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AKA OhOneWS6
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Discussion Starter #1 (Edited)
What next??? (Update 04-27-10)

First off, Huge thanks to Tom @ Jet Boat Performance for the suggestion on the allen bolts. They worked perfectly as did the throttle bracket. :)devil

I took the boat out this weekend and finally got rid of the dead spot at 3200 RPM. It was all a timing issue. Now I seem to have hit a brick wall at 4200 RPM and 51 MPH. I know there is more left in there. I'm just not sure where to look.

Some questions:
1) What MPH should I expect out of a Jacuzzi YJ pump at 4200 RPM?
2) How much HP does it take to turn a YJ 4200 RPM?

I am not looking to go super fast with this boat. I would like to see 60 - 65 MPH with the Pontiac motor.

This is a very low budget project. Thanks to help from a lot of friends old and new, I am total out of pocket on this project ~$1000. I'm guessing that makes my $$$ per MPH ratio a hell of a lot better than most.


TIA,
Matt
 

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Boat Nut
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5,131 Posts
verify the tach is correct, speeds in the ball park for 4200 small boat. Jacuuzzi pumps generally are easy to overpower in stock form. How about a little engine info for starters, c/r, carb size, intake manifold, exhaust type.
 

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AKA OhOneWS6
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Discussion Starter #3 (Edited)
18' SleekCraft Rebel. Speculation from KRE (Pontiac specialist) was ~425 HP. Holly 800 DP, Edelbrock Performer RPM, Hardin log exhaust with snails. Someone else started this build and the motor was already done so I have no idea on the CR. Engine specs below.

Engine specs.
-Pontiac 400 .030 over, Stock steel crank, Pontiac Super Duty Forged Rods, JE NHRA Forged Pistons
-6X Heads
-800cfm Holly double pumper w/1"spacer
-Crower Cam-297HDP
240/242 @ .050
297/308 advertised
.500/.500 lift
112 l/s
-Comp Roller Rockers
-Comp chromoly pushrods
-Comp lifters
-Comp Double Roller Timing Set
-ARP main studs
-ARP rocker studs
-SFI 12,000 rpm chrome balancer
-Edelbrock Performer RPM intake
-Glyptal paint lifter valley
-High Torque Mini Starter
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #4
:crickets:

I'm kinda stunned. Not even the typical "ditch the and Pontiac" and "get the energizer kit" comments. I thought someone would at least know how much HP to spin that pump those RPM. If it takes 425 HP to spin that pump 4200 then I would know I have to look somewhere else.

Anyone... Tom...
 

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I think just looking at your parts and pieces that you're going to need 100-150 more HP to go 60-65 mph with your combination.

I don't want to be the bearer of bad tidings, but I think your engine might be doing the best it can in it's present form.

I think your at 350-400 real HP with your current deal. Just not enough in my opinion.

RR
 

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Boat Nut
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Don't know didley about Ponchos, so here goes.... I'd guess you have 1) a little too much duration in tha cam, some thing around 280 or so would suit you better. 2) and open plentum intake would suit the jet application better, dual plane imo serves no purpose, since there is no need for low end torque, below 3000 rpm, this may be a different case with the YJ Jacuzzi. 3) The 800 carb would be IMO to be a little too small, as well. A good 850 is hard to beat in the jet boat application. This is assuming the tune is good on the motor; timing, ignition system, and fuel system.
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #7
I think just looking at your parts and pieces that you're going to need 100-150 more HP to go 60-65 mph with your combination.

I don't want to be the bearer of bad tidings, but I think your engine might be doing the best it can in it's present form.

I think your at 350-400 real HP with your current deal. Just not enough in my opinion.

RR
First I want to say thanks for the input. Your not going to hurt my feelings on this deal at all. Like I said in my first post, $1000 for 51 MPH, my $$$ per MPH is better than most here. I'm am curious why you think 350 to 400 HP. Kaufman has been building Pontiacs for a long time. Most of the parts came from there on their recommendation. I would think their estimate would be close. Not disputing you at all. You may very well be right. Just wondering why you think the HP would be that low.
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #8 (Edited)
Don't know didley about Ponchos, so here goes.... I'd guess you have 1) a little too much duration in tha cam, some thing around 280 or so would suit you better. 2) and open plentum intake would suit the jet application better, dual plane imo serves no purpose, since there is no need for low end torque, below 3000 rpm, this may be a different case with the YJ Jacuzzi. 3) The 800 carb would be IMO to be a little too small, as well. A good 850 is hard to beat in the jet boat application. This is assuming the tune is good on the motor; timing, ignition system, and fuel system.
Thanks Sleek. The one thing I noticed when I pulled the plugs was that 1,2,7,8 looked good. 3,4,5,6 looked lean. I was thinking the dual plain or the 1" spacer might have something to do with that. I may have another carb I can test with. A friend has a freshly rebuilt 850 with a new throttle plate just sitting on a shelf.

The carb I have has had some work done at some point. I don't know the history but the choke horn has been shaved and the power valves removed. It looks to have been done professionally. It has a nice smooth finish on the surface where the horn was removed. That could mean jack chit though.

Since it won't cost anything, I will borrow that 850 this weekend and see what happens.

Any other suggestions?
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #9 (Edited)
Here is a little more info. Ignition is an HEI. Not sure where it came from but it is new. I put a new MSD cap and rotor (brass contacts). The wires are new 8mm spiral core. New plugs as well. I had a really bad flat spot ~3200 It would stumble so bad I really had to feather it to get past 3200. This was fixed completely with a curve kit and the lightest springs. Now when I floor it there is no hesitation and it spins up to 4200 almost instantly.

Fuel pump is a new Holly blue. Holds ~6 PSI steady at WOT.
 

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You say a spring kit helped the ignition problem at 3200, did you check the timing at high rpm (full advance), or only at idle (initial advance)?

How does it act when you hit the wall at 4200? Additional throttle makes it bog down, or you have it wide open at that point?
 

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Seriously off center
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I don't speak Pontiac, but here's a couple thoughts.
I have a feeling you need a bit more initial advance. 4200 is real weak and barring something major (cam timing off, low compression, no secondaries) I would think you'd have more rpm especially with a YJ.
By 460 standards, that cam has too much duration for as little lift as it has. The carb is ok if it's in good shape. I run 830 cfm at 5100 with a Stealth dual plane. Edelbrock says that manifold is good from 1500 to 6500 so I doubt that's the hold back.
Check your timing, give it a couple degrees more and test it.
 

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What is the secondary stamping on your heads (on the acc mount below the valve cover rail) normally -4 or -6 or -8)

Some 6X's have huge chambers (near 100cc) and would result in pretty weak compression, even the smaller chambered ones are pretty "soft" for a 400

For comparision my +040 400 in my sprint boat has a chamber volume around 50cc (smallest chamber head milled 080 !!!)

See "in boat vid" post for my iron headed (class restriction) 400 Ponty
 

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I would not be surprised if you were not making 400 hp at that rpm. Loosen up your pump and get a few more rpm's and maybe get a little more hp.
 

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I'm kinda with slowride on this. BUT, built many a hot rod Pontiac back in the day, and every one I ever put together liked single planes. Dunno why, or care, but they worked. Given your plug readings, you're seeing what I used to see regularly 15-20 years ago. Might well have sumpin to do with head design and why the REAL hot rod Ponchos (421-428 SD) had low rise single plane dual quads on them. (Pontiacs like high duratrion, smaller lift BTW. Built into their ports to increase atomization and velocity!)

You're engine will be fine in a boat! Not gonna tell you to change it, lord knows we need more Pontiacs around. Slowride pointed you in the right direction with the timing. That is CRITICAL in a Pontiac. Not 1 or 2 degress off, has to be perfect! The HEI is NOT hurting you, it's fine.

I would throw a couple degrees more intital advance on it, provided it doesn't exhibit starting, detonation, or idling issues. I'd also look seriously at your carb. You didn't specify what you had, but 850 is what I would recommend.

Lastly, if none of these fix the RPM problem (I beleive you have enough HP to drive that pump with a pretty aggressive impeller), then it lies in the valve train. Springs mainly, but then you are experiencing valve float.

Ray
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #15 (Edited)
What is the secondary stamping on your heads (on the acc mount below the valve cover rail) normally -4 or -6 or -8)

Some 6X's have huge chambers (near 100cc) and would result in pretty weak compression, even the smaller chambered ones are pretty "soft" for a 400

For comparision my +040 400 in my sprint boat has a chamber volume around 50cc (smallest chamber head milled 080 !!!)

See "in boat vid" post for my iron headed (class restriction) 400 Ponty
I do not see a number like that. I see "H237" & "D<N" on both heads by the accessory mount, 6X on the center exhaust runner and GM7 on the #2 exhaust runner GM8 on the #7 exhaust runner.

Cool vids. That is one bad ass Poncho.

You say a spring kit helped the ignition problem at 3200, did you check the timing at high rpm (full advance), or only at idle (initial advance)?

How does it act when you hit the wall at 4200? Additional throttle makes it bog down, or you have it wide open at that point?
32* initial. Never checked high RPM. I have verified that the timing mark on the balancer is at TDC. I am using a Snap-On advance light to check it. The wall at 4200 is WOT.

I'm kinda with slowride on this. BUT, built many a hot rod Pontiac back in the day, and every one I ever put together liked single planes. Dunno why, or care, but they worked. Given your plug readings, you're seeing what I used to see regularly 15-20 years ago. Might well have sumpin to do with head design and why the REAL hot rod Ponchos (421-428 SD) had low rise single plane dual quads on them. (Pontiacs like high duratrion, smaller lift BTW. Built into their ports to increase atomization and velocity!)

You're engine will be fine in a boat! Not gonna tell you to change it, lord knows we need more Pontiacs around. Slowride pointed you in the right direction with the timing. That is CRITICAL in a Pontiac. Not 1 or 2 degress off, has to be perfect! The HEI is NOT hurting you, it's fine.

I would throw a couple degrees more intital advance on it, provided it doesn't exhibit starting, detonation, or idling issues. I'd also look seriously at your carb. You didn't specify what you had, but 850 is what I would recommend.

Lastly, if none of these fix the RPM problem (I beleive you have enough HP to drive that pump with a pretty aggressive impeller), then it lies in the valve train. Springs mainly, but then you are experiencing valve float.

Ray
According to the person that origianlly started this project the carb is an 800. I can't verify that because the choke horn is shaved so the part # is gone. It looks to have been done professionally. It has a nice smooth machined finish on the surface where the horn was removed. The power valve is blocked off.

At 32* initial it is starting to kick back occasionally when starting. I was going to add a toggle switch on the ignition so I could spin the starter first to help with this. It has a high torque mini starter. Idle is fine, no indication of detonation.

I am almost embarrassed to say that the vacuum advance is hooked up. I was going to use the screw method to lock it out this week before testing again on Saturday.

Thanks to everyone for the input so far. I know I am close. Hopefully just a little more tuning. While 60 would be nice, My main goal is to get all I can out of what I have.
 

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Boat Nut
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32* initial is huge initial timing, can't hear detonation with O/T exhaust. They make a fixed positioner for the vacuum advance mechanism, when the canister is removed, might check into that. Need to see where the total advance really is, too much is worse than too little. Check the spark plugs for black specks, if there is any, it aluminum from the pistons. Easy to melt down a piston in a jet boat with too much timing. Not enough timing, you will sometimes get a pop out of the carb, may be some issues in the carb that need addressed, and the timing is masking the problem.
 

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First I want to say thanks for the input. Your not going to hurt my feelings on this deal at all. Like I said in my first post, $1000 for 51 MPH, my $$$ per MPH is better than most here. I'm am curious why you think 350 to 400 HP. Kaufman has been building Pontiacs for a long time. Most of the parts came from there on their recommendation. I would think their estimate would be close. Not disputing you at all. You may very well be right. Just wondering why you think the HP would be that low.
NHRA factors these engines at BELOW the factory claimed power rating. The 400/370 hp engine(the biggest Pontiac made), is rated by NHRA for stock eliminator use at 340 hp. That is an indication that the engine is not a real good choice for making power.

For example, the 427 Ford engine is factory rated at 425 hp, but NHRA "factors" it to 510 hp, makes the cars add weight, and they still crush the class wherever they run, as do the 428 Cobra Jet cars(335 factory vs. 370 factored).

Not saying your 400 CAN'T be made to put out more power, but with what I see on your parts list, I don't think it's doing over 400 - especially thru Logs with stock, Iron heads.

Hope that explains my logic. Just drive it and have fun.

RR
 

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Matt , hate to be the devils advocate here but what concerns me after reading thru here is that Jacuzzi YJ's (axial flow jets) do not "compare" to mixed flow jets in terms of characteristics and for that matter diagnosis They (YJ's) tend to run much higher RPMs vs speed vs power etc , Its not uncommon for a BBF/yj ("B" impeller) combination to run 5200 5400 WOT with 50ish for speed (example my POPs brand new 78 Omega with a 320 hp rated 460 H&M Ford new off the showroom floor would "scream" down the lake at 5200 and around 48 mph (fully loaded) Quite honestly the 4200 rpm figure your seeing suggests to me that your way down on power for some reason or your tach is nuts. If this was a Berk type jet, 4200rpms with for example and "efficiantly operating" jet with A impeller would compute to around 250 hp ! This chart cannot be applied "pound for pound" to Jacuzzi however . Call me later I'd like to try to help Tom
ps a YJ "B" typically compares somewhere to a Berk "A")


H.P. 9.5 9.25 AA A B C
150 2900 3050 3200 3600 3800 4050
200 3200 3350 3500 4000 4200 4450
250 3450 3600 3700 4300 4500 4800
300 3800 3950 4050 4550 4800 5100
350 4050 4200 4300 4750 5100 5350
400 4250 4400 4500 5050 5300 5600
450 4450 4600 4700 5250 5500 5850
500 4650 4800 4950 5400 5700 6050
550 4800 4950 5100 5550 5850 N/A
*THESE RPM VALUES MAY VARY ACCORDING TO HOW YOUR BOAT ALLOWS THE PUMP TO LOAD
HORSE POWER REQUIREMENTS ARE AT THE PUMP SHAFT
 

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Have a look here for the ID code

http://images.google.co.nz/imgres?i...g&imgrefurl=http://www.wallaceracing.com/head

It will be a 4 or an 8 stamped on the flat machined surface

4 = 93 cc chamber
8 = 101 cc chamber

Either one will yeild a pretty lame compression ratio

A swap to a set of smaller chamber factory heads will yeild good results
#16, 64 etc (D-port non SD) etc are around 72cc and bigger valves (2.11 / 1.77)

You really need to check your total timing, should like up to 38 degrees with that weak compression and down to 32 with a set of heavily milled #16's or similar

If its not locked out (dizzy) that amount of initial is a disater waiting to happen. Try the initial at around 18 and restrict the mechanical advance to give around 34 total for starters. Test from there

Get a copy of Jim Hands book on street / strip Pontiacs. A wealth of information over a lifetimes tinkering with budget Ponty's using stock factory parts

Cube for cube theres no reason why the Ponty shouldnt run with the competition. I would put factory 400 Ponty stuff against factory 400 Chevy stuff (or Ford ??) any day in a budget type deal like this, just use the "right" budget parts and tune properly

Agree its nowhere near 400 with the current gear but to get there wouldnt take much
 

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AKA OhOneWS6
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Discussion Starter #20
32* initial is huge initial timing, can't hear detonation with O/T exhaust. They make a fixed positioner for the vacuum advance mechanism, when the canister is removed, might check into that. Need to see where the total advance really is, too much is worse than too little. Check the spark plugs for black specks, if there is any, it aluminum from the pistons. Easy to melt down a piston in a jet boat with too much timing. Not enough timing, you will sometimes get a pop out of the carb, may be some issues in the carb that need addressed, and the timing is masking the problem.
That was checking the timing @ 900 RPM with the vacuum disconnected and the port plugged on the carb. I believe the light springs start to come in ~800 RPM. I'll get a light on it and see where it is at 4200.

This is logs with snails not OT exhaust. no audible pinging and no specs on the plugs. I already looked for that.
 
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