383 performance problem
 

My freshly built 383 SBC gives me trouble...lots of money invested but still no breakthrough in performance... heres my story:

Tore down my tired 350 Mag because it was not good for more than 52 GPS on my 22 Pachanga.....honed the block 030 over, new forged pistons, 5.7 rods, cast 383 stroker crank, cr. 9,5:1. Heads stock 76cc, large valves.
EMI Thunder exhaust, CompCam XE 262 H, Merc high rise manifold, Q-Jet with DA powertips, initial 10 degrees, fully dialed in 32 degrees, K&N Airfilter.
Did everything in accordance to Dennis Moores SBC bible.

Was hoping for mid 60s at least, theoretically the engine should put out 350 hp minimum.

BUT-all I get after 15 hours of break in is 58 GPS, spinning my 23 labbed Mirage only 4400 rpms.

Checked compression-perfect, tried different powertips on the carb, readjusted ignition, but to no avail.......

Is it possible that my stock heads are the "bottleneck" in my setup? That they simply wont allow enough airflow to take advantage of all these mods? Could this be a Carb problem?

What speeds are you guys running with your 383s in similar boats? Any help appreciated, I am really out of ideas!

What's your exhuast like after the manifolds? If I remember right, some of those older Pachangas had a unique, but restrictive exhaust, exiting at the rear corners of the boat. Water lift??...somthing like that.

liquid lounge, exhaust is open, threw away these ugly drum-style mufflers.....installed inline baffles at the tips, they are not very restrictive, but their effect in noise restriction isnt too restrictive either...

How are you getting to the tips? If you are using 2 90Deg elbows
to the tip, and they are tight 90's, this will degrade a high performance motors' output more than most would think. Reason I think this could be a problem is I just went through this very thing on a side exit exhaust, the motor[509] just wouldnt spin past 4700rpm's. Had a custom riser made and straightened my exhaust plumbing, now 5200rpms.

Play with the ignition timing. You should be able to go as high as 36-degrees BTDC without a problem, but don't go any higher than what is necessary to increase performance. If you still need more a little more top end, you may need a little more camshaft. Consider using a Crane H272-2. This cam idles well, especially in a 383, and you don't need long pipes to prevent reversion. Here is a link to the Crane H272-2 camshaft card.


I run 383s in my 27 Magnum and my 18 Donzi.

Preuni- just re-read your post. I dont think your that far off speed versus HPwise. It would not be unusual for a boat like yours to require 15HP/MPH , that would be 90HP in your case...pretty close to the 350hp you were hoping for[assuming your old mag was the 250hp version] Also, your rpm's are a little low...this is why I thought about the restrictive original exhaust...try dropping down in pitch as I think your mouse would like 5000rpm, if it still wont get there, then you have another problem i.e. exhaust, induction, ignition,etc
Just a side note- I think Dennis Moore makes for some great and valuble reading....the only thing he's trying to sell is his books, but I don't think he is the end all, gospel, King Neptune of marine engine building.

I agree with ForrestC...
 

...you might need more flow with the extra cubes.

I went a little bigger than the one he recommends, with a little rumble at idle...you definately know it's there.

With that cam and those heads, depending on carb and timing, you may be making max hp around 4,600-4,800 RPMs. Where do you want to make the power?

I'm not sure what heads came stock on that 350 Mag, but if it were me, I would look into some heads with 170-180cc intakes, and bigger valves, smaller chambers (more compression) along with a little more cam- but that's just me.

My 383 in my old 4,000lb 23' slug spins a 23" 3-blade around 5K RPMs.

Trash the heads and look at getting something with a more modern combustion chamber (Vortec is first on the list, World Products if you want to spend more). Also, that cam has a power range of 1300 to 5500 RPM. I'd expect maybe 52-5300 as the max with a 383 or 400 so somthing is not right. Bump that timing up there to 36* and see what happens (run high-test fuel and watch/listen for detonation... very important with those older style heads... Vortecs will allow an easy 10:1 btw). You're holding it back with the timing.

Preuni,

Bruce Wolff (S.W. Michigan) just finished a pair of naturally aspirated 383sbc's for a dude in Chicago that owns a 27' Magnum that I think runs at about 78mph now. He's done several small block chevy's for marine apps. He has several combinations that he builds from mild to wild. You might try giving him a call. Shop # is: 616-422-1090

What was your prop before you changed the motor? You say that you're spinning 4400 with a 23" lab mirage. My old 24' Concord with a 454 mag would turn a 23" @ 5200, so I'm thinking that you're over proped.

If you do decide to change the heads, look at the new vortec heads. They are a excellent flowing head and the price can't be beat. They're only a couple of hundred from the dealer. Add a performer rpm intake and you'll definetly gain power. Just be sure to recalc the compression ratio.

Like Cord says recalc your CR. I seem to remember that Vortec heads are 64 CC chambers. I'm running 76 CC chambers on my SBC's with World Products Torquer II heads. I had to go that route because my compression is over 10:1. But I agree with Tom, I think your heads are your limitation.

I did some reverse calculations using the numbers you gave, and BAM's speed calculator. All things being equal I think your doing pretty well. There calculator says your running 375 HP. Which was the difference in HP needed to go from 52 to 58. Not too bad.

Did you port match your intake to the heads? I measured the increase in size of the intake port to the heads when I matched mine and I had an increase of 22% on the intake and 17 on the head. That big of a difference will really smooth out the air flow and build power.

Actually, you'll be over 10.5:1 with the Vortec heads (combustion chamber volume is advertised at 64cc's but in reality they come out more like 61cc's) so scratch what I said earlier. The WP Sportsman II's (72cc) would probably be a better bet, though the expense would be much more than that of the Vortecs. To use the Vortecs, you would need to change pistons in order to make it exceptable for marine use (unless you like paying for race gas). The Sportsman II;s will probably get you right at about 10:1, and with the fast-burn combustion chamber you should be able to get away with using premium fuel.

I was going to mention something about the prop as well. That cam will allow you to produce a ton of torque down low (torque curve should be flat as a board), but still that's a lot of prop for being behind a small block in a single engine application I think.

This board really rocks! Thank you guys for all the info.
first thing I will do is bump up the timing to 36 deg. and see what happens. Next thing is that the heads will have to go, I am sure they are contributing to my problem big time. Anybody selling a pair of ported WP Torquer II heads with 72cc chambers??
That motor should spin my 23 Mirage at least 5K, the boat is light (2900pds) and the hull is built for speed......
Just tried a 21 Mirage today, 4800 rpms 60 mph GPS. Still too slow, considering that the boat has a SternJack...On this board I read apost a while ago that a Pachanga 22 with an 406 ran 72 GPS, so there has to be another 5 miles or so in mine!
!
Thanks again everybody!
Andy

Preuni:

I don't understand why you are being advised to increase ignition timing to gain top end!! This theory is wrong. The more timing is advanced the less top end power you have. That is why M.S.D. sells a timing retard system. I have used it in my drag racing days to retard the timing when pulling gears to gain top end. While 32 * advance is not alot, I don't see how going to 36 * will help you much, if any at all. I think that your problem lies in those cylinder heads. What size valves do you have in them? I have a set of 2.02 intake, 1.60 exhaust 292 casting #, angle plug turbo heads that are mildly ported ( just deburred ), 3 angle valve job, but they have 62 cc chambers. I am looking to sell them. I don't think I will ever use them for myself. If interested let me know.

Retarding the timing takes away power and makes the engine respond like a dog (think back to the old days when the octane dropped and the timing had to be knocked back in order to keep those old muscle car engines running). I think he's down on power all across the board and bumping the timing up a couple of notches would help the engine build power.

It works on our Fuel dragster... :D

KAAMA, I need to talk to this guy who's running 78 MPH in his Magnum 27 with a pair of 383s. That's impressive!

ForrestC,

Well, if I remember correctly that is what I was told. I don't know the dude who owns the boat neither do I know what mods have been done to the engines/boat, but you're more than welcome to call Wolff and perhaps he can give you the owners number, but Wolff is the one who built the engines. 616-422-1090

BTW, I don't know much about the 27' Magnums and/or small blocks either, therefore I don't really know if that speed (78mph) is really a stretch or not----it certainly sounds fast. I just know that those 27' Magnums are very cool looking older boats. I always see one in St. Joseph with small blocks and tail pipes coming out from the deck some how and over the transom. Some older dude owns it and when I see him at the lauch he walks around that boat prouder than a peacock!

ForrestC,
I think the boat that Kamma is speaking of is Greg's from Gorilla Powder coating in Crestwood, IL. I'll try to run by his shop and get his phone number for you. His boat was featured on The Lovely Lady's of Motor Sports a few years ago. The whole boat was restored. Here is a pic I took of it a few weeks ago.
Dan

Thanks!
 

Magnum 27s are great looking and great running rough-water boats, but with their heavy lay-up, they are not at all light in weight. For that reason, you really have to work for MPH on the top end. I'm running a pair of 383s in my 27 Magnun with 200cc intake 64cc Dart Iron Eagle heads (9.2:1 CR), Crane H-272-2 cams, Stainless Marine exhausts, and I'm in the low sixtys MPH at best; however, that's with old 1.61:1 Volvo 280T (with power trim) drives and Hill 27" pitch propellers. I'm sure that the Volvo drives and their limited prop selection is killing the top end, and for that reason, I'll be installing a pair of Hydromotive nose cones and getting some additional work done on the Hill props by Hill Propellers. Some day soon, Bravos, Arnesons, or something will be in the works, but for now I'll be working with these old Volvos.

Thanks again for the contact.

Hey Forrest...
 

I currently have a Volvo 280 drive (with a Hydromotive nose cone I installed- not fun), and I'm having trouble finding a top plate to attach an external steering ram.

Are you running external steering? How is the tie bar and ram attached to the drive?

BTW, 27" seems like alot of prop. I am also running a Hill turbo 3-blade. What size do you need? I can check around...

I hear ya on the old Volvos...no one has performance parts for my old drive...

Havasu Hangin, I'm turning 4600 to 4700 RPM with the 27"p props, but there is a 300 RPM mis-match between the props (the port side turn only 4400 RPM now). I guess this happened since they weren't built at the same time. I'll have him tweak 'em and match 'em for about 4800 RPM. Prior to the 27" I ran 24"p Volvo-Penta Ultra props and they would turn 5600 RPM but wouldn't hook up on the top end (high % of slip). I wanted to bring the RPMs down a little to increase the cruising range, and that's why I went with 27"p as a starting point. On thing I find with prop testing on the Volvo Aquamatic setup is that they have more prop slip on the top end than I've found on Mercrusier setups. I'm keeping my fingers crossed that the nose-cones will help reduce the prop slip at full speed. I'm sure that matching the props will help as well.

As for steering, no external steering - just Volvo power steering on the inside. When I go to the next out drive setup, you can bet it will get external hydraulic steering. I tie bar the two drive together using a stainless-steel hiem-joint tie bar from a TRS setup shortened to 30" and attached where the 280/290 steering torque compensation trim-tab was removed. It works fine and doesn't drag in the water.

No one that I know makes one, but you can build a solid external steering attachment point on a Volvo Aquamatic drive. A few of years ago I built a stainless-steel steering-ram attachment plate that bolts to the top of a 280 drive using three of the drive-cap bolt-holes for a friend of mine's X-18 Donzi. Basically, it's a piece of 3/8" stainless plate cut to cover the top of the drive with a hole in the middle to allow access to the screw-dipstick, and three holes for the three cap-bolts. It used three stainless-steel spacers that fit tightly into the recess of the out drive cap where the attachment bolts go. These spacers, which are about an inch long, raise the stainless-steel steering plate just high enough to clear the drive's cap. You can accurately locate and weld the spacers on to the plate or just bolt it all together using ARP stainless steel bolts.

The best way to go about designing the plate to insure that it will work with the steering ram that you have, is top build the plate out of 1/4" plywood, to mock it all up to make sure the steering doesn't bind at any angle, before you commit to having it cut out of stainless-steel plate. If you can't find any stainless steel spacers at you friendly fastener shop, these stainless-steel spacers can be found in many automotive disc-brake calipers. The trick is to find the correct caliper repair kit at the auto supply. Bring your magnet - some are more "stainless" than others.

Thanks Forrest...
 

...that make sense. I was wondering how a custom plate would sit on top of the cap, and still fit flush in the cap bolt holes.

I heard Speedmasters in Florida was making a plate for the tie-bars, so I called them. He wants $100 for one, but I'm not sure if it will work for a ram.

Well, I hope the nose cone helps your slip. Those lower units are pretty blunt, and may be causing your problem. The pic below is what mine looks like with the cone installed.

ForrestC,
Nice boat!
I stopped at Greg's shop but he wasn't in. His Dad says the boat runs low 70's but didn't have exact numbers. I know he runs a GPS Speedo so the numbers were pretty accurate. He did not have Wolff build his engines. I'm 90% sure he has Merc drives on the boat. I told has Dad to have him check the board. He is not a member yet!!! I'll stop by next week and see if I can talk him into checking out the board.

Dan

I have a 383 in my 18' powerplay... I built it over the winter and now have 55 hrs on it.. its around 400hp.. my stock 350 mag spun a 21' at 4500 for 58.6 mph and now with the 383 it spins a 25' at 5300... for at least 72-73 mph

traviss, what kind of heads you are running? Vortechs?
What exhaust and cam?
Andy

Forrest,

the hydromotive nosecones will make a difference on the volvo 280. I picked up 3-4 mph on my 18 Donzi with it.

Blowout is significantly reduced also and you will be able to trim higher.

I talked to Wolff today and he said those 383's that he built for that 27' Magnum make about 375hp each and push the boat from about low to mid 70's.

Yes..I am running the vortech heads... screw in studs.. guideplates... guides machined for high lift cam... springs to match cam..

roller cam is 222/230 duration.. .509/.528 lift on a 112 LSA.
( I used 1.6 rockers so mine is acutally .543/.563 lift..)

Exhaust is all aluminum EMI's... with the riser water going out dumps in the transom instead of going out the exhaust..


Travis

Kent / Havasu, UPS just delivered my two Hydromotive Volvo nose cones, and Havasu, it sure looks like it going to take a little doing to get 'em installed properly and faired in. Did you guys need to clean up the inside of the nose cone to get a tight fit? The reason I ask, is beacuse when I hold it in place it against the lower unit, there seems to be a few gaps here and there. Also, what kind of filler did you guys use to fair it in?

Preuni good luck with the 383. From my experience, the 383, even with a mild cam and (or) 76cc smog heads from yester-year, is much stronger, smoother, and in may cases quieter, than the equivalantly setup 350. I also have an 18 Donzi with a big and heavy TRS outdrive and a budget-built 383 (76 cc 441 heads, UEM Claimer flat tops, and a Crane H-272-2 cam), and I can honestly say that this engine is the best all around running engine that this Donzi ever had in it. With a 23" pitch Mirage prop, it has incredable bottom-end and mid-range, and a 66 MPH top end. With any luck, I may be trying a 24" pitch 3-blade Hydromotive prop soon. You have to remember that this is a heavy, short, 24-degree bottom boat with a giant outdrive. Hay, I may need a nose cone on this boat's TRS outdrive as well!

Forrest- When I spoke with the guys at Hydromotive, they made it seem like it would be a piece of cake- far from it.

I saw the same thing you saw- the cone does not seem to fit very well. I had BIG reservations when installing, because it seemed like it was not made for my bullet, and you have to get it perfectly straight. I even had to start over one time.

I took the drive down to the metal, and even did some grinding on both the cone and the bullet to get a snug fit. For lining it up, I had the drive upside down, and eyed it off the skag. Also, I eyed it from above using the centerline of the top plate in relation to the shaft.

It still didn't look snug, but that's what Hydromotive told me to do. I then used the Sea Goin' Poxy Putty that came with the cone to tack it on. More grinding and sanding...also be careful to keep the putty off the drain plug on the bottom.

Before backfilling, I also took some material off the sides of the cone, to streamline it a little, and make it easir to fill.

I used some 4x4 Bondo for backfill. What a pain- I was not as good as I thought at body work. Took me 4 tries to get it right. I've heard there are better fillers out there- after 2 seasons, I have a couple hairline cracks in the filler at the bottom. I have been told that this is from flexing- if I had welded it on, then I may not have the small cracks.

Good luck!

BTW- I'm going to WPM on Friday to get the wing plate made for my external steering- thanks again.

Preuni- my engine made 457HP with 10-1 pistons, the same cam as Travis, and ported Edelbrock Performer RPM heads (on dry headers).

Oh boy. I have two to do. :eek:

Thanks for the heads up!

Forrest,

My donzi originally came with a hydro nosecone but it came off after several years. It was not put on straight and had auto filler bondo on it.

I replaced it with a new hydromotive cone. It also did not fit exactly so I filled and ground for maximum contact and also insuring exact straightness. I used Marine-tex as filler for fairing. Actually gained a mph with the straight installation and no problems with the filler coming off like the aut body filler.

The TRS should not need a noscone at speeds under 75. Everyone I know that tried them on boats under 75 actually lost a little speed.

Kent

Kent, thanks! What kind of prop is on that Volvo 280t?

14 x 26 Mercury Chopper. Modified for Volvo. A bit big for the setup but nice cruise 63@4500rpm.

(The Volvo has been replaced with a high-x Bravo drive now)