3.6 GT powerhead details

**Hillclimber** · 10-26-2016, 02:40 AM

Hi Frank

Thanks for the info. To my knowledge there are none of these V8's in England, hence no knowledge so I am on a big learning curve

**Hillclimber** · 10-26-2016, 02:45 AM

To prove the concept of my project, I will initially run with 8 carbs with float chambers so these (the inlet) will be horizontal. If successful, I then upgrade to EFI, CDI, and the 8 expansion chambers.

**powerabout** · 10-26-2016, 06:31 AM

Originally Posted by Hillclimber

To prove the concept of my project, I will initially run with 8 carbs with float chambers so these (the inlet) will be horizontal. If successful, I then upgrade to EFI, CDI, and the 8 expansion chambers.

Do you mean standing up the engine like it was as an outboard or making 90 degree adapter for the carbs and laying the engine on it back/exhaust?

**Hillclimber** · 10-26-2016, 11:34 AM

Sorry, I mean with the crankshaft horizontal and putting on 8 separate carbs. Its a mid engined car so exhaust may run through the car and exit on passenger side. Lots of things to consider.

**powerabout** · 10-26-2016, 11:57 AM

did you have in mind to use the original carbs with adapters?
Perhaps lay the engine on one side so your inlet is horizontal might be easier?
Working out a coolant flow will be another challenge depending on how you mount it?

**Hillclimber** · 10-26-2016, 12:44 PM

Yes engine will be on one side. I am waiting for arrival of engines from USA but I think I can cut the 4 dual carbs to make 8 independents each with a float chamber. Otherwise I will use 8 Mikuni as used on the Rotax engines.( I have lots of jets for them). With 8 you can tune each carb to cylinder requirements at circa 6800rpm (my CVT operational RPM) and hopefully avoid piston seizures.
Currently I am having to consider a tank of iced water on board plus radiators + fans to get to the operational temperatures suggested/recommended by Racer. I am also considering CO2 injection into the coolant as its much less weight than racing with a tank of iced water!
ANY thoughts/ideas on these problems, by anyone, appreciated since I am in complete new territory. and I love a challenge.

**powerabout** · 10-26-2016, 01:01 PM

I'd say electric pump(s) and radiators would end up being the easiest at the end of the day.
The carbs are individual its the throttle blades that are grouped into 4 lots of 2.
You might want to set up a bench to run the engine to ensure it runs properly before you do anything else.
Then lay it down in the workshop to get it to run after you alter the carbs.
www.epc.brp.com

**Hillclimber** · 10-26-2016, 01:38 PM

Great for the help/advice !!
Just looked at the BRP parts list (thanks) and can see the throttle blade arrangement. Looks like a problem I can solve.
Electric pumps definite, I am taking no parasitic loss's from the engine. My calculations at the end of the full development programme is 525hp and a top ten placing at top England Hill Climb - Shelsley Walsh. Job done in 2019 when I will be 75yo and can retire gracefully.

**powerabout** · 10-27-2016, 11:36 AM

here is some horsepower from a V8, I would hazard a guess that the only factory part is the crank?
http://www.screamandfly.com/showthre...ight=monty+efi

**PanRonnie** · 11-02-2016, 03:14 AM

you should use a mercury instead of an evinrude

http://mercuryracing.com/mercury-rac...-crate-engine/

**Hillclimber** · 11-02-2016, 03:34 AM

No - I only race two strokes!

**rude tim** · 11-02-2016, 09:41 PM

The engine has 8 single carbs from the factory.

**frank jackson** · 11-03-2016, 10:52 PM

you will most likely find the mikuni carbs easyer to deal with . The brp jets are getting harder to get and expensive ....jmo..

**Hillclimber** · 11-08-2016, 01:40 PM

All of my research and current deliberations of how to make the most out of the OMC 3.6GT powerhead indicate that one needs to increase RPM to get extra/increased power. My calculations indicate that the "Standard wide rings" are going to be travelling at their safe limit of 40,000 Ft/sec2 at 7000 RPM. What happens at 8 or 8500 RPM?

Previously, to increase RPM on other engines, I have converted to "Dykes" rings (L shaped - very thin - fitted close to piston crown - and OK for 100,000 ft/sec2) but the standard OMC pistons do not allow space for this modification.

My calculations of the 3.6GT with EFI + 8 separate expansion chambers + CDI conclude that 8750 RPM is where I need to be aiming and obtaining about 500 HP.

I.E. - The existing design pistons will fail.

So does anyone know if 3.6L pistons are available un-machined allowing Dykes rings to be fitted or is there an "After Market" supplier of Dykes ringed pistons?

ANY comments or advice appreciated.

Peter