It's not cheap, but if done right, it can be very streetable. Here is the list of components to address in order of importance:

Head flow
Compression
Camshaft selection
Exhaust selection
Intake manifold selection
Valvetrain geometry/stability
Finding lost hp mods

Head flow:
Contrary to popular belief, when running a plastic intake manifold on an LS1, airflow at .600" is virtually meaningless. There are several reasons why. First, an LS6 intake will start to lop off airflow above 265cfm. A stock FAST 90mm intake seems to lop it off around 275cfm and a ported FAST 90 seems to lop off flow above 280cfm. What all this means is that most all airflow gains above 280cfm will go un-noticed when you bolt a plastic intake up to it. The real trick is to pack in more airflow in the low and mid lifts. If you look at all of the top running heads/cam vehicles, they will all have heads with excellent flow at .300,.400 and .500".

Tony Mamo from Airflow Research and I have discussed this theory at great length and we decided to build a set of heads that maximized the airflow at the low and mid-lifts, even if it meant limiting the airflow up high. This is challenging with a 3.900" bore as too large an intake valve will be shrouded by the chamber wall and cylinder bore. Based on the success he's had with opening up the chamber walls for 4.00" bore motors with the AFR 205s, Tony Mamo opened up the combustion chamber walls of my 205s from 3.900" to 4.000". This gave more space for the 2.02 valves to flow well in the low and mid lifts. But when you open up the chamber, you also lose compression. This means you have to mill more. To get to a 57cc chamber, we had to mill the new 205s close to .060". Most of the time, head flow numbers are posted in unmilled form, but when milled, they will often drop dramatically. Tony Mamo was very conscientious with his valve jobs to make sure the head flow in milled form was outstanding. Here is what my 205s flowed on a 3.900" bore at 28" of H2O:

AFR 205s with 57cc chamber:
Lift.........200", .300", .400", .500", .550", .600"
Intake.....158,.. 220,.. 264,.. 285,.. 296,.. 300
Exhaust.. 122,.. 178,.. 217,.. 232,.. N/A,.. 241 (with pipe)

While there's nothing special about the flow numbers at .600", look at the numbers down low. Most unmilled heads flow in the low 140s at .200", the high 190s or low 200s at .300", and high 240s at .400". Since we're trying to maximize airflow within the flow limits of the plastic intake manifold, a gain of 20 cfm at .300" and .400" will show huge hp gains (over 20 rwhp) whereas a flow gain of 20 cfm at .600" will show virtually no gain. Case in point: I used to have AFR 205s and I swapped to AFR small bore 225s. The 225s flowed 20 cfm better at .550", 22cfm better at .600", and 25 cfm better at .650" than my old 205s. Guess what? We gained virtually 0 hp with the swap. We were even running a .650 lift cam to take advantage of the airflow. Nothing. The moral? Concentrate on getting more airflow within the flow limits of your intake manifold (ie, better flow at low and mid-lifts). Make sure your heads flow big numbers after they're milled.

On a side note, the 205s still retained the standard CNC porting from AFR. No additional material was removed. This meant that the airspeed was very high and throttle response is fantastic. My fuel economy has increased compared to running the AFR 225s.

 

So for a engine with a LS6 intake, it doesn't make sense to worry about cam lift above the max flow of the intake? So if my heads flowed 270cfm at .550, then there's no reason to use a cam with more than .550 lift?

 

Compression:

Compression is your friend, especially when running a larger camshaft. Raising static compression will really pump up torque, but so will raising dynamic compression. Every 1 point increase in static compression ratio (SCR) will increase your torque 3-4%. There are limits to how much you can run on pump gas, but you can cheat this limit with tighter quench and better tuning.

For my quest to 500 rwhp, we chose to get static compression into the upper 11s and dynamic compression into the upper 8s. A 57cc chamber coupled with flat top pistons and 2cc valve relief made my compression fairly high for pump gas, but we got some additional help with a .041" head gasket (Fel-Pro 1041). The thin gasket raised our compression from 11.50:1 to 11.92:1 (compared to a stock .053" gasket), but the tighter quench made the motor less prone to detonate at 11.92 than it would at 11.50:1.

The intake valve closing point of 48 degrees ABDC at .050" made my dynamic compression 8.86:1. With the tight quench and outstanding chamber design of the AFR 205 heads, I get 0 knock retard on 93 octane. Ignition timing at peak torque is 28 degrees and 30 degrees at peak hp.

 

Tony,

How did you get those numbers as to where the manifolds "lop off" the airflow?

 

your .200 numbers are really good. my tfs heads dont seem to shine until .300 and then take off above that. thats in milled form.

 

my tfs numbers show:

.200, .300, .400, .500, .550, .600
137.9 219.0 273.5 306.0 315.3 322.3
115.7 176.7 228.7 250.0 258.0 263.1

running a ported fast and a torquer v.2 it looks as though i may be leaving some on the table in the lower end of the spectrum. time for a bigger cam and sheetmetal intake

 

Camshaft selection:

While this can be a black art, there are some consistencies with 500 rwhp cams out there. Most have between 235-240 degrees of duration on the intake and most have between 240-244 degrees of duration on the exhaust. Lift is important in that you want to get as much in early as possible. Fast ramps work great on the intake lobes. The Comp XE-R lobes are very fast off the seat and will put the lift in the .600" range. They're pretty aggressive in duration at .200, but there are others that are faster. The new Comp XFI lobes and LSK lobes put even more duration at .200" than the XE-R lobes and have more lift. If your head flow does not fall off above .600", then it makes sense to run the higher lift lobes. Not because of the airflow gains above .600" as much as the greater valve curtain area they provide below .600". Because my AFR 205s stalled above .600", we chose to run the Comp XE-R lobes in this 500 rwhp build.

The intake valve closing point is the most critical component in camshaft selection as it determines where your your engine will make peak power and how much dynamic compression you'll have. The tuned runner length of the factory plastic intakes tend to force a torque peak at 4800 rpm and a power peak at 6300 rpm. The intake valve closing point that seems to correlate best with this peak is around 44-46 degrees ABDC at .050". Anything past that will cheat the peak past the 4800/6300 rpm levels. Ever see torque curves with double humps? This is a classic case of the intake valve closing point and overlap combining to force the engine to peak past the design of the intake manifold. See the graph below for the double torque peaks at 4800 and 5700 rpm as an example:


The exhaust lobe needs to be matched to the flow of the head and exhaust system. If you view the strong flow of the exhaust on my AFR 205s (81-82%), you will see that a big split between intake and exhaust was not necessary. On my cams, I like to have a fast lobe off the seat. This will keep the exhaust valve closed longer in the power stroke and give me an increase in torque. Comp XE-R lobes are outstanding in this area.

Overlap is another tricky item for the quest to 500 rwhp. Most cams fall into the 15-20 degree at .050" range. If your exhaust is very good at scavenging, more overlap is usually better. But because my car is a daily driven street car on pump gas, we limited the overlap to 16 degrees at .050". Keep in mind, as static compression increases, the engine does not need as narrow of an LSA. With a nearly 12.0:1 SCR, a 112LSA made sense. Had this been a stock compression motor, a narrower LSA would have made more sense.

 

That's what I was looking for... I just needed to wait for Chapter 3

 

Exhaust selection:

To make big power with a street motor, you need an exhaust that sucks...literally (David Vizard quote). When running a cam with lots of overlap, backpressure is not your friend. But when building a daily driven street car, too free flowing of an exhaust often means too loud. Not in my case.

You want the best headers you can find. For an LS1 F-body, it would be QTPs or Kooks in 1 3/4" size. For a Vette, the LG Pro Long tubes reign supreme. A high velocity merge collector on the header collector is typically worth some nice gains in the mid-range and is known to squeak out a few extra ponies up high as well.

Merging the twin pipes coming off the headers is a critical item for power and sound quality. Vettes have it easy because an x-pipe easily fits and the sound quality is awesome. F-bodies are handicapped because of space constraints. For 500 rwhp, you want to run dual 3" pipes after the headers and you'll want them to merge into a 4" intermediate pipe. Anything smaller will run the risk of flow loss. Most y-pipes on the market slam the 2 pipes together like this:



When the pipes meet at close to a 90 angle, the flow is going to be lower and the sound is going to rasp and drone at 2000-2300 rpm. By using a Flowmaster merge collector or better, your sound quality will improve since the gasses meet side by side as opposed to ramming into each other. Here are a few pics of my exhaust.









Notice the dual 3" pipes merging into a 4" intermediate pipe, then a 4" cutout. After the cutout, the pipe is reduced to a 3" SLP dual dual catback. Compared to open headers with 20" extensions, my motor lost 1 hp with this y-pipe, but gained 10 rwtq in the 2500-4000 rpm range. From a sound standpoint, the rasp/drone is gone with the better y-merge collector. The difference between running with an open cutout and closed exhaust through the tail pipes is 9.5 rwhp. Not bad at all.

 

Intake manifold selection:

Ported FAST 90 all the way if you want 500 rwhp in a 346. But not just ported by anyone. Choose a porter with a proven track record of power gains. Tony Mamo is the king when it comes to extracting all the airflow possible from the FAST intakes. When running a plastic intake manifold on an LS1, airflow at .600" is virtually meaningless. There are several reasons why. First, an LS6 intake will start to lop off airflow above 265cfm. A stock FAST 90mm intake seems to lop it off around 275cfm and a ported FAST 90 seems to lop off flow above 280cfm. You get around 2.2 hp for every cfm of flow increase. That extra 5-7 cfm may not look like much, but it's additional flow going into the head. If your heads will flow the number, that extra 5-7 cfm will give you 10-15 rwhp more power.

A sheet metal intake changes all of this theory. Because they don't lop off flow at 280 cfm, it's possible to make more power with head that flow better in the .500-.700" range. Flow at .200-.300" becomes less important. But since you can get 500 rwhp with a dual purpose intake like a FAST 90, a sheet metal intake in not necessary in this build.

 

Excellent write up! So the guy that ported my heads was'nt just blowing smoke when he said that the heads would make nice power with the higher average flow numbers than peak numbers. I may be getting you to custom spec me a cam soon to extract the full potential from my combo. This seems like sticky material!

 

Valvetrain geometry/stability:

RPM is power. You can't make 500 rwhp NA in a 346 without lots of rpm. This means the valve train needs to be stable at high rpm. Spending more on better springs is important. I chose the AFR upgrade spring (part # 8019). Erik Koenig from HK Enterprises (HKE) set up my spring height to 1.775". This got the spring pressure to 170 lbs on the seat and 450 lbs open.

Reducing valvetrain weight is important too. Titanium retainers are needed. I also used the AFR upgrade hollow stem intake valves. These lightweight 2.02" valves only weigh 98 grams. For comparison, my 1.60" exhaust valves weigh 97 grams each.

For rockers, I used the all-new Yella Terra Ultra-Light rockers (part number 6645). These are shaft-mounted rockers that have the same weight or less than the stock rockers (over the valve) and will enhance high rpm stability. HKE shimmed the rockers .050" to get the best wipe pattern on the valve stems.

Comp R hydraulic lifters (part number 875) were chosen. The new GMPP Cadillac lifters would have worked well as would Morel lifters. Plunger depth was set to .035-.050". The rocker bolt gets around 3/8 to 1/2 of a turn past 0 lash. In my case, a 7.400" pushrod worked best. Keep in mind my heads have been milled .060", I run a .041" head gasket and the rockers were raised .050". Most people make the mistake of running too short of a pushrod when making their selection. The Yella Terras seem to like a longer pushrod than stock.

 

Very nice informative write up Patrick..thanks ..

 

Finding lost hp mods:

Reduced rotating mass, reduce friction, and eliminate any incoming flow restriction. Lightweight flywheels and clutches help. My Textralia steel flywheel and clutch is 6 lbs lighter than stock. An LS7 clutch is a few pounds heavier than stock. An aluminum flywheel may free up some ponies on the dyno, but it will hurt your 60' times, so I did not choose to run one. Aluminum driveshafts make more power. Stock rear ends make more power (although mine has 3.73 gears because I wanted to go quicker).

An underdrive pulley may only show 3-5 rwhp on the dyno, it's usually worth a tenth in ET reduction. I run an electric water pump. Although some tests have shown it to be worth 4-6 rwhp, on my car it show nothing. I do love how my car cools down fast in the staging lanes though.

Reduced incoming air restriction at the air box and anything in between it and the throttle body. In my case I chose to eliminate the 85mm MAF and run a straight pipe and run the car in speed density.



Many will report that an 85mm MAF is not a flow restriction at 500 rwhp, but I just like the way my throttle response is at low rpm when not running the MAF.

 

that is one badass trans am...

 

Very nice writeup.

 

Looks like you can squeeze another couple hundred rpms out of this. Did you try some pulls to 7,000?

 

There were 2 other runs where the car did not make as much power, but you can see the curves and how well the engine pulled past 7000 rpm to the 7200 rpm rev-limiter:

 

holy ****..........subscribed

 

What are you using the throttle activated microswich in that pic for? Is it part of a nitrous kit? Do you have any nitrous numbers for your setup yet?