The Tomlenson street/strip heads flowed almost exactly in middle of flows numbers for cleaned up big port heads retrofitted with Stage One valves and Gessler competition port heads. It was dynoed on 93 as they did not have any race gas available that morning. Cheryl
It's not that you can't do it with iron heads. Unless you get a great deal on a set of used, ported iron heads, your going to have the nearly the same money doing a set of irons to support 500 HP, with cams of less than 20* of @.50 overlap (street car) than alum heads cost, that have far more potential down the road. JW
This is a legal PSMCDR motor circa 2009.. NHRA spec compression (13-1), heads and intake as factory produced. We played with the cam a bit to raise the torque peak, to allow for consistent launches on bias ply tires. 3900 lbs car ran consistent 12.30/40 times at the events in full pure stock trim. JW
Not my definition, but TA's: "serious bracket cam, but still streetable with all of the good stuff. Ported heads highly recommended. TA roller rockers and valve springs required. This cam makes serious Power. Rough idle. 10.5:1 or more CR." And, we are still talking a hydraulic cam here - not a roller or solid. I agree the potential and detonation resistance of the aluminum heads is greater (almost out of the box), but a good flowing set of competition ported iron heads on an optimized 464 can bring close to 650 HP with the right compression, hydraulic cam and supporting cast (race gas). My issue was that some people seem to think the iron heads are so anemic (get it), that they can't even muster 500 HP in a well ported condition. Yet, our street/strip ported iron head combo on 93 pump gas was able to go well beyond that well over 20 years ago. Cheryl
Cheryl, DCR is just one factor. While your above example might have a DCR in the pump gas range with a big cam, you'd have to drive it like Miss Daisey:grin: because once you really got on it, I'd suspect it would detonate anyway with iron heads, especially ported ones. Ported heads move a lot more air, and the big cam would have a lot more overlap, so cylinder pressure might be more than you think even with a DCR in the proper range. A quote from Pat Kelly's article I'm always linking, "Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors." My unported iron heads with 9.4:1 SCR, 118 cam, and a DCR of 6.89 would ping at moderate throttle without a little race gas mixed in.
Larry, no detonation on 93 while running 11.7s at 4100 lbs. You also read the part about dc being fixed and measurable in each engine? When it let loose at the track some 4 years later in full street trim in the 11 teens on race gas, 13:1 compression and Gessler heads, there was no detonation damage to the cylinders, heads or pistons. The spun bearing on #3 was fatal though. My main point here is that 500 hp is an easy target for ported iron heads and has been done so in many different ways for so many years that I can't believe anyone can even question it anymore. Maybe you just aren't doing it right? Cheryl
Maybe I'm missing something here:grin: I'm not saying you can't attain 500 HP with ported iron heads, YOU CAN. I'm saying you can't do it with untouched iron heads unless someone has used a huge cam and a lot of compression to do so, but I've never seen that. I'm also saying that it is easier to do with aluminum heads because right out of the box, they flow right there or better than the best ported iron heads. If you can port your own heads, great, but if you can't, to get a set of iron heads to flow the best they can will cost a ton, you might as well just buy aluminum heads. Again, I'm not questioning that you can make 500 HP with ported irons, I'm just saying it is EASIER to do with the aluminums. When I took delivery of my 470, JW told me it would run happily on 93 pump gas, and it does, BUT if I was going to take it down the track, he would like to see me mix in some 110. That was pretty close to an exact quote. I know that too much octane has the potential to slow you down, but to me, it is cheap insurance against detonation. 2 years ago at Cecil, a friend of mine was leaning his carburetor because he saw increasing trap speeds as he jetted down. I asked him if he was running any race fuel in the mix, and he told me no, just 93 pump gas. I told him you are risking detonation, but he disregarded my comments. At the end of the day, the engine was pissing coolant from between the head and block. We figured a head gasket, but when he replaced it at home, the engine started blowing freeze plugs repeatedly. He ended up disassembling it and getting a new block I believe. He told me he saw no signs of detonation. I don't know what else to think. I would never go down the track without some race gas in the mix. I'd rather be safe than sorry. Just my .02
The X-factor is that there are SO MANY variables besides a simple CR and DCR that determine the octane tolerance of an engine. Many more factors with the overall application rather than the engine itself exist. A newbie enthusiast or tuner should be especially cautious. If you've solved that puzzle a few times it's really no big deal. Same with the 500 hp mark.
Here was the original post in this thread.. How hard is it to make 500 HP with a closed chamber/iron headed 455...using Poston S-Divider Aluminum intake and headers? Flat tappet cam & stock rods. Is it really necessary to invest in major port work on iron heads? Looking for good street manners and a reasonable degree of reliability. If it sounds close to stock all the better. Gonna have another big block built - gathering info from the best place possible-right here @V8Buick. Thanks in advance. So, let's disect this and answer it, for those of you who are confused.. How hard is it to make 500 HP with a closed chamber/iron headed 455...using Poston S-Divider Aluminum intake and headers? Flat tappet cam & stock rods. Not hard at all.. Poston Intake is a step backward, but still useable. Flat tappet cam and stock rods are no issue. Is it really necessary to invest in major port work on iron heads? You will spend between 600 and 900 dollars porting heads to the 260cfm range at .500 on the intake.. a reasonable target for "mildly ported" heads, to support 500 HP in a 93 octane motor, with a reasonable camshaft. Cost actually depends on who does them, and where you live. This is over an above the $7-800 worth of parts/rebuilding work to stock cast cores.. You now have a lot of money invested in 260 cfm iron heads. Any aluminum head, for not much more money, is considerably better, right out of the box. Looking for good street manners and a reasonable degree of reliability. If it sounds close to stock all the better. This is the sticky part. Rule of thumb.. the better the cylinder head, the less cam required to get to your goal. And the smaller the cam, the better everything is, in relation to drive-ability, longevity and maintenance requirements. The cylinder head on a BBB is the single most important part when it comes to airflow, and resultant power output. The best "bang for the buck" without any question, is aftermarket alum heads. Even box stock TA or Edelbrock heads, with a 230* hydraulic cam and the rest of your parts, will get you to your goal, without major sacrifices in low rpm engine performance. JW
Here's an old thread that kind of follows the same subject and has lots of good info in it: http://www.v8buick.com/showthread.php?19716-Smallest-cam-to-make-500-hp&highlight=500hp
That is from 2003, so I'd like to think things have changed somewhat. For one thing, we do have hydraulic roller cams now.
That does not change the fact that even with mildly ported iron S1 heads and a comparatively small flat tappet hydraulic cam, the 455 made over 500 HP on 92 octane pump gas long before the advent of the almighty roller. Cheryl
Mildly ported? Probably means different things to different people. According to JW, you need 260 CFM intake flow to support 500 HP. Is that mild porting?
Well Larry, if you read the thread they did not even bother to port the exhaust side and called it a mild port on the intake. Cheryl
