lets build a tunnel rammed jet boat engine

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.

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.

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..

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?

This page on jet boat stuff is pretty handy.

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

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

got the tunnel ram yesterday, looks good.
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

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

Vern

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..
found a 1407 edelbrock also for $200 that looks clean, waiting till I get further along into this to buy carby's I think

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..

IMO I'd ditch the Eddys and pickup a pair of HP holleys

When I heard used "looks good" and Edelbrock 750 in the same post I thought the same thing. ^^^^^^^^^^^^

i typically use holleys but that's $1500 plus additional fuel lines and linkage, eddys are simple and I have had good luck with them on other builds. mechanical secondaries would be nice tho.. it was $150 more or $1750 more...

Not if you go used on the Holleys. List #6109 are inline 750 double pumps with square bowls I believe. Not saying you will find used ones as cheap as the Eddy's but they are out there.

http://www.ebay.com/itm/Holley-4-Barrel-Carburetor-Carb-6109-750-CFM-Double-Pumper-4150-Tunnel-Ram-2x4-/181694788613?hash=item2a4dda7405&vxp=mtr I bet he would take a lot less, then all you have to do is find it's brother.

I would put quick fuel aluminum carbs on it, but, it might be silly to swap them out for a maybe 20 hp bump at best, when I am running logs..

Try the Eddys, I hope you get some good ones.