Heads = Zero HP Gain

[minytrker]

I sent my stock 243 heads off to a well known shop and had them do there magic, port, polish, valve job, and so on. I also went with thinner head gaskets per there instruction. I also added bigger injectors. I had 430/390 before and did 431/391 after the heads. Per the machine shop I needed 7.350 instead of the 7.4 push rods, so I swapped them out. The preload was now in limits so I retuned the car but it doesnt seem any faster. I can see from the data that the heads are flowing more air, they just aint making anymore hp. The dyno sheets look exactly them same like I didnt change anything. How can heads make zero hp. The well known shop claims the lowest thay have ever heard of or even seen is 20rwhp gain from there work. The said I should see 20-50rwhp gain. I have the car a little rich at 12.2 with 26deg of timing at wot.

[Doc]

What kind of intake and exhaust (manifolds) setup are you running?

[minytrker]

02 Electon Blue Z06 430hp/390tq (before CNC heads) (431/391) after
237/242 .603/.609|CNC ported heads|Halltech CAI|FAST 36 injectors|NX TB150 wet shot|Powerbond UD Pulley|LG Pro headers|Borla Stingers|DTE Transmission Brace|Harden Output Shaft|Ram HD Clutch| B&M Ripper Shifter|Slotted & drilled rotors|Tuned by LS1 Power Tuning

[SSpdDmon]

Did you try leaning it out to 12.6~12.8 with 28-29 degrees of timing? Will it take that much?

[minytrker]

No I had it at 12.2 for nitrous along with the timing. I dont see going to 12.8 and 28-29deg of timing picking up 20-50 rwhp like they claim I should have. I am going back to the dyno next week again and Im am going to try leaning it out and more timing just to see, because Im sure they are going to use it as an excuse.

[Trippin]

Typically on an engine dyno we look at BSAC. Or Brake Specific Air Consumption. This is basically a rating of how efficiently an engine converts air to HP.

If your moving more air and making the same power, assuming the tune is correct, then my suggestion would be that the camshaft and cylinder heads are not getting along. A large cmashaft can make up for the fact that the cylinder heads don't flow to a certain extent. But then improving the cylinder heads now makes the cam seem that much bigger.

What cam does the head shop recommend for their cylinder heads? 237/242 @ .050 seems fairly large for a 346.

I've had the best luck with a 224/228 Comp XER lobe.

What manifold and throttle body are you using?

[minytrker]

They recommend my whole setup, I ordered everything from them. I have the stock ls6 intake and stock z06 tb which is a 80 I think.

[Trippin]

If your going back to the dyno next week then I agree with Speed Demon. Run a timing loop to see what it wants and then lean it down. I've seen the LG headers and Random cats make some pretty good power at much leaner AF ratios than what you might think.

[minytrker]

I wil try it but I only had 26-28 deg wot and a/f of 12.8 with cam only when i did the 430/390 and it made the exact same numbers and it has the exact same hp and tq curves now after the heads. Thats the werid part, you would think the heads would make the hp and tq curved atleast a little differnt somewhere.

[Black02SS]

If your going back to the dyno next week then I agree with Speed Demon. Run a timing loop to see what it wants and then lean it down. I've seen the LG headers and Random cats make some pretty good power at much leaner AF ratios than what you might think.
Listen to him on this subject. :) He has very good info and knows what he is talking about. And I will agree 110% with the above statement.

[Trippin]

Tell me about the changes in airflow you saw that lead you to believe the motor is using more air.

[minytrker]

Im just at more g/cyl now vs before.

[Trippin]

How much more?

What are the actual values before and after?

[redhardsupra]

Im just at more g/cyl now vs before.
how much more? do you have any before/after logs with that?

[minytrker]

I will try to find the logs from both dyno runs before and after heads. After talking to the owner of the shop he agree's that 12.2 vs 12.8 and even a couple of degs of timing will not fix the problem. He wants to inspect the heads personally because he said this has never happened. He said the least he has ever seen was 20 and has seen as much as 50rwhp gain from the same heads. Since a cnc machine does the work he is thinking it has to be either valve related or head gasket. So I am pulling the heads and sending them back on Monday.

[redhardsupra]

my money's on dyno being..well, a dyno--arbitrary and unprecise. if you get extra airmass, you should get extra horsepower out of it, unless you're killing it with too much/too little spark, and your AFR being completely off. heads usually add 0.10g/sec and that's a lot of extra power.

[minytrker]

my money's on dyno being..well, a dyno--arbitrary and unprecise. if you get extra airmass, you should get extra horsepower out of it, unless you're killing it with too much/too little spark, and your AFR being completely off. heads usually add 0.10g/sec and that's a lot of extra power.

It made zero hp and is still the same exact speed. We ahve 2 vettes we race and there are the exact same speed. We ran them another 10 times or so and they are still the same as before I did the heads. How do I post my log file? I uploaded to my server but cant post it. Here is where I uploaded it but it doesnt work there for some reason.
http://www.ls1powertuning.com/tuning

[Trippin]

my money's on dyno being..well, a dyno--arbitrary and unprecise. if you get extra airmass, you should get extra horsepower out of it, unless you're killing it with too much/too little spark, and your AFR being completely off. heads usually add 0.10g/sec and that's a lot of extra power.

Actually you could get extra air mass and blow it right out of the exhaust without converting it to energy to push the piston down. This is generally the case with efficient exhaust ports and "oh 2 much" camshaft. So in Minytrker's case, his camshaft, that was working very well with unported heads, now with ported heads, blows the cylinder down too quick and effectively moves more air through the engine but doesn't make any more power. :frown:

Hence the reason BSAC becomes an important number to look at. Yet most ignore it as a diagnostic tool and just focus on how much power they made.
I guess I got spoiled after running an engine dyno for 20 years with full instrumentation.

Seems like I should write a PID and keep track of this on chassis dynos. Don't most people peg the MAF reading early on anyway? Or figure out some way to cheat it with a resistor or something? In which case the reading isn't true anyway so the whole thing is useless for this type of cal.

I'm still curious about his before and after readings.

Just E-mail the log files to s o c a l d i e s e l at earthlink.net