[KEV]

hey guys! Merry Christmas! wanted to know what kind of flow numbers you have on stock 670 heads. NO PORTING, totally virgin!

also, what is the standard/normal flow coeff of a stock 68-70 4bbl cast iron intake?

thanks for the info!

------------------
Kevin Swaney
Gold '66 GTO, 389 4 spd with Trips
13.042 @ 106.64 mph

[KEV]

hey guys! Merry Christmas! wanted to know what kind of flow numbers you have on stock 670 heads. NO PORTING, totally virgin!

also, what is the standard/normal flow coeff of a stock 68-70 4bbl cast iron intake?

thanks for the info!

------------------
Kevin Swaney
Gold '66 GTO, 389 4 spd with Trips
13.042 @ 106.64 mph

[Jim Hand]

Kev,
The flow numbers for 670 heads will be very close to the numbers provided in the 6X post earlier. Using a head that flows 250 @28" average at .55, an iron '71 Q Jet intake that has the runners correctly aligned with the head ports will flow close to 92% of the heads alone. (intake and head together flow 250 X .92 = 230). If a 4 bbl carb and air cleaner are attached to the intake, the overall flow will be around 88-89% of the head depending on the carb type and size. Jim

[KEV]

hey Jim! first thanks for the formula on flow and thanks for the examples. Your examples hit home as im going to build a 406 here shortly.

i think im getting this but i have a few more questions...

the way i calc it (and you did as well) to make 450 HP i need about 219 ish flow at 28". that gives me a peak HP @ 5185 shift @ 10% above that gives me approx 5700 rpm. i understand all that. what i dont understand is why porting would not help or show a benefit at the same RPM?

here is my goal, a 450 hp motor on pump gas running a '66 Tripower. i posted on the old board as to the flow coeff of a '66 Trips and did not get any info. i have heard it is not that great an intake. im guessing high 80s???

here is what i dont understand. im going to make the assumption that i am not running at 100% VE and i am not fully filling the cylinder. if my heads are flowing 212 (stock) and my tripower intake is only flowing 89% then my total flow would only be 188 (which would calc out to max HP of 386 HP). now if i port the head to 240 and i run 89% im now flowing 213. so by porting the heads i compensate the poor flow of the intake. the unfortunate part is that im still shy of my 220 mark i need. how do i know if i am totally filling the cylinder and need more flow with a test such as yours?

now lets say i use the 220 flow and an intake that flows 92% (think that is what your other post stated) that give me 202 flow. now im looking at the issue of PHR that has your car in it. im using 3900 lbs (think im a little low on your weight but will suffice for what im trying to explain) and the 11.880 1/4 time and 112.34 mph. i calc you at 462 HP. 462 HP should need 462/.257/8 = 224 cfm (im assuming that this is a TOTAL flow calculation not just head flow) that is a 22 cfm diff which is about an 11% diff from what the formula "says" you need and what you are actually running with intake attached. this may even be less with the carb and air cleaner on. why the large difference???

i re-read my Pete McCarthy book where he posts some flow #s for a set of 96 heads. they were measured at 10" and were 120 @ .500 if i conver that i get 200 cfm. im confused by the fact that this car was running in the 120 MPH range. Another set of 96 heads measured at 10" 131 cfm at .500. converted gives me 218. these heads were on a car running 10.38 at 128 mph. i dont know the weight of the car but the flow #s dont seem to add up. i would have expected these numbers to be much higher. hmmmmmm.... maybe that is the point your trying to get me to understand.

just trying to get a better understanding. i already have a set of 670 that are supposed to flow in the low 220 range, maybe i dont need much port work???

thanks again for your help!
(sorr so long)


------------------
Kevin Swaney
Gold '66 GTO, 389 4 spd with Trips
13.042 @ 106.64 mph

[Pete D]

Man, this board is sooooooo cool! Great info!

Anyway, I am in a similar situation as KEV. I want to run a tripower with 670 heads. The main difference is that I have a 421. I am really interested in the pros and cons of tripowers. I have read somewhere that they will flow 900 CFM. If another combination will produce more power, that is fine too. I will still use the tripower for "formal" occasions.

I have three intake set-ups actually. The tri-power, a stock Q-jet with Q-jet, and an Edelbrock performer with a 650 spreadbore holley. I just missed getting a 2X4 Offy manifold. I imagine I will have one someday. Something about those dual quad 421's in '63 won't quite leave the back of my mind.....

Jim H, Jim "OM" T, Tom H, you guys are the best!

[Jim Hand]

Kev,
So many questions and so few answers! The reason I have run so many test runs over the past 12 years, and will probably continue to do so as long as I can, is to try to get answers to questions about effects of all parameters on real at-the-track performance.

Here are some positive aspects we are sure of:

1. Track performance on a multi speed/rpm car is not dependent on peak HP! Rather, it is dependent on the total average power of the engine during the entire rpm the load is on the engine. Reread Tom Hand’s post on exhaust selection, and note the comments from Ed about this subject.

2. Peak HP numbers from a dyno test do not necessarily directly relate to performance at the track! Such things as transmission/converter loading/operation, power used by belts and pulleys, where in the rpm range the power is developed, exhaust system used, restriction of on-the-car air filters and cleaners, fan power used, alternator power used, wheel bearing settings, tire pressure, wheel alignment including rear end alignment, traction, and many other factors, may drastically affect final performance at a track.

3. Using airflow to estimate power/rpm can give us usable and practical info about what is generally needed, but will never accurately predict final performance. The VE of the engine, which is dependent on CR, cam efficiency within the rpm range used, tuning effects of intake and exhaust, mechanical losses within the engine, mixture velocity through the intake system, and a host of other areas, will define the final power output. Two engines with the same airflow capability, or even air used, can have serious differences in performance, depending on where the power is made, and how it is spread over the load range.

4. The formula normally used to calculate HP based on drag strip performance determines power at the wheels. Dyno power of the same engine may be completely different!

From an idealistic standpoint, we would like enough airflow to guarantee that it is adequate for our specific setups, but along with that, we want the best possible port velocity and low lift flow numbers. Unfortunately, these three areas are not always mutually compatible. That is why we have suggested, based on our research and testing, that best performance will be obtained with heads that have a good balance of these three attributes. I would like to quote a paragraph from the 1999 Edelbrock Catalog, page 98, and I would suspect they know about as much about this subject as most:

"Bigger is not always better. A large flow number doesn’t always mean more power. This is especially true with street cylinder heads and in some cases, race heads. Velocity is as important as flow. A smaller port volume generally equates to higher velocity for better street performance. The speed of the mixture determines how tightly the combustion chamber is packed. The more tightly packed the combustion, the more pressure is developed when the mixture is ignited, pushing the piston with more force for more power. For example: A large port and a big flow number at .600 lift means low velocity (especially off-idle to 3500 rpm) and results in less throttle response. For the street, velocity is the key to overall performance".

Kev, in regards to Tri Power, many have and are running very well with this system. I suspect you could use the high 80 percentile area (of heads alone) for estimating air flow through the entire system.

I am not sure what you where indicating about relative numbers on my engine, but according to my measurements and calculations, the engine is not using the total head flow of 254 cfm, at least for developing peak HP. But again, it is not peak power, but total power during the entire rpm range the engine is loaded that determines track performance, and this is true for any combination.

Huge airflow numbers are not required to run well and do not guarantee that a car will run optimally. I know a fellow in the Boston area (Don Greene) who is running mid 10’s in a 3600# car with heads ported by Pa. Jim Taylor that only flow 240 cfm at 28#. I also know these heads have a good balance of low lift flow and velocity! Don is running a good solid roller cam in his basically stock short block 428, along with a carb and intake that he has selected based on at-the-track testing. It has taken him several years to reach this level of performance, but it again proves that performance is in the combination, and not in one individual item. Also, this car is only a license tag away from going back on the street, so if Don wanted, he could call it a "street car"!

Don’t ever give up on going quicker and faster! It is usually a combination of little gains, rather then the one giant bonanza, that makes our cars perform as we wish/want. Jim


[This message has been edited by Jim Hand (edited 12-26-1999).]