Mo' RPeeeeeM's?

« **on:** September 28, 2010, 11:17:31 AM »

18 foot jetboat with jacuzzi yj with american turbine conversion. "A" impelller
463 olds w/ Ga heads Ported quite a bit
180lbs compression.
comp cam 42-231-4, 230@ 50 installed straight up
single Holley 750 DP w/ mech secs, plug color is a nice tan.
Offy turbo thrust manifold. Intake manifold vacuum at idle is 11.5
MSD ignition and dist. +12 advance
Bassett over the transom water injected headers. No thermostat, engine temp is always 100F or less.

This thing runs great but, I can only get this motor to rev to 48-4900 rpm, sure its 61mph, but this thing should get to 6k rpm no?
I'm getting parts to build up a holley 850, and give it some more cfm, anyone think i should try otherwise?

For the olds guys what carbs, impellars and rpms are you running?

thanks

« **Reply #1 on:** September 28, 2010, 12:01:59 PM »

your gunna need about 700-750hp at 6k to get to 6k and that motor is probably not making that much hp

« **Reply #2 on:** September 28, 2010, 01:11:09 PM »

Ok, here's the american turbine impellar chart

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

ok 6k is probably too high of an expectation. I think I should at least be able to get it to 5400.

« **Reply #3 on:** September 28, 2010, 03:29:34 PM »

I wouldn't want to spin an olds to 6k for very long or very many times. And if your plug color is good then I wouldn't swap the Carb, but you can check manifold vacuum on a wot run to see if the Carb is too small. I would take a closer look at the ground strap on the plug and see where the timing mark is and check for speckles on the ceramic and if no detonation maybe put more timing in, what is your total and base timing? The camshaft could be degreed way off if it was installed " straight up" and it could be retarded or advanced, but no way to know without degreeing the camshaft.

« **Reply #4 on:** September 28, 2010, 03:40:37 PM »

Well, i'll let you know how long it lasts at 6k. If it ever gets there, hahaa

base timing is 12 and full advance is 33.

I haven't degreed it, and i know i should. But installing it straight up is 106 at intake centerline as suggested on the cam card.

Im really leaning toward upping the carb to an 850, i have done a bunch of reseach and it's looking like i need around 800cfm min for the displacement.
I know it varies, but what vac at wide open would indicate too small a carb?

Any olds guys out there runinn' around 5500 rpm with an A impeller

« **Reply #5 on:** September 28, 2010, 06:52:59 PM »

Impeller efficiency drops like ton of crap at or near 5200 RPM, once over that, your literally just "adjusting" the loading and unloading of the impeller and limiting cavitation...

Your setup sounds very close, maybe the tune is off or your pump is lagging in setup.

A little more info is really needed, but if you are "shooting" for 6,000RPM then I think you will be leaving something on the table..

Shoot for a MPH... More can be done for that. I have seen 540" big blocks not make 6,000 without a lot of tuning and ingenuity with an A impeller...The speed difference from 4900 to 6000 RPM will be negligible if you don't change the pump setup IMHO....

GT

« **Reply #6 on:** September 28, 2010, 07:29:03 PM »

Quote from: double-d on September 28, 2010, 03:40:37 PM

Well, i'll let you know how long it lasts at 6k. If it ever gets there, hahaa

base timing is 12 and full advance is 33.

I haven't degreed it, and i know i should. But installing it straight up is 106 at intake centerline as suggested on the cam card.

Im really leaning toward upping the carb to an 850, i have done a bunch of reseach and it's looking like i need around 800cfm min for the displacement.
I know it varies, but what vac at wide open would indicate too small a carb?

Any olds guys out there runinn' around 5500 rpm with an A impeller

I think an 850 double pumper is a good call...But wont get you to 6K, why did you pick that RPM BTW, just curious....

My dads freinds Olds runs 5200 RPM like it has a governor on it, Berkeley pump with an A Stainless and a Trick plate loader, boat does 70 MPH with three people and a cooler of boat sodas...

I know for a fact it has an 850 dp because I dialed it in...

Also has a 1" open spacer on a Edelbrock Victor intake...

GT

« **Reply #7 on:** September 28, 2010, 07:43:04 PM »

double-d, You said Offy turbo thrust manifold, and single 750. Is that the single carb tunnel ram ?

« **Reply #8 on:** September 28, 2010, 08:52:59 PM »

Quote from: propless on September 28, 2010, 07:43:04 PM

double-d, You said Offy turbo thrust manifold, and single 750. Is that the single carb tunnel ram ?

Single carb tunnel =

Just my opinion $:-\$

GT

« **Reply #9 on:** September 28, 2010, 09:31:25 PM »

Quote from: GT Jets on September 28, 2010, 08:52:59 PM

Single carb tunnel = Just my opinion $:-\$

GT

Yea, thats kinda what I was gettin at. If thats what he has, its a HUGE plenum to try to feed (for lack of a better term) with a single carb, not to mention the funky flow to the corner cylinders.

Not sayin thats you problem, but if I remember right those manifolds wanted a big carb.

« **Reply #10 on:** September 28, 2010, 09:44:22 PM »

I bought a new jet boat olds/jacuzzi WJ in 1975--on the test drive, the motor ran 5600 rpms and the sales guy told me I had a strong motor. They didn't have GPS, but it ran a measured mile in just less than 1 minute, so low 60s MPH. Well in year 2, the tach broke and when I replaced, rpms dropped to 4900, but the speed was the same. Hmm, must have been one of those "closer" tachs.

« **Reply #11 on:** September 28, 2010, 09:48:50 PM »

Quote from: Sanger Pete on September 28, 2010, 09:44:22 PM

I bought a new jet boat olds/jacuzzi WJ in 1975--on the test drive, the motor ran 5600 rpms and the sales guy told me I had a strong motor. They didn't have GPS, but it ran a measured mile in just less than 1 minute, so low 60s MPH. Well in year 2, the tach broke and when I replaced, rpms dropped to 4900, but the speed was the same. Hmm, must have been one of those "closer" tachs.

I didn't know they had E bay tachs in 1975..

Hi Mark!

Sorry for the jack double d

« **Reply #12 on:** September 28, 2010, 10:30:31 PM »

ha! they probably had the tach switched to 6 cylinder

i picked 6k because that is what the cam is rated to.

yup single carb tunnel ram. I don't know why people frown on 'em, it's pulling good vac, other then they have no bottom end on the street, on a boat that doesn't matter.
offys carb selector says the manifold only needs a 650-700 with single carb, they don't specify displacement though.

GT so are you saying to go dual carbs? do you know what cam your buddy has? I would be happy with 5200 @ 70! it would be cheaper to change the cam.

here's an article i found, looks like an 850 is the min.

http://www.popularhotrodding.com/tech/0302phr_oldsmobile_455ci_engine_build/index.html

Dyno Results
STOCK REBUILD

With an Edelbrock Performer manifold,
a Demon 850-cfm carb, MSD ignition,
and Hooker headers

RPM TORQUE HP
3,000 525 300
3,100 522 308
3,200 522 318
3,300 521 328
3,400 525 340
3,500 529 352
3,600 533 365
3,700 532 375
3,800 528 382
3,900 522 388
4,000 516 393
4,100 507 396
4,200 500 400
4,300 492 403
4,400 481 403
4,500 471 404
4,600 459 402
4,700 447 400
4,800 433 395
4,900 424 395
5,000 413 393
5,100 404 393
UPGRADED LEVEL 1- Same as the
stock rebuild, but with COMP cam,
rockers, springs, and pushrods

RPM TORQUE HP
3,000 490 280
3,100 490 290
3,200 494 301
3,300 496 312
3,400 507 328
3,500 527 351
3,600 531 364
3,700 536 377
3,800 538 389
3,900 538 400
4,000 536 408
4,100 526 411
4,200 520 416
4,300 513 420
4,400 507 425
4,500 501 429
4,600 494 433
4,700 485 434
4,800 474 433
4,900 465 434
5,000 456 434
5,100 449 436
5,200 442 438
5,300 435 438
5,400 422 434

UPGRADED LEVEL 2- Same as upgraded level 1,
except for the Offenhauser
Tunnel Ram, and dual Holley 750-cfm carbs

RPM TORQUE HP
3,000 512 292
3,100 514 304
3,200 518 316
3,300 520 327
3,400 526 341
3,500 535 356
3,600 538 369
3,700 541 381
3,800 537 389
3,900 531 394
4,000 526 401
4,100 518 404
4,200 510 408
4,300 505 413
4,400 498 418
4,500 493 423
4,600 488 427
4,700 481 430
4,800 473 432
4,900 464 433
5,000 456 436
5,100 455 442
5,200 450 445
5,300 447 452
5,400 440 452

« **Reply #13 on:** September 28, 2010, 11:14:49 PM »

double-d,

I really want you to take this for what is is worth, which may be very little to nothing... $:-\$

Those dyno results if you were to plot them on a curve, cross "too early" to be a real powerhouse in the jet boat application. (look at how early the torque tapers off)....

Automotive thinking will get you into trouble every time.

I have gotten in to too many debates regarding this very subject, so i wont go there...For now.

Your setup is horse power friendly but torque poor. There are a few things that I would look into before going crazy and please do the research before actually changing anything.....

First off, I need some clarification on what you mean by "pulls good vacuum". In what regard? Your vacuum levels with a T/R at speed should be spooky low, like in the -.5" to -1" should be obtainable I would think....If you have a high vacuum number, it would be due to not getting the most out of the T/R or a small carb choice.

Single carb T/R's are notoriously unbalanced, meaning you need to play with rocker arm ratio's and jetting, not to mention spark plug heat ranges and gaps to get them to work right...Not worth the fuss IMHO...
(I know that sounds funny, but I had a 377 SBC that wanted smaller ratio rockers in the corners according to the dyno numbers and pyrometer readings...

I want to say it was a camshaft chosen by Mondello Performance, but know nothing about it other than it sounds like it wants to eat up the universe at idle, extremely lumpy...

Jet pumps require a ridiculous amount of torque to achieve their potential, that being said, the torque requirement does not taper off like that of a car or a prop boat. It gets convoluted as hell the more you dig in to it...

Don't focus on RPM, focus on speed, it is a bigger picture way of looking at it, FWIW, you can sometime reduce RPM, but pick up MPH, take a rebuild from a worn pump as an example....

I am not trying to criticize in any way, just trying to point you in a different direction, jets are a different animal than anything with wheels or props...Many will disagree and "they" are wrong....

GT

« **Reply #14 on:** September 29, 2010, 03:01:58 AM »

Quote from: double-d on September 28, 2010, 10:30:31 PM

yup single carb tunnel ram. I don't know why people frown on 'em, it's pulling good vac, other then they have no bottom end on the street, on a boat that doesn't matter.
offys carb selector says the manifold only needs a 650-700 with single carb, they don't specify displacement though.

I dont care what Offy says about that manifold, they dont work. Pulling good vac doesnt mean squat when the fuel is falling out of suspension before it gets to the corner cylinders. And yea, I had one (with a 750 on it). Changed to a duel 4 top and the motor was wayyy happier, more responsive and even idled better (with 660s on it). Just look at that manifold for a second. Imagine how the a/f mixture has to travel to reach those corner cylinders. Down the carb, then turn 90 deg, travel all the way to the front or back of the plenum, then another 90 deg turn down into a runner. All while trying to not let the fuel drop out of suspension. Meanwhile every time you stab the throttle, the carb basically shoots fuel directly down the center cylinders runners. I bet if you check your plugs closely the center cylinders look more rich, and the corners look more lean.

Another thing to consider about carb sizing and manifolds. Lets say you had a duel plain intake and a 600 carb. When a cylinder tries to draw air it basically sees a small plenum (half the total size because of the divider) and a 300 cfm carb (it can only draw from half of the carb because of the divider).
Same carb but on a single plain intake, now each cylinder can draw from a larger plenum that is fed by the full 600 cfm.
Your tunnel ram has or should have a divider in the plenum (like a duel plain intake), so basically your feeding each cylinder with a huge plenum and a 375 cfm carb. I know, theres an opening under the divider in there, but because of the huge size of that plenum it doesnt do much to help. Thats why that intake needs a big carb. If you dont mind the imbalance between cylinders they will work OK for cruising around, but not for high performance. Thats why they make a duel 4 top for them.

I would bet that motor would run better with a Victor style single plain intake, like GT said his dads friend has. But if you want to stick with a tunnel ram, get the duel 4 top and another 750.

« **Reply #15 on:** September 29, 2010, 06:05:23 AM »

WOW !!! This is like porn to me guys. Keep it up

Mmmmm Olds TR's 6K rpm Oh yeah that's what I'm talking about

« **Reply #16 on:** September 29, 2010, 06:50:13 AM »

Quote from: GlassCutter on September 29, 2010, 06:05:23 AM

WOW !!! This is like porn to me guys. Keep it up

Mmmmm Olds TR's 6K rpm Oh yeah that's what I'm talking about

SERIOUSLY!!! I was thinking the same exact thing. GT and Propless are making me a pitch a tent while learning a shitload in the process. This is awesome. Love this stuff!

« **Reply #17 on:** September 29, 2010, 11:46:12 AM »

I am in a similar situation with my 21' charger. The Panther pump is fresh with a bronze sleeve, blueprinted, and jeto. Just installed a 502ci ford
that is balanced, seriously ported heads, 10/1 compression, a degreed comp cam( 270-280 dur, 538-554 lift ), Edelbrock Performer RPM, roller
rockers, 12 deg initial- 36 total timing, and 750 vac sec Holley. Machinist with dyno estimates 500hp. Engine is very strong and tune is good
but at WOT 60mph at 5000rpm is all it will do. I am thinking I need at least an 850cfm Dp or possibly street avenger carb. Any suggestions.

« **Reply #18 on:** September 29, 2010, 12:32:28 PM »

IMO more rpms are not neccesarily the answer ,Your Olds engine will have a much greater chance at sustaining usefull "life" (despite all the oiling mods one could make) partly because of its inherant design, if it was built to make power to a little under 5k and if made to produce enough "grunt" to swing a big Impeller, AA, to 9.5 (which your Jet bowl can accept) It would have a mad hole shot and should move plenty of water to put you close to your speed goal , Were currently building a BBO for a mid west customer and will post up some pics and info on it later call if we can help Tom

« **Reply #19 on:** September 29, 2010, 01:07:35 PM »

Glass cutter/ Ford lover,

Since you’re enjoying this sooo much, I’m gonna need 4.95 per min, pay pal accepted! Haha need to pay for a dual carb set up!

Gt,

11.5-12 I think is good vac at idle, not sure at wot yet.

I took the choke off the side of the carb a few years back, after some reading last night, i discovered there is a vac circuit there that is now open, I'll plug it with, I don't know what yet, and see if more vac is gained.

If you sbc wanted smaller ratio in the corners, that would equal less air/fuel right?

Sounds like your saying that jet boats need torque at the upper end of the power curve. Since a later-closing intake can enhance top-end torque at the expense of low-end torque has anyone run their cam 4 degrees retarded and had better results?

Right now the plan of attack is to get a vac gauge, that I can read while doing 60+ w/ the 750, then step up to the 850 and check it again.

Propless, I gotta stick with a single carb for now. I’ll check the intake to see if it’s dual plane, but I know Offy made a single plane upper for jet boat use.
I’ll check the plugs and see if the outer cylinders are leaner.

« **Reply #20 on:** September 29, 2010, 02:38:00 PM »

Quote from: double-d on September 29, 2010, 01:07:35 PM

Glass cutter/ Ford lover,

Since you’re enjoying this sooo much, I’m gonna need 4.95 per min, pay pal accepted! Haha need to pay for a dual carb set up!

Gt,

11.5-12 I think is good vac at idle, not sure at wot yet.

I took the choke off the side of the carb a few years back, after some reading last night, i discovered there is a vac circuit there that is now open, I'll plug it with, I don't know what yet, and see if more vac is gained.

If you sbc wanted smaller ratio in the corners, that would equal less air/fuel right?

Sounds like your saying that jet boats need torque at the upper end of the power curve. Since a later-closing intake can enhance top-end torque at the expense of low-end torque has anyone run their cam 4 degrees retarded and had better results?

Right now the plan of attack is to get a vac gauge, that I can read while doing 60+ w/ the 750, then step up to the 850 and check it again.

Propless, I gotta stick with a single carb for now. I’ll check the intake to see if it’s dual plane, but I know Offy made a single plane upper for jet boat use.
I’ll check the plugs and see if the outer cylinders are leaner.

Not to beat a dead horse here, but vacuum numbers at idle mean nothing....

There is a reason if you want it (engine is under a load at all times on a jet and timing at idle will totally change these numbers)...
And there are several reasons for playing with rocker ratio on some engines, there are times when the dynamics of the induction/exhaust systems simply like it, I don't have any information to back it up other than watched it real time on a dyno.

Use a lead pellet to plug the small hole on the side of the carburetor, the vacuum source was there to pull heat riser heat into the choke housing, it really depends on what choke setpu you have/had...A .177 caliber pellet works well.

Retarding the camshaft may make the situation worse. I gotta run right now, but I will be back..

GT

« **Reply #21 on:** September 29, 2010, 06:42:17 PM »

I can turn about 5000 mabey 5500 with an a but im runin a tunel ram and dual 660s and a 540 lift 305 duration cam and c heads with bassets and 10.5 to 1 compression

« **Reply #22 on:** September 29, 2010, 10:33:46 PM »

for the guys with dual carbs, are the mech or vac secondaries?

its a dual plane upper manifold so that sux. Maybe I'll get my precision sawsall out.

Checked the plugs and they all looked pretty close in color but the ones in the back looked more rich. Definitley not what i was expecting according to what was said.

New vac gauge on the way. So when I run this sumbitch, I should be looking for the lowest amount of vacuum when i romp on it from dead stop or cruz on the primarys then floor it? Obviously its not vac at max rpm. Or do both say something about engine performance? I'm diggin into a holley carb book tonite to find out more on manifold vac.

double D
( . ) ( . )

« **Reply #23 on:** September 30, 2010, 12:15:45 AM »

Quote from: double-d on September 29, 2010, 10:33:46 PM

for the guys with dual carbs, are the mech or vac secondaries?

its a dual plane upper manifold so that sux. Maybe I'll get my precision sawsall out.

Checked the plugs and they all looked pretty close in color but the ones in the back looked more rich. Definitley not what i was expecting according to what was said.

New vac gauge on the way. So when I run this sumbitch, I should be looking for the lowest amount of vacuum when i romp on it from dead stop or cruz on the primarys then floor it? Obviously its not vac at max rpm. Or do both say something about engine performance? I'm diggin into a holley carb book tonite to find out more on manifold vac.

double D
( . ) ( . )

quick olds and I both have 660s, there mech 1 to 1 (prim and sec open at the same time, kinda like mini Dominators).

As far as I know Offy never made a top that didnt have the divider, even my duel 4 top has it. I dont think I would cut it out, its already suffering from a lack of velocity in that plenum because its to big. Cutting the divider will make it worse (IMO).

Back corners rich would indicate an overly rich mixture. With the low RPM your turning the mixture is sitting around to long in the plenum (lack of velocity, because its to big), the fuel is heavier so it settles to the lowest point (the back of the plenum). I would leave the mixture alone, its better than running the fronts lean. And thats what will happen if you try to tune for a good mixture on the rear cylinders. If you where running higher RPM (moving more air/fuel through the plenum to increase the velocity) and the mixture was a bit leaner, then you would start to see the lean corner/ rich center issue.

Vacuum at max RPM will tell you if the carb is to small, a carb thats to small for the motor will be a restriction and have a higher than normal vac reading. But thats another area of debate that I'm not going to set foot into. Because the rules seam to change when a tunnel ram is involved.

Think about the fact that quick olds is running 1320 cfm of carb on a tunnel ram and turning around the same RPM as GT mentioned with a Victor manifold and 850 cfm. Tunnel rams are different animals and like lots of cfm (IMO).

I think (IMO) you might get a few RPM gain (not to mention better fuel distribution) by switching to a Victor style manifold or even a good duel plain and the 850. Then work on the pump set up to gain speed. Theres more to gained speed wise with the pump set up than by just adding RPM, and the Olds will be happier. What has been done with the jet (besides the conversion), loader ? droop ? diverter ?

Another thing just to think about, when I first put the single 4 tunnel ram on my old boat it lost 150 RPM compared to the duel plain that was on it (same carb). Once I got the duel 4 top and 660s, then the motor came to life. Thats why I hate those manifolds sooo much.

« **Reply #24 on:** September 30, 2010, 08:43:07 AM »

jetting is 78/84
plug color this week is going to look a bit more rich, it's been 110 outside the last time i ran it, but the rpm has always been the same.

the jet...
stainless A, rex marine performance ramp scoop, 4 degree wedge, and place diveter.
has about fifteen tanks of gas throught it since rebuild.
I'm considering a mini droop.

double-d

Ralph Brunt

double-d

bbfsouthwind

double-d

GT Jets

GT Jets

propless

GT Jets

propless

Sanger Pete

GT Jets

double-d

GT Jets

propless

GlassCutter

FordLover

torquer460

jet boat performance

double-d

GT Jets

quick olds

double-d

propless

double-d