supermx96

I have already the 2,85 pulley that can make more boost than waht i have run this summer. But with new aluminum head with more flow i think it can affect the # of boost to the down size that is what i need to know or calculate to know if the hp gain will be good...

supermx96

I will try to contact Bob...

To make sure what i do with that.

blue thunder

No way to pyro the exhaust. I started at 28* and worked up till no improvement than backed back down 1*. 30* is pretty common in supercharged apps. I didn't dyno the engines.

Old Navy

The reason I ask is, when I got my boat it was totally stock and it had the timing backed off to 30 or so deg total. The leakdown test indicated burned exhaust valves @ 144 hours.

MILD THUNDER

iTrader: (3)

The 177 is great on a mild 454. however, in my opinion, once you add some healty cams, good flowing heads, you will be limited.

You are correct that you will probably loose boost psi with the new heads/cam. however, you will make more power. I would consider a upgrade to a 250 or 256 blower. They work great on a modified 454. You will be able to make 7lbs of boost, but to do that after the mods, you will be overdriving the daylights out of the 177. The blower shop makes a really nice 250 sized blower. Used B&M 250 blowers are around cheap. Run a dominator if you are staying single carb. Most guys will tell you that you dont need that big of a carb, etc, etc. Roots blowers are hard to overcarb, and love unrestricted airflow above them. how come a 250 blower will normally make more power with twin 750 holleys over a single dominator? Don't get caught up in that going to a smaller 800-850 single carb talk. Run a big carb and tune it right. Merc knew what they were doing with the single dominator on a 177. its not a blow thru or N/A engine.

I would think a proper cam swap, intercooler, and 250 blower, you can probably run 8-9 lbs of boost, and make some really nice power, even with your stock heads. Install some headstuds, MLS headgaskets, and go. If you boat in freshwater, lose the water thermostats, and keep them cold.

Cost wise, a pair of heads will cost you at least 2-2500 bucks for a decent set. In my opinion, if you were on a budget, the larger blower with more boost and chiller would net bigger power gains. Although your heads are iron, your static compression is really low with the stock pistons. GM square port heads aren't as bad as some guys make them out to be, especially on a blower app. You can make some power with them. If I remember right, the stock cam is pretty decent for a blower motor. It's ground on a 114LSA. A upgrade to a Roller cam would net some gains, but not necessary.

My boat has built up 454's with dart alum heads, custom roller cams, 250's blowers, and some other goodies. 7lbs of boost, single dominator, 84mph on gps. Same boat, same drives, ran 70-72 with 500EFI mercs (not my boat but another old 38 Fever). have no idea what mine dyno at, but they run great and been together for about 6 seasons. Best i could get out of the boat with the 177's at 5psi, was 77mph. Bolting on the 250's and 7psi, got me 84mph. Leakdown tested yesterday, 6-9% leakage. Not bad.

SB

iTrader: (1)

Just so you know what you are starting with:

Carb: Holley Dominator: Jetted 98 all four corners. 6.5 High FLow Power Valves (not standard ones) Front and Rear
SC: 177 CID
Heads: CHevy Iron Rectangle Ports 2.19, 1.88 valves
Compression: 7.5:1 (yup!)
Cam: Merc 400 / 420 / 425 / 525SC
Crane Part#132561 Grind # H-228/312-2S-14 T1.2
Duration at .004” : 298, 306
Duration at .050”: 228, 236
Lift with 1.7 rocker: .530”, .551”
LSA 114LSA
ICL 109 ATDC , ECL 119 BTDC

Quick heads up on 525SC:
T-Bolt Module does not reach total timing until 4200 or so rpm. One the two 525SC's I tweaked real timing was few degrees different than stated on module, so use your gun to set total correctly, again at or just over 4200rpm Always go further to see when timing advance stops to make sure you got there. Total specs should be on the flame arrestor, I believe somewhere around 36 degrees?.

Plugs are Delco MR41T's

supermx96

Thanks for the engine info spec.
The total timing should be at 35 deg.

SB

iTrader: (1)

So......my vote is:

Good cylinder head. AFR 305 if want aluminum and RHS if you want cast iron. With 7.5:1 going aluminum for detonation control is really a non issue.

Cam change: guaranteed. Hydraulic roller to get these BBC heads flowing some air.

Back to cyl head: I'd strongly recommend looking into a reduced CC combustion chamber to help give you some more compression.

AS Blue Thunder stated (and BTW, his boats hauls with his 177cid fed 454 based engines but I advise you not to drive like him. LOL. ) compression will be your friend to help make up for the lack of air the 177cids will provide in comparison to the bigger blowers.

supermx96

If i will go with aluminum head at what comp ratio can i go without having problem at 5-6 psi boost?? 8:1 8:5 ???

Now with the stock setup i ran it at 5.5 psi the upper pulley is 3.368 in dia and lower 7 in dia i have fond a 2.850 in dia that i have not trying, the boat is now stored for the winter

I know with bether head flow i will drop my boost but i dont want to run it below 5 psi with the 2.850 in dia pulley.
So i need to calculate that point. I need to know the stock head flow to make any comparison of hp gain and boost lost....

HaxbySpeed

I did this one 4 or 5 years ago and it's still runnin strong. Stock 525sc cam, carb, blower, stock pulley made about 4.5 lbs. Edelbrock RPM heads and compression bumped to 8.5. A little more boost and a bit more rpm and you'd be close to where you want to be. There's a bunch of different ways to do it and they're almost all relatively cheap and easy.

http://www.offshoreonly.com/forums/a...blem-525sc.jpg