I am building a Twin Turbo 427 Big Block Chevy for my V-Drive boat. I am using the old Banks set up but have decided to ditch the carbs and convert it to EFI. I have built tons of engines but this is my first BBC and my first turbo engine build.

My question is related is static compression ratio.

I was going to run my mid 1960's rectangle port heads with 109cc chambers. I found that there a lot of people looking for these heads for their #'s matching restorations and they fetch a hefty price. I sold the old cast iron junk to a guy restoring a '65 'Vette and I purchased a pair of AFR Marine 305cc Aluminum heads. The combustion chambers on the AFR heads are 121cc. I already ordered my JE pistons and they will be here any day. With the AFR heads my static compression ratio is now going to be around 7.75. Is this going to be too low? I am planning on running 15 to 18 psi boost Max. I have an NOS set of Rajay 310E10's that I am going to run. I am mainly concerned about off boost performance and drive ability. It is a 19.5 Mini Day Cruiser size V-Bottom boat and will be mostly used for cruising with occasional WOT bursts.

Any info would be greatly appreciated.


Earle

 

The EFI will give great starting and throttle response once it's tuned good.
It will be a plus to get the fuel out of the intercooler. You will pick up 12% air flow that the fuel was taking up.
Be prepared there is a learning curve so EFI is best for someone who's not easily frustrated.
Read up on it a lot.

Have you selected what ECU you want to use ?
Picking a brand that someone near you is familiar with and can help with tuning until you learn it will be a big plus.
Any of the popular brands will do a fine job. Spending more money will not make the engine run any better.

For gas the 7.75 cr will work OK. I'm using 8:1 and it runs great. I run E85 so next time I'm going to go up to 8.5 or 9:1

The Rajays will work good to about 15# boost. Then the small exhaust housings will restrict the flow and more boost won't make more power.

 

12% more flow. That is awesome.

I have been reading about the EFI stuff for a long time now. I have not decided on a ECU yet but the FAST XFI looks good. Are you happy with yours? I work for a motorsports company and we have an engineer that worked for an EFI company for many years that is going to help me once the engine is together. A family friend worked for Gale Banks for 25 years and he said he will help me out if I need as well. He said 7.75 was good but I read the forums a lot and see most people run higher compression. I was worried that it might be a dog off boost.


Thank You for the info Mark,



Earle

 

The FAST XFI is a fine unit but as I said any popular brand is capable of achieving the same results. Some are more user friendly than others but any of them can make the same maximum HP. My first ECU was a Haltech E6K and that did a great job for me on open loop.

Since the plan is to switch to EFI then at the same time relocate the throttle body(s) so that they are after the turbos.
That removes the vacuum from the compressor.

 

My Friend at work told me that the ViPec ECU's are awesome. Anybody here have hands on experience with them? He said they are super user friendly and they make a marine version.

Link:

http://www.vi-pec.com/page_files/marineECU.html