I am seriously considering doing a heads and cam package. I live under California's smog laws so I can't be too radical. My car will be mainly street driven.

While doing my research I feel myself being pulled in two general directions. Premium after market heads, or ported and polished LS6 heads. The after market heads have a geat pedigree with a premium price, PP'ed heads look stock with a practical price.

But my main concern is the volume of the intake runners and their effect on throttle response. Most aftermarket heads for my application have intake runners in the 205 - 215cc range. While most PP'ed LS6 heads seem to have runners in the 230cc range. Now big runners make for big flow numbers which translate to big dyno numbers. But my car will be mainly street driven with some spirited weekend driving, I'm more interested in better throttle response across the full operating rpm range and big heads can result in sluggish performance at low rpms.

So how much does the bigger intake runners effect low rpm throttle response. Should I be concerned about an extra 15 - 25cc increase in intake runner volume?

I know this isn't your typical which part is best question. But I appreciate any insight everybody can give me.

 

I don't have an answer, but I would try contacting AFR or Charlie Williams at RPM and maybe they would have some answers/advice

 

One consideration when choosing between factory/aftermarket heads, is the aftermarket ones come with the highest quality components, such as springs, valves, retainers, etc. They also have been perfected over the years as to their CNC programs, and flow characteristics. I hate the old saying, "you get what you pay for", but I'm happy I went with top shelf heads.

 

LS6/Z06 heads have 210cc intake runners. Moderate porting is all that is needed for great streetability. Larger volume means lower velocity and sluggish throttle response at low to mid-range rpm.

Roger T

 

Thanks for the responses.

Of course I would like to hear what Tony of AFR has to say. But since he is an aftermarket manufacturer I think we already know which direction he would lean to.

 

I have written volumes on this...

Your combination/goals beg for a high flowing small port.....can you feel the difference from a less efficient (much larger) port that flows similar?? Bigtime....I would recommend you searched and invest alot of time before making your decision. Part throttle response and tip in is dramatically improved with our design....its the reason I strived so hard to engineer a small high flowing port. At the time everyone scoffed at it....not so any more (now some try to copy it). Best thing is you can still make BIG power with that head and the right set-up....once again proof in point is my 224 cammed 346 that laid down 475+ on a half a dozen different dyno's (very optimized package of course).

Not the mention the AFR head is the only head legitimately emissions legal with a CARB number etc.

I know that an AFR 205 is perfect for you.....do your homework and in short order you will know as well....and you do get what you pay for.

Feel free to call me directly if you like...(661)705-8508

Have a good Holiday weekend guys

-Tony

PS....My involvement with AFR has no reflection on my response with the exception being I know AFR has the perfect head for you. As a knowledgeable engine builder (the reason I built a flowbench and got so deep in cylinder heads many years ago in the first place) my advice would be exactly the same. The key to a really world class head design (and the power curve that yields) is not always removing material....its actually more about adding material in all the right places. When you start with a so-so generic stock casting and bring it to a porter, without the use of epoxy or weld his hands are tied and can only make the port bigger in an attempt to get more flow. Our head is 6 cc's smaller than an OEM 243 casting yet flows 50 CFM more air due to its dramatically different shape....trust me I spent more time carefully shrinking that port in the right places than enlarging it. And obviously going smaller and getting more air from any hole is alot more challenging than going the opposite direction. The end results yield dramatically more air speed which packs the cylinder and is much more resistant of reversion issues that less efficient designs fall prey to....a port that has high airspeed and high volumes of flow is a lethal combination and will run much harder from the crack of the throttle to redline.

 

Which is why I also suggested contacting Charlie at RPM.

FYI, I had a H/C upgrade a couple of years ago, AFR 205 with 220/224/114 cam. It gave me about 65 more hp/tq at the wheels (I'm not really into dyno numbers). Car passed 1st smog last Jan. The only difference I noticed on the street was a slight lope at idle and the noisier valvetrain.

As for track performance, I only gained about .5 sec/lap at WSIR, which is run mostly in 4th gear. At Buttonwillow and Spring Mountain, (tech tracks with a great portion of a lap run in 2nd and 3rd gear and at part throttle) my laptimes fell by 3 sec/lap, which is a significant increase in performance.

 

I recently went with AFR's. One thing to consider is bumping compression and a thinner gasket. The higher compression will also help in the head whip department.