Rather than turn this into a who knows more contest, I'd rather see us simply post the build combos, and learn from the results. That's what oso once was all about. After all, its a forum for guys who own high perf boats, sharing their info and experience.

Here's something to look at:
ealash's oval afr motor = 3.25" pulley = 3.4lbs boost
mike;s 305 afr motor = 3.25" pulley = 4.2lbs boost

Loose blower vs tight blower can cause that too

What I noticed on marks build , was the steady decrease of boost as rpm increases. Most roots blower builds I've seen on the dyno, usually take a dip in boost in the peak torque area and start going back up again. That is when the blower is able to keep up. Like 871's, 10-71s, etc.

as can the cam profile.

Without posting dyno sheets with all data being recorded and older sc's being used this is all pissing in the wind for comparison.

But, it's winter so we are discussing anyways.

What exhausts where used on both ?

Both had dyno headers .

Both made great power IMO. I'd like to see what they would have done with a 8-71 and 6psi at 6000rpm. My guess would be WELL into the 700's and prob a lot more resistant to detonation from hot air .

I can tell ya a 250 blower driven at 60% over netted 160* intake temps. At a little over 100% over, intake temps soared to 230*. I can only imagine what a 177 spinning 145% overdriven is making for heat . there's a reason those blowers were made for 4k rpm tow truck engines. A stock 525sc Spun that blower at 11k rpm. I personally wouldn't try adding another 3k rpm of rotor speed without an intercooler or at least some IAT gauges.

eddie,thanks for sharing the info on your build.i believe a little fine tune in the boat to get the afr in a safe range is going to make for a good running,long lasting engine.to me even though these two builds are somewhat different they are both almost the same.when choosing parts for mark,s engines i had a specific goal.to run on 89 oct fuel,to make 650 reliable hp and to run a long time before needing to be refreshed.i believe i have met all these goals.in my mind it was never a competition between builds,after all,when i was working with bob on parts selection i did not know you even existed.i will say that from my own experiance with the 177 blower ,keeping it,s max rpm low will prolong the blower and the engines life.i am sure mark will have good reliable power for a long time as will you.

And that means ?

Well, not some marine log manifolds. Lol.

I know what your asking though. What diameter primary tubes, how long, etc. I believe mikes shops BBC dyno headers are 2 1/8 primary. I don't know what eleash shop had, but they didn't look small.

I haven't found forced induction engines nearly as sensitive to exhaust "tuning" as NA, but I haven't much data to support that. Generally I've seen blown stuff simply like a non restrictive big pipe stuff. Like stellings steroid headers, stainless marine gen 3 with 5" diameter elbows and tails, etc.

My guess is slight cam difference, blower difference, or both. My blower could be a little looser, it was rebuilt not to long ago, but that doesn't mean a whole lot really. The cam profile is a little different which probably played a roll in the boost difference too. It could be other small factors too, but hard to say what the exact difference is without testing each blower on the same platform or switching them between engines to isolate.