HP # puzzles me

[caribbean20]

Took the boat out to Elsinore yesterday to sort out latest engine mods. The motor is a BBC 502 casting # 10237300, aluminum heads, EMI Thunder exhaust, Vic Jr. airgap intake, roller cam (580 lift, 240@50 duration) and Holley 850 marine carb. Pump is a fresh Berk 12JG with a mag./bronze AB cut, ride plate and shoe. RPM @ WOT 5,000.
Per the Berk HP chart, this equates to about 370 HP. Seems low to me with this combination. Would have thought somewhere in the 450 HP range, thus about 5,400 RPMs. Pretty sure the tach is accurate. Does this make sense (i.e., "only 375 HP").
On the bright side, got ever so close to my 70 MPH goal with a 68.8 on GPS. Boat is a 1988 Caribbean, 20.5 semi-v, so the speed is in the ball park.

[Daytona100]

Whats the compression?

[caribbean20]

I believe a little over 9.0 to 1. Have not run a compression check, although the motor is still pretty fresh (about 60 hours, run hard).

[AZKC]

The 9:1 is whats holding you back, I would think. That cam/carb would like a little more pop I'll bet.

[caribbean20]

Good question and point on the compression issue. That is a subtle fact that escaped me. Unfortunately, no quick fix there. I do have a compression guage and will check next time out.
Anyone know how to convert compression PSI to a ratio (e.g., 9:1) for a stock 4.466 bore 502, or where to find it? Put another way, how much PSI should I expect "if" the motor has 9:1 compression ratio? I am now kind of curious since you guys raised the point.
Tough to reconcile, all that dough and I am still south of 400 HP!! Yikes.

[AZKC]

Don't think you can convert psi to comp ratio accurately:confused: As far as PSI on a comp gauge I would think around 125-150 but you want them all pretty close to each other. This is all non scientific, from the hip info, you understand;)

[Jetaholic]

The actual cylinder PSI is relevant on the intake duration of the cam. With a long intake duration, the valve is held open longer, thus allowing some of the air in the cylinder to escape on the compression stroke, thus dropping your cylinder pressure.

[caribbean20]

Jet, noted, good point. Intake stroke cam duration affects cylinder PSI. That's why I have to pay people to do this stuff, been too long in an office.

[FILUCKY]

A bigger cut impeller will a lot of times keep a N/A motor from reaching its higher RPM (were it makes its power) so the impeller chart will appear as if your not making as much HP when in reality you are still making your 400+HP but you are only making 370HP at the RPM that your AB impeller wil let your motor turn. So if you want to get all your Hp to the pump you will have to cut down your impeller, Which i would not recomend since your boat does not sound like it is a "race" boat and a smaller cut impeller will make you lose your low RPM cruising along with more wear and tear on your motor due to haveing to run more RPM all the time at any given speed over your current impeller.

[Squirtcha?]

with a mag./bronze AB cut, ride plate and shoe.
This may sound like a stupid question, but are you sure the impeller is a Berk?
Can't remember the exact conversion, but I believe an Aggressor is at least a full cut higher (bigger) than a Berk.
Berk A is equal to an Aggressor B (or thereabouts).
If it were an Aggressor AB, it would be absorbing 431 horsepower with those rpm and hp numbers you posted up.
Just want to make sure you're looking at the proper chart info.

[loudpipessavelives]

i dont really know about the hp figures for a 502 but it would seem like it would be more than 370.... but i also dont know the rpm range of your cam and intake also the size of your heads i think that would have to do with alot of it..i always thoguht that the victor jr style intakes were more of a higher rpm but i could be wrong... im no a mechanic and am only going by my experience... those charts are sayin that my 468 is about 325hp at 4800 wiht an ab, and i wouldve though that it would have more hp than that ....i did my homework on my cam and intake selection, althouhg my heads are open chambers off a 396 which might be holding my motor back a little ... good luck on your 70mph goal!

[Nucking futs]

I run an Agressor BC in my cruiser at 5900 Which would be a Berk AB. Whats my h.p. Squirtcha? I ran a stainless A @ 5200. Will they match? Everytime I try to use that calculator thing, Been emailed to me about 6 times and I can never get it to open. Im not that computer savey to figure it out.

[caribbean20]

Lucky, I also thought about the RPM range, but it seems to me a fairly mild 502 ought to be making max HP around the 5k range, not a whole lot higher. I did a cut down on the impeller thing on a previous mill and the RPMs went up, speed did not budge. Guess I would just have to do a dyno run on this mill to be sure.
Squirt, not sure about the make of my "AB," but you may have a point there. GS Marine here is SoCal did the pump so I guess I could just call Greg. I was fairly pleased with the top end gain with the last bit of work (about 5+ MPH), but the complication was that I did the pump, ride plate, shoe and motor work all at the same time, so its impossible to tell what did what. Other than the fact that the usual axiom held true, about $1k per 1 MPH.

[Moneypitt]

The 370 HP# seems about right for what you've got at that RPM.....Real world HP numbers are an eye opener compared to dream numbers off a desktop dyno or something simular. The HP figures I see on here really make me laugh most of the time:D ..........BTW: Volumetric air pressure at sea level is 14.7 psi. If a compression gauge shows 147 lbs. that would be 10:1, or close to it. As mentioned, there are several factors that affect actual readings, but with a gauge you are looking for equality across the cylinders....If you have real numbers for cid, chamber, and dome, you can do the math and get real close to actual compression ratio........:idea: ...MP

[squirt]

I've also seen my share of "550hp" motors spinning an A impeller to just 5000 rpm. A good pump rarely lies and what rpm your spinning your cut of impeller is the hp your motor is putting out at that rpm. I think Squirtcha is probably right in that you have an aggressor impeller that is seeing around 430hp.
Don
PS you could always stick a 100 shot on it and you'll blow right thru you 70 goal :D

[Squirtcha?]

I run an Agressor BC in my cruiser at 5900 Which would be a Berk AB. Whats my h.p. Squirtcha? I ran a stainless A @ 5200. Will they match? Everytime I try to use that calculator thing, Been emailed to me about 6 times and I can never get it to open. Im not that computer savey to figure it out.
Need your speeds for both those impellers too buddy. Post it up and I'll run it for ya.

[bp]

Took the boat out to Elsinore yesterday to sort out latest engine mods. The motor is a BBC 502 casting # 10237300, aluminum heads, EMI Thunder exhaust, Vic Jr. airgap intake, roller cam (580 lift, 240@50 duration) and Holley 850 marine carb. Pump is a fresh Berk 12JG with a mag./bronze AB cut, ride plate and shoe. RPM @ WOT 5,000.
Per the Berk HP chart, this equates to about 370 HP. Seems low to me with this combination. Would have thought somewhere in the 450 HP range, thus about 5,400 RPMs. Pretty sure the tach is accurate. Does this make sense (i.e., "only 375 HP").
On the bright side, got ever so close to my 70 MPH goal with a 68.8 on GPS. Boat is a 1988 Caribbean, 20.5 semi-v, so the speed is in the ball park.
that's a mild engine, so rpm seems about right for an a/b bronze. i doubt it's berk, unless you know for sure. the engine -may- be making 450 somewhere, just not at the rpm you're maxed at. it's a curve, and unless you've dynoed the engine, you don't really know what the hp curve looks like. if you want to pick up a bit more rpm, have it cut to a b, and you'll pick up a little more, but that doesn't mean the speed will pick up very much. if the speed is almost where you want it, try some different thing on setup to get over the hump.
nuckin, with a bronze b/c at 5900, i'd say 725 or so, since i turn a bronze c 6100 (at 107)

[Nucking futs]

Need your speeds for both those impellers too buddy. Post it up and I'll run it for ya.
With the aggresor BC gps at 76.8 the last time I was out at Laughlin But it has seen 78.2 at BR twice
With the stanless "A" I never gps it but it was quicker. Lets say 70 for shits and giggles. I know its on the low side but lets just see what happens

[caribbean20]

bp, understand and agree on the need for a dyno run to get the correct curve, but my belief is that a "mild" 502 as you described it would usually max out HP around the 5k range. I would understand a small block needing to scream past 5k to max out, but a mild 502 ??
Funny thing is, although true by the standards of the guys posting here, never thought my 502 with 4 bolt mains, forged crank and pistons and the other goodies would be considered mild ;)

[Nucking futs]

nuckin, with a bronze b/c at 5900, i'd say 725 or so, since i turn a bronze c 6100 (at 107)
I wish I was making 725 HP. It's an alium. Aggresor B/C, I think right around 550 HP Its A heavy boat it will run 70 all day long.

[Squirtcha?]

The chart comes back with 594 hp with the 76.8 mph. Using the 78.2 mph at BR it shows 612 hp
With the stainless A (provided it's an Aggressor too) shows 533 hp.
Soooo I guess to answer your question, no it doesn't match up.
61 hp is a pretty sizeable difference.
The only explanation I could even think of is, you weren't in your powerband at 5200 rpm, or there's a problem with the program.
I've always found it to be pretty darned accurate with regards to my own ride though.

[Oldsquirt]

bp, understand and agree on the need for a dyno run to get the correct curve, but my belief is that a "mild" 502 as you described it would usually max out HP around the 5k range. I would understand a small block needing to scream past 5k to max out, but a mild 502 ??
Funny thing is, although true by the standards of the guys posting here, never thought my 502 with 4 bolt mains, forged crank and pistons and the other goodies would be considered mild ;)
For a little comparison, you should look at the GM 502HO. With 8.75:1 compression, it has peak power of approx 450hp at 5000-5200rpm. The biggest difference between your engine and the HO is you have WAY more cam than is used in the HO. Your cam is even quite a bit bigger than the cam used in the ZZ502/502 which makes 502hp at apprx 5200rpm. Given this, you might want to consult with a cam specialist(like CStraub here on HB) to see if there is anything to be gained by swapping to a smaller cam.

[Nucking futs]

The chart comes back with 594 hp with the 76.8 mph. Using the 78.2 mph at BR it shows 612 hp
With the stainless A (provided it's an Aggressor too) shows 533 hp.
Soooo I guess to answer your question, no it doesn't match up.
61 hp is a pretty sizeable difference.
The only explanation I could even think of is, you weren't in your powerband at 5200 rpm, or there's a problem with the program.
I've always found it to be pretty darned accurate with regards to my own ride though.
The stainless is not an Aggresor. More towards the berk but I think It's A GHT.We figure the HP to be in the 600/625 range.Like I said, I never did GPS the "A" so the speed might be up there as well, but the engine never came on like it does with the B/C

[caribbean20]

Oldsquirt, I had a much smaller cam in the mill before the mods last winter. The mods were the aforementioned roller cam, roller rockers, Vic Jr. intake, shoe, ride plate and pump rebuild with a "whatever brand" mag/bronze impeller. For this package, I relied on the judgement of Greg Shoemaker, GS Marine. The motor used to turn 5,175 rpms with a loose pump and top end of 63 on GPS.
After the work, I am now at 5,000 rpms and 68.8 mph top end GPS. The motor does load up a bit in the no wake zone, but to be expected with the larger lift and duration.
So . . . my only issue now is am I leaving some HP (and top end) on the table because I am not in the meat of the HP/torque range for this combination? My understanding was that I had the same equipment to which you referred (i.e., the 502 HO or ZZ502 with 450++ HP, I do have the aluminum heads).
Seems to me I have the following options (because the fun is in the journey, not the destination)):
1) Pay to have the motor removed and some dyno time, remove all doubt.
2) Try a smaller impeller in the belief that max HP with this package is higher than 5k.
The boat does run fine now, but you know how it is, hate leaving anything on the table. Opinions (it is, after all, winter)?
Happy Holidays everyone!!!!

[MACHINEHEAD]

The 502/502 has a 224/234 @ .050 cam and will make 510 hp at 5400 with Eddie manifolds and 850 demon. I would say yours would run closer to 525 @ 5600. I would go through a timing check. 38 deg. by 2500 rpm with your comp ratio would be safe. Second check your fuel preasure @ WOT after 15 seconds, 5psi min. This may get you 70. Should you change impellors and sacrafice your cruise, I wouldnt.

[MACHINEHEAD]

Noticed your 850 marine. Do not use anything but a 10x3 or 8x3 spark arrestor. I did a very good comparo article for Family Performance Boating 2 yrs ago. Try to look at the article online. The wrong arrestors on marine J-tube carbs can vary the mixture from 11 to 1 A/F to 13.5. Crazy!

[78Southwind]

Noticed your 850 marine. Do not use anything but a 10x3 or 8x3 spark arrestor. I did a very good comparo article for Family Performance Boating 2 yrs ago. Try to look at the article online. The wrong arrestors on marine J-tube carbs can vary the mixture from 11 to 1 A/F to 13.5. Crazy!
Can you provide a link to this article or copy and past it? It looks like their server is down.

[MACHINEHEAD]

Dont have a copy, but got one of those cool laminated article boards from the publisher! Yea something is wrong with thier web site.

[sleekcrafter]

here is a link to the story, the website is still down, but it was an article written by Bob Teague. http://www.innovatemotorsports.com/resources/marine-carb.php

[MACHINEHEAD]

Thats not the story I did. But very good info. I had tested 6 different arrestors, on the same day at the dyno, and tweeked the jetting a little to get them to run. Some just wouldnt run well. In fact one test was aborted due to a real lean condition, high 13s A/F I think. It was that billet oval arrestor everyone likes to run about 12x7x3. It also has a 1" spacer ring below its base to keep it up and off the float adj. screws on a holley. We all thought that was part of the problem. The air would straighten out to much and seriously affect A/F ratio. We had put almost 10 jet sizes in it with almost no effect! Funniest test was the stock 310hp Merc arrestor. 8x1.5''. made almost the same power as the 8x3 and 10x3. And this was a 600+hp engine! The point of the story was dont just put any arrestor on and run it. Some just dont work at all.

[MACHINEHEAD]

Go to buckaroocommunicatins.com and select "websites" then "F and P boating" then "archives" then "JAN 2003" FILTER FORENSICS. Just the front page though, no dyno charts. Looks more like a advertising type page for future customers to buy ads. oh well

[caribbean20]

Machine, funny you should mention the spark arrestor. My arrestor is 5.75" diameter and 3" tall, pretty standard from what I have seen. Last time out, I ran the motor w/o the arrestor for 1 pass and the rpm's actually dropped by 100 - 200 rpms. Really surprised me. My conclusion was that the lack of arrestor affected air flow, thus less rpms. I sure did not conclude that my arrestor was too restrictive.
Thanks for the information and I will have a look. Does my experience make sense (i.e., no arrestor, less performance)?

[MACHINEHEAD]

That does seem to be the trend with J-tube marine carbs.

[MACHINEHEAD]

Did you try the other checks, timing ect.

[caribbean20]

Machine - I just downloaded the article to which you referred, will have a read, thanks for the link Sleek. No I have not made any other adjustments, I did that test the last time out before starting this thread.
2 Questions, I have not rebuilt my Holley 850 marine carb for at least the last 5 or 6 years and intend to buy a new one. Holley, Rochester and Carter are the only carbs I remember back from my car days. I see the Barry Grant Demon carbs seem to be quite popular. Any suggestions about a new carb for a fairly mild lake motor (specs noted above)?
Also regarding timing, my last experience here was pointing a timing light at the harmonic balancer on a car. Is there a more convenient and precise method with my MSD ignition? I can easily turn a distibutor, but don't want to fry the motor.

[jbone]

Very interesting thread.
I've got some questions that are very relavant to this topic, so I don't this it is too much of a hijack.
I've got the ZZ502 in my 21ft open bow jet. I've got the Dominater (American Turbine) 12S pump with an A impeller, backcut shoe, ride plate and inducer with a full setback. I get about 5050 rpms at 65-67 gps depending wind and temp. The boat is very heavy, lots of stereo equipment and 4 batteries.
I've wanted to change my impeller to get more hp as mentioned in this thread. With the heavy boat, will it hurt too much on low end to get an impeller that will allow me to reach 5200-5300 rpms, and wich impellor would get me in that range? The ZZ502 reaches peak hp between 5200-5400 rpm with a max of 5800 rpm. Like said, am I giving away hp by not hitting the higher rpms?
Also, I have the Billet flame arrestor from Hardin with the K & N marine filter element. What are your thoughts on this one. I was having difficulty getting ggod color on the plugs. Seemed to always run a little lean. I also tried the no arrestor thing for comparison and did not notice anything, so I assumed the arrestor was fine.
http://www.***boat.com/image_center/data/500/3295engine1.jpg

[SmokinLowriderSS]

If you cut the impeller to a "b", you should hit your target RPM, maybe find another 10 or 20 HP or so, I don't really know what the HP curve on the ZZ502 looks like. The B impeller will reduce your acceleration, how much is going to be hard to quantify here, as well as raise your cruizing RPM that same 300 RPM roughly, for the same speed.
Try this plug reading instruction:
Reading spark plugs (http://www.dragstuff.com/techarticles/reading-spark-plugs.html)
The area you are interested in is that third that is all the way up inside the plug where the sun don't shine. This area is colored when all is wide open under full power because the combustion chamber heat totally cleans off the other two areas. It will take a special plug reading flashlight with the magnifying glass to view it correctly. Plugs cannot be correctly read by just quickly looking at them with the naked eye. You see people doing it all the time because they do not know how to read plugs.

[MACHINEHEAD]

The HP curve of your 502 is very flat. Going from 5050 rpm to 5200-5400 may get you 10-20 hp. Not worth it in my opinion. If that is a J-tube Demon and your arrestor has the 1" adapter neck, do not run that arrestor! My experience has also been that the 750-850 Demon marine carbs are pretty lean. Going up 3-4 jet sizes on both ends is not unusual. Secondly a 8.5 or 9.5 power valve is also recomended (to cover a lean transition) if not already equiped. Also, I do recomend a 850 Marine Demon for Carib20. These recomondations are with the 10x3 and 8x3, since this is all I run now.

[MACHINEHEAD]

J bone. Just looked a little closer. If thats an Air Gap, try an open spacer, 2'' if it will fit. Put another two sizes in the secondary, in addition to the above mentioned 3-4, if you run a spacer. Also check your WOT fuel preasure after 15 seconds as well. If no change in plug reading, check your high speed air bleads (Mighty Deamon). Ive seen no change in mixture on the dyno with a 8 jet size increase. The culpret was a poorly machined hole in the high speed air bleed. Took an hour to figure that one out!

[MACHINEHEAD]

J bone. Get rid of those little glass fuel filters. Run something for high HP marine use. Or put the fuel preasure gauge on first and see if they are a restriction. Remembere these preasure checks need to be done at WOT. so get a long hose so you can read it while leggin' it.

[jbone]

Machine head,
Thanks for the ideas.
There is a Super Sucker open 2 inch spacer under the 850 marine Speed Demon, and yes that is an Air Gap. I went up about 8 jet sizes 1 at a time, but never noticed any difference, so I went back to original. 85/91 I think. I'm not sure what you mean by the 1" adapter neck.
On the plugs, I'm no plug reading expert, but they always looked very white and clean, even with the 8 sizes up in the jets.
On the filters, I'll look at upgrading them but, one has the screan removed to see if there is a restriction and there was no difference between to the 2 tanks.
My fuel pressure has not been a problem since I put the Mallory 140 marine pump on there. I have watched it at wot throttle and it is good.
Can you tell me more about the air bleeds. I'll take a look, but I'm not sure what or where they are. Does the Speed Demon have these?
Oh, the only mod to the engine was the installation of Crower roller rockers. 1.8 on the intake 1.7 on the exhaust. They were off an engine with very little run time. I thought they would do better than the stamped steel 1.7's.
Thanks,
J

[MACHINEHEAD]

The problem may be the air cleaner! 8 jet sizes, you should have seen something on the plugs. A mighty demon will have removable air bleeds found just above the venturi. A reg. demon will be non removable in the same location. I have only seen the removable type with poorly drilled holes. The adapter neck is 5.125 inside dia. ring that may be seperate or fixed to the bottom of the spark arrestor. Basicaly get rid of it and try jetting with a 10x3 or 8x3 arrestor. That is what these carbs were meant to use. The rockers are a great choice!

[jbone]

thanks
J

[caribbean20]

Jbone, looks like we are running almost the same equipment, although your hull is newer than mine. Mine is a 20.5' (not counting swim steps) and lots of stereo stuff also (though only 2 batteries). About the only difference may be the droop snoot that I installed last winter (I also have shoe, ride plate, diverter, etc). Did you put the droop on yours?
My best top end is 68.8 with medium load (just me and 30 gallons of gas) 3 weeks ago at Elsinore. Looking for 70, just once (downhill, with the wind, if need be)!!! Sounds like we can do some benchmarking on future mods.

[jbone]

I also have the droop.
I hit 67.8 at the river. Alone with about 40+ gals of gas. It was down river.
I'll pm you with my info and we can talk.
J

[jbone]

I can't pm you for some reason.
give me a call at 619 661 2671 evenings to share info.
Jason

[caribbean20]

probably my firewall. my e-mail address is dkerner@adelphia.net.
Regards,
Doug

[bp]

machinehead, i've been running 850 mighty demons for 4 seasons (not marine). when we first installed them, i pulled the engine and went back to the westech dyno, mainly to tune them. i don't run power valves, so the carbs are squared, but what we found, and what we were told by westech, was that these carbs are generally rich with initial settings. although they ran fine on the dyno and made great hp, i fought with 'em for 1 1/2 years before reading everything i could and talking several times to a bg engineer, and finally getting the problems addressed.
the first thing i was told was that the transition slot absolutely must only have 0.020 showing under the throttle plates. that can never be changed or altered, as the feed through the transition slot is critical for acceleration, and factors into the hi-speed circuit. idle must be adjusted with the mixture screws. to accomodate this setup, i had to drill holes in the primary throttle blades (2 5/64). after doing that, and getting the idle circuit working correctly, i also shortened the pri/sec linkage, not to make them open at the same rate, but sec begins to open when the pri is about 1/3 open.
the only significant jetting changes i made (from dyno measured AF) involved the IFRs, where i've gone to 42, 43, or 44. i'll only change mains one size, depending on DA conditions, 91s if the air is terribly good, 90s if d/a is above 3000, and rising. i'll also change hi speed bleeds, which helps engine acceleration rate.
dunno if any of this makes sense, but the carbs have worked pretty well over the past 2 years, from 500' d/a to over 5000' d/a. plug color is always good, even though it -seems- to be a -bit- rich.
i run k&n's over "modified" spark arrestors. off or on, i see no real change. it would seem to me that if the carbs are setup to run a correct a/f mixture with a restrictive air cleaner, removing that air cleaner would create a leaner condition?

[MACHINEHEAD]

All of the testing that I have done with BG carbs has been W/J-tubes. Usualy the first thing out of Steve Brule's mouth is "does it have J-tubes". I say yes and I get a head shake and a chuckle. If you call Westech these days about J-tube BGs he will tell you to be carefull or just bring it in to be safe.