MILD THUNDER

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..

MILD THUNDER

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....

Griff

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.

ezstriper

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

Old Navy

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.

fireboatpilot

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.

Old Navy

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

737jetmech

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

blue thunder

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.