice the amount of a/f. Which is a much denser mix.

hellbents10

iTrader: (10)

If it runs better NA then its going to run better with boost, if the fuel is good for it.

otherwhitemeat

iTrader: (3)

FYI.........just because you can throw more boost at an engine....or the turbo can make more boost, does not mean your heads/motor can flow it, or make any more power with it. Regardless of the size turbo you have on it.

BigRich954RR

iTrader: (1)

Why though this is kinda on the lines of what im asking. This is what i here but i cant understand it. IF IAT temps stay the same or close to the same adding PSI should make power and flow shouldnt matter cause cfm though ports will stay same but just a much denser mix flowing though
.

otherwhitemeat

iTrader: (3)

There are a # of reasons...I don't know all of them...but one is the air going through the motor gets super heated trying to go through those small ports...regardless of IAT's..That's way I think my lt1 turbo set, and others, was maxed out on power before the turbo was done .... Think about this way....at some point if you put pressure to a garden hose....at some point the hose can only pass so much weather that 20psi or 50psi the out put will be the same...it just back pressure with no out put gain.. I have seen 3 lt1 car with more turbo then the heads can flow can in general the rwhp is around 1100 regardless of how much you turn it up..thats it! It's all it can pass through.. That way im going to a dart block with brodix heads. They will be able to pass more volume/air.

LS1Silverado05

iTrader: (41)

I guess Jason at LPE is wrong?...

Cobra Commander

iTrader: (12)

Why not? The higher cfm head is going to run out of steam at a higher rpm.

otherwhitemeat

iTrader: (3)

About what?

LS1Silverado05

iTrader: (41)

See Post #4... It seems everyone here would argue that statement. Im sure LPE has some R&D to back it up tho...

Beaflag VonRathburg

iTrader: (176)

That tiny quote is very vague. To an extent it doesn't have as large as an effect as an NA engine. That quote makes no mention of the boost required to make the same amount of power.

otherwhitemeat

iTrader: (3)

Oh I see.....you can only fit so much through a hole....regardless of the pressure behind it......
If this was not the case, I would be able to max out my turbo on the lt1 that I had.....but I can't. Nor can others with simmular set-ups......the just turn up the boost theory only goes so far....then your done. There is nothing to argue..you cant just keep turning it up to get more power...at some point...with out other mods, your done.