I got a question about RPM and speed

[todd magerus]

I got a 1979 20" sea ray with 350 with a 260 outdrive I had tiwn turbos on it and one went out so I had to take them off so now it's back to stock. It ran about 40 to 45mph at 4200 rpm with the turbos. now with them off it runs about 35mph at 3500rpm I got a 19 pitch prop. the motor should run 4200 to 4600 rpm do you guys thing I need to change the prop out or is it something else. how fast should the boat go?

Thanks

 

[180shabah]

Re: I got a question about RPM and speed

boat that size should run 40-45 WITHOUT the turbos. Was this engine built for forced induction (low compression) and now doesn't have the umph needed to push a boat?

 

[todd magerus]

Re: I got a question about RPM and speed

I have a iron head 377 small block, with 9.5 to 1 flat top pistons, that's about all I know about the motor

 

[180shabah]

Re: I got a question about RPM and speed

I'd say a compression test is in order...

Did you turbo it or buy it that way? Is it a uscg complient install?

 

[todd magerus]

Re: I got a question about RPM and speed

The motor was rebuilt 2009 and the turbos was on it when I got it. the boat runs great just wont get to the RPM's or to the speed it should be at.

 

[180shabah]

Re: I got a question about RPM and speed

...the boat runs great just wont get to the RPM's or to the speed it should be at.

That is why it needs to be compression tested...
What does it have in it for a cam?

 

[todd magerus]

Re: I got a question about RPM and speed

I don't know what cam is in it. I will do a compression test. If I run the boat with the trim all the way in at WOT will that make it do that? I never use the tilt and trim.

 

[todd magerus]

Re: I got a question about RPM and speed

If I don't trim out will that keep the boat from hitting the rpm that I need to?

 

[HT32BSX115]

Re: I got a question about RPM and speed

I never use the tilt and trim.

You really need to adjust the trim when you're running on a plane to get it to run the most efficiently.

It'll be obvious when you find the "sweet spot".


You got any pictures of the "before and after" with the turbos?

 

[todd magerus]

Re: I got a question about RPM and speed

I don't have after.

 

[HT32BSX115]

Re: I got a question about RPM and speed

VERY COOL


Since those are not jacketed hot-sections on the turbos, THey must have gotten VERY HOT under load.....

With 9.5:1 comp ratio there couldn't have been much boost before it started to detonate.......

 

[JustJason]

Re: I got a question about RPM and speed

Well that's different, have to admit i've never seen that before. Any more pictures of the "before" or any info on the manufactorer of the turbo setup.

with 9.5 to 1 flat top pistons

That would be way to high in a forced induction motor. It's should be more like 6 or 7 to 1. With a static compression reading of 60-70 pounds ish.
9.5 to 1 would give you a compression reading, static, of way over 150, much to high to already to stick a blower on to. You need to start as shabah say, with a comression test. My guess is all 8 cylinders are probably around 60-70 psi.

How's the idle... will it hold at 6-700 rpms or did you have to turn it up to keep it idleing?

 

[todd magerus]

Re: I got a question about RPM and speed

No they didn't get to hot and no detonate only about 6 to 8 of boost

 

[todd magerus]

Re: I got a question about RPM and speed

How's the idle... will it hold at 6-700 rpms or did you have to turn it up to keep it idleing?[/QUOTE]

The idle is fine it will hold that

 

[todd magerus]

Re: I got a question about RPM and speed

Rayjay turbos