putting a bigger blower and a chiller on my 500hp
 

Any suggestions or advice would be appreciated. I have a 1999 advantage 28 sport cat . I have a stock 500hp with a 250 mega blower 5psi no chiller.I just purchased a 420 mega and a chiller should I do anything to the heads or cam . also I have a xr drive with 1.5 gears.what would be safe boost I was thinking 7-10 psi . please any advice would be nice. I don't want to blow up motor. Motor has 200hrs

a good set of heads and the right cam with the 420 and chiller would make the boat a rocket but 5-6 lbs boost with the 420 with a stock hp500 won,t be a slouch by any means.

Do you think 7-10 is to much also what cam what heads

i think 7 would be my max on the stock engine.i,m no cam expert but a 525 efi cam or a crane 741 should do the job.with the addition of the heads&cam i think 9 lbs boost would be a safe number.we all love power but we also need to keep it safe.edit in,the afr 305 is a nice head.

What heads

I'll check them out thanks

I talked to co performance and they said there was no need to replace cam and heads they were good wouldn't make much difference in performance

Free advice from somebody on the phone??? You got what you paid for.

The carbed HP500 cam was never that good to start with on an NA engine. It s on a 110 lob sep and reverted water at idle. Not really a good blower cam either.

With 200 hrs on it, it needs at a minimum, new springs and a valve job and better head gaskets.

7-8lbs is the max I'd run.Your at 200hrs,time for springs in about 50-100hrs,so might as well freshen heads and get yourself either an hp500efi or crane 741 cam.this should get you an easy 700hp.

I'd go with the 525EFI cam, or the 168741. Very close in specs, but the 525 EFI cam is a 114 LSA , the 741 is a 112 LSA. Either one will be an improvement over the stock HP500 cam.

I would freshen the heads up at minimum, new springs to match new cams, valve jobs, head gaskets, etc. I'd keep the boost level to around 7lbs to start with, and go from there.

I think you are going to see some nice power gains. Theres a few who have upgraded their stock 575sci engines, (502 with 250/256 blower), with an 8-71 blower package from Dyers. The power gains were substantial, even without upping the boost. If you were say running the 250 blower at 5lbs non intercooled, and go to the 420 blower, intercooled at 6lbs, you'll be making quite a bit more power at wot..

6psi of cool air, will be much better than 5psi of hot air.

I would pull heads install new valves and springs new 10 retainers and locks,install mls head gaskets ,install500 or 525 cam ,if running pump 91-93 octane keep boost to 7max 30max timing to keep it safe shpuld be around 700 hp

i am not familiar with co performance but for them to say cam&heads won,t make much difference is wrong.i would shy away from any shop that does not know what cam&head upgrade can do for performance.

The 500efi and 525efi cams are quite a bit different, and in my opinion, the 741, or 525efi cam, will kick the 500efis azz in this application.

Stock HP500 specs
222/230 110 LSA
.576/598

500EFI specs
230/236 114 LSA
.598/610

525EFI specs
236/244 114LSA
610/632

Crane 168741 specs
236/244 112 LSA
.610/.632

The much larger 420 blower , is gonna be a good improvement in power above about 5,000 engine rpm. Below that, its not gonna make much more power than the 250 blower, maybe even less due to the small overdriven blower making good low end power. In order to really see the gains from the larger blower, I recommend spinning the engine in the 5500-5700 range to take advtange of the larger blower, and you need a cam that works well there.

The stock heads dont flow very well. Crappier flowing heads, will like more duration than an engine with afr , dart, etc.

Another often overlooked thing is the safety factor. Smaller cams can build more low rpm cylinder pressure, which can lead to detonation. I personally would dyno the engine, and give it the timing it likes, with a proper timing curve. I dont believe in one set magic timing number, to be "safe" . Ive seen alot of guys slap blowers on their engines, and run retarded timing thinking its "safe", and end up tuliping exhaust valves in a short time.

Fwiw, the 600sc mercury engine, 502 ci with 420 blower, ran 33 total timing. The 525sc engine, ran 35 deg total timing. The key is not bringing all the timing in too soon. Blower motors arent NA engines. Mercury didnt bring max timing until until nearly peak HP with their stock sc timing curves. I personally have written 3d timing maps, that have shown an increase in low end torque, with as much as 10 deg less timing in the peak torque area, and as much as 30hp more at peak HP area with a tad more timing there.

And of course, fuel tune must be good as well. Im not sure how a cam with 6 deg less intake duration, and 8 deg less exhaust duration, is comparable as far as saying "either one is fine" . There will be a substantial difference in the upper rpm power band , by changing 6 degrees of intake duration and an additional 8 deg exhaust duration with same LSA

My recommendation is from builds that i have been involved with, seen the results, and as well as a couple cam software programs that some engine builders use. The 500efi and 525efi cams, are quite a bit different, and on a deal like that, could be a substantial amount of power difference at wot.

Fwiw, same build you have, 525efi cam, chiller, 871, 7lbs , made 760hp at 5600 on a buddys build, and has ran great for years.

my plans are to pull heads and do a head job. also I was going to put clamedic gaskets. I really want more hp but I do want to be safe and reliable. It was cp performance I talked to and also teaque. . not a lot of help. I would like to gain some torque and mph . I have a xr drive with 1.5 gears . and I do have a super chiller and 750 holley carbs

Clamedic gaskets ? Where does one buy those ?

What kind of dressing do you put on those ? Can you get it over the counter or is it prescription only ?














Sorry. Weird mood today. Just sounds like an STD or something. Hah.

so if i understand correctly ,are you saying cp performance and teague marine told you a cam&head upgrade won,t do much for performance?

Yes sir

yet they both sell aftermarket heads&cams!makes sense to me.

i guess i,and many others must be wrong!

Not saying that .I'm just confused and I want to do it right 1st time .I want the best performance for what I have. Don't wanna hurt motor .

Maybe it's because of the Bravo XR.

He'll be past the limits of it already. He has a 28ft single engine cat, not a 22 single or a 28-32 twin.

i totally understand the concept of not wanting to spend a boat load of money and using parts you already have but i don,t think the op understood what cp told him.as i posted earlier his engine will be a decent runner with the stock hp500 heads&cam BUT no way will it compare to the engine with a good set of aftermarket heads&cam properly sized for marine use.and nobody wants to have problems with their freshly built engine.no matter the direction he goes the proper tuneup including a fuel system that can handle the engines demand is vital or it can fail.all i am saying is a good set of aftermarket heads&cam will absolutly make more power than his stock parts will and anybody that thinks otherwise is either confused or in denial.

HP500, Dart Pro 1 heads, 525 EFI cam, 250 Blower shop blower kit.

I can get heads and a cam but I have that 420 mega blower and chiller that I am going to use. I got rid of the 250 mega. Would aluminum heads be better especially cause of weight. Who would be a good place to get that 525 cam

the 420&chiller will work nicely.

So a 525efi cam. Can i use the same heads that I have

Also I was gonna run 2 750 holleys from my previous 250 mega setup . will those be enough if i richen them up

They will work. No need to "richen" them up necessarily.

If you went with new good flowing heads, cam, chillers, they might be on the borderline being a bit small CFM wise. With the stock heads, I think you'll be just fine with those carbs.

Will you be dyno tuning these engines?

No the motor is in the boat didn't want to pull it . I'm pulling the heads off though wanted to have them rebuilt . That is why I wanted to get a cam since upper end would be off . If I decide to use these heads should I change anything on them for better Flo or lift etc?

Set them up for the 525efi cam

that's big power & torque

Esp from a 250 blower without an intercooler

I have the 420 mega blower with a chiller not a 250

I'm also running at 4000 ft not sea level

Basically a duplicate of a 525efi cam posted by Mild Thunder a few weeks ago http://news.compperformance.com/wp-c...I-Camshaft.pdf

Will this cam be good for carburetored

Also do I need to change lifters etc for this cam swap

You may think you are saving work by pulling the heads in the engine bay, but that is not the case. It is a huge PITA working in an engine bay. Pulling the motor and having it on a stand will save you a ton of work especially if you want to swap the cam. Aftermarket heads may not gain you a whole lot on the intake side (with blower) but would definitely help on the exhaust side, especially if you are going to spin it higher...the right cam will help take full advantage of the heads also.

Here's a thought, do not pull the motor, just do the blower and chiller (in the boat) this year. Accumulate some hours on it and collect some parts over the summer. In the fall, pull the motor and take your time, do it right. Who knows, by then your boating needs may change and you could be looking at other boats?

so I just pulled heads think god I am boarder line headgasket blow out actually was barely leaking