you still up haha, yeh got it red one.

ok 240sport baja 88 has a wind fairing like the outlaws:evilb:. my height was 5 1/2 with add on steering had to drive with the chinewalk by sawing your arm back and forth so the hull was even and my arm was moving very fast.:evilb: my boat with about 670hp went 83.2 gps ran out of prop I needed a 28 b1. boats for sale but needs work it has a light weight scoop in the back its a pro stock one. anyway with the light hatch and was making a new back seat my boat was under 4000lbs. 24degree small pad over 70 my chines were out and my tabs were light have 280s k from merc. theres a 250 ol the guy had a 525 merc with a 3'' raised imco box12'' set back it ran 81.3gps with a b128 he moved up to a 600merc and a 2'' shortie but added a 1'' spacer to set a height of 3 to 3 1/2'' its been a over a year since we talked:eek: has not been on site.

my new boat will be 3 to 3 1/2 '' when done its a single 28 saber.

hey don't I now you from way back, who got the bat:drink:

I got the bat bro LOL!! been long time since I said that LOL!

haha I see you post here and there.:coolcowboy:

38 scarab avs 4" drive hieght
-2" imco's
bravo 1's late model after '02
bravo 30pitch 4 blade supposely labbed.
just got the boat 2 weeks ago. been out only once with previous owner. Saw 80 mph 5000rpm flat lake water.still was climbing.
previous owner says 83 to 85...5150 rpm. but...... boat is hard to plain. Do you guys with the higher drive hieghts (38 footers) have to use alot of tab to get on plain? what are my options to get out of the hole a little better and not loose to much top end?

I am not familiar with your setup. But from what I have read, most would try a small spacer or a 5 blade prop. I will be trying new props myself after I raise mine from 8" to 5".

a 5 blade would loose some rpm correct? so does anyone have a prop sugestion? mabey a 5 blade 28 pitch? thanks

Lowering the drive shaft height or adding blades will likely scrub speed but either will make it easier to get on plane. I believe that a 38' boat w/5-blade props will also significantly increase the chance of Bravo Drive failure due to reduced prop slip. Using your tabs and breaking the props loose is a sign to me that you set up is close :drink: With 5-blades, you might see + 1-2 MPH...is it worth the extra drive stress?
Consider trying a set of B1 28P. They should make it easier to get on plane and you may pick up a few more HP with improved acceleration.

Thanks,
the boat had 26 bravos when in Az. owner stated it ran 75-78 at 5700 rpm. 28's might be the way to go. but would smaller pitch props be easier to blow out while trying to plain?

I would say it is the other way...the 30P will blow out sooner as the are tying to grab more water while pushing the same weight.
B1 28P should be easy to borrow for a quick test. If you like the result, you might be able to trade someone on OSO.

alright, will try.

ttt Thought this might help the guy asking about a shortie.

I wanted to update the post and give my results. I raised my engine and drive up 3". Propshaft centerline was 8" now it is 5". I gained a solid 5MPH just by raising the drive. The boat rides better, flatter and faster with less trim, cuts through the waves much better. Planes off with a Mirage prop and still had 30 PSI of water pressure. Best speed of 74MPH @ 5200 RPM with 25 pitch Mirage plus lab finished with double cup. That is 9.8% prop slip, I have a 26p Bravo I can try but I do not know if any other prop will do better than that.

I am right at 10% slip with my 232. 600hp stock prop depth of 7.5". I will be raising with a -2 later this season. Be nice if I saw 5mph more. That would put me low 80's and I'd be happily done then. Now 78mph @ 5250rpm with 25M+. Have to over trim a bit for that though.

It seems to equate to about 2MPH per inch. You should gain 3 to 4MPH, I would try the prop you have now first. I still have a little work to do to hit 80MPH.

just waiting for my motor still for the saber its drive height is set at 3'' if we set the konrad ace up right:eek:, hope to have motor by next week:picard1: since the new boats been here for almost 8 months. so maybe by aug I will have some test ## shooting for 100 plus. and my 24 ol ran flatter with the higher drive height too. I may have to steel that motor but it will be slower.

ttt Maybe this will help.

If you can still get on plane with the Mirage 25P there is likely more MPH left. In our testing with twins we ended with +10 MPH moving from -5" (with Mirage 27P) to -2" with Bravo 28P. 3 of the 10 MPH was due to the efficiency of the IMCO shorty case.

I have a 1998 Baja Boss 509 m3 procharged 750 hp. I am running a new XR and standard lower. I have a Imco 2" shortie and wanted to know if it would bolt right up or if i need to change anything for it to fit ? I am running a stock Bravo 30 prop.

Yea, its all about the money at this point. I am working on a raised extension box project. Still in the planning stage at this point, I would like to go back 16" or more and up 2" or more.

I have not done one before, but it should bolt up.

Yes it will bolt up. Make sure to put shorter bolts in the anode plate.

2" shortie
 

Oh, I forgot to mention that the Imco shortie came off of a Fountain that is a Left Hand Rotation. And its going onto a Baja that has been a Right hand Rotation. Does this make a diffrence ?

No.

Chris

ttt

Jeffwav
Thank you for loading the past post. Sometimes while taking notes I wasn't sure if setback boxes and twins were being were being described. From the information you gathered and what you shared. If I may run this by you. On a twin with boxes I should run a straight edge in front of the drives back to the lower units. And with the cavitation plate parallel with the bottom of the boat. The prop shaft should be 3.5 to 4.5 below the straight edge. Does that sound about right? Thanks again for your time. PS if its not is it ok to call you?

I'm not the expert, but from what I have found yes. It seems like 3.5 to 4.5" is a very conserative depth with boxes. Some of the guys here are running 2" with boxes. I do not have a ext box and my drive is 5" deep, a mirage 3 blade prop still planes off well. I could have easily went higher but the engine would hit have the hatch.

Keep asking questions, but I think the comments on the prop shafts 4.5-5" below the bottom are for a single engine boat. As you have a twin, IMO your best setting will likely be 2-2.5" range. On our boat, we run a B1 prop at 2" below.You can space down, but it is a really expensive to raise the engines twice. Some of the Fountain race boats are set up at 0-3/4" below the bottom...definitely 5-blade range.

Thanks guys for your input I will keep in touch have a great weekend!

K, I'm all stock, but re-doing my rear transom and want to know if I'm decent ball park for prop depth.

1986 Sonic 36SS with stepped hull.
415 HP 502 MPI with TRS drives
Set at between 4" and 5" depth.
Labbed 25p Mirage plus props.

Does this sound ok???

1988 32' Hydra Cat, twin 700's, 12" Stellings boxes at neutral, Imco Sc's with -2 shorties. Started at 2 3/8" above. Got up on plane no problem but very loose in the rear over 85mph. Down right hairy over 100mph. best speed of 106. Spaced drives down 1/2" at a time. Settled at 1 1/2" down, 7/8" above bottom of hull and picked up 9mph for best of 115mph so far. Running 36P Bravo 1's and will get up on the rev limiters at 6K but takes a minute. Gonna try regearing the lowers to 1:36's and a different prop pitch. Still playing with 20% throttle left to go so hoping for 125mph or so in the near future?

Shorty lower Drive
 

I have a 1991 292Sr1 Formula with 502s running 26B1 5150rpm getting 77-80 all trimmed out.Thinking if I put shorter lower unit on should be better.
1.Can a imco shorty bolt up to a Bravo drive?
2.How short should i go?
3.What will be my increase in speed.
4. What will it cost????

Thanks for your advise....

Cool, my old thread is still alive. There is a ton of good info on this thread. First thing you need is to find out how deep your drives are.

I'm going to revive this thread because it has a lot of good info in it.

My Boat is a '89 Formula 292 w/ 650 hp 509's
I'm running 2' Sportmasters, with long skegs, 28p Bravo I Labbed props (they are a true 28p, they are 30 castings)
ITS Boxes.
I'm 5" below the hull.

My best was 80 mph @ 4800 with the hatch cover off and 100 gallons of fuel.
Hatch Cover on I lost 4 mph and 200 RPMs with the 28's and fumes for fuel.
Hatch Cover on with Bravo 26's (stock) 78 MPH 5150 RPMs and 60 gallons of fuel.

This weekend I'm going to try some labbed 27 mirage plus props. I'll report back. I'm also going to start trimming off the excess skeg. They are at least 3" to long, but I'm going to start by removing 2".

endeavour32, is the hatch choking off air circulation ?

would that screw w/ the afr ?

What's that hatch weigh?

I need more airflow into the engine compartment. Donzi has a slick set up on the sides of the new ZX hatch. This winter I'm going to replicate them and put them on my hatch to increase the air flow. The one thing I don't want are large racing scoops taking over my hatch. What I think it boils down to, is hot air vs cooler air. I'm going to try cracking my hatch and see what happens. I just need to make sure don't crack it too much or it might come flying off.

I know when I was a kid I would always move the engine box forward a bit on my dad's boat and I could always gain a few mph. I think it's pretty common with boats that have a relatively sealed up bilge, it's just more noticeable with larger engines. When I bought my engines, Tinkerer said he experienced the same thing when the engines were in his Scarab.

Lesson here is, if you want more speed, make sure your engines are getting plenty of cool air. It's a pretty cheap way to gain some speed. As you can see by my testing I lost 4 mph from that, and that alone!

Mine would fade about 200 rpms after about 30 seconds of wot...most of the problem was the the heat emanating off of them heating up the air in the engine compartment.

I built a fresh air intake system for the engines that only allowed the to draw air from the outside, and problem solved.

I also had to add additional ducting and blowers on the inlet side to turn the air in the engine compartment, since the engines aren't pulling in air anymore.

I also made different outside air inlet grills that had alot more open area than the different sized ovals that were in the stock pieces.