360 vs gen 3 hemi

[cha74ngr]

i have 1974 factory 360 with thermoquad and longtube headers. its a daily drive. this possible to build motor with more hp and mpg like gen 3 hemi?

 

[heminut]

Anything is possible! Sign from an old Speed Shop;

Speed costs money son, how fast do you want to go?

 

[cha74ngr]

400hp. if 360 is capable being build with balance of hp and mpg like 3 gen hemi i would keep it. if not i would be interested gen 3 hemi swap. i know they both cost money.

 

[cha74ngr]

i also woundered if i build it to 408 stroker can i achieve this goal? keep light foot if i wanted and mpg? even if i keep light foot, best maybe 15mpg ?

 

[Chryco Psycho]

Easily done with a sroker 360 build , you want to be careful with head cam & intake selection & EFI will help a ton with power & mileage .

 

[Heywodja]

Stroker combos are plentiful, Blueprint engines has them for sale with a warranty.

there is a TON of info on sister site www.forabodiesonly.com

 

[57fury440]

If your Challenger has the original 360 then I would keep it and build that engine. 400 hp from a 360 is not that hard to do and you can get better milage by using fuel injection as said above.

 

[moparleo]

But , Gen III 5.7 has 100 more hp before you do anything to it.
If you are going to build the 360. You will probably stroke it and the biggest HP maker will be aftermarket cylinder heads. That is where the power comes from. Might be cheaper to swap a 5.7. Almost a bolt in with the current after market support.

 

[cha74ngr]

if i build 360/408 and get 20-22mpg with light foot, i'll be happy. 5.7 hemi is good option too.

 

[Jm73340]

20-22 mpg is probably wishful thinking Although I guess it’s possible. I got 18.5 with my 408/5spd combo in my 73 with a light foot coming home from Carlisle.

 

[cha74ngr]

maybe it depends what kind stroker combo you have? have you heard of 408 strokers getting 20+mpg?

 

[Jm73340]

Well yes as I said, I guess it’s possible. Mine is a ’88 360 roller block with “Iron Ram” EQ heads prepped by Hughes. Hughes roller cam 228/236*, Rhodes lifters, Forged rotating assembly from Hughes, ProFlo3 EFI and a tremec 5speed.

 

[moparleo]

That makes a 5.7 a real bargain especially if you keep the factory EFI. 345 HP stock, 20 mpg with correct gearing.

 

[Katfish]

I'm in the middle of a 5.7 swap, and trust me it's not cheap.
Costs wise, you'd be miles ahead with the 360, plenty of cash leftover for gas......

 

[moparleo]

Why is your swap costing so much ? Lots of aftermarket stuff ? Was it a complete used motor ?

 

[Katfish]

It's all the extra cost, even without the crate motor, only paid $6k for that, cost would still be more than upgrading the 340 I took out.
You can reuse most of what you have staying 360.

- motor mounts $200
- headers $1k
- radiator / fans $750 - $1k
- starter $100
- wiring / ecu $2k
- oil pan $500
- flex plate $125
- set-up for trans KD solution $500 - $1k
- the list goes on and on.......

 

[moparleo]

OK, I can see you are just buying everything new and top dollar stuff. OK I guess there are different ways to go. You could also spend the same to upgrade all the parts on a 360, except maybe the Ecu kit, mounts. The other stuff isn't really based on the engine type if you use the same grade of parts. Let us know how your swap is coming.

 

[cha74ngr]

i did think of doing gen 3 hemi swap 5.7. if i decided to go 5.7 hemi, i would keep my 4 speed od, electric fan ,mini starter, and efi intank fuel pump. then i would need so far:

- donner motor
- ecu /wiring
- oil pan
- flywheel
- motor mounts
- headers
- radiator

im sure there are more parts needed for this swap.

 

[cha74ngr]

yes 360/408 is easier build if i go this route. i add efi mpfi.

 

[Rob C]

In order to build a LA 360 to current HEMI 5.7 levels, what you really need to do is look before you leap into the project and understand why and how the HEMI makes the power it does.

First and foremost, the modern engine has certain advantages over the older LA. What the LA needs to have done to it is meet or match the advantages.

Carb of FI? This is your call since a really well tuned carb can certainly bring how most of the goods. Then there is the intake. I would simply just use a Edelbrock rpm here.

Here is the toughest part. Cylinder heads. Your going to need to meet the head flow of the HEMI engine. Get the best flowing cylinder head up top. Meet, at the least, the flow rate specs of the HEMI head.

Exhaust, same as above.
Camshaft. This can be tricky since the HEMI has a Hyd roller and if you don’t want that expense, choose carefully.

The one thing modern cars have the older ones do not have but could really use is there transmissions. This opens the door on many fronts. It also helps keep the camshaft small.

You can make a 400+ hp 360 with bolt on parts.

Zero deck flat top pistons such as the KB-107’s for an approximate 10-1 compression ratio, Edelbrock 750 carb, rpm intake & cylinder heads with headers and a (generic & lame) cam of 280/280 (@050 - 230/230) - .480 lift will make 400+ HP.

If you ported the 360 heads well, you can drop the duration and increase the lift to take advantage of the cylinder heads flow abilities and make the power.

For mileage concerns, you’ll need that OD transmission & proper gearing. This should be well thought out for the reason coming next. The one mention above which I actually have done and will say it helps a bunch for such moves for mileage is the Rhodes lifters. This helps lower the cams rpm range and save fuel by the lifters design. It’s design will shorten the duration of the cam making it smaller for not only fuel savings but more torque.

There is not a lot of OD options for us. The typical 4spd automatic is OK. For manual transmissions, I’m not entirely fond of the gear split. If your car is an automatic, your choices are limited unless you drop serious coin on something like the 8 spd TCI (IIRC) transmission. As far as a manual, a Tremac can be done in 5 or 6 gears.

Remember to do the math for your final drive ratio with the transmission you choose to use. For those that don’t know, that would be your gear ratio in the rear end multipled by the OD gear.

Example;

OD gear of .69 X the rear end gear of 3.91 = 2.6979 or rounded up to a 2.70 gear ratio. Match this to your intended tire size and check with an online calculator for the approximate rpm’s and speed at your cruising speed and rpm. Also make sure your cam isn’t to big for this final gear ratio, tire size and rpm it will carry on the Hwy.