Young Performance

I think that the Merlin heads contributed a lot to the power increase. Just after I did those 3, I did another just like it with Dart Pro 1 345's. I knew the head was big. The customer bought them used at a good price and wanted to eventually run a Procharger, so I decided to use them. Everything else was identical to John's 3 engines. It only made 550 hp with the aluminum heads. I had a hell of a time even getting that much out of it. Obviously, the heads were just to big. I still didn't think it would hurt it that much.
I can't run wet headers on the dyno so it is def. helping with power. I would absolutely love to run them wet, but can't figure out a way to do it without the neighborhood *****ing. We did run all of the accessories, including the p/s pump.
The boat has picked up quite a bit of mid range and top end speed, so they are definitely making more power. I am about maxed out on injector as well. At the stock pressure, the injectors are good for just over 600 hp. With a higher base pressure, you can squeeze 650 hp from them.
Bottom line is that I didn't think the heads were doing that much for power, but they must be. The raised exhaust port and larger 11/32 valves are making a bigger difference than I thought.
Eddie

Young Performance

Forgot to add that since i don't really do any stock engines, I don't have a baseline for a stock 500 efi.
Eddie

bobl

Good info. I built a huge aluminum box that I dump the wet exhaust into, then mufflers out the top and water drains out the bottom. I measured 85db on a 900HP Whipple motor standing about 10 feet from the box at WOT vs 120 db open, so it works pretty good and didn't hurt power at all. We are in the country so we don't really have any restrictions to worry about. The added benefit is I have no heat in the dyno room. Even when I run dyno headers I dump them into the box and just plumb enough water to keep everything cool. About 99% of everything we do is marine. I do believe running wet exhaust costs a significant amount of power over dry tails. One of these days I'll have to actually do a comparison test. I just have to figure out how to run them dry on my setup.

Bob Lloyd
Full Throttle Marine

Young Performance

My problem is that it isn't my dyno. I use it, dyno my own stuff, and come and go as i please, but at the end of the day it isn't mine. They do mostly street and drag race stuff, so they have no use for wet exhaust. The problem is trying to make it work both ways. That's what I haven't been able to figure out. I would also love to see a back to back comparison to see the hp difference. There is no doubt that there is a difference. I'm just not sure how much. If you ever find out let me know. Thanks
Eddie

frontline

Thanks guys can anyone recommend specific info on which heads afr-dart cam 741?, who sells throttle body and who can remap efi box?

articfriends

iTrader: (1)

Lets get a few things straight: a STOCK hp 500 makes 505-510 hp at the crankshaft and that is using the sae J-1349 dyno correction factor. Every performance shop except for most oems uses j-607 which will typically give you hp numbers that are more generous to the tune of 5 %, to the average guy this sounds real technical and confusing BUT what it really means is that 510 hp that merc gets magically turns into 535 hp on most dynos using the older, more generous J-607. Add some dry headers which should be worth 25 hp that hp number now becomes 560 hp, so a fresh stock merc hp 500 with dry headers on a dyno is now a "560 hp" motor even though NOTHING has been really changed. Add a better cam, bigger throttle body and a set of Merlin heads , which by the way ONLY flow about 1.3% better at .600 lift intake/4% better at .600 lift exhaust (un-ported): (merlin Grumpy Jenkins 310's vs GM 990 317's))
http://users.erols.com/srweiss/table...hevy_Big_Block
and I wouldn't be surprised if that 560hp could become 600-610 hp. Now, if a guy had some high hour hp 500's and they weren't putting out the hp like they did when they were new , yes, the boat would pick up a decent amount of speed but without investing in a seriously performing head don't expect a ACTUAL 100 plus hp change, Smitty





"You need to understand that Mercury Racing has been for a long time establishing for them selves an engine horsepower rating on the Racing engines only that represent approximate horsepower at the prop or less drive losses. When others look at Mercruiser engines ,ie the MPI's, EFI's, 496's and now 502HO's etc. they are using engine crankshaft horsepower as their advertised horsepower rating, no drive losses or horsepower at the prop.
On the Mercury Racing HP500efi the engine really makes about 505-510 HP at the Crankshaft and about 470-480 at the prop with its Bravo Drive losses.
The Mercury Racing hp525efi makes about 550-560HP at the crankshaft and this results in about 525HP at the prop in a Bravo XR ( bigger drive losses in an XR)
When Mercruiser 496HO's for example are measured at the prop they have shown to be about 390-400HP at the prop in a standard Bravo 1 or 1X drive.
The differences here are mostly due to the way two different divisions of Mercury Marine choose to rate and measure their engine offerings horsepower and this has obviously created a lot of confusion for customers who view them all as Mercury Marine engines.
Kind of a simple way to remember:
If its Mercruiser black its at the crank
If its Mercury Racing Blue its at the prop

Also keep in mind that most aftermarket marine engine manufacturers like ourselves measure our horsepower at the crankshaft on dyno's with most using corrected outputs with all accessories running on the dyno.

Hope this info helps with some of the confusion.

Best Regards,
Ray @ Raylar"

articfriends

iTrader: (1)

If you are looking for a real noticeable hp gain invest in the best heads you can afford, stay away from out of the box "world" heads as they barely flow more than stock rectangle ports, Smitty

HaxbySpeed

Here's one I dyno'd for a customer, built by an OSO advertiser.

500EFI, AZM monoblade, the same merlin heads with a little clean up and port matching, all accessories, full wet exhaust with factory tails, stock cam. 300rpm/sec. standard correction. I don't think the heads did anything for it in this situation.

My dyno is generally very conservative but I think you'd need a hell of a camshaft to make 600 with this one. I don't even know if RMbuilder could pull that one out of his hat, and I've seen him come up with some incredible results.

I've seen around 30hp on a 600hp engine from wet to dry, but the biggest problem I find is the difference in tune up from dyno headers and an airflow turbine to wet exhaust and a flame arrestor is huge. With a variable load dyno and the engine in complete trim you can really get close on your fuel map before it goes in the boat.

I can do a controlled back to back, wet vs dry on the next one on the dyno if anyone wants?

Raylar

I have a great deal of respect for both Bob at Full throttle and Eddie Young as engine builders and testers so please all take may comments here as not the only or last word but as just to what I have seen and done with Merc EFI engines. Both are being as honest and candid as their situations and test facilites can provide and we can all agree that almost no two dynos in seperate ownership are going to provide the same test outputs all based on correction factors, calibration, machine type, wet versus dry exhaust, and propshaft versus crankshaft measurements.
My expierenes would lead me to say that based on the construction and design of the World iron heads in question here and the cost of a full new set of heads that money might be better spent upgrading the flow characteristics and performance of the stock GM iron heads. (Remember here that Eddie stated the stock iron heads were rusted up beyond good reuse) I think we must also realize here in this case that in a triple engine boat even adding 75-80Hp for three engines to achieves 225-240 HP increase for the boat is going to produce some nice added boat performance in an efficient hull type.
What we always seem to find in both the HP500efi and HP525efi engines is that its really more the intake manifold and in the case of the HP500efi the throttle body also that tend to be the power limiting parts. We did some pretty good experimenting on heads, head flow to power development, intake manifold conditions and restrictions as well as manifold modifications to determine where addtional power was possibly hidden in these engines. what we ultimatly found was that the use of an good (optimized) aluminum head with its resulting better compression ratio changes allowed, a rework to the intake base manifold and our plenum redesign along with the monoblade throttle body made the best power increases and volumetric efficiences. I think on a HP500 efi with its E-top headers and a good cylinder head, reworked intake manifold and throttlebody and the correct camshaft selection 580-600HP is very achievable on a good corrected dyno test. To get to the 675-700HP we achieved on the Raylar HP675efi engine package we had to do special cnc and valve size upgrades to the stock Merc/Edlebrock aluminum heads to increase the very poor stock flow numbers, take the engine to 540 cubic inches, design a new camshaft profile, rework the intake manifold base, design and build a new intake plenum to accept all the stock HP525efi hardware and fitment, upgrade injector size to 55lb/per hour injectors, change the firing order to the new 4/7-2/3 swap (18726542) and do some reporgramming on the stock HP525efi ECM and keep compression ratios at 9.5 to 1 for 89 pump gas operation.
I think this thread is good infor for those out there with HP500 efi engines as it gives them some possibilities for upgrading their engines based on budget and power requirements.
My advise is if you are going to have to rebuild an HP500efi I would start by adding cubic inches with a healthy bore size increase, having a good shop or head expert massage the stock heads for better flows, select a good camshaft from a recommended camshaft expert like Bob at RMBuilders, rework the stock intake for better flow and add the monoblade throttle body and DO NOT FORGET TO PUT CORRECT PROGAMMING OF THE ECM TO MAKE THE WHOLE THING RIGHT!
I am attaching a few pics of the Raylar HP675EFI engine so you can see the new plenum, just remeber its whats inside the plenum that you can't see that really makes it work.

Best Regards,
Ray @ Raylar

HaxbySpeed

Nice looking piece, needs more Raylar stickers. J/K.
what kinda torque does that bad boy make?