Zeppelin654
Member
- Joined
- Sep 26, 2019
- Messages
- 7
- Reaction score
- 4
I have a 1975 hallett bubbledeck full stringer jet boat. I bought the boat last year and realized the engine was smoked. I decided to rebuild the engine myself. It is a blown bbc full solid roller deal on gasoline. 8:1 CR, 31 degrees timing, 93 octane, 8 lb boost, NO intercooler, Iron heads, 2 1/4" headers.
Previously it had 1:1 pulleys (41 tooth top and bottom) with a mild (about .550 lift) hydraulic flat tappet cam. Made 6 psi. Maybe 600 or so hp.
The new build specs are:
Machine work done by Andy Jensen at Jensen's Engine Tech
Cast case non stripped rotor 6-71 blower
SRP pistons (calculated 8:1 compression now)
Total Seal file fit rings (gapless 2nd ring) .033-.034 ring gap
Forged shotpeened rods
Scat forged balanced crank
Clevite bearings
Melling m77 oil pump
10 Qt dooley oil pan
Gen IV bbc block (now 472 cubic inch)
World Products Bill Jenkins 1-043C 119cc iron heads
Cometic Stainless MLS 5 layer .070 headgaskets
dual valve springs with dampers
Comp 1.7 ratio roller rockers
Comp .135 wall 3/8 pushrods
Crower solid roller lifters
Comp 11-771-8 solid roller cam (242, 248 .646, .653 110 lsa)
Blp 3 piece timing cover
Rollmaster torrington timing set
ARP EVERYTHING
MSD 6M-2L, MSD hvc 2 coil, and pro billet hei distributor (locked out, 31 degrees BTDC advanced timing)
Moroso Ultra 40 8.65 wires
NGK heat range 8 plugs
2.5% over pulleys (40 tooth 1/2 pitch upper and 41 tooth under)
Jomar Professional stud girdles
Basset 2 1/4" coated headers
Dooley air scoop
Two side mounted Holley 850 four barrel carbs with 78 jets (square)
Weiand carb adapter and intake manifold with burst panel
Holley 190 GPH billet mechanical fuel pump (7 psi) 1/2" lines
Main bearing clearance is .033
Rod bearing clearance is .028
crank endplay is .0045
cam endplay is .004
Ring end gap is .033-.034
472 cu. in.
7.97:1 comp ratio
VE: 74.4%
I had it dyno'd and it made:
741 hp and 693 torque at 31 degrees timing on 93 octane
727 hp and 682 torque at 28 degrees timing on 93 octane
^ both peaks were right at 5900 (hp) and 5300 (tq) and 8 LBS BOOST
It had a berk jc pump with bronze A impeller and diverter. Loader hung 3/8" below keel. On the water it ran a best of 79 gps mph with just me in it. Of course, I can't leaver anything alone. I had the pump rebuilt and added a split bowl, mini droop, inducer, stuffer, the works. Trimmed the loader to right around 1/16" below keel. Sorry for the long intro, but my MAIN QUESTION is related to the engine.
I want to increase boost and make more power I can. This is a lake boat ripper if you will. Not a drag boat, but I run it really hard all the time. I probably run it 20-40 minutes at a clip. All between 4000-6000 rpm. Never goes below 60 psi oil pressure with 20w-50 gp-1 synthetic blend driven racing oil. I DO NOT run it on 93 octane. I ran it all last summer and for the future on 100LL AV Gas (no mixing) Factoring in a compression ratio or 8:1, IRON heads, NO intercooler, and Av gas, how aggressive would you guys think I could go? ( am not going to intercool or switch to aluminum heads or go to a larger slower spinning blower anytime soon because I already blew a bunch of money on the build last year, the pump build this year and the new exhaust. Maybe later but definitely not now)
I made 8 psi with the 2.5% overdriven setup which put my effective compression ratio at 12.4 (the altitude I run the boat at is usually around 1100 above sea level which should take .15 off the final compression ratio which is nothing, but I wanted to mention it)
If I overdrive the blower 5%, I should see about 8.6 psi putting me at 12.7 effective CR
If I overdrive the blower 8%, I should see about 9.2 psi putting me at 13.0 effective CR
If I overdrive the blower 10%, I should see about 9.8 psi putting me at 13.4 effective CR
The new exhaust I had custom made, is a set of swept back shorty 2.5" primaries w/ super short collectors (I know those are probably too big, but I just did it thinking I can always use them later if I go bigger at some point). I figure these will lower the boost number a bit.
To finalize my question:
It ran on the dyno on 93 octane, 8 psi, 31 degrees timing. no detonation, no issues.
I put 20 hard hours on it over last summer running 100% Av Gas, 8 psi, 31 degrees timing. no detonation. no issues.
I already changed the jets to 81's (from 78's), and put the 10% pulley on the blower. This is 9.8 psi (maybe lower b/c of the bigger exhaust), 13.4 CR. Do you guys think Im playing with fire based on my 100 octane av gas and 28-30 degrees timing?? I was under the impression that if you increase one pound of boost, you need two more octane points. If it ran great on 93 pump gas at 8 lbs, I should need at most; 4 more octane points (97 octane). Right??? or am I crazy??? Do I need more jetting to pull that off?? lower than 30 degrees timing?? I appreciate all advice, information, real world results, opinions. Obviously you can't just say "oh yea, it'll be perfectly fine!" or "It will blow up with the first turn of the key!" but I cannot make up my mind. Thanks a lot fellas!!!
Previously it had 1:1 pulleys (41 tooth top and bottom) with a mild (about .550 lift) hydraulic flat tappet cam. Made 6 psi. Maybe 600 or so hp.
The new build specs are:
Machine work done by Andy Jensen at Jensen's Engine Tech
Cast case non stripped rotor 6-71 blower
SRP pistons (calculated 8:1 compression now)
Total Seal file fit rings (gapless 2nd ring) .033-.034 ring gap
Forged shotpeened rods
Scat forged balanced crank
Clevite bearings
Melling m77 oil pump
10 Qt dooley oil pan
Gen IV bbc block (now 472 cubic inch)
World Products Bill Jenkins 1-043C 119cc iron heads
Cometic Stainless MLS 5 layer .070 headgaskets
dual valve springs with dampers
Comp 1.7 ratio roller rockers
Comp .135 wall 3/8 pushrods
Crower solid roller lifters
Comp 11-771-8 solid roller cam (242, 248 .646, .653 110 lsa)
Blp 3 piece timing cover
Rollmaster torrington timing set
ARP EVERYTHING
MSD 6M-2L, MSD hvc 2 coil, and pro billet hei distributor (locked out, 31 degrees BTDC advanced timing)
Moroso Ultra 40 8.65 wires
NGK heat range 8 plugs
2.5% over pulleys (40 tooth 1/2 pitch upper and 41 tooth under)
Jomar Professional stud girdles
Basset 2 1/4" coated headers
Dooley air scoop
Two side mounted Holley 850 four barrel carbs with 78 jets (square)
Weiand carb adapter and intake manifold with burst panel
Holley 190 GPH billet mechanical fuel pump (7 psi) 1/2" lines
Main bearing clearance is .033
Rod bearing clearance is .028
crank endplay is .0045
cam endplay is .004
Ring end gap is .033-.034
472 cu. in.
7.97:1 comp ratio
VE: 74.4%
I had it dyno'd and it made:
741 hp and 693 torque at 31 degrees timing on 93 octane
727 hp and 682 torque at 28 degrees timing on 93 octane
^ both peaks were right at 5900 (hp) and 5300 (tq) and 8 LBS BOOST
It had a berk jc pump with bronze A impeller and diverter. Loader hung 3/8" below keel. On the water it ran a best of 79 gps mph with just me in it. Of course, I can't leaver anything alone. I had the pump rebuilt and added a split bowl, mini droop, inducer, stuffer, the works. Trimmed the loader to right around 1/16" below keel. Sorry for the long intro, but my MAIN QUESTION is related to the engine.
I want to increase boost and make more power I can. This is a lake boat ripper if you will. Not a drag boat, but I run it really hard all the time. I probably run it 20-40 minutes at a clip. All between 4000-6000 rpm. Never goes below 60 psi oil pressure with 20w-50 gp-1 synthetic blend driven racing oil. I DO NOT run it on 93 octane. I ran it all last summer and for the future on 100LL AV Gas (no mixing) Factoring in a compression ratio or 8:1, IRON heads, NO intercooler, and Av gas, how aggressive would you guys think I could go? ( am not going to intercool or switch to aluminum heads or go to a larger slower spinning blower anytime soon because I already blew a bunch of money on the build last year, the pump build this year and the new exhaust. Maybe later but definitely not now)
I made 8 psi with the 2.5% overdriven setup which put my effective compression ratio at 12.4 (the altitude I run the boat at is usually around 1100 above sea level which should take .15 off the final compression ratio which is nothing, but I wanted to mention it)
If I overdrive the blower 5%, I should see about 8.6 psi putting me at 12.7 effective CR
If I overdrive the blower 8%, I should see about 9.2 psi putting me at 13.0 effective CR
If I overdrive the blower 10%, I should see about 9.8 psi putting me at 13.4 effective CR
The new exhaust I had custom made, is a set of swept back shorty 2.5" primaries w/ super short collectors (I know those are probably too big, but I just did it thinking I can always use them later if I go bigger at some point). I figure these will lower the boost number a bit.
To finalize my question:
It ran on the dyno on 93 octane, 8 psi, 31 degrees timing. no detonation, no issues.
I put 20 hard hours on it over last summer running 100% Av Gas, 8 psi, 31 degrees timing. no detonation. no issues.
I already changed the jets to 81's (from 78's), and put the 10% pulley on the blower. This is 9.8 psi (maybe lower b/c of the bigger exhaust), 13.4 CR. Do you guys think Im playing with fire based on my 100 octane av gas and 28-30 degrees timing?? I was under the impression that if you increase one pound of boost, you need two more octane points. If it ran great on 93 pump gas at 8 lbs, I should need at most; 4 more octane points (97 octane). Right??? or am I crazy??? Do I need more jetting to pull that off?? lower than 30 degrees timing?? I appreciate all advice, information, real world results, opinions. Obviously you can't just say "oh yea, it'll be perfectly fine!" or "It will blow up with the first turn of the key!" but I cannot make up my mind. Thanks a lot fellas!!!
