Help..my lab swims faster then my boat

[dog_faces]

:biggrin.: I just bought a 1987 Z29 w/ twin 454mags and alphas. I took her out for a test spin and and only ran about 50mph :bawling: (no gps yet). The motors only have about 150 hours on a stock rebuild and I have 19 pitch props. Does this sound right or do I need some major work?:banghead:

[Cuda]

What rpm?

[dog_faces]

That's the weird part..with the motors trimmed half way up and the hammer down I was only turning 4500 rpm. The next trip out I'm going to take my hand held GPS and try to get a better speed reading.

[joseph m. hahnl]

4500 is weak for a 19"pitch. a 19"pitch is pretty small for twin 454s. what is the peak Rpm range on the sticker?




joe

[Cuda]

I think it should run low to mid 60's with those engines. Donzigo's Z33 run 60, with 330's.

[BigGrizzly]

I bet your trim tabs are draging, the were installed too low. I have seen two 27 Datonas with that problen. The nose is draging. the ride is great but slow and I bet plows right through wakes .

[Garrbo]

did u get that one on ebay? the blu one? anyway it def sounds bad, u should be overspining with small props, u should be on 23-24p about and getting 4800-5200 rpm with stock 330+. my oppinion only:)

[dog_faces]

I thought a 19 pitch prop seemed to small, but I don't really know what size to run. I don't know what the max rpm is on my motors so its hard to judge what prop I should run. I was hoping to run about 70-75 mph with twin 454's but I guess I'm dreaming. The trim tabs seem fine but the boat does ride nose down. Does anyone have any suggestions?

[zimm17]

Get the engines checked out. I wouldn't go to new props until you can find out why you aren't over spinning 19's. Maybe find someone with a prop dyno- that'll let you know if it's the engines or the setup of the boat, like the previously suggested nose down running post.

It could be a million things, but to start I would pull the spark plugs and check them out- make sure they are nice brown color. While the plugs are out do a leak down or at least a compression test on the engines and post your results.

Change out the fuel filters too.

Keep us informed on your progress.

[Donzigo]

If you are thinking speeds in the 70s, yeah, you are dreaming. The history of the first Z-29s and it's lengthening to become the Z-33 will explain it.
(*you might want to throw me a call, I'll explain it)
I am running a pair of Gen 4 -454s, w Bravo Ones, w 23 in Mirage props. The original Z-33 with that configuration was designed to go 60MPH and that is exactly, (by GPS), what my boat does, at WFO of 4400/4500 RPMs. My guess is that you package should be in the 55/60 range. (see earlier*). IMHO, the 19 pitch is too small. Your engine should be at 4400/5000 RPMs. You might want to run with the trim tabs up or nearly so. The boat is very heavy and once on plane, should need little or no trim.

You have a seaworthy, classic design, which will give you many years of reliable boating; and, if I may say so, still has lots of eye-appeal. Name other boats designs, of similar age & footage, that can boast that...........very few. But, a speed-demon, she is not. I took the speedometer off my boat and replaced it with a much more useful instrument.........an engine synchronizer. Every new guest always used to ask me about speed, and they would read out the numbers, and tell me that their freind's boat goes a bazillion miles an hour faster than mine, blah, blah, blah. I got so tired of listening to that BS. Now, without a speedometer, I say: "Speed?.........well, how fast do you think it will go?" They reply: "Well, my freind has one just like this that goes 89.9 miles per hour". I say: "Imagine that, this one does an even 90.0 MPH"...........Shuts them up every time, then we go have fun!

Richard Aaron
727-867-7020

[BigGrizzly]

Even thoe the tabs don't look like they are draging the fact that the bow is draging is a dead givaway. My Criterion did it and M son's 22ZX did. If they don't pull up 10 degreese from the plaining they are wet. I think 7o-> is a drean with stock motors. The engines should top out around 4800 RPMs. It should pull a 23 inch prop with 1:50 lower unit.

[gpapich]

I have an X-18 which normally runs 60.1 mph per GPS SBC w/ TRS-280 and a RH 21 cleaver.

As part of the purchase inspection, I had a dealer look at it. The "technician" (I use that term loosely) ended up swapping #4 and #6 ignition wires at the plugs after doing a compression check. When I first dropped the boat in, it started roughly and loped like it had a hot cam. I figured it had as the seller was a amateur racecar driver and had swapped cam, intake, and ignition.

It definitely seemed down on power as the best I could get was 45mph initially, even trimmed and aired out. I didn't know any better but I finally decided to trace the wires and found the mistake. I immediately got 60mph out of it. Big smiles ensued...