WHY are heads not as "important" with FI as they are when talking about N/A or NOS setups? I have read several threads about how heads are not as important on FI builds, and am wondering why this is? I mean, if head "A" has the ability to flow more than head "B", wouldn't "A" always make more power? A good set of ported heads would make the same power than a set of unported heads, but it would be able to do so with less boost, correct?

Shawn

 

One thing alot of people get caught up in is boost PSI. Its all about CFM. A set of ported heads will make more power at the same boost level as an unported set. Most people just crank the boost up a few more pounds to compensate. I was also told that the air charge would be a tad cooler because of being less friction and resistance.

 

i think thats a big art of it, why buy $2g heads when you can get the same power or more with a 80 dollar mbc

 

Not true.
N/A motors need ported heads to help them breathe. FI motors (specifically supercharged; don't know that much about turbo applications) are not as dependent on this. However, FI cars still benefit greatly from free-flowing heads, especially if they have been optimized for FI with special attention to the exhaust port flow and enlarged chambers to reduce compression a bit. Then add in a cam that is ground to take advantage of the head flow characteristics, and you have a killer combination that will flow big cfm and produce excellent power at lower boost numbers, plus have a lower detonation threshold than you would see with a set of heads optimized for N/A or N20 applications (milled, more attention to intake side, small chambers, etc.). In a nutshell, anything that improves airflow into and out of a motor will make more power. Combinations of things can magnify this effect. However, just as in N/A applications all the components must compliment each other. A huge cam is not much good without better heads and exhaust, a 90mm intake and throttlebody don't help unless you are flowing enough air to take advantage of them, etc.

 

have you pushed your car higher boost wise? your car is making excellent power with 6 psi.

must be the heads!

 

Ill tell you the real reason that heads are not as important.

Its all about money, you already spent all that cash on FI kit, so now you dont have to impress with your dollar total as much.

Seriously though, have you looked farther down the page, there is about a 10page post about this exact topic.

 

Well in my case I am using a smaller blower unit. So I want to get the most power out of it without overspinning it. (That much) That is the main reason I am for getting heads on a FI car. Plus I will upgrade later to a T or YSI trim.

 

I agree every little bit helps, but i have seen some guys with turbos put on better flowing heads etc and after than not run any faster.

One example is Mike Murrilo (mustang guy) back in 01-02 at the world ford challenge. He torched a hole in his nice ported $$ heads and was gonna be out the rest of the race.. Well he ended up buying a set of stocker TFS heads from the one of the vendors at the race and he cleaned them up a little and had them machine for o-rings that night.. Put them on and had it running at like 4 am and first pass ended up going as fast or faster than he ever went.. 7.8x @ 185 (28x10.5 non w) or something right around that.

I'm not saying that they dont help, becasue they do but i would rather spend my $$ elsewhere.

Just my .02.

Phil

 

It is already in the works; 3.4 compressor pulley is in, will probably get a 7.65 crank pulley later this week. This will spin the head unit to 59962 rpm at 6500. Max is 62000, so this will be getting close to exceeding the units efficiency range. I am curious to see how high the IATs get and whether I will need to back out any more timing. Got clutch issues to tend to first, though.

 

I take it you do your own tuning?

 

You probably know him; Corey Henderson, Henderson Performance Technologies in New Braunfels.

 

It's all about the money... heads don't give you the same bang for your buck as with an N/A setup.

 

Look down the page...
https://ls1tech.com/forums/showthrea...=359688&page=1

Mods you might even want to merge these two threads.

 

A good H/C setup actually helps alot.I would rather hit 700hp with a good H/C and 14lbs rather than a stock H/C and 20lbs of boost

It's all about efficiency

 

I posted this on the other thread:

Here's a very academic, but fairly accurate desription of why superior heads and intake benefit forced induction applications.

Let's say you have a stock displacement 346 that makes 400 rwhp. Add a better set of heads and intake and the power increases by 40 rwhp.

So if the rwhp is now 440 rwhp at 1 bar (14.7 psi), then if we add 1 bar of boost, we should theoretically (under ideal conditions) produce double the power or 880 rwhp.

The point is, almost any part that gives you an airflow gain naturally aspirated will give you the same gain in proportion to your boost. In this case, the 40 rwhp gain N/A was worth 80 rwhp at 14.7 psi boost. Of course, you have to account for heat and additional driveline losses, but the formula is sound. Make airflow increases and watch the gains mulitply once you turn up the boost.

You guys who say higher flowing heads don't benefit forced induction are only looking at it from a dollar standpoint. Sure you can turn up the boost for less, but the formula is pretty proven...free up cfm naturally aspirated and watch that power go up in proportion to your boost.

There's even a great article in October 2005 Popular Hot Rodding that backs this all up. They used a 6.0L iron block, AFR 225 heads and made over 1100 hp.

 

650rwhp with 10 psi vs 15 psi... Which one is 'better?'

It depends.

Variables are heat, money, efficiency and octane.

 

Yeah, I read all that too. It boils down to this, stock heads will only flow so much, once you flow enough air that the heads are a restriction you have to upgrade. Simply turning up the boost or pulleying up to flow more air will only work until you reach the point where the heads/cam combo can't flow any additional air. At this point you have already gone beyond the setup's efficiency range and your IATs will be excessive, you will be pinging like a pinball machine, and will likely lift the heads and blow a gasket or break a ring land, or whatever; catastrophic failure is just a matter of time. Heads/cam combination is just as important to FI as it is for N/A because it is all about volumetric efficiency. I wish when I bought my heads from TEA that the AFRs had been available. I believe that for a FI application, TEAs AFR FI heads are the best out there. Check out their exhaust numbers; unreal. You will flow more air, and they will handle higher cylinder pressures without lifting like the stock castings do because of their thicker decks. If you want a serious head for FI with room for growth, this is the one. Expensive? You bet. Worth the money? Depends on your goals. If these are out of your price range for the forseeable future, or overkill for your goals, check out their 6.0 FI heads....talk about an airflow bargain. My heads are the 5.7 stage 1.5s and when it is all said and done and I have reached my 650 rwhp goal, I would attribute close to 100 hp to the heads and cam setup. Is that worth the $2600 I paid for them both. Hell yes, that is only $26/hp.
90mm intake and tb....I might consider them once I know I have, or am about to reach my current setup's limitations. Until then, they would be unnecessary and any contribution they would make would be at an extreme cost/hp. Not a wize purchase at this time unless they could be gotten at a substantial discount from retail, like less than 1/2 price.

 

I'm running a set of ported 6.0's that flowed 299/219 supposedly. If I had the chance to just swap heads I would, just to see what would happen. I'd probably swap to a set of AFR 225's with some touch up porting (if reccomended).

 

someone check my logic.

lets say you have a 75mm tb chooking a 15psi blower setup, you install a 90mm tb and at around the same rpms your going to have less PSI but the same horsepower? Because the same amount of air is goin into the cylinders but there is less restriction or PSI. Because PSI is related to the restriction in the intake.

Is that logical? or am i just wrong?

 

If (and that is a big if) the 75mm tb is the restriction, pressure in the manifold will be lower than 15 psi. Once you upgrade the tb, pressure in the manifold will rise if the heads/cam/exhaust are a restriction. Pressure in the manifold may or may not be 15 psi. Power created will depend on whether there are additional restrictions.