Weiand 177 boost??
 

According to some of the charts i have been looking at, and if my math is correct, I should see 7.5-8psi with the pulley combo i am running. However, I only see about 5 psi.

I am running a fairly large roller cam, so not sure how much that should effect it. Sounds more like its time for a refresh on the blowers. Not sure how many hours are on them. My ratio is 2.3:1 with the current pulleys on a 454CI..

fixx
 

Boost is measured on what the engine is not using, sounds about rite for a 177 and i wouldnt go much more then what you have with out innercoolers..It also wouldnt be a bad idea to send them out for a refresh,pay a little now or a bunch later if one were to self distruct..

Read so much were guys went to smaller pulleys on stock 525's and ran 7.5-8lbs with no intercoolers and no issues. Thats with iron heads also. I am running aluminum heads, which should help.

Not really looking for more power. If a rebuild will allow me to still make 5psi, but running a larger pulley, and not spinning the blower as fast, I'll be happy with that. Although some intercoolers and 8psi sounds more fun....:drink:

I was overdriven at about 2.55:1 on my 525SC with a smaller top pulley and saw just shy of 8#. At 2:1 stock it is 5.5# of boost.

Realize that boost pressure is also dependent on load. Rev the boat in neutral with no load and boost pressure will not move much. When I first got the Pantera, the boost showed a little more than 6#. The propslip was very high. I lowered the drive an inch deeper, reduced propslip from 25% to 17% and boost instantly went to almost 8#.

A switch to a bigger roller cam made little to no difference in the boost pressures.

Keep in mind that the stock 525SC's only had 7.5:1 compression and that is why you can run higher boost on them.

If your cam is not a good blower profile cam you can just blowing the boost right out of the exhaust, those blowers do not like lots of overlap and do like cams ground on a 114 centerline as well...Rob

You have aluminum heads which probably flow pretty good. Boost is the lower on good flowing heads as they have less restriction. I think a refresh on those blowers is just bearings and seals. The rotors are straight extruded metal, so I am not sure if you can set them up tighter to have less leak by. I own a 177 but am not an expert on blowers.

177's have the B&M style teflon rotor seals, no adjustment. The Blower shop is about $1000. each for a rebuild which is seals, bearings and a few other wearable parts which they return all the parts back to you, plus shipping it both ways. If your having fun with those maybe a step up to 250's or 420's whould give you a fix.

Not so fast-My Mercruiser 177 does not have teflon seals on the rotors. Maybe other versions did, But I have not seen those.

You are correct . 177's are Weiand (no teflon) . B&M made a 174 that had the teflon strips.

If you have a 3" top pulley, 7" lower and 454 cid you psi should have a threoretical 8.26#. I'd guess your top pulley is slipping. Touch it soon after a hard run and see how hot the pulley is to tell about slippage.

I too have the 177 mercruiser blowers and they do not have the teflon seals.

also be carefull on your flame arrestor had a h/p one from eddie marine that allowed almost no boost, talked to weiand, told me to try without....picked up 4.5 psi could not believe it !! so watch out there..Rob

How do figure the 8.26#????? That is in the ballpark, but actual boost pressures will vary depending on the flow of heads and if there is an innercooler.
Also, do you mean his belt is slipping???? The pulley can't really slip unless the teeth are bad and that would only happen for minute until its destroys itself.

the 177 blower has rib belt drive not gilmer tooth, usually 6 or 10 rib a weak tensioner spring could be the culprit

I have a formula to calculate theoretical boost. This formula seems quite accurate if all is in order. I know it has been dead nuts on my 3 pulley changes.

Yes, pulley slipping under belt is what I was saying. I know on the smaller blowers when you get down in the 3" pulley range, this can become an issues. Maybe its a tension issue like doggiedave mentioned that shows itself when the contact area of the belt/pulley interface decreases too far.

FWIW, on a driven belt system, if I said the belt was slipping that would have indicated slippage between the belt and the crank pulley (driving member). The belt would have been slipping under the driven pulley. Since I said the pulley was slipping it meant the blower pulley. The belt (driving member) is driving the blower pulley and if the pulley is not moving at the correct surface speed, it means the pulley is slipping. If I said the blower shaft was slipping it would mean the keyed shaft inside the pulley (because the pulley is the driven member) and of course that would not last too long. Its all good Griff....... :o)

My 177 10 rib belt would start slipping and I replaced it about every season, so I know what you mean. Just making sure I understood what you were saying.

I saw 5 PSI with standard pullies and 8 with smaller ones.I still have a set of smaller ones from my 177's if your interested.Also think i have a lower pulley and some belts.

Hello, I am interested in your smaller pullies and belts. What sizes and how much? Condition of the belts? Will measure mine tomorrow to compare sizes. Thank you....Kevin

I also have 2 of the splined shaft merc type pulleys. They are something along the lines of 2.85" diameter.

Griff, what indicated to you the belts were slipping, low boost?

If I was cruising around 3500rpms and pushed the stick forward quickly, it was sluggish and the boost would only go up to about 4-5lbs when it should have went to 7-8lbs. I got the 10 rib belts at NAPA for about $40 and always just kept a fresh one on the boat. I actually had one completely shred apart during a high speed run.

Sounds like it was slipping all the time most likely, just less when new. What was the diameter and your cid? I'll tell you what your theoretical psi should have been w/ zero slippage.

It was not slipping at all until the belt would get worn. I had it for 300hrs and only had the slip happen twice with belts with more than about 75 hrs. I just started replacing them at the beginning of every season and never had another issue. Boost was consistent at just under 8# which was correct for the pulley size I had. The 2.75 top is the 8# pulley for the stock 525SC. I don't remember the exact size of mine. I think it was a 2.81 top and the stock 7" bottom. The engine is long gone anyway.

Here's what mine looks like with the 3.25 blower pulley. 6.09 is the boost PSI, the formating from excel is screwy.

top 3.25 3.5 3.75
bottom 7
11200
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.153846154 469 14.7 6.09

Here would be a 454 with a 2.81 top pulley. 10.14 is the theoretical boost pressure. I think your pulley was slipping all the time Griff at elevated rpm. That's why you went through belts. I haven't replaced a belt yet. Just a thought for those that are working these issues now. I know this boat is long gone for you.


top 2.81
bottom 7
12954
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.491103203 454 14.7 10.14

Well, you can calculate boost on this all you want and it still might not be real world. Head flow, load, obstructions-ie intercoolers, come in to play. One sure fire way to tell if your belt is slipping is there will be black dust on the tensioner arm. And your boost gage will bounce a little especially at high RPM's. My combo is a 7" lower pulley, 2.85" upper and it makes 6.5 psi @ WOT. On paper it "should" be more but I have good flowing iron heads and an intercooler. Boost is backed up, pressurized, fuel and air waiting to go down the next runner with an open valve. Higher boost does not necessarily equal higher HP.

That is correct, the formuala just gets you in the ballpark and uses a VE of .9 on the unboosted intake tract to account for inefficiencies of the engine airflow. That is actually conservative for a well designed engine package. But I suppose there are engines out there with lower VEs that would indeed produce more boost yet less power. What one would not expect is less boost because the engine can only really flow 100% of its cid, without help. Of course that can be off too. But the formula I use is generally within 5% of actual. If you are off 20% actual vs theoretical it indicates you are not getting the rated cfm out of the blower for whatever reason.

BT :cool:

Sounds good, thanks for the clarification.

I'd bet old navy that you could switch to a 3.25 inch pulley and loose very little boost from your 6.5, in fact you may gain if slippage goes down. Spinning these little blowers too fast and creating heat will also be a deterent along with slippage due to small pulley. Just a thought, here is your theoretical assuming 454cid. 6.78psi

top 3.25
bottom 7
11200
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.153846154 454 14.7 6.78

No, probably not, thats 6.5 below the chiller.

Ah chiller, gotcha.

If a 454 with a 177 blower makes 525HP with the 3.25 top pully, what can you expect if you put the 2.85 smaller top pully on? HP gains, speed gains?

Around 25hp. The problem is the 177's lose efficiency and create more heat the faster you spin them.

So using the boat "normally", I.E. just cruising with short blasts here and there, shouldnt cause too much excessive heat. Right? Also may see a mph OR 2???

1-2mph is realistic. Cruising is not really affected because you're barely into boost, if at all. If you run a smaller pulley, change the blower lube frequently.

Griff, bought the 2.85 pullies, but dont have belts. Would you happen to know the NAPA part# for the belts you used to buy? I know its a long shot, but arent they expensive from a blower company? Not to mention, hard to find?

Gates Micro-V K100540

Sorry Guys. I started this thread, and my info was all wrong. For some reason, I thought it had the smaller pulleys. I have the 3.25 top, and 7" bottom. Measured them today. So seems i am not far off!

My engines are basically 525SC's, with dart alum heads, pretty agressive roller cams. With my current props, I only turned about 5000-5100RPM. I plan to spin them to around 5300-5400, as they really make quite a bit more power as the RPM's increase (cams). Good thing is that even with my current pulley, at 5400, Im spinning the blower at 11,718 RPM. If I went to a 3.05 pulley, i'd be at 12420 rpm. Im debating what would be better, spinning the engines say at 5600RPM, or at 5300 but spinning the blower faster..

Make sure that belt is on the "tight" side or it will probably slip. Once installed assuming a 2.85 pulley, I have had the best luck with the tensioner using the tightest half of the setting, looking at the allen head stop bolt in the slot on the drive snout-If that makes any sense..

Mild thunder-What are your current props?

any chillers for 177 blowers around? Is it 100 HP gain?

You would not gain 100 h.p. with that tiny of a blower. I would tend to think to gain that much just because of a cooler, you would need an engine about 540-598 C.I. and a 14-71 blower IMHO. I would think a real world increase would be 25 maybe 50 H.P. at best with any of these coolers.

They do make a chiller for them. I can't remember who however. I don't think it was Weiand