lets build a tunnel rammed jet boat engine

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lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 3rd 2014, 3:08 pm

hey guys, building a new engine for my jet boat this winter and would like some opinions or experience from the crew here, I am new to boats. just bought a 1977 spectra 19 with a 460. currently has a Berkley jc pump with an "a" impeller. so, wanting to build a 600 hp deal that is done by 6500 rpm. I have to go through the jet this winter anyhow so changing the impeller is cool.
I have plenty of blocks and a couple sets of d3 heads and I think a set of dove-c's somewhere.
needs to run on 91 swill, been playing with a couple ideas:
4.390 x 3.85 -11:1 comp
ported dove-c's
weiand tunnel,  750 eddy's
solid flat 290/298 257/265 .650" on a 110 in at 106
1.5x 1.5 x3mm rings
normal prep, roller rockers with girdle, big pushrods, edm lifters, etc..

same deal but 4.440 x 3.85
or tfs 290's or scj-a's

my sim program seems to think it will be 600-620 @ 6000 rpm with the 4.390 package and ported dove-c's but my experience thinks it may be 550 ish.. trying to keep it budget friendly  Laughing
build to start in a couple months, getting parts gathered up now. what do you guys think?
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Re: lets build a tunnel rammed jet boat engine

Post  gt350hr on December 3rd 2014, 7:43 pm

Go to 106*lsa on the cam and run it straight up. More torque is what you want. The jet is the same as the water brake on a dyno . About 6,500 regardless of the power the engine makes beyond that or RPM it "can" achieve.

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Re: lets build a tunnel rammed jet boat engine

Post  Lem Evans on December 3rd 2014, 8:14 pm

A narrower lsa for sure...110* is too wide i.m.o.....per the application. 108* damn sure will work. If you have wet exh. system...it will have to be considered.

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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 3rd 2014, 8:42 pm

I looked at some grinds on a 108, basically the same but 108 sep. for whatever reason the sim thinks it will lose power. I played with icl to see what changes it made but they were all worse. it seems to think a an ivc of 71/72 is best I guess. intuitively I like narrower l/s to come on earlier and fill the mid range and since it is head limited the 108 should be better.. not sure why it kills it on the sim?
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 3rd 2014, 8:49 pm

well, if I put it on a 108 with a 102 icl it is splitting hairs with the 110 cl on a 106 icl, that means it is sensitive to the evo I guess of 83
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Re: lets build a tunnel rammed jet boat engine

Post  Lem Evans on December 3rd 2014, 9:00 pm

6t6mustang wrote:I looked at some grinds on a 108, basically the same but 108 sep. for whatever reason the sim thinks it will lose power. I played with icl to see what changes it made but they were all worse. it seems to think a an ivc of 71/72 is best I guess. intuitively I like narrower l/s to come on earlier and fill the mid range and since it is head limited the 108 should be better.. not sure why it kills it on the sim?


I have a poor opinion of sims......per the application 108* lsa will have more perfomance in the jetboat than the the 110* deal....the 106* thing may be better yet....I have not been there yet.

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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 3rd 2014, 9:05 pm

yeh, I don't solely rely on it but it is helpful, I have always been within 5% from sim to dyno numbers so I know it isn't a total waste, however, experience is king! I appreciate your words of wisdom lem..
the only compromise I have is logs, wifey don't want headers around the kiddos so.... Rolling Eyes
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 3rd 2014, 9:30 pm

ok, lets hear some cam reccomendations , I found a 108 ls from howards it like with more lift and a fast lobe, it is only 28 degrees from advertised to .050", real fast ramp makes power but concerned about getting it to live..
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Re: lets build a tunnel rammed jet boat engine

Post  IDT-572 on December 4th 2014, 12:07 am

Lem Evans has been grinding custom Jet boat cam since Moby Dick was a Minner !!!!!!!!!!! If you want it to run give him a call, you wont be disappointed Wink
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Re: lets build a tunnel rammed jet boat engine

Post  the Coug on December 4th 2014, 6:59 am

Guy if you trust that Sim so much go for it then when it doesn't work right, then call Lem. No use in doing it right the first time when you can do it twice....
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Re: lets build a tunnel rammed jet boat engine

Post  DaveMcLain on December 4th 2014, 8:59 am

I think that 6500rpm is quite unrealistic in a jet boat and 5500 is a better target rpm. I have a 454 small block Chevy engine that I built with jet boat in mind and it makes 630 horsepower at 5700 and 600 at about 5000rpm. Torque is 632 at 4700rpm. The cam is 250 at .050 ground on a 108 sep in on 108. One of the tests I did on the dyno was to run the engine using water cooled boat exaust manifolds just to see what that did to the power. It took away about 50 horsepower and a similar amount of torque which I didn't think was really horrible but it's something to keep in mind.


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Re: lets build a tunnel rammed jet boat engine

Post  rmcomprandy on December 4th 2014, 12:07 pm

I don't know a whole lot about JET boats other than the few Jet Drad Boats I build engines for.

To me, the JET acts just like a torque converter and has a stall speed so, making it work well below that point is almost useless in a wide opem throttle situation.
The lowest RPM level any of my customer's boats ever see at wide open throttle is 5,800 RPM and it just climbs from there but, they are high horsepower engines so, finding the lowest speed the engine in question will operate at wide open throttle is paramount.

I will say that one, a 12-71 supercharged application, has a 116 degree separation and it certainly ran better than the 111 camshaft previously in it when it had a tunnel ram.   JUST because it is a JET doesn't mean there is simply one type camshaft which will be right.

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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 4th 2014, 12:52 pm

that has been my experience with jets, basically a loose convertor. my boat currently flashes to 3k with the flick of the throttle and loads the engine from there up, with a rock stock 460 it spins 5k rpm.. the 557 I did for a buddies boat liked to spin 6400 with a b impeller a was looser yet. so a 3500- to 6500 power band with good torque is what I am after.
not sure why some hate sim programs, i would guess that it belongs to those who have not used a good one or just decide to let someone else make the call on part choice for them..It seems odd to me to think about an engine builder who doesn't have a need to further his knowledge of their passion? it shows trends and honestly poses a lot of questions about valve events mostly to me.
hey, I fully know lem, Charlie and Oakley are bbf ford masters and don't benefit from sharing knowledge they have earned unless they are supported by us. but, I have been doing this for 30+ years and still don't feel I have the knowledge I would like to have.. every engine likes something a tad different..
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 4th 2014, 12:57 pm

DaveMcLain wrote:I think that 6500rpm is quite unrealistic in a jet boat and 5500 is a better target rpm.  I have a 454 small block Chevy engine that I built with jet boat in mind and it makes 630 horsepower at 5700 and 600 at about 5000rpm.  Torque is 632 at 4700rpm.  The cam is 250 at .050 ground on a 108 sep in on 108.   One of the tests I did on the dyno was to run the engine using water cooled boat exaust manifolds just to see what that did to the power.  It took away about 50 horsepower and a similar amount of torque which I didn't think was really horrible but it's something to keep in mind.

good info dave, thanks
not sure why you think 6500 is unrealistic? the impeller will dictate where it loads the engine as far as power band.
yeh, I would love some over transom headers but you gotta make compromises for the family ya know, I was thinking it might kill it about 50 or so..
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 4th 2014, 1:06 pm

the Coug wrote:Guy if you trust that Sim so much go for it then when it doesn't work right, then call Lem. No use in doing it right the first time when you can do it twice....
thanks for the sales pitc.... er, tech?..
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Re: lets build a tunnel rammed jet boat engine

Post  rmcomprandy on December 4th 2014, 1:41 pm

6t6mustang wrote:that has been my experience with jets, basically a loose convertor. my boat currently flashes to 3k with the flick of the throttle and loads the engine from there up, with a rock stock 460 it spins 5k rpm.. the 557 I did for a buddies boat liked to spin 6400 with a b impeller a was looser yet. so a 3500- to 6500 power band with good torque is what I am after.
not sure why some hate sim programs. .

I have 3 engine power simulation programs and I use them once in a while ONLY for something "ballpark" simply because given the same valve event inputs, all 3 generally disagree with each other when getting specific.

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Re: lets build a tunnel rammed jet boat engine

Post  DaveMcLain on December 4th 2014, 2:23 pm

6t6mustang wrote:
DaveMcLain wrote:I think that 6500rpm is quite unrealistic in a jet boat and 5500 is a better target rpm.  I have a 454 small block Chevy engine that I built with jet boat in mind and it makes 630 horsepower at 5700 and 600 at about 5000rpm.  Torque is 632 at 4700rpm.  The cam is 250 at .050 ground on a 108 sep in on 108.   One of the tests I did on the dyno was to run the engine using water cooled boat exaust manifolds just to see what that did to the power.  It took away about 50 horsepower and a similar amount of torque which I didn't think was really horrible but it's something to keep in mind.

good info dave, thanks
not sure why you think 6500 is unrealistic? the impeller will dictate where it loads the engine as far as power band.
yeh, I would love some over transom headers but you gotta make compromises for the family ya know, I was thinking it might kill it about 50 or so..

I guess it just depends on how you're going to use the boat but from what I've seen an impeller that allows the engine to turn about 5500rpm is a good compromise to allow the boat to be reasonably efficent when cruising at 3000rpm or so. If you're not going to do any moderate speed river running or cruising then I guess you could certainly go for more RPM from the engine.

From what I've seen anytime you water cool the exhaust power takes a pretty big hit but it's a necessary evil in a boat application.

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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 4th 2014, 2:31 pm

rmcomprandy wrote:
6t6mustang wrote:that has been my experience with jets, basically a loose convertor. my boat currently flashes to 3k with the flick of the throttle and loads the engine from there up, with a rock stock 460 it spins 5k rpm.. the 557 I did for a buddies boat liked to spin 6400 with a b impeller a was looser yet. so a 3500- to 6500 power band with good torque is what I am after.
not sure why some hate sim programs. .

I have 3 engine power simulation programs and I use them once in a while ONLY for something "ballpark" simply because given the same valve event inputs, all 3 generally disagree with each other when getting specific.
I guess that is how I use mine also, for trends or looking to see what a combo should make in theory. but it has been damn close, a lot..
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 4th 2014, 2:38 pm



I guess it just depends on how you're going to use the boat but from what I've seen an impeller that allows the engine to turn about 5500rpm is a good compromise to allow the boat to be reasonably efficent when cruising at 3000rpm or so.  If you're not going to do any moderate speed river running or cruising then I guess you could certainly go for more RPM from the engine.

From what I've seen anytime you water cool the exhaust power takes a pretty big hit but it's a necessary evil in a boat application.
well, It has an "a" in it now which should allow around 5500 rpm depending on power input. I'm not racing it really, fun lake boat, it cruises about 3500 now. I would think I would want it to peak past where the impeller would try to hit the wall slightly instead of before?
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Re: lets build a tunnel rammed jet boat engine

Post  DaveMcLain on December 5th 2014, 11:31 am

This page on jet boat stuff is pretty handy.

http://www.jetboatperformance.biz/pages/calculator.html


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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 5th 2014, 12:22 pm

nice, thanks for that dave..
so getting back to the combo, do my goals sound reasonable with ported iron stuff and a "good solid lifter flat cam?"
it would seem 1.3 hp/cid should be easy enough, I will rescind asking for cam events since "the coug" thinks I am freeloading the site without contributing, lol Rolling Eyes
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 9th 2014, 1:33 pm

got the tunnel ram yesterday, looks good. Very Happy
need list if anyone has some used stuff:
another 750 eddy
jet boat pan and p/u
roller rockers
small diameter distributor, mag p/u prefer
msd 6 box

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Re: lets build a tunnel rammed jet boat engine

Post  CP598 on December 15th 2014, 12:18 am

Pretty sure I still have a set of aluminum roller rockers, 1.73 I will double check and let you know.

Vern
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on December 15th 2014, 12:31 am

thanks cp 598, hopefully 7/16" stud versions..

got a 6al box off craigslist coming
thinking I will make an aluminum pan myself.. can't seem to find a used one and for $400 with p/u I might as well just fab one and get a kickout and baffling etc.. pirat
found a 1407 edelbrock also for $200 that looks clean, waiting till I get further along into this to buy carby's I think
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Re: lets build a tunnel rammed jet boat engine

Post  6t6mustang on August 4th 2015, 11:03 pm

bringing this back up with an update, almost back together, ended up picking up a set of dooe-r heads milled to 65 cc's, ported with stainless valves for a good deal, so the combo will be:
466" dish piston stock type rebuild, balanced
10.1:1
dooe-r heads (365 cfm)
lunati solid cam 257/265 .650" 110/106
howards solid edm lifters
scorpion rockers
3/8"x.080" pushrods 8.750"
weiand tunnel ram, ported and plenum work
two eddy 750's
msd 6al and dizzy
scored a 10 quart milodon pan, notched it for the jet and moved the oil pickup
melling police car pump and arp shaft
waiting on the intake to get a trim and then it is lake time..


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