May just have to pop 1.3 drive on and old prop- to settle whether engine changes are issue or not- tempted to customize prop more- but then wouldn't be able to sell prop then this puzzle kinda sucks eh? appreciate the help

btw where is the best spot to install air temp sensor?

I owned an AO 26. I purchased the boat from an owner that installed an IMCO 3 inch raised box and kept blowing motors before he could find a good X-dimension and prop. I was amazed on how different props and drive heights using spacers affected the performance of the boat. Eddie Young built the motor and got Art DiNick on the phone to get some guidelines on where the X-dimension should be and we found the sweet spot. I don’t think it’s your engine upgrade but your drive height that’s causing the problem. Call Art and he can help you as he built these boats for a while and still runs a 3100.

Getting the old drive/prop on would go a long way to isolating losing 10mph.

Of course...check the X dimension before pulling the new drive etc

You put a 30p prop on...got your rpm back up to 5600-5700?

Twin blower carbs have better fuel distribution and more flow at WOT. Blowers don't like vacuum at their inlets, so if the carbs don't flow enough, it will impede the flow/boost potential. B&M tried vac secondary carbs as well. They work, it's all about the airflow potential of the engine.

This is a photo of my 420 Megablower BBC intake. Assuming the 250 intake is the same thing.


Not sure this is stock...but there's a boost pressure port at the rear of the intake. You could probably drill/tap anywhere along the rear rinner here. In the center would not interfere with flow as much. Should be short enough to not interfere with the distributor.

Or if you don't have a sprung back fire plate, then you could use that to make up another plate with some meat to drill/tap there.

There may be port on the 250 blower bottom you can use. I'll check my 420...but it's packaged up atm.

Thank you, Ive talked to Art before. will do.

excellent advice, I believe thats the hard truth- I believe it is the blower and carb change- but your right- no since guessing, one or the other improvements will need to be
undone to accurately diagnose- thank you sir!

fyi, I went from 1.35 ratio to 1.5 , reason i needed to go up in pitch, otherwise , still good input- thanks

Ok Everyone; UPDATE; so , i appreciate everyone's feedback, seems we were chasing our tails, my apologies, so I had dual holley double pumper 750 carbs installed by my mechanics, upon recent inspection,I found;
1) a couple fuel inlet fittings loose-(leaking fuel)( re-tightened)
2) found loose linkage fittings(tightened) and adjusted.
3) when engine cover was completely closed, throttle cable was being restricted, Raised engine cover 4-5 inches-and it opened up beautifully, accelerated rapidly, confirming 30 pitch prop to low!
with the labbed 30 pitch Bravo 1, this engine revved freely to 6000rpm( rev limiter setting) so just swapped back to my labbed 32 pitch bravo 1. taking out within couple days- will update accordingly

QUESTION; anyone know what the difference is between a satin finish vs polished.

additionally; I checked x dimension, 1 " low- so will be looking for a -1" Imco lower. or relative lower, also recommended by Art Dnick at AO.

QUESTION; how much additional top-end, ya'all expect it would produce with the Imco lower ?

if after these discoveries AND eventually installing imco lower. if not surpassing 100mph i will be next looking for larger blower, thanks again,
any additional feedback or recommendations, i am open to suggestions.

Boat-On, Rock-on, and enjoy the summer !!!

Ok so the dual 750 carbs installed, I found out they are NOT Boost Referenced, ??? i was told this is not a problem, seems to be running good and I cant be certain that the lean condition on one bank is caused by this or the
problems I found and corrected, I will return with update in couple of days