A few years ago I had a few of local club members tell me to get the heads hogged out. After reading "Superchargeing the SBC" I just had the exhaust ports done for $300 at TEA and I had the Chambers CNCd along with a 3 angle valve job. I never flowed them but this is probably close to
.100/50.0
.200/104.1
.300/148.6
.400/175.5
.500/186.6
.550/191.3
.600/192.9
Thats what a fellow club member (chris) flowed with TEA's porting. We have very similiar combos. The book said that spending alot of money on heads was useless and if they were a good set of mild heads that had a I/E ratio of 75% or better that they would be fine. Stock LT1's have a somewhat poor I/E ratio. The blower will FORCE the air though the intake ports and somewhat though the exhaust ports depending on cam overlap.

So Chris had his stock heads re-worked by RPM and they added alot of mid lift exhaust port flow. Chris was thinking about AFR 190's, And I thought of the book and said it was a waste, I also put the motor in the Engine analizer program and the AFR's gains like 8hp at peak and 3 hp average. For $1750.

I have seen alot of guys in here spending thousands on head work just to slap on a s-trim/powerdyne/p600b. Chris is maxing out his s-trim and I substuted a T trim with similiar pulley combos. The T-trim added about 3.5psi and wasn't being maxed out. It gained about 70hp at peak and 30hp/30ftlbs average. For $1750.

Anyways what do you guys think about spending big dough on heads, when are the factory heads with mild porting done? I am guessing I have around 640 at the crank and if I did some basic maintance I could easily reach 660 or more with these mild stock heads, slapping on a T-trim will put me in the 740 range with the same heads. I am interested in seeing how Chris does on the dyno, the differences are

his ported intake ports vs. my stock
his 2.75 pulley vs. my 2.85
his trw pistons vs. my lighter srp's
his 3.5 mufflex and LT's vs my edelbrock shorties and borla
his 1 quart aftercooler tank vs. my one gallon

BTW my roommate bought the engine analizer for $150 and after putting in my combo and comparing dyno graghs it pretty darn close, right down to the 380ftlbs@2500rpm.

 

I'd say it really depends on your goals. If you intend to keep the car running on pump fuel, then you will reach a limit with how much boost you can run on pump fuel.

Now given that fact, ported heads will allow you to flow more volume of air per "lb" of boost. For instance, say you maxed out at 12lbs on pump fuel and stock heads because it starts running into detonation. Now with ported heads and 12lbs boost, you're moving a ****load more air volume through the engine and making more power, but you're still at 12lbs boost. On the same token, with ported heads you could make the same power level as you did with stock heads, but at a much lower boost level.

For a book to say it's useless to port the heads is somewhat of a relative term IMO.... Useless if you only want to build 500hp maybe. There is a reason why nobody is making 900wrhp on stock unported heads and pump fuel.

Mike

 

Good post from Mike. IOW: question answered!

Rich

 

good post, i was wondering how much hp could be made with stock heads and intake with a powerdyne 6 psi kit and if it was worth the $$ to get a set of heads or just have mine done up. im new to FI. what kind of HP limit would I be looking at with stock heads/intake? I saw you said somethingabout 500hp but is that just a rough guess? or pretty accurate? Id like to do a little more than that, and plan on stroking to 383 forged with the 6psi kit and maybe a 50-100 shot,....do I need aftermarket heads or would stock heads with a good portjob work for this? I know to get the most I should be buying another set of heads,....but thats not what im asking, can I get by with stocker's ported initially and look to new heads down the road?

 

afr 215's would be a good head setup to look into in my opinion

 

I guess what I am getting at is why do people do heads before they will switch to a bigger head unit??? Nice example above mike, lets say you have LT1 with mild heads and an S-trim or p600b. 12lbs is pretty standard and makes good power with intercoolers. Lets say 600hp at the crank. Now go out and buy some AFR's. I dont think you will pick up the 40hp like you would have on a NA motor, and you STILL have a maxed out blower. Sure you'll be seeing less boost but CFM hasn't changed. Stepping up to a bigger head unit first is a better idea. Those who have looked at the compressor maps with the s-trim pulleyed up on an LT1 have probably realized that they are way off to the right side of the map. The strim and p600b and better suited for smaller cubic inch motors like the 4.6-5.0's. The larger head units offer better efficiency, lower IAT's and a combo in the middle of the c. map.

I realize at a point the stock heads are done and something with bigger ports and valves are needed, but with a bigger head unit that point it pretty high IMO, like 700 at the crank if they have had some mild porting.

I think cylinder pressures have more to do with running pump gas than boost.

I'm not trying to ruffle feathers here, just trying to question the logic.

 

Thanks Rich.

The 500hp I referenced earlier was just a reference. Every combination will be different and it's impossible to say what each one is capable of.

I'm not that familiar with the Powerdyne kits. I know they used to be considered an entry level type blower capable of moderate gains. I also believe that 8psi is pretty much maxed (on stock unported heads) out for a Powerdyne unless things have changed with them. That being the case, if you ported the stock heads, your boost will go down significantly but your power may, or may not go up. My point being, I think you'll run out of blower capabilities before you run out of head flow or hp limits on stock heads. Take this for instance. If you have a 383 with great flowing heads and decent cam, you could probably hit 500 flywheel hp. If your blower is only capable of flowing enough air to make 475hp, then it actually becomes a restriction to the engine. By the time the engine revs into a range where it starts to make serious power, the boost will fall off and become a restriction.

If it were me, I'd figure out a target hp or ET range and then map out a plan to achieve it. Try a search on Powerdyne and find out what others have made with them etc.. If their hp doesn't match what you intend to do, then you may need to step up to a higher flowing blower or turbo.

Mike

 

just have your stock heads setup for your blower. thats what i had my guy do and only cost me $500 bucks

 

Thats what I did and it works.

Blown 94 you have a maxed out head unit and you are about to add more motor to the combo. Mike is right, it probably is a restriction compared to a CIA. At a certain rpm it might(or not) be able to catch up and provide a small amount of boost. But you will be spinning the crap out of it and the IAT's will be high, so high that it might be more efficient to just use a CIA. I'd say dyno both setups but that could be more than what you want to do.


So mike and rich what do you guys think, I am just trying to get people to see that they need more blower before they need different heads. Its different if you are buying your d1sc and afr's together but for most of us we go in steps and I think the bigger unit needs to come before the head swap. mike you are right about the end goal, its all about where we are headed, I always wanted 500/500 and I am there, now its about fixing the oil leaks. But if I were to go further people have said get some afr's, and I think they are wrong. A t-trim should be next and my engine analizer agrees.

 

I'd venture to say that a large percentage of people that buy blowers, started out with ported heads and cam. Once they had that, they wanted to step up in power and the next logical choice is: blower, or nitrous.

Now back the stock head scenario. Whenever you have restrictions in air flow path (on a SC engine) whether it's too small of a throttle body or too small of headers etc.., that restriction builds boost. If you look at boost as a measure of restriction it's easier to understand how heat comes into it. The more restriction, the higher the IAT's. Once the IAT's get hot enough, then you run into detonation and have to pull timing etc..

Now, comparing 12lbs of boost from a S-trim to 12lbs from a T-trim given the exact same engine? I guess you'd really have to look at the compressor maps and analyze it for effiency range, flow, rpm potential, IAT temps etc.. I'd venture to say that the gains, if any, would be minimal considering the cost of stepping up to a larger head unit. I think you'd see way more gains from a good ported set of heads than stepping up in head units IMO. Especially considering the cost investment is pretty close either way.

I've seen guys make over 600rwhp on a S-trim with ported, aftermarket heads etc.. I've never seen anyone come close to that with stock, unported heads and an S-trim, or T-trim. I think 500rwhp is the highest I recall seeing from a S-trim with stock unported heads. I believe that the restriction in flow causes the IAT's to rise too high to control detonation. Again, no proof of that because I haven't completely researched it. I'm just going from what I've seen over the last 6 years on this board.

Now to the example you gave being 600hp with mild heads and S-trim. When switching to ported heads, or aftermarket heads the boost will drop unless you pulley back up to meet the 12lbs. Less restriction, less boost everything else being equal. Once you pulley up and retune, it should be much MORE than a 40hp gain. This has been proven over and over again. And, I've never seen anyone truly max out a S-trim with stock unported heads.

And just so I understand, you dont' think boost has anything to do with cylinder pressure????

Mike

 

I wish I had more time to give a good response, I'll be short and then I'll off on vacation and I'll be back sunday for more. Anyways, I am not talking about stock heads, I am talking about stock heads with mild porting, I know three cars with stock heads with porting and maxed out blowers. My makes 540 though a M6 street twin and 12 bolt. Whats my drive train loss 15%, so thats about 620 at the crank. My oil is 9 months old and all the other lube could be changed too. maybe its more than 15%, anyways I'm about 625 at the crank, on stock LT1 intake ports with a 3 angle valve job. Exhaust ports are Stage 1 TEA. Headers are 1 5/8. At peak power my blower is soo far off to the right of the compressor map that efficiency is in the mid 50's. I really cannot gain any more power from this unit. Flow is basically maxed. Changing head units would raise my efficiency and lower my IATS at the same boost level. With lower IATS I could add a pound or two of more boost. With a new set of heads the boost would lower but I am STILL moving the same amount of air CFM =HP right? The blower will not move more air because you have better heads.

Stock heads have a limit and ported stock heads have a limit, I think that ported stock heads will allow more power than a powerdyne, p600b or strim will provide with used with a bigger head unit, my very mild heads prove that. Mike you can also be right because every combo is different and has its quirks but with cost being the same I would need a T-trim to gain my power right? I am out of pulleys.

 

I think at the level you're at right now, you could honestly go either way and see relative gains. I will say that I don't think that S-trim is maxed out in HP. I've seen more than a couple S-trims close to, or over 600rwhp. Jim (INTIMD8) comes to mind and reached 620+rwhp with an S-trim and well ported stock LT4 heads/intake. I don't know his exact combination (at that time) and he may have been over-driving that head unit past it's rated specs.

If you were to add ported heads, you will def. drop in boost unless you have a worse restriction somewhere else. But, that doesn't necessarily mean you'll drop any horsepower if you re-tune with the new lower IAT's and in fact you could gain hp at a lower boost level. Remember, boost is just a measure of restriction, not power.

A T-trim may be more efficient at the compressor, but the flow restriction in the heads could easily put that heat right back in there before it reaches the combusiton chamber. Restrictions = higher IAT's = higher boost levels.

Are you running any kind of intercooler or aftercooler setup?

Mike

 

Well I have an aftercooler and a larger water tank tank. I also have a 7 inch crank and 2.85 blower pulley. According to vortech this setup "redlines" at 5900 rpm(49,994rpm). Of course I run the engine up to 6200-6300 and see no power inprovements over what it is at 5900. It basically stays at 540hp from 5700 and up if I remember right. At 6300 its spinning 53384. I think at this rpm the blower just isnt doing anything but blowing very hot air. The s-trim is most efficient in the 25-35k range and at 53,000 efficieny is off their map and I would guess it would be at 58-59%. Using the T-trim, I could move the same amount of CFM(like 1100). Spinning the Trim at 45K is supposed to yield 1100cfm, and 65% efficiency. And all this numbers do not take into account for belt slippage but thats another post. I still come to the thought that your heads are only as good as the blower feeding them and that people with small head units dont need a set of AFR's or another brand, but they do need some port work, esp on the exhaust side. You are right about alot of people doing the H+C car and then wanting a blower. "how much boost can I run on my 11-1CR car???"

My combo could put down 560 realistically maybe 575 with a stroke of luck but that is really pushing it. I am interesting in what jims car has besides ported heads. I am probably due for some bigger headers, muffex and stronger ignition. (and more porting) Ditching the ET streets would help also.