383 Stroker won't rev past 4000rpm - Chevelle Tech
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  #1  
Old Jul 25th, 06, 1:22 AM
SneakyPete SneakyPete is offline
 
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Default 383 Stroker won't rev past 4000rpm

Hi all. I have prowled on here for a while, and broke my cam in following the great instructions posted on this site. My 383 is in a boat, and not in a Chevell, therefore I apoloigize in advance if I aggrivate any of you for not being Chevelle related.
My Motor:
383 SBC short block built by Wheeler Power Products.
Vortec heads, beehive springs, stamped 1.5 rockers. 9.75:1 C/R
RPM Air Gap intake, Edelbrock 750cfm (marine) carb.
Comp Cams flat tappet cam 12-268-4 "Best cam for modified 350 TPI with improved chip, injectors, plenum, runners and exhaust." I used this cam due to the wide LSA to prevent water from being sucked back thru the exhaust. I checked with Comp Cams and they said it was a geat choice they use all the time for marine applications.
Camshaft Specification Table
Part Number 12-268-4
Engine 1955-1998 Chevrolet
262ci-400ci
8cyl.
Grind Number CS XE268H-14
Description
Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.479 0.48
Duration At 0.006 Tappet Lift 268 280

Valve Timing At 0.006
Open Close
Intake 24 64
Exhaust 78 22
These Specs Are For The Cam Installed At 110 Intake CL
Intake Exhaust
Duration At 0.05 224 230
Lobe Lift 0.319 0.32
Lobe Separation 114

PROBLEM: The motor will not spin past 4200 rpm. A marine application is kind of like a dyno, ie constant load. My desktop dyno says the motor has 487hp (5500 rpm) and 475tq (4500rpm). Wheeler figured 410hp, and 475tq. Either power level is more than enough to swing the prop that is on it. The motor runs super strong, and pulls hard to 4000-4200rpm, then just spins no higher. There is not rev-limiter, as it will spin high in neutral. I don't think the prop is too big (ie too much gear), because of how hard it pulls everywhere else. I have the secondaries at the richest possible (12% fatter than stock), but it made no difference when I had the stock secondaries in there. I have not been able to verify if the secondaries are opening. I did make sure the choke was fully open, from what I understand that can keep the secondaries from opening. Is it possible this combo is not creating enough vacuum to open the secondaries? The plugs look rich. Timing is set at 36* total advance, in by 3400rpm. Any ideas? Any help is greatly appreciated, and sorry for not being totally on topic.
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  #2  
Old Jul 25th, 06, 1:26 AM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

Here are links to a couple of videos that I shot. Good gearhead stuff with sound, but it also shows the behavior of the boat, and how easy it gets to 4k, then just falls on its face. Thanks again!!


Idling at the dock
http://www.youtube.com/watch?v=5q-rbQZyUVU

Short Video of it getting up on plane, then to full throttle real quick. This only about 1/3-1/2 throttle till it gets fully planed off. See how easy it gets on plane.
http://www.youtube.com/watch?v=ZTFE6WSVcDY

Longer Video of the motor starting, getting on plane, and hitting about 62mph.
http://www.youtube.com/watch?v=eo2hdwzHrMo

Longest Video, shows a some cool shots of the lake, and specifically the gauges. Notice how fast it winds from 3000rpm to 4200rpm (or so) when I punch it, then it just doesn't spin any faster. Speedo is on the left (and on the fritz), tach on the right, water temp lower left, oil pressure lower middle, and fuel on the lower right.
http://www.youtube.com/watch?v=a-ezhr7j39M
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  #3  
Old Jul 25th, 06, 2:57 AM
BACK FROM THE DEAD BACK FROM THE DEAD is offline
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Default Re: 383 Stroker won't rev past 4000rpm

i say look HARD at that Edelbrock carb. especially if you are running a HV fuel pump. i went through three of them and figured out the hard way (in spite of what Edelbrock tells you) that with any more than 5-6 PSI fuel preasure,they go PIG RICH. the fuel goes right past the needle and seat at the float. some are even worse like 3-4 PSI. you must use a regulator with these carbs. as far as the secondaries opening,unless it is one of the AVS (vacume secondary ones) there is really not a way that they shouldn't open unless there is something sticking or blocking them. if i am right you will be killing your cylinder walls with the raw fuel washing off the oil ,so good luck.
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  #4  
Old Jul 25th, 06, 5:34 AM
Tom Mobley Tom Mobley is offline
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Default Re: 383 Stroker won't rev past 4000rpm

what Back said. Get rid of that carb, try a Holley 750 vacuum secondary or one of the imitators. I recommend you buy a brand new in the box one that nobody has messed with. Don't fiddle with the power valve or any of that stuff, just get a fuel line that fits it and and put it on. You may want to think about a fuel pressure gauge too. Boat builders do strange stuff, like but 1/8" pipe outlets on the tanks. Since it's a boat you could use one the fuel lines that has a gauge built in, get somebody to drive while you watch it.
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  #5  
Old Jul 25th, 06, 11:17 AM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

Thanks guys. I just bought a Mr Gasket regulator and will try that at the recomended 5.5psi. I had the secondaries at 12%richer than stock, up 3 sizes because it would rattle at 4k and not spin past there, so I thought it may be going lean on top. When I put a new distributor in, the rattling stopped, but it still would't spin faster. Like I said, the plugs do look rich, and I have also noticed gas in the water behind the boat near the pipes when I am not moving, so I assume unburned gas is being shot out the exhaust. I never even thought of the gas washing the cylinders, good call. I will drop the jetting back to stock and try the regulator next time I go out. Thanks again. In your experience, do you think the stock jetting from edelbrock is sufficient for a 383, or would I need to richen or lean it out? The stock settings for this carb (#1410) are as follows .113 Main Jet Primary, .104 Main Jet Secondary, .071x.047 Metering Rod (primary only), orange 5" step un spring, .0935 needle and seat, amd the pump drive link location is at the middle top hole. I really can't afford the Holley right now, so I have to deal with this one unitl Santa leaves one in my stocking. Thanks again!!
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  #6  
Old Jul 25th, 06, 12:28 PM
BillK BillK is offline
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Default Re: 383 Stroker won't rev past 4000rpm

Pete,
Need more info on boat, which drive, drive ratio etc. I am figuring a 4000 lb boat with an Alpha drive will probably need about a 14/19 Mirage or similar.

The basic rpm range listed for that cam in the Comp catalog is only 1800-5800 rpm, so you might be out of the cams range also. If the fuel system is stock, there is a check valve in the tank outlet tube that is a pretty big restriction. They are usually marginal even for the stock engines. I think someone makes a high flow valve, but not sure who it is. A lot of guys remove the valve completely, but that kills the Coast Guard approval on the fuel system. The 750 Edelbrock should be enough carb if jetted properly.

Personally, I think you are pushing your luck with a true 9.75 compression on pump gas with cast iron heads, especially a boat. Definitely don't want to use marina fuel, most of it is 91 octane at best.

You didn't mention your location, but you might want to find someone with a dyno that goes on the drive and see if you can take the boat to him and make a couple of "pulls" on it. It will give you a lot of information so you will have some idea where and what to start changing. Without it you can spend (waste) a lot of money guessing.

Hope this helps,
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  #7  
Old Jul 25th, 06, 2:33 PM
idunno idunno is offline
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Default Re: 383 Stroker won't rev past 4000rpm

You may need to do a few things just to isolate where the problem is. The most easy is to take the air cleaner off . Run it up to see if it magically rpm's higher. I see where the air cleaner is pretty close to the hood opening and I am wondering if there is a possibility of a low air pressure in the eng bay coming from the outside air rushing over the hole that has little area around it. Literally sucking the air away from the air cleaner. The second is to just change the prop pitch regardless of the mph you desire to simply see if the engine will in fact increase in rpms. It may be loaded for all its worth with the current prop. I dont hear endine misses that would come from spring issues. Look into the intake manifold under the carb and as far into the int port as you can for a dark soot. That would be a indication of 2 possibilities. First is the valve spring is unable to control the valve closing and the second would be a possibility of exhaust being trapped and killing the intake signal, from the water exhaust and only 6 degrees of ex. duration spread.
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  #8  
Old Jul 25th, 06, 3:48 PM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

I am using a 25p Mirage. The Desktop Dyno says my tq peak was at 4500rpm, and the hp peak was at 5500, so I figure it would pull to at least the tq peak. It is a 21ft Checkmate Enchanter, with a fairly lightweight hull, and I figure it weighs about 3500lbs. It has an Alpha, but not sure of the gearing. The cams range it 1800-5800, and this is only pulling to 4200 at best, this is the first motor I have built, but I thought the cam still would have plenty left in it. I initially thought it was going lean on top, but the plugs don't show that, and it doesn't smell like that. The old owner had put a Targetmaster motor in it, and it would only pull to 4k as well, but that motor was spinning a 23p cleaver, and I always assumed that it just wasn't powerful enough to spin the prop. The only piece that is left over from the old motor is the ignition amplifier. I am working on getting another one. I am using a Holley 110gph fuel pump. I have not tried the smaller prop on the new motor, but I will do that as soon as it stops raining. Its just weird how it charges hard to about 4000, then hits a wall.
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  #9  
Old Jul 25th, 06, 3:52 PM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

Thanks for the tips guys, I will try them next time I go out.
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  #10  
Old Jul 25th, 06, 4:40 PM
dreis454 dreis454 is offline
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Default Re: 383 Stroker won't rev past 4000rpm

I'm with those guys Try a 750 Holley , I bet it runs better. I have never been a fan of them edelbrocks
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  #11  
Old Jul 25th, 06, 5:22 PM
69-CHVL 69-CHVL is offline
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Default Re: 383 Stroker won't rev past 4000rpm

Valve springs good?
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Old Jul 25th, 06, 5:23 PM
69-CHVL 69-CHVL is offline
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Default Re: 383 Stroker won't rev past 4000rpm

Never mind...saw that you have the 'hives.
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Old Jul 25th, 06, 7:27 PM
70 beater 70 beater is offline
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Default Re: 383 Stroker won't rev past 4000rpm

They just repaired a car over here that was laying down like that,it was the module in the HEI distributor.They've been trying to get that right for about 3 weeks.

Just thought I'd suggest it,didn't see that you listed any ignition parts.
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  #14  
Old Jul 25th, 06, 7:38 PM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

Quote:
Originally Posted by 70 beater
They just repaired a car over here that was laying down like that,it was the module in the HEI distributor.They've been trying to get that right for about 3 weeks.

Just thought I'd suggest it,didn't see that you listed any ignition parts.
That is kind of what I thought, and was recomended to me on another forum, so I swapped in a whole new Distributor with a new module, no dice. Although, with the old Dist. it sounded like it was doing the death rattle at 4k, but not at 3800, with the new dist, not rattle at all.
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  #15  
Old Jul 25th, 06, 7:49 PM
SneakyPete SneakyPete is offline
 
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Default Re: 383 Stroker won't rev past 4000rpm

Guys, I'll try and give a quick run down of where I have been with testing different stuff.
1. Cam break in on trailer, stock jetting, plugs look rich. No performance data due to being on trailer.
2. 1st sea trial, didn't run it hard or high, half the plugs on same intake plane look rich, half look lean (same plane)
3. Pulled carb, disassembled, cleaned, put in the fattest possible secondaries (I do believe at some point I spun it to 4k, on another day, and heard it rattling, and assumed it was lean on top, hence the fatter jets-can't remember when I noticed the plug issue). Checked edelbrock fuel filter, looked fine, flowed fine. Ran it again, plugs look rich, wet, sooty.
4. New fuel/water separator. No change.
5. Added pressure regulator, ran fine up to 2200rpm, didn't go any higher-kids in the boat. For some reason took it off before going for a WOT run.
6. New distributor, maybe picked up 100rpm.
7. Took it out by myslef, not much gear, no extra people (above had at least one other in boat). 4200rpm, 62.7(gps) --200rpm more than before, .7mph more than before
8. Next I will put the regulator back on, drop the jetting back to stock, and put the smaller 23p prop on.--I should also change the oil and check if its gassy smelling.
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