Opie, looks like it didn't make quite as much difference in speed for you as it did for me however still glad to see it gave some improvement.

By the way which ignition do you have? If it's the Thunderbolt V you may be getting into the rev limiter (I encountered this problem). I assume you have tweaked you timing for max performance already but if you haven't you might want to.

Another thing that you might want to check is airflow in the engine compartment, there is a very interesting thread on this in the tech section.

BTW I rarely ever use my tabs to get on plane even with the IMCO 2" shorter lowers.

Regards,

Ian T.

That's fantastic news :cool: . But it looks like I'll be stuck till spring:(. Did take the bride out for a 78 mile spin to look at the Fall colors , but it was rather chilly and breezy. Oh well, it gives me some thing more to look forward to;). Trouble is , I'll have bigger engines next year and have to try one thing at a time:rolleyes:

Who'da thunk...FREE HORSEPOWER:confused:

I also noticed that the wake was longer/narrower than tops out.
with b-4 I had a squared off "table top" shape to the wake. Now the wake looks more like a single screw, long and skinny.
The boat now will porpoise like it had too much out drive -out trim at lower numbers.
I guess you could say the whole rig ran higher in the stearn, and with the mirages, I didn't seem to get the benefit of the bow rise capabilities.Maybe a pair of 4 bl power tech or bravo's are in order. What do you guys think? You know.. a better surface piercing type prop?
I did notice my differential power turns in the marina were a lot less effective.
I had been told that slow speed manuvering with differential power would be reduced. With a good cross wind I'm not sure I would be able to get the nose around.

ignition
 

OPP's Sorry, My ignition is stock with the stock 8 degr. settings. Just a Edelelbrock RPM airgap manifold with Edelbrock 750 cfm marine carb. IMCO thumper exhaust with "tuned" mirage props.
That's it.........I also trailer this rig and there is no bottom paint.
Just clean gelcoat
The one carb trimmed out great but the other backfires thru the carb like a lean condition between 3800 and 4600 rpms. I have richened it up as far as I can go with no help(way past the other one) I even swapped the carbs and the problem followed the carb. Im going to pull it and check it out this winter but not sure if I should fight warranty or check for blockage somewhere.

I dont think I've gotten into the rev limiters. I can turn 48/4900 RPM. I"ve been told the 89 thunderbolt IV didn't have this feature in 89

Opie, your right , 89 Thunderbolts didn't have built in rev limiters:( . Saw 6000 one day going through (or over) a tugboat wake:rolleyes:. Had to grab the sticks real quick.
When you tried swapping props...you were using 25" Mirages correct:confused:
I try to run my trim at 0 ( parallel to bottom of boat) and mine will porpoise unless I use some tab. The only time I don't use some tab is WOT and I can also trim it up higher (like 6 or 7 ) on the indicator and it will hold the bow up and GO.
I know reversing the props can make the boat feel totally different. I don't know if thats good or bad:confused: Gotta try and see I guess:cool:

Opie,

You mentioned that your motors were 330's, you might want to try some higher pitch props as you might make more power at a little lower RPM.

I think you are right about the TB IV not having a rev limiter. My boat has 1997 motors which had the TB V ingitions with limiters.

Ian T.

Any one got some used 27's mirages for rent for a test run?

Showoff:p Hey Opie , you someplace warmer than Jersey. Their talking a low of 29 in the Philadelpia area Sunday night:mad:
Fogged and antifreezed mine today:
You might do better with 27's since 330's max hp is a little below your 48/4900 rpm range :cool:

Tulsa OK.
Warmer but still not bikinni weather. Lots of rain.
Sat, the last time I was out it was 60.
Back to business.......I was told if I get the RPM's down around 46 I lose all the benefits of the Edelbrock RPM airgap manifold and exhaust manifolds?
Any thoughts?

Hmmmmmmmmmmmmmm, well just like a chain is only as strong as it's weakest link...an engine is only as powerful as IT'S weakest link. In our cases that's probably the "peanut port" heads. They historically produce the most torque at lower numbers:( and guess what turns your prop :confused: . Right , torque. Hp is only a mathmatical equation based on torque.
The small port size is restrictive to high flow and rpm numbers:(
If you got the rpm's down around 43/4400 you might transfer that extra 2/300 rpms into mph:cool:
I mean I wouldn't go out and buy 27's yet. Unfortunately all I got is 25 and 23 Mirages and 27 x 4 blade Machs , but the Machs are only good for small boat anchors. My cuz had them on his Fountain when he bought it...switched UP to 28 Hydromotives and picked up speed and rpms:eek: