More HP for HP 500
 

I am considering changing the heads and cam on my HP 500's. I am very interested in the AFR 315 cnc heads with a Crane 741 cam. I would like some advice from the engine experts out there. Do you think the 315 cnc is the right head or the 305 with cnc'd chambers. I spend most of the time running 3500-4000 rpm. I am looking for alot of mid range torque and a solid 600 HP. Thanks in advance for the advice. Jeff

Re: More HP for HP 500
 

Jeff:
Your choices for heads and cam are excellent companies and great parts. The problem is there is no way your going to see 600HP out of your HP500 with just those changes.To ge a HP500 up to 600HP the easiest and most cost effective way is to use a Whipple supercharger with Dustin's reprogram on your ECM. The other question is do you have an XZ or XR drive to take the extra power? Consider these thoughts before you get yourself in a one way trap.
Raylar

Re: More HP for HP 500
 

Pro Charger

Re: More HP for HP 500
 

change the heads to 305 intake runner and put a hyd rollersomething around 242.int 248.exh at .050 lobe cnt on 112. and change the comp ratio to 9.5 to 9.7 and install a 950 holley and msd ingition and the motor should make around 615hp. and reliable,

Re: More HP for HP 500
 

Raylar,
Thanks for the advice.
These are 1998 HP 500 carb motors, when I am finished with the upgrade I want them to look stock, so no supercharger.
CMS Racing,
I will have the heads milled to 114cc combustion chamber, AFR says this is worth 1/2 a compression point, so that should be approx. 9.25 to 1. How is the idle and water reversion with the cam you described?

Re: More HP for HP 500
 

idle is good with the 950 holley on top the tail pipes will have to be altered to work . I use IMCO to change all my pipes around. they will work on anybodies tail pipes for mods. best to add on and go throught the transom .but addind dumps and restricting water flow entering the exhaust to (2) 3/16 holes should work. I have done a lot of 500hp upgrades at my shop and the combo should work good for you. get the comb. chambers to 110. cc and 0 deck the block.to get the comp. up

Re: More HP for HP 500
 

I also have a pair of carb HP500's (1999) They were just rebuilt but I left them bone stock. I was just wondering if there is any advantage in converting to MSD ignition. Fuel economy, HP or torque?

Re: More HP for HP 500
 

CMS Racing,
Do you think the "741" cam is too small? I will spend most of the time in the 3500-4000 rpm range with little wot time. Jeff

Re: More HP for HP 500
 

Stroke it to 540 while you are at it.

Re: More HP for HP 500
 

Wags382,
Are you going to upgrade the exhaust manifolds?
Are you planning on running @ 5500 RPM +?
Bob

Re: More HP for HP 500
 

IF you go with good flowing heads, you won't need a large cam. . .the heads will do the work.

Chris

Re: More HP for HP 500
 

Chris & Wags,
I agree. Those heads (with an 80% I/E ratio) and that displacement need approx 232*/236* on 112* LSA, a .60x"/.61x" lift. No more than 4* I/E split. Duration in excess of 236* will not increase peak torque #'s, just the RPM you reach them. RLW on this forum is making 706 HP, N/A, with a 540 CID motor, dead reliable, with AFR 305's and a cam(under 240* & .630" on both sides)
Bob

Re: More HP for HP 500
 

Bob,
I plan on using the Gil offshore exhaust that came original on the HP500 carb motors.I plan on max rpm of 5400-5500. What head would you use the 315 cnc or the 305 with only the chambers cnc'd ? I would love to stroke to 540" but the motors have low hours and I want to take the money that I saved on the bottom end and put in the heads. Jeff

Re: More HP for HP 500
 

FYI...

I also have 1997 HP500's (carb motors) that I was inquiring about raising the HP to around 600HP.

I was talking to Bob Teague this weekend at the Scope Poker Run. He gave me a few suggestions. He said get rid of the Gil exhaust (causes rversion) and get a good set like CMI. Get the MSD ignition. He also said to go with aluminum heads. He said the "new" oxegenated gas these days is destroying heads like crazy (I think he said the seats or valves??) It won't destroy the aluminum ones.

Re: More HP for HP 500
 

Teague was smoking crack. Or possibly he sells CMI's and not Gils. ;)

My last motor had the standard low profile Gil HP500 exhaust risers with silent choice to boot. Cam was the Crane 741. No revesion what so ever.

Re: More HP for HP 500
 

I run with a buddy of mine who has the hp500 with the gils. I run the hp500efi CMI's, and we are dead even in speed. Both of us have 288 sunsations! The Gils are not a problem.

I'm watching this thread because he wants to produce 600 hp too.

So who has done it?

Re: More HP for HP 500
 

On another board we are waiting on some dyno problems to get fixed and then we will have a 509 with some figures. With a lean condition he is at around 560#/ft but with an A/F of 16/1 they haven't pulled it past 4900. The cam is under 230 duration on this one.

Bob, as you and I have talked with the cylinder heads today, cams don't have to be agressive to make power. Attention to duration at .100/.200/.300 is also an important factor. You may need an intake lobe that packs the cylinder and then shuts down quickly at .200 and on, where as the exhaust lobe may need to stay open longer under the curve.

Also the larger cams with these good heads make narrow power bands. Fine if you got a 5 speed and gears but we don't. By selecting a camshaft short on duration and moderate on lift you get good velocity into the chamber during boat cruising speed. . .3200 to 4000 and at max rpm of 4600 to 5600 for most the RAM effect occurs and packs the cylinder to make power. By doing this you have a broad power band to use and your happy at all speeds.

Chris

Re: More HP for HP 500
 

Thats why so many custom cams (especially marine) are being ground today. The majority of shelf grinds available are designed around cylinder head flow #'s from 10 yrs ago. These new heads and the flow #'s they make with either CNC or custom porters have vastly different cam requirements, especially low/mid-lift, splits, and duration. Then add in wet exhaust and peak power in by5400-5600 RPM, and it gets very specialized.
Bob

Re: More HP for HP 500
 

Jeff,

You are heading in the right direction. The exhaust is still o..k. but the tailpipes will have to be reowrked and if you have silent choice that will cause a reversion problem also. Give me a call, there is a local guy in Painesville who I will give you his number for the exhaust stuff. TOP SECRET.(440)796-8225

Andy Bloom

Re: More HP for HP 500
 

CIG 3, so are you saying that when this engine produces 600hp, useing the gils, there will be reversion problems?

Re: More HP for HP 500
 

I had a set rebuilt last season for a friend. He had gils with silent choice and had problems. THe cause of the problem is the water enters the gil tails in the elbow. I had a guy build me a set or tails that introduced the water 1 1/2" from the end of the pipe and that fixed it. Also with a big cam and the silent choice I couldn't get it to work without sucking water.

Re: More HP for HP 500
 

The gil's have three different top elbow pieces. Different hights! My buddy's are stock and are definetly not the low ones, I wonder if yours were?

Re: More HP for HP 500
 

Andy Bloom,
Next time your at the shop we need to talk horse power instead of airfoils. Also I am way ahead of you, when I was removing the silent thunder this winter I saw the end of the pipes were the old style, so I took them to my top secret friend in painsville and reworked them to the new style. I installed HPI silencers for a much better sound than the silent thunder .

Re: More HP for HP 500
 

I notice that we have some other people looking for the same thing that I am out of the HP 500. I work with a local race engine shop here in northeast Ohio, I send him some work and use my boat for real results and he helps me. We would like to place an order with AFR, I will be purchasing 2 sets of heads, If we can add 2 or more sets to the order we can get down to wd price plus a little for the shop. P.M. me if interested. Jeff

Re: More HP for HP 500
 

only 600hp with AFRS? I thought the hp numbers in the magazine showed 200 hp gain ?Sounded too good to be true or is it?

Re: More HP for HP 500
 

Plumbers Crack,
That engine was cammed much larger than what we need in our pleasure boats. The boat would fall on its face from loss of low end torque and never hit the rpm needed to make 700+ hp. I chose the 741 cam as a starting point for this combo, but I must agree with some of the previous posts in this thread that a custom ground cam that might have less duration than the 741 might be the way to go. I thought 600 hp was a realistic and obtainable goal, I will be the last one to complain if it makes more hp. Jeff

Re: More HP for HP 500
 

WAGS382
the crane cam 741 looks like a good starting point. it very similar to a custom comp I have ground. sorry it took so long to get back to you very busy at the shop .

Re: More HP for HP 500
 

CMS Racing,
Thanks for the reply. Do you think the 315 is too big for the 502?
Jeff

Re: More HP for HP 500
 

I like to run aruond 300 to 305 int runner on a 500ci motor that is only going to make power to 5500. to 5700.

Re: More HP for HP 500
 

On the AF heads are the exhaust ports raised? With the motors side by side this will push the exhaust 1 inch total closer to each other.

On my 2001 500efi's with the cmi headers I don't think there will be enough clearance. What da ya think?????

Re: More HP for HP 500
 

Yes, the exhaust is raised .600" like most others.

Chris

Re: More HP for HP 500
 

The only aluminum heads I have heard that are not is the Eldebrock.I don't think they have very good port velocity.

What about the pro 1"s??

Re: More HP for HP 500
 

Strip Poker 388
AFR told me the exhaust is raised .375".

Re: More HP for HP 500
 

Does the 741 cam help the performance of a stock HP 500 (carb) ?

Re: More HP for HP 500
 

no disrespect to anyone but no way now how is a 500hp carb motor with a cam and 315cc cnc ported heads going to make 600hp at 5400-5500rpms. sorry it is just not going to happen on pump gas. save your cash cmi's are not going to do anything beter than your gill's. in a perfect world with afr heads, bumped up timing a little, bumped up comp. a little and good cam you might gain 100hp. a stock 500hp is like 465hp.

Re: More HP for HP 500
 

While we are on the subject, on a carb HP 500 what rpm's do you prop for to obtain max top end speed?

Re: More HP for HP 500
 

4800-5200 - labbed 26 4 blade on a 288 sunsation ,

Re: More HP for HP 500
 

So on a side by side installation the stock cmi headers should not touch.

I wonder if there is enough slack in the hose to accept the .375 higher exhaust port to line up with the tail pipes???


What do yall think??????


Rob

Re: More HP for HP 500
 

Hey Jeff , Drew here, You can always do what I did Blow A Motor and step upi to 540,s... Runnong a strong 80 plus right now !!!

Re: More HP for HP 500
 

if you use the CMI with the flex flairs the tail pipe has some adjustability. If you buy a used set even if they are the cool collar design make sure the tail pipe connection is the flex flair design the one they make for Mercury are not.