Head Games-AFR
 

Have you guys seen the Head Games article in the Dec/Jan issue of Family& Perf Boating magazine?

I have been toying with the idea of installing a different head assembly on my stock '98 502MAG MPI. Dennis Moore's book suggested such a thing for more torque and HP's.

Not being a Tech guy, I do understand the concept, I have been hoping for an article on this subject.

Excuse my ignorance, but what is the difference between a 502 GM crate engine and my 502 MAG?

According to the article the stock crate motor pulled 530HP's on the dyno? Then the AFR head, cams and intake swap added about 200HP's.

Can one assume similar results on a stock 502MAG 415Hp's to net 600HP's +?

What else would/should need to be done, an exhaust header would make sense to me. ECU calibrations? What else?

How much is something like this going to cost?

Thank you in advance for any input.

Jamal

Anyone?

Is this a stupid/ignorant question or has no one read the article.

If it is an old beat to death topic, please let me know.

Thanks,

Jamal

Jamal,
I read this article also and I figure they started with a 502/502 HP crate engine from GM Performance parts. I am not an engine guru by any means but I would think that your engine would respond to these heads quite well. I would think that the power output would be limited by the efi intake manifold your 502 mag has. I know that John Lingenfelter used to work some magic on the 502 EFI's but his work does not come cheap.

AFR
 

AFR BEST BANG FOR THE BUCK BAR NONE. WE HAVE RAN 2 SETS ON OUR RACE BOAT ALL SEASON AND HAVE HAD NO PROBLEMS.:D

I'm building a pair of Dart 540's with AFR 315 CNC heads. I usually use Dart CNC heads. The castings are nice, better than the AFR SBC castings I've used in the past in automotive applications. Out of the box, their flow is hard to beat, and the thick decks are nice, especially in a marine application. I bought mine bare, but fully CNC'd with copper-berrylium valve seats and hard anodized. There was alot of nice detail work, including hand plending of the seats to to ports and around the guides.

I'm putting them on the flowbench with some different intake combinations, so I will be able to verify AFR's flow/cfm claims. Actually, I'm using Del West valves, so I'm expecting a few cfm better than what AFR claimsI should have the engine's on the dyno by Thanksgiving, we'll see how they do.

The head game is AFR flows their exhaust ports with a pipe on the end of the port. The pipe increases airflow up to six percent making the numbers seem higher.

Jim V, Can you improve on these AFR heads?

The difference between the crate502 and MPI502 is the heads and cam and the EFI. You are best to stay with a proven package for the MPI. If you change the heads and or cam then you will have to change the ECU program. The question is will some off the shelf ECU reprogramming work with this combo. Who knows.

I read the article and I don't think the dyno testing that the magazine did wasn't thorough enough. It was a little mis-leading and not really fair because they didn't test the heads back to back on the same engine. They removed the stock heads and then added the AFR's but then they added several OTHER hi-perf modifications/components to the test engine as well and it showed the AFR's making 200hp over the stock heads---------and that is fine BUT they should have also done a HEAD SWAP-----A HEAD SWAP ONLY! I wrote the editor a letter about it. It wasn't as informative as it should/could have been. My .02 of course :(

Plus, from other articles I've read, Westech's dyno is rather 'generous'. It makes for great magazine articles.

Marty

A 2.300 intake valve should flow about 400 cfm @ 700 lift. The exhaust about 300 cfm. I dont remember what the AFR heads flowed on my bench. Many don't understand the difference between a marine head and a drag race head. A drag race head is designed to flow at 800 lift and higher. Most cnc heads are cut for drag racing or max flow at 800 lift. To get this the venturi area has to be larger. The venturi area in a marine head should be smaller to maintain air speed and to peak at a max lift of maybe 650.

The same with the exhaust port example the Canfield heads flow a butt load of air at .850-.900 lift but are dead at lower lifts. Im not flaming Canfield or AFR, they make a great product but I dont think they have a different cnc program for marine applications.

Jim V,
So what would be a good "Marine Head" for a N/A 496 Stroker to a 502-509 inch motor?
Is there one particular head that would be good for this range of size engines or is it more specific on displacement?
5500 max rpm and around 9:1 - 9.5:1 Compression ratio.
Thanks for any reply.
Russ

Edelbrock marine oval ports? Anybody like those???? 1400 bucks from summit hard anodized with inconel exhaust valves.........

What's your verdict on them Jim? I haven't heard anybody that uses them......

I was hoping that this would have been a simple head & cam swap etc. with a proven reliable kit.

Thanks for the input, as I kind of knew that this would be too good to be true. It usually is.

Any proven bolt on kits out there for a MAG 502 MPI? Motor runs great, I do not want something that needs to be dialed in with trial and error.

Thanks,

Jamal

If anyone has dyno tested the AFR 315 CNC'd heads or flowed them on a flow bench please post it here for us---thanks!

KAAMA,

I'll have flow bench results with AFR 315 CNC ported heads within the next week or two. I ordered my heads bare because I prefer Del West valves over Manley, or whatever else AFR uses, and I'm just waiting on the valves to be back cut. Should be done anyday now.

Both 540's will be dyno'd within the next month with AFR 315's, Crane 741, Holley 850, etc. The last component I need to order is the intakes, and that decision is partially based upon some hatch clearance measurements I'm waiting on from Doug1. It's either Victor Jr's or Airgaps. I'll probably end up with the Airgaps cause I've got a tight fit and I don't think I can squeeze the Victor Jr's in.

RLW, thanks but that website is limited in the castings they use and I could find any test data on the AFR 315 CNC head.

Monty, I've been waiting so much in anticipation by chewing on my finger nails that they're begining to look like I've been using a chain saw on them! The suspense is driving me crazy! :crazy:

Monty---Why are you using the Crane 741 instead of the 771 ???
Crane recommends the 771 for 540 and bigger cubes.

Monty, I don't believe an 850 is enough carb for ported heads on a 540. Look at the bsfc and A/F ratios on one of ours with a 1050.

Rod

Rod,

I hear what you're saying about using a Dominator, I briefly considered it, but I'm building my 540's to maximize mid-range power and torque and the 850's were a better fit, I beleive. Those BSFC numbers and A/F numbers don't look that bad. Generally, .50 - .55 bsfc is what can be expected from most engines NA engines. Obviously, highly tuned racing engines or forced induction engines will have different results/requirements. Most NA engines generally make best torque(max VE) at around 11.8 - 12.2 A/F ratio, and best power in the 12.8 -13.0 range.

With 540 ci it's not too hard to build more power and torque than the TRS drives can reliably handle, especially with good heads. There's always the tendency to go big when it comes to choosing heads, cams, intakes, etc but I've always focused on desinging the engine for it's realistic application. If I had #3A drives or better, beleive me, the engine's would be alot more impressive.

I'm not building the engine's for maximum power or rpm. My goal is only about 600-625hp. RPM will be limited to ~5500 for the sake of reliablity, throttle response, area under the curve, ease of maintanance, and compatibility with what the drives can handle.

(540 x 5500)/3456 = 860cfm @ 100% VE

My engine's will probably average 85-90%, so even at 90% VE, the engine's will only require 773cfm at 5500 rpm. Even at 6000 rpm, with 90% VE they only require 844cfm. Obviously, the carbs will be maxed out, but at anything less than max rpm, the result will be very good throttle response due to the strong venturi signal.


As for using the 741 cam vs. the 771 cam, Again I just felt it was a better fit for my intended rpm range and 9.0 compression ratio. I actually debated between the 731 and 741. While the 741 is generally recommend for 454-502 ci engines up to 6000rpm, it's also recommended that dry headers and a 10.0+ compression ratio be used. While my displacement is about 10% larger, I'm only running 9.0 compression and wet Stainless Marine manifolds up to ~ 5500 rpm. The duration fits my rpm range, and the lift and lobe intensity is such that they won't beat up valve springs or require alot of valve spring pressure. I don't want to worry about changing springs and lifters every year.

Hey Monty:

Considering what you drive on the street, I admire your restraint on the 540s.

Yeah, LOL. The reason for my restraint is mostly due to my wife. For some reason she has a real aversion to being stranded out in the middle of Lake Michigan on a boat, so durability and reliability were my primary considerations. It's self-serving in the long run.

Monty, this what we use and why. The cam you have chosen is more than what is in the engine that the dyno sheet is from and AFR heads should flow more than stock VE numbers.

You obviously have a wealth of knowledge and I'm not trying to start an argument, just share a little of what has been working for us for the last few years.

CID x RPM x V.E. / 3456 = CFM

That formula is still being quoted by magazines and companies etc...but times have changed. 10 years ago a carburetor would require 10 inches of water to pull signal and shear fuel. Now they can can pull and shear fuel at only 3. Remember 20.4 inches of water (wet) is the cfm rating guide with reputable designers.

20.4 = 1.5 hg.

CID x RPM x V.E. / 2820 = CFM
540 x 5500 x .9 / 2820 = 948 CFM

The Society of Automotive Engineers (S.A.E.) established a standard test vacuum of 1.5 inches of mercury for a 4 barrel carburetor as a test standard. Most carburetor manufacturers and custom carburetor modifying companies measure their carburetors using dry flow CFM (cubic feet per minute) and some companies will only flow 1 barrel, then multiply times 4 to arrive at their overall CFM air flow numbers.

A carburetor in actual use on an engine has to supply fuel for the engine to run, and this is called wet flow. For example: A standard carburetor rated at 750 CFM actually tested on a wet flow bench will flow 690 CFM to 700 CFM. This is why industry professionals have always suggested that after you calculate your engine air flow supply CFM requirements, you always buy a larger CFM rated carburetor.

After all that, I agree that the 850 will probably be more responsive up to the point that the secondaries open. After that I think the dominator will walk all over it as well as be more fuel efficient. If you need a dominator to try, I'd be happy to borrow you one.

Rod

Rod,

You make some very good points, and I'm not disagreeing with you either. You're entirely correct about accounting for fuel displacement in the cfm calculation when discussing wet flow vs. dry flow. To be honest, this is the mildest engine I've ever built. Actually, it's the first carburated engine I've ever built, so everything has always been dry flow.

I've always used FAST programmable EFI before with wide band O2's. I feel alot more comfortable with my laptop than a screwdriver and a jet kit, but I've already got so much going on this winter with the boat, converting to EFI would have put me in jeopardy of not being ready come spring time. Next winter I'll add the EFI, that's one reason I'm trying not to invest too much in the induction system at this point. Part of my engine combination decision was based on the current situation, as well as what I'm planning for next year. Plus I'd rather wait for the new FAST or Big Stuff III systems which should be out by then.

Additionally, I've already got engine hatch clearance restraints that are limiting my intake selection, which in turn affects what carbs I can use. Most intakes with a 4500 bolt pattern are much taller, such as the Super Victor, and would never fit under my hatches without adding scoops or raising the hatches several inches. Even a 1" spacer is most likely not going to fit, which is probably worth a cheap 20 hp. I'm willing to raise them an inch or so, but I don't wnat to get more involved than that, and scoops are out of the question - so says the admiral, lol. When I go to an EFI manifold next year with a forward mounted throttle body, the hatch clearance won't be as much of an issue.

In any event, I think that the 850's will still support my target 600hp at 5000-5500 rpm. I'm sure the Dominators would give me some additional power above 5000 rpm or so, but I don't see what good it's going to do me if I'm already pushing the limits of the TRS drives as is. Maybe I'm underestimating what I can get away with without sacrificing too much drive reliability. It's just that I've been told be a few people (BAM, etc) that anything over 500hp or so is asking for trouble with them.

Monty, no problem here at all and please let me know if I can help in any way. Thanks

Rod

Thanks Rod. I'm new to high-performance boating, my previous boats were cruisers, and my previous engine expereince has been high-performance automotive. While they are mostly similar, there are some unique characteristics that need to be addressed. I have heard many good things about you and your shop, and I appreciate the time you took to look at my combination and offer suggestions. It is always beneficial and valued to have experts offer opinions and suggestions.

Here's something to consider....
 

This is only what I have based on my experience, but when I originally built my 540's with a mid-grade porting job on the Dart Pro-1 310cc heads, hyd roller cam 236*/244* on 114* lobes with I an HP830cfm Holley carb. With that carb on Tom Earhart's dyno it produced 630hp @5400rpm. Tom commented that in the 20+ years he has been dynoing engines he never saw an engine follow as well as mine did that day with the carb/engine combination/set-up. I asked him to translate what he meant by "follow" and he said it had very crisp throttle response and the power curve was "right there".

The next year I had the heads FULLY ported and increased the comp ratio by about 1/2 a point. Only this time I added a HP950cfm Holley carb and we headed for Tom Earhart's dyno again----however we still took one of my 830 Holley's with us too for comparison. The only time the 830 out performed the 950 was at 3000rpm and below otherwise the 950 beat the 830 by 16hp at best. If I remember correctly the 830 began to fall off at between 5200-5400rpm and that's where the 950 continued to make power up to as high of RPM as we wanted to run it which was 5700rpm. At best the 950 made 16 more HP on top over the 830 and varied between 1hp/tq and 16hp/tq from 3000rpm up to 5700rpm. The 950 still gave me good idling charctoristics on the dyno and in the boat it will idle just as well as the 830 did-----@775-825rpm in neutral and @550-600rpm in gear with 32" Bravo One props. I don't have the dyno sheets in front of me so I cannot be as precise as I would like.

I'm sure the Dominator would give you a little more yet as Rod has mentioned. He has given some very good info here and it's really nice and interesting to see all the differing comparisons. However, if 600hp is your goal, I am quite confident that you'll get all of that and MORE with the AFR heads, 741 cam and an 850 Holley. ;)

Kaama,
I'm not disputing what Rod said. He was kind enough to offer me and others some very good advice and suggestions.

If it weren't for the engine hatch issues and the limitations imposed by the TRS drives, I'd be running Dominators with Victors/Super Victors. I know I would make more power with Dominators and the taller single planes. However, don't discount the performance benefits of increasing your compression when comparing your dyno results. Obviously, the bigger carb accounted for some of that. You didn't state what your static compression ratio was and is, but in the 9.0 to 11.0 range, increases in compression generally have the most benefit in terms of percentage.

But unfortunately, I don't even know if I can fit a Performer RPM or Airgap RPM under the hatches without rising them some. That limits me to a 850 cfm 4150 carb , which I beleive is the largest Holley Marine carb available.

Assuming a Dominator and a single plane would give me 30-40 more hp around 5500 rpm, what's that (x2) going to translate into in terms of boat speed? 1-2 mph? Is reworking the engine hatches worth it?

You guys are a bad influence, lol! Here I am trying to be good and conservative, and you're putting thoughts of "more power" in my head.

By the way, anyone have any idea what the mechanical efficiency of a built Velvet Drive and TRS combination is? i.e. if I have 600 flywheel hp, what would I typically estimate my "prop" hp to be? The reason I ask, is that the boat currently has 15 x 21 props on it, which I will need to replace. Just trying to get an idea of what props I should start out with.

The bravo uses about 30 hp at the 500hp range and the TRS with trans about 50 or 10%.

I totally agree---Rod always offers great advice/help! :)

In my previous post I was actually trying to discourage you from going out and spending more $$$ on a carb when I am quite sure the 850 will net you the 600hp you are looking for. :)