Next month im going 306, crank question.

[Dbeck002]

My shop is very well experienced. They have a car that featured in one of the MMFF magazines (which i have seen in real life). Very well recognized.


Anyway they will be doing a full bottom end rebuild for me.

Wiseco forged slugs
Forged I beams
chromemoly rings etc...

Its a light street build except they want to use my stock crank resurfaced and chamfered etc... He said if i pay the extra 500 for a new crank, i can just make it a 331 stroker because the stroker cranks cost the same as the standard stroke cranks.

I told him i want the 306 because i want to boost, i need better cruising gas mileage which is why im going either turbo or vortech for low RPM efficiency. 331 gas mileage is poor.

So my question is should i go with the stock crank i have now and use that? It is seasoned and has been proven in my engine now that makes 302 rwhp and 331 rwtq.

What do you guys think?

 

[Rick 91GT]

If you want to stay 306 use the stock crank, however since you are swapping in decent rods and pistons go with the stroker. A 331 doesn't have to have poor mileage, it's all in the combo. Larger displacement is a good thing

Our blown 331 93 Cobra had over 26mpg on a 180mile trip, made 425/465 to the wheels at the time, stock Cobra wheels and tires 245/45/17 and a 3:55 gear.

 

[304billet]

do a 306 longrod, use a 5.4 length rod. great rod ratio and if u ever want to stroke it u won't have to change the rods.

I would just use ur stock crank.

why Wiseco, why not Ross, CP or JE, more recognized brands?

and why chromemoly rings? why not Sealed Power file fit ring set, plasma moly first, cast iron second, stainless steel third for a street car.

 

[Rick 91GT]

I'd also suggest a good plasma moly top ring set cast iron second....

 

[Dbeck002]

Rick I have AFR 165s, will that be ok for a street blown 331 on a stock block?






I am really worried about reliability and gas mileage guys, this is my daily driver and i really want it to perform for both economy and performance, yes that is do-able.

Our blown 331 93 Cobra had over 26mpg on a 180mile trip, made 425/465 to the wheels at the time, stock Cobra wheels and tires 245/45/17 and a 3:55 gear.

holy crap what is the recipe!!




Anyway thanks for all the suggestions guys, 304billet how much more will those pistons rings cost as opposed to the basic setup i had intended to be installed?

I dont want to break the bank.

 

[Dbeck002]

I forgot to add, im leaning towards the 306 with stock crank.


Those stock cranks are pretty strong as a matter of fact, im not worried about breaking it.

I will probably do the 306 and bolt a turbo on it run 6 psi and call it a day.

again, if i do 331 my shop suggests to keep it NA because of stock block issues.


P.S I will talk to them about the pistons and rings.

 

[Michael Yount]

Any boosted 5.0L based motor isn't going to exactly be a Honda when it comes to fuel economy.

As Rick said - they can be set up to get relatively good fuel mileage -- 26 on the highway is better than some stock cars get. The challenge of course is around town mileage -- which is mainly a function of keeping your foot out of it.

Also -- if all the high-buck internal pieces are going in a stock block be careful -- power levels can rise easily in a boosted 331 to where the stock block itself can crack/break. It happens all the time. The block is the weak link -- you may not need to spend $$ on some of the internal parts when the stock pieces are already stronger than the block they're going in.

By the way, if bottom end is what you're looking for -- you may want to consider the K-B positive displacement blowers -- they'll be more bottom end friendly than a centrifugal (Vortech) will be. The turbo can be set up for bottom end or top end depending on how the unit is sized.

Fuel mileage/drivability will also depend heavily on tune - so budget for some quality time spent by someone who knows what they're doing tuning the car.

 

[Dbeck002]

Any boosted 5.0L based motor isn't going to exactly be a Honda when it comes to fuel economy.

As Rick said - they can be set up to get relatively good fuel mileage -- 26 on the highway is better than some stock cars get. The challenge of course is around town mileage -- which is mainly a function of keeping your foot out of it.

Also -- if all the high-buck internal pieces are going in a stock block be careful -- power levels can rise easily in a boosted 331 to where the stock block itself can crack/break. It happens all the time. The block is the weak link -- you may not need to spend $$ on some of the internal parts when the stock pieces are already stronger than the block they're going in.

By the way, if bottom end is what you're looking for -- you may want to consider the K-B positive displacement blowers -- they'll be more bottom end friendly than a centrifugal (Vortech) will be. The turbo can be set up for bottom end or top end depending on how the unit is sized.

Fuel mileage/drivability will also depend heavily on tune - so budget for some quality time spent by someone who knows what they're doing tuning the car.

thanks for the response michael.


But i actually do not want a KB because they boost at such a low RPM and i want to stay out of boost when cruising. Which is why i opted for the centri or turbo.

I just think a turbo'd 306 with 3.27 gears would get awesome gas mileage when cruising and will be plenty fast on the street.

I will use a stock block but i am aware of the maximum power capacity of the block. I dont intend on making more than 425 rwhp anyway.

I will be using forged I-beam rods.
undecided pistons and undecided rings
stock crank
bored out to 306
AFR165s (i have these on my motor now)
holley manifold
custom turbo cam

goal is 425 rwhp

 

[Michael Yount]

Dbeck - you're behind the times -- they make bypasses that sense vacuum level and allow the blower to not make boost to reduce parasitic losses at low rpm. You forget that nearly every production car made with a blower uses positive displacement blowers -- and they're trying to meet CAFE fuel economy numbers. I believe with the proper selection of parts and tune the positive displacement unit will be MORE fuel efficient at lower rpm than a centrifugal -- that's why I suggested it.