kumar75150

On a NA car, are intake flow numbers more important than exhaust flow numbers?

kumar75150

Also, if you had to pick heads for a stock bore ls1 motor, would you pick heads with a 205cc chamber that flow 300 intake and 230 exhaust or heads with about a 225cc chamber that flow 310 intake and 215 exhaust?

Richard@WCCH

iTrader: (3)

A little more info about the car would help. What trans, rear gear, tire dia., camshaft, intake manifold and exhaust. I find it's usually best to try and fit the heads to match other aspects of the car.

Good luck,

Richard

Cstraub

iTrader: (1)

Intake numbers will give you the potential that the engine can make. Runner volume needs to be matched to CID and intended max rpm range.

Chris

kumar75150

well I have a 395 cid motor thats all stroke

My heads have pretty good mid lift numbers but they seem to stall pretty soon. They flow 299/207 at .500 lift and flow 309/215 at .600 lift. Only 312/222 at .700 lift. This bench does read 6-8cfm lower than a couple other benched I have seen for what its worth.

cam is a 244/250 .634 .625 112 lsa; I keep thinking about changing the cam to something with similar duration, little less lift (my heads stall by .634 anyway), and a more aggressive lsa like a 109

I am thinking about switching to the AFR heads. I should be able to run higher compression (at least 11.2:1 and prolly a little more) because I am thinking the big cam is bleeding off some compression.

My current setup isnt bad except for the low end tq. I guess part of that is the big cam and 1 7/8 headers but my graph is almost IDENTICAL to the 500hp Cartek and LGM heads/cam graphs.

car made about 480rwhp/450rwtq; since then I have bought the 90mm FAST intake and 90mm TB which should push it to 500/460ish.

Just looking for ideas since the car is gonna be apart again soon.

CHRISPY

Your heads look pretty good imo. I would wait to see how the AFR 225 heads work.
Those would definitely be a better choice for your combo

kumar75150

thanks

my only hesitation about the 225s is that about 3/4 of the people I have talked to say that 2.08 or 2.1 intake valves are way too big for a stock bore motor

Cstraub

iTrader: (1)

What is the target Max RPM?

chris

kumar75150

doesnt really matter

I am gonna end up spraying the car withing the next 2 months so I dont have a need to spin it high. Right now the rev limiter is set at 7000rpm. Making 485 peak hp at 6400rpm right now and makes about 470 at 7000. I am not sure how much the 90mm setup will change that.

Cstraub

iTrader: (1)

based on a 6500 rpm level, I don't see the need for 225 cc intake runners.

Chris

BigTex

iTrader: (16)

That brings up a dilemma: most ported stock castings are going to be a 225+cc runner volume. Lets leave the AFRs out until they become fully available and tested.

From the other discussions, you match your cam specs to the engine setup. If the heads aren’t opened up enough to get high flow numbers (but keep a small runner volume), then you need more duration to support that motor, correct?

What are the trade offs:
larger runner volume with higher flow & smaller cam
OR
smaller runner volume with less flow & more cam

CHRISPY

For 395 cubes? I think you should have another look

Cstraub

iTrader: (1)

Large heads on a street car make for slow throttle response and peaky power. I always get yelled at for bringing these up, but due to budget spending to make power, the boys in NC know what it takes. If on average they run a head in the 230 to 240 CC range for 358 CID to run 9500 rpm, then what sense does it make to have a street engine of 346 to 400 CID that runs 6500 to need more intake volume. Better yet, we run 269 CC heads on 500 CID boat engines for max rpm of 5500. Sure 454 Mag engines had GM square ports of 320cc runners on them from the factory, but if I had to sell engines for boats, I would use something that produced good peak numbers also, if I want overall performance then I want the head that gives the best numbers over the curve.

Chris

BigTex

iTrader: (16)

Thanks for the reply.

Can you have your cake and eat it too? Can you have a set of common ported 225cc heads that flow 320cfm and run a camshaft to compliment them that regains torque and throttle response? Or are you stuck with peak HP gains and lower torque?

Cstraub

iTrader: (1)

Tex, you were correct above, large head small cam is the answer. Most of the engines I get to do the cams for that have great heads love short duration and moderate to high lift on the intake when they have good heads. Shorter if the engine is over headed. Problem is Tex small cams don't sell. . .just human nature to buy big. . . Biggy Fries, Biggy Drink, Big SUV, Big Screen, when in reality something smaller will do the job.

Chris

CHRISPY

Well my heads have 235 intake cc's and flow 327 @.600.

Makes 462RWHP at 6000rpm and 437RWTQ with a 236/240 110LSA cam through heavy clutch, heavy DS, 12 bolt, LS6 intake, stock MAF, stock throttle body, waterpump and all accessories.

Very conservative tune on pump gas. It also makes 400RWTQ at 3000rpm and up.

Race gas with appropiate tuning and open exhaust headers would be in the 485RWHP/460RWTQ range easily

kumar75150

The low end TQ is one of my main problems/concerns.

My car doesnt hit 400tq until right at 4000rpm.

Cstraub

iTrader: (1)

Example 2 barrel engine cammed:
Performance Unlimited in Mirmar FL, Tel. number available
170 CC heads Flowed around 250 cfm at the sweet spot, porting HVH
2 barrel holley, prepped
355 CID
Performer intake untouched
12 to 1 with flat tops
Iron manifolds
462HP at 6500
483#/ft at 4800
Flat tappet cam in the 570 lift range and duration at .050 at 250
Yes thats flywheel. .and yes thats a race car. . .
Point being. . .with a well matched combo power can be made simply.

Chris

Cstraub

iTrader: (1)

I posted that 2 barrel. . .and thought . .. what is the point. . .back to the point. . . yes the heads are 2 big.. . .simple as that. Over head it, under cam it. Under head it. . . over cam it.

Chris, nice bullet, those are good numbers for the combo.

Chris