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View Full Version : New set up, Tunnel jet.



DEL51
06-13-2002, 04:38 PM
I have a tunnel hull,19ft Centurion,with an A/B cut impeller, performance intake grate,and ride plate.This boat had a tunnel rammed 477 chev that ran 6500 rpm. I am new to tunnels and am curious if this seems high.I intend to run a mild blower motor this summer and want to keep the rpms under 6400.Do tunnels load the pump as well as v- type hulls? After I install the new engine, if the rpm is high, should I try to adjust the shoe depth to alter my rpm or change to an A cut impeller.I am detuning the motor until I am satisfied with my tunnel skills. Thanks for your input,DEL51

comin' unscrewed
06-13-2002, 04:45 PM
Sounds high to me. My 77 Southwind tunnel with a fairly stout 468 inch Chevy and an A/B (Berkley JG) turned 5800. When I went to a B cut and a bigger cam (roller) and it turned 6150.

DEL51
06-13-2002, 08:37 PM
Thats what I thought, i may have to check out the tach.I guess this is where I will start once I get the engine in.

wsm9808
06-13-2002, 09:47 PM
del, did you ever check out that red and white 21ft Liberater at Fox marine that I emailed you the pics of last fall? It is still for sale and I was wondering if anyone had seen it and knew first hand how it looks. It is too far from me to go look at and find out it is a piece of crap when I get there.
Sounds like you finally found a hull for your motor.

DEL51
06-13-2002, 10:11 PM
I e-mailed him and he sent a picture.It was located in ohio. I was patient and found a nice boat for 1500 less.Although its not a 21, i am very happy with the condition of boat and trailer.The hull is all white, I have a clean slate to add some type of graphic design.I am thinking of vinyl graphics and if I want to change the look,just peel em off.I purchased the boat from a guy in N.E.Texas.I saw the add on dragboats.com. It came with the engine mounts,msd ignition,gauges,and a nice pump.I need to get a cover made. I will do some mods in the future, it doesn't have a place diverter.I am going to just run it, as is, this summer to get a baseline and learn how to drive a tunnel.How is you setup doing? I thought I read that you were upgrading the power. I don't know if that liberator is still for sale but I did keep the e-mail he sent. Are you looking for something bigger? Let me know if you need the address,I think I still have it.
[This message has been edited by DEL51 (edited June 13, 2002).]

Blown509Liberator
06-14-2002, 07:24 AM
I have a tunnel hull that turns a well prepped SS Legend A cut impeller at 6000 r's with 842 hp. The keywords is "well prepped".
As for your question of "Do tunnel hull load the pump well?" Yes if the center sponson is set for a pump. There are a few tunnel that are not good pump boats. The center sponson needs that rounded keel with that bump in front of the pump to help load it. Once you get near century mark you will see how critical underwater hardware set is, That is where shoe depth and nozzle and ride plate angle will come into play. Good luck with it and be safe...

wsm9808
06-14-2002, 05:11 PM
Mine has been flawless since I went through the engine and pump last fall, and I was going the put a new blown engine in right after memorial weekend, but there was some problems getting lifters and I didnt have all my parts for the new motor untill yesterday. So now I'll wait till after 4th of July weekend before I swap them out.
That Liberator is back on boattrader, but I think it is priced way too high for a project boat.
Sounds like you have a good plan for your new boat. As far as learning the way a tunnel handles... be carfull on the turns. I was used to spinning around in an old shallow V hull and bought a 19 Liberator tunnel in 1987, I tried to cut it into a turn like in the V and it took a bite and tossed me right out of the boat, but they ride so good compaired to a sallow V it is hard to want anything else once youve owned one.

MikeF
06-15-2002, 02:37 PM
Originally posted by comin' unscrewed:
Sounds high to me. My 77 Southwind tunnel with a fairly stout 468 inch Chevy and an A/B (Berkley JG) turned 5800. When I went to a B cut and a bigger cam (roller) and it turned 6150.
Hey CU, I gotta know what "cam" turned your B impeller @ 5800! I have a similar setup to your's, and am looking for the correct cam for mine. Please email me with the info. Mike

comin' unscrewed
06-15-2002, 03:33 PM
Originally posted by MikeF:
Hey CU, I gotta know what "cam" turned your B impeller @ 5800! I have a similar setup to your's, and am looking for the correct cam for mine. Please email me with the info. Mike
Mike,
I was turning an A/B impeller 5800. The cam at that time was a Sig Erson PN 125021. Solid lifter flat tappet .610/.625 lift, 308/314 adv duration, 268/274 @ .050, 108 LC. It can still be had here:
http://www.herbertperformance.com/Catalog/Camshafts_and_kits/Erson_Cams/erson_cams.html
Then in 1993 I had GS marine rebuild the jet and cut the impeller to a "B". I also went to a solid roller cam from Chet Herbert. Part# CB6H. .670/.690, 300/310 adv, 255/265 @ .050, and I don't remember the lobe centers or seperation. Herbert (Doug) still sells a part# CB6H but it's got different specs.
How similar is your set up? Same hull? LMK.
Take care,
Steve

MikeF
06-15-2002, 05:42 PM
Originally posted by comin' unscrewed:
Mike,
I was turning an A/B impeller 5800. The cam at that time was a Sig Erson PN 125021. Solid lifter flat tappet .610/.625 lift, 308/314 adv duration, 268/274 @ .050, 108 LC. It can still be had here:
http://www.herbertperformance.com/Catalog/Camshafts_and_kits/Erson_Cams/erson_cams.html (http://www.herbertperformance.com/Catalog/Camshafts_and_kits/Erson_Cams/erson_cams.html)
Then in 1993 I had GS marine rebuild the jet and cut the impeller to a "B". I also went to a solid roller cam from Chet Herbert. Part# CB6H. .670/.690, 300/310 adv, 255/265 @ .050, and I don't remember the lobe centers or seperation. Herbert (Doug) still sells a part# CB6H but it's got different specs.
How similar is your set up? Same hull? LMK.
Take care,
Steve
Thanx a bunch! I have a Liberty shallow V that was a record holder for many years (prior to me owning the boat). A Southwind tunnel took the record away about 5+ years ago (darn!...it did hold the kilo record for about 20+ years though). I'm getting ready to put .010 over (.070 total) 9.5/1 +/- pistons in to run on pump gas.
Will that cam work with that low a compression ratio?
Oh yea....They are square port heads too.
Thanx again for the help!, Mike
[This message has been edited by MikeF (edited June 15, 2002).]

bp
06-16-2002, 06:22 AM
mikew, i don't have a bump in front of my intake, and i don't have any problems with pump loading, at least at 103. maybe if i were going faster, i'd need to alter the area in front of the suction piece; don't know.
the centurion tunnels were really nice boats. they were early air entrapment tunnels and can be setup to go really fast. a buddy of mine bought one new in '79, and besides being fast, it was impressive how smooth the ride was. i do think you need a new tach though.