408 Stroker Conversion - 1974 Bronco

[Aggie Charlie]

Greetings,

I am planning on installed a Blueprint Motors 408 Stroker (EFI) mated to a 4R70W Transmission. With that being said, I am wondering what Gear Ratio would be the best fit for this conversion. I am currently running a 302 V-8 with a 4 BBL Carbureator with a C4 Automoatic Transmission. I have a Dana 44 up-front with a Ford 9" Rear, both are geared to 4.11. At 70 MPH, I am running 3,000 RPMs. I am thinking about a 4.56 or a 4.88 on the new conversion. I currently have 2.5" Suspension Lift with a 2" Body Lift, and will be going up to a 3.5" Suspension Lift with a 2" Body Lift. A Hydro-Boost Brake System, and 4-Wheel Disc Brakes will also be installed in-lieu of the Front Disc and Rear Drum set-up I have now. Finally, what are y'all thoughts on the 3.5" Extended Travel Suspension Lift from Tom's Offroad?

Any & All Comments Would Be Greatly Appreciated!

 

[EPB72]

Add your desired tire size as well ..

 

[Aggie Charlie]

Tires are Falken Wildpeak MT - 35" x 12.50" on 17" x 9" US Mags Indy Wheels. This tire size is the current one, and will remain on the 408 Conversion.

 

[73azbronco]

4.1 in my opinion. My 347 has no issue with 35s and 4.1, oh, but i do have a 5 speed manual, so

 

[m_m70]

Add your desired tire size as well ..

This^^^^^^

And......what do you want to do in your Bronco??

Crawl it? Wheel it?? Cruise it??? All of these and road trip as well?? That really is the big question

 

[Aggie Charlie]

This^^^^^^

And......what do you want to do in your Bronco??

Crawl it? Wheel it?? Cruise it??? All of these and road trip as well?? That really is the big question

Tires are Falken Wildpeak MT - 35" x 12.50" on 17" x 9" US Mags Indy Wheels. This tire size is the current one, and will remain on the 408 Conversion.
Will be taking it around the Texas Hill Country for light rock crawling, with nothing too crazy, and on off-road trails that are in the area. I pretty-much drive it daily and have no issues with it. Basically, I would like to configure it to drive around Texas (and keep up with my wife's 2022 Bronco). I would say 60% On-Road & 40% Off-Road. I hope this helps.

 

[bronco italiano]

How long have you been waiting for the Blueprint motor to be built?

 

[Aggie Charlie]

How long have you been waiting for the Blueprint motor to be built?

Waited 9 Months due to piston issues. Finally arrived in Late November, and now ready for install.

 

[Broncobowsher]

4.56 if you are more for highway cruising.
4.88 if you are more for the off-road.

 

[Aggie Charlie]

4.56 if you are more for highway cruising.
4.88 if you are more for the off-road.

I greatly appreciate your input. Thanks!

 

[rocknhorse76]

What have you done to the 4R70W? Mine worked fine with my 351W but didn’t play nice with my 408. I’m in the process of rebuilding the 4R and upgrading the internals.

 

[Broncobowsher]

I've been thinking about this. I have never driven the Blueprint 408, so I don't know the low end of the power band and how it will drive off idle. So long as the engine has good drivability, I would aim for about 2000 RPM at 60 MPH. With that much displacement, I might even cheat that down to about 1800 RPM at 60.

Right now I would be swapping in the 6R80 if doing it from scratch. I don't know the background on why you picked the 4R70W. If you already have parts to head down that path, good. It is a perfectly good choice. But if starting with a clean sheet of paper, I would go straight to the 6R80.

 

[Aggie Charlie]

What have you done to the 4R70W? Mine worked fine with my 351W but didn’t play nice with my 408. I’m in the process of rebuilding the 4R and upgrading the internals.

I am getting the motor and transmission installed at Lone Star Ring & Pinon in Katy, Texas. Eric O' Sullivan suggested the 4R70W as he has had luck with them in the past, and has done several conversions and upgrades.

 

[Aggie Charlie]

I've been thinking about this. I have never driven the Blueprint 408, so I don't know the low end of the power band and how it will drive off idle. So long as the engine has good drivability, I would aim for about 2000 RPM at 60 MPH. With that much displacement, I might even cheat that down to about 1800 RPM at 60.

Right now I would be swapping in the 6R80 if doing it from scratch. I don't know the background on why you picked the 4R70W. If you already have parts to head down that path, good. It is a perfectly good choice. But if starting with a clean sheet of paper, I would go straight to the 6R80.

Thanks for the advice on the setup. The 4R70W is already at the shop to be installed. Eric O' Sullivan with Lone Star Ring & Pinon will be doing the install. I think there will be some trial and error with getting everything "tuned in" correctly. As I see comments from everyone, I am leaning to a 4.88 Gear Ratio.

 

[m_m70]

I am leaning to a 4.88 Gear Ratio.

I think that's a great choice of gear!

 

[Aggie Charlie]

I think that's a great choice of gear!

Thanks for the response. So looking forward to the conversion!

 

[bronco italiano]

DO you have the extra coin to have the motor dyno/broken in before install just in case there are any problems?

 

[Aggie Charlie]

DO you have the extra coin to have the motor dyno/broken in before install just in case there are any problems?

No I do not. I wish I did. I am going to leave it with Eric O' Sullivan to take care of that. He has a lot of experience with that and would take it through the paces.

 

[73azbronco]

Can't say enough to try and get 30 minutes running off the EB. Fixed a few minor leaks which have not been an issue since

 

[Soylent]

DO you have the extra coin to have the motor dyno/broken in before install just in case there are any problems?

Aren’t they broken in, cam wise, already enabling them to dyno them and provide you the numbers?