Awesome! What they going on?

Do they do the work themselves or sublet ? Either way, get references or reviews on whomever does the work, even if them. And yeh, make sure they know marine...quiz them on what margins and guide clearances they use. Don't just go by 'Yes, we do." Might as well get all the installed (not on paper) spring psi info too. This stuff can be important so it doesn't bight you in the azz.

They are going on a pair of 575's in my Velocity that I tore down for no good reason. They looked great inside, but the boat was new to me and I wanted to know what I had. In the end I know I will have bigger cams, bigger blowers and better heads and fresh bottom ends. :D

I was going with Dart IE 308's, but even through Atech, I couldn't beat the price on these heads. My last personal motor had a set of 308 Iron Eagles worked over by Jim Valako and they made killer power. These will have boost to help thing along though.

What heads are you not using??(what was on the motors)?

Im assuming the stock 575 GM heads.

You're gonna make quite a bit more power than the stock 575! :drink:

This guy is on it! LOL.
Yeah Phragle they are stock 575 heads. The heads are in nice shape but I tend to get caught up in that "for just a little bit more money I could...(insert whatever part or upgrade here)"
I also seem to go well over budget on any build I do for myself...I think the two things might be related. LOL

Very true. Part of why I bought them bare and putting together with my own parts. BUT, if its worth it to buy it all as a package, then I'd say buy it that way, and then go thru and check guides and valve job, etc. That goes for any head imo. AFR's heads drop shipped with an inconel valve upgrade, do not come with "special" marine seat width valve jobs for forced induction marine, or special guide clearances. They are the same head, that you get if you were ordering them for a Chevelle street build, just with an inconel exhaust valve, unless of course you buy them from Teague, who machines them in house, or someone like that. If they are coming from AFR's factory, than it is what it is.

Engine quest's recommendation for guide clearances on those heads is .0015"-.0016", exhaust .002"-.0025", and they are marketed for marine engines and big power truck puller applications.

I totally understand this! Story of my life ha-ha.

So much for wondering if you had a decent set of older alum heads you werent going to use for sale cheap.... lol

I have a 50 hour set of AFR 335cc full Cnc I will be selling if that piques your interest.....

Why you gotta be so big headed??? I am building a 489 so Im looking for something a little smaller.... Thanks though...

I have some peanut port heads in the back of my truck for ballast while plowing.need a pair.:D

Allready have a pair.....

I think I have a can of aluminum paint. I can "convert" a set of these 575 heads to aluminum if you want.

I know, I usually have a hard time fitting through doorways. Haha

That things gonna fly

After doing a lot of research I think I'm leaning away from the EQ heads for this build and I'll state the reasons why.

First, it has nothing to do with the quality of the head. From what I'm reading and hearing they're a good head.

However, I don't think the head is going to meet the needs of my build primarily because the intake runner is too large (320 cc). I'm building a 509" MPI engine and there is a lot of restriction in the throttle body and more importantly the intake manifold. With a 320 CC intake running, it's probably going to have most of it's power gains above 5000 rpms and this engine is going to be a 5200+/- engine.

EQ also makes a replacement GM head but looking at the spec sheet, there's no real advantage (in my opinion) of going with that head because it doesn't have a rolled valve angle, raised exhaust port, upgraded valve seats or bronze guides for example. So even though it's cheaper, it doesn't meet my needs.

I feel that I need to put a head on this package which has a smaller intake runner such as the Edlebrock Performer RPM, Victor Jr, AFR 290 or largest port being the Dart Iron Eagle 308 CNC.

I ran a Dart 308 Iron Eagle on my old 540 MPI build. Ports were still much larger than the MPI intake runners even after extrude honing. Engine had fantastic low end torque and was a runner. Was around 600 hp but major intake mods and .610 lift cam.

Thanks for the info! I'm expecting this build to be around 500/525hp.

Just my opinion, but i wouldnt write a head off simply on port volume. If the part is designed properly, it will have better airspeed and flow. The stock merc head has similar volume, however, the overall flow and port speed is lacking. Hence why if you were to swap that merc head, out for even a 335cnc afr head, you will still likely see more torque and power across the board from better cylinder filling.

Big ports dont necessarily mean poor airspeed, and small ports dont necessarily mean better airspeed.

I know of a builder who recently did a pair of 525 merc upgrades. 525 has edelbrock rectangles, which arent big flowing heads, and have a 315cc port, made 650 plus ft lbs of torque, and around 590ish hp at 5300.

Id be hard pressed to believe, that the EQ head, with its good airflow, good wet flow characteristics, would perform any less than those edelbrock stock exhaust port location heads .

The afr 290 is a sweet head, but whats the price difference ?

Arcticfriends has a thread going with a lot of dyno time wth the mpi intake and different throttle bodies

Ive seen where guys go in and port heads , and gain power afterwords. If properly done. This sometimes involves doing some bowl blending, thinning of guide bosses, and other cleanup. The material removed that increased flow, also increased the actual volume of the port. But the engine made more power and torque from better low lift and mid lift airflow and cylinder filling.

Pour an intake runner on most of these heads, esp ones that have had some cleaning up, and compare the actual cc's, of both ports, to the advertised port volume. You may be surprised.

I've been watching it, it's a great thread. Very informative.

The intake runner/plenum is going to be modified but not the TB on this build unless the owner wants to invest in it.

There's no data out there that I can find supporting running the EQ heads on a 502/509 MPI build. I have to put my name on these and I'm not going to take a chance with an unknown combo. They may very well be a good choice, I'm just not willing to take the chance without hard data for this exact combo. If it were my own, I might take a chance but not with someone else.

Phragle, a friend has a nice lathe in his garage and modified his EFI intake a number of years ago so he's gonna hook a brotha up! I'll also port match the intake to the head.
[ATTACH=CONFIG]551227[/ATTACH][ATTACH=CONFIG]551228[/ATTACH]

Buddy of mine is doing a stock headed/fairly stock intake build 502mpi and is expecting about the same 500-525 hp result. You should see 525 easily in the iron eagles and some intake massaging easily. If not 550

With the intake being such a choke point, even if mildy worked on, I would think the larger runner heads (320) which include OEM would not be a 'good' choice. I would think the Iron Eagle 308's would be the better choice here.

A lot of thinking huh ?

BTW: Speaking of 'smaller heads' On the net , Saw a few AFR 300 's (roval) go nuts on power. One 460cid and one 555. 460 had 11.1 compression and went to 800hp. I believe the 555 went 850.

BTW#2 Panther: I would strive for a little better transition into the top of those MPI runners than what is shown in the pic. At the min, round over that center divider. Remeember, air has mass, and when it goes into those runners as in the pic, air will try to flow towards the center of the runner (again, at the runner) and effectively make that section of the runner act if it was narrower.

I agree! I think that pic was taken right off the mill and it was smoothed over by hand. That's what I intend on doing with this.

Also, Dart now has a CNC 308 which I think is a good choice over the regular 308.

Its actually a 330 cc iron eagle in the cnc version.

runners are too big... and the chamber size is too large also.

Pretty sure its basically a ported 308. When you port a chamber, it gets larger. Same goes for ports. Hence the 330cc and chsmber grows from 121 to 126.

Id personally take the benefits of valve unshrouding, and low lift airflow gains, with a ported chamber , over 5cc worth of volume

Compression ratio would be too low so the gains could be lost. Would have needed to build the engine around the head in my opinion. And again, not really looking to test the theory on someone else's stuff.

I'm not sure if you've worked with the MPI's before but the intake runners are very long and restrictive. The throttle body is also very restrictive. Because of that it's a restricted engine and need to have a good amount of port velocity and make power in the mid-range up to about 5200-5400 rpm. I'd rather put a smaller port head on it that's going to maximize flow within the operating range and in general that's going to be something with a 280-290 port size.

I'm sure it would work, just not certain it would be the best choice. Also, taking compression away can also be a negative affect.

Too many generalizations and assumptions regarding port volume and head performance. Head performance comes form flow and velocity. They have to work together. The velocity factor comes form the minimum cross sectional area of the port and on a conventional BB Chevy head this area is usually just past the push rod "pinch". Mean flow numbers are what they are, and the smaller the cross section, the more velocity the port will have. Old school BB Chev heads like the OEM rectangle ports and older Brodix and Canfield heads that were designed after that have a lot of volume in the front of the port with large minimum cross sections ( big rectangle port) but have relatively small bowls. Then you can look at something like a Dart or AFR and you see the port is a lot smaller in the front with smaller minimum cross section and more of the volume is in the bowl, after the short turn. You can have three different 320cc cylinder heads and have three completely different velocity profiles and three completely different power potentials. I just finished a set of AFR 315's and did a 2.300 intake valve upgrade with a lot of bowl and short turn work. I didn't change the minimum cross section at all because it's already a little on the big side for what i want but the work increased the airflow significantly, so now the velocity will be closer to where I want it through the minimum. These heads are probably in the 325cc range now, bit with the small cross section of the 315 and they will out flow the 335 cnc. My guess is (without measuring them) the EQ heads are probably relatively small in the front and will work fine on a 500+ci engine with the right cam. They're not ideal, but for the price could be made to work real well. I wouldn't lose a minute's sleep over using them.

Here's the 315's I'm doing. I'm leaving the burr finish.

https://scontent-iad3-1.xx.fbcdn.net...c9&oe=572EB5D4
https://scontent-iad3-1.xx.fbcdn.net...ce&oe=577130E0
https://scontent-iad3-1.xx.fbcdn.net...92&oe=5765AEDA
My office...
https://scontent-iad3-1.xx.fbcdn.net...e6&oe=57269ABE

For those interested in numbers:
Flow: (4.50 bore, 2.125" pipe on ex)
right / left / ex

.2 165.5 / 164.2 / 120.8
.3 249.2 / 245.6 / 204.4
.4 306.9 / 300.5 / 249.7
.5 351.7 / 344.7 / 277.3
.6 382.9 / 364.2 / 290.2
.7 398.1 / 382.9 / 302.7
.8 404.2 / 394.6 / 313.4
.9 411.0 / 401.9 / 318.2
1.0 412.1 / 405.6 / 321.7

Right port on 4.60 bore (just for reference to AFR's numbers)

.2 166.0
.3 250.7
.4 312.4
.5 357.0
.6 389.3
.7 403.0
.8 406.2
.9 412.8
1.0 415.4

Great explanation scott.

I see way too many people generalizing over a port volume, rather than talking about the port itself, and how its designed. Pretty much everything you said, is what my cylinder guy has told me in coversation.

I think generalizing that a 320cc head wont work, but a 308cc will, without any further discussion of the port, is incorrect way to put a combo together. I also disagree that a static compression number, is a make or break of an engine combo, within reason. Ive seen 9:1 engines smoke 11:1 engines.

Sometimes the final performance numbers tell us something. I am changing some things on my engines this winter. I will be redynoing the engines, on the same dyno as i used previously, and am looking forward to whether they gain, or lose, based on my choices made, and ultimately how the boat runs when its together.

A set of cnc heads would have been nice, but the budget only goes so far.

I have said a few times now that I'm not looking to use something that I haven't seen results I can go to the bank with. I also said a few times they might be a good choice but I don't feel they're ideal for me for a few reasons. We can speculate all day about port design, flow characteristics, cross sections etc but until I see that it works for what I'm doing I am not going to recommend spending someone's money and rolling the dice. I don't mind innovation but I don't use my friends money for R&D. It's really that simple...

Having said that, I still appreciate all the input.

I've got an odd question. I don't believe I've ever seen it asked so here it goes.

Why haven't I ever seen a flow bench done with an intake manifold bolted up?

Like in my case, you have a very small and long intake runner that could be potentially matched up to a large intake runner.

When porting and flowing, would it be beneficisl to have the intake bolted up so it's a part of that equation?

I'm not a head guy so I'm just curious?.