What do my heads need to flow to match my cam?
 

My cam is TN-233XR 233/239 duration, .569"/.577" with 1.6rr, 111lsa. My heads have been home ported twice with bigger valves. I didn't get them flowed and have not had the car dynoed since the new motor. I will get it dynoed soon.

Also, if you made an error in matching your cam to heads, would it be better to error with the cam being bigger than the heads could flow or vice versa?

Of course, you want them to match as close as possible.

Thanks for your opinions,

Mark

Re: What do my heads need to flow to match my cam?
 

Between 270 and 300 cfm would make good power as long as your intake runners aren't too big.( 180-205cc's) is cool. Now about your cam. You never want a cam that makes its power at say .600 lift when your heads peak flow #'s are around .450-.500. Here's something to remember about cylinder heads: Port Velocity. the faster the air gets in the more low end torque your motor will make. If you have two sets of heads that flow about the same amount of air, and one has 180cc intake runners and the other has 220cc runners, the 180's will make more torque in the lower rpm range. This mostly applies to a street/strip car that doesnt make power at 8500rpm like a full race motor.

Re: What do my heads need to flow to match my cam?
 

The heads will be best matched when they flow the most air at a valve lift
at which the camshaft can produce with a decent amount of duration.

IE:

170 CFM @ 0.300" Lift
190 CFM @ 0.400" Lift
200 CFM @ 0.500" Lift
202 CFM @ 0.600" Lift

If the cam has a good amount of duration at 0.500" lift, the cylinders will fill
with more charge.

Looking at the valve profile following the cam lobe will determine the effective
duration. A 1.6 rocker ratio, instead of 1.5 will enhance the period at higher
lift where the heads flow best.

By keeping the head runner volume modest (~ 180- 200 c.c.), the flow values normally increase at low
to mid engine RPM where the valve duration is highest to make best VE numbers.

What's that sig I once read? "How do you make a bad head look good? Slap it
on a big c.c. motor".

Re: What do my heads need to flow to match my cam?
 

What does a stock intake runner flow?


Man this is complex. I have done a search before and attempted to read some very complex stuff.

Does anybody else run my cam?

Mark

Re: What do my heads need to flow to match my cam?
 

Depends on the valve size. For a 1.94 intake, I found these numbers:

60.2 CFM @ .100"
119.1 CFM @ .200"
170.9 CFM @ .300"
198.9 CFM @ .400"
206.4 CFM @ .500"
200.9 CFM @ .600"


The trick is to get the head flowing best at lower valve lifts for a street engine.

Valve jobs and chamber work will benefit more than porting the runners.

For example, a head that flows:


109.1 CFM @ .200"
140.9 CFM @ .300"
178.9 CFM @ .400"
206.4 CFM @ .500"
240.9 CFM @ .600"
250.9 CFM @ .700"

Will be worse for your application using the cam specs listed in your first post.

Re: What do my heads need to flow to match my cam?
 

:rolleyes:
The cam makes it's power at .600" lift? WTF? I say put the cam in with the most lift that you can for the duration you want.

Your heads flow the best at .500" so you are going to say to ut in a .500" lift cam. :rolleyes: Think about this. How long are your valves going to be open at peak flow? With the .500" cam they won't be open long at all. With a .600" lift cam they'll be at peak flow once it hits .500" and then again when the valve is closing. That's why people say mid-lift numbers are so important.

Re: What do my heads need to flow to match my cam?
 

No offense intended, but I think you've got things reversed:

You really need to match the cam to the head flow, and a bunch of other factors about the engine, the driveline, the vehicle weight, and what it is you want the car to do. IN OTHER WORDS, the cam should be the last thing selected after you know everything else. Valve timing is a dependant variable; you adjust it to get the most from the other parts.

Trying to match head flow to a given cam is very difficult, and will probably be very unrewarding in terms of power and performance.

If you are going to select your cam or have it done by a pro, good head flow numbers are very important. Without them every thing is just a "rectal extraction". That kind of choice often leads to a vehicle that runs like s***. ;)

FWIW, erring on the small side with cams is the preferred route...which VERY few folks ever take.

Re: What do my heads need to flow to match my cam?
 

Oldsstroker.......
I believe I've done what you suggest .
68 Nova, turbo 400, 3:73 12 bolt, 3450lbs with driver,26" tall tire.3050 stall.
406, afr 195,10.3 comp., scat 4340, H-beams, Air-gap, 770 street avenger, Comp xe274, 1.6 crane rr's.1 5/8 headers, flowmasters.
Everyone say's the cam's too small, and they could be right. However, since the car is a street/strip piece, what would you do next to make it quicker?
Some say the heads are too small, the cam's too small, the carb's too small, but I think it's a good combination, as is. So, what's next? I don't mind experimenting, and I am open to all opinions. Others please post. Thanks

Re: What do my heads need to flow to match my cam?
 

Nitrous maybe? :D

Re: What do my heads need to flow to match my cam?
 

Welcome to the "zoo"! It took you a while to post, huh?

To give you an informed opinion on what's too big or too small, I'd need to run your combo thru a few simulators, both engine and vehicle. That's more for Bret (SStrokerAce) as that's part of his business.

Generally, I'd say that if you wanted MAX power from a 406, your heads, etc might be a little small, but I expect the car is very driveable the way it is. Did you mean 3500 converter? It should have one strong launch, as your combo probably has lots of midrange torque. What does it run inthe 1/4? The speed will give a good idea of FWHP since we know the weight.

If you want to run faster, budget should be a very real consideration. Serious airflow improvements are going to be costly, so how fast do you want to go?

IMO, too many people think "bigger is better" as far as cams, carbs, etc. go. Not necessarily. You give up something when you go bigger, and that's often dirveability. If you like your combination, that's very important. You are the one who lives with it.

Good luck. Hang around.

Re: What do my heads need to flow to match my cam?
 

Ok, so my car is at it's birth weight (stock poundage...fat & heavy). What does this tell me as far as picking the correct cam?

Do I have a good cam for a heavy car?

Thanks,

Mark




PS This is not my dailey driver & I want to be faster at the drag stripe.

Re: What do my heads need to flow to match my cam?
 

Do you have the valve event timing available?

I think those specs would help determine if the cam is retaining cylinder pressure
to produce good torque early in the RPM to launch that "fat and heavy" car.

If the cam is designed to make power later, what are your transmission details
and differential setup?

Just a guess, but I'm thinking that cam is fairly wild and will need some gearing
and a t-con (if auto) to get the motor into the power range.

Re: What do my heads need to flow to match my cam?
 

Good cam for a heavy car? LOL! Your car is a lightweight! :D

Anyway, I might be the only person that thinks this way (I doubt it) but I don't think you shouldn't even factor weight into the equation when picking a cam. A heavier car just needs more gear (and if you have an auto, then more converter also.) More gear usually needs more cam. In my opinion your cam is fine. The better the heads you get, well, the more power you'll make.

I would definitely put more gear in your car since it's not a daily driver. Heck, with the T56's .50 6th gear, I would put more gear in it even if it were a daily driver :D


By the way, this is coming from a guy that drives a 96 Impala SS everyday that has 4.10s and a converter that flashes to 3800 behind a bone stock motor. ;)

Re: What do my heads need to flow to match my cam?
 

I have a stock 6-speed with 4.10s in the back. The clutch is a stage II kevlar. As far as the valve timing, Bryan at pcmforless said he has advanced it a lot for the cam. I think it's set at 28-30 degrees at idle anyway. That's all I know about my timing.


Thanks,

Mark

Re: What do my heads need to flow to match my cam?
 

I meant the valve timing. IVO, IVC, EVO, EVC (or even the intake centerline),
not the spark timing. There are a few guys here that will be able to calculate
the cylinder pressure based on the valve timing.

The 4.10's are good fit for heavy cars. Good multiplier happening there.
With such a stout rear assembly, I'm assuming you are using a slick?