Engine block and performance upgrades questions

[Sevik]

1. Are engine blocks all the same through 84-01? My MJ got half of the mileage, so I wanted to use that block with 99 XJ perks. 

 

2. Will M90 supercharger be able to give any decent boost with 4.7 stroker kit? Boosted tech. claims 7 psi boost with the smallest pulley, but that's for 4.0. If not:

 

3. Which upgrade will be better for low-mid range torque? Stroker or supercharger kit? 

 

Thanks! 

 

 

[edit: Just saw Alexia has a stroker and a SC on her truck, hope she will give some feedback]

[Megadan]

1: Yes and No.  Renix era blocks have a provision for a knock sensor, HO models do not, otherwise they are pretty much interchangeable.

2. The M90 is actually sized out to about a 4.0L engine at max.  They will work fine for low boost, but can't flow enough air in relation to the engine to create higher boost levels, unlike a turbo, a roots blower creates boost pressure based off of resistance to the airflow it displaces at a given rotor speed relative to the engines VE at the coinciding engine RPM.

3.  General rule of thumb says the supercharger, but there are a lot of factors to account for.
 

[ftpiercecracker1]

Later model (HO) 4.0s have extra ribbing cast into the blocks. Makes them stiffer.

 

Older renix blocks, supposedly, have a higher zinc or nickel content can't remember which. Makes them more resilient to wear.

 

 

 

And if you really want to go full tilt, look up the new edlebrock 4.0 cylinder head.

 

 

 

P.S. I'm pretty sure Alexia is a dude ;)

[cruiser54]

1: Yes and No.  Renix era blocks have a provision for a knock sensor, HO models do not, otherwise they are pretty much interchangeable.

 

2. The M90 is actually sized out to about a 4.0L engine at max.  They will work fine for low boost, but can't flow enough air in relation to the engine to create higher boost levels, unlike a turbo, a roots blower creates boost pressure based off of resistance to the airflow it displaces at a given rotor speed relative to the engines VE at the coinciding engine RPM.

 

3.  General rule of thumb says the supercharger, but there are a lot of factors to account for.

 

I've seen HO blocks up to 96 with the threaded hole for the knock sensor. 

[Megadan]

 

1: Yes and No.  Renix era blocks have a provision for a knock sensor, HO models do not, otherwise they are pretty much interchangeable.

 

2. The M90 is actually sized out to about a 4.0L engine at max.  They will work fine for low boost, but can't flow enough air in relation to the engine to create higher boost levels, unlike a turbo, a roots blower creates boost pressure based off of resistance to the airflow it displaces at a given rotor speed relative to the engines VE at the coinciding engine RPM.

 

3.  General rule of thumb says the supercharger, but there are a lot of factors to account for.

 

I've seen HO blocks up to 96 with the threaded hole for the knock sensor. 

 

Did not know that one. Gives me a wider year range to look for.

[Sevik]

can this hole be plugged with just a bolt? I assume chrysler ECU doesnt have any need for this sensor

[Eagle]

can this hole be plugged with just a bolt? I assume chrysler ECU doesnt have any need for this sensor

 

It's not a "hole," it's a threaded boss -- a blind hole. The Chrysler ECU doesn't use a knock sensor, but there's not need to plug to hole.

[HOrnbrod]

 

can this hole be plugged with just a bolt? I assume chrysler ECU doesnt have any need for this sensor

 

It's not a "hole," it's a threaded boss -- a blind hole. The Chrysler ECU doesn't use a knock sensor, but there's not need to plug to hole.

 

 

Eagle, these knock sensors can be located basically anywhere on the engine in any threaded hole (1/4 or 3/8 NPT I assume?) since it's just a listening device connected to the Renix ECU?

[Megadan]

The placement of knock sensors is a somewhat sensitive thing.  OE's spend quite a bit of time finding a position in the block that sees the least amount of background noise (engine running sounds) but still in a good enough location near the cylinders to detect pin.  Not sure how critical this is on an older system like the Renix units, but on a lot of modern cars that knock sensor location gets a lot of thought, and the sensors and ECU themselves get calibrated and tuned to the noise they are supposed to hear.  Moving the sensor location can increase or alter the background noise it is supposed to ignore to a level that may trigger the ECU to pull timing.  I ran into this issue with a previous Isuzu when I moved the knock sensor up the block closer to the head. The valvetrain is noisy from the factory , and it was causing it to pull timing and run poorly.

[Sevik]

 

can this hole be plugged with just a bolt? I assume chrysler ECU doesnt have any need for this sensor

 

It's not a "hole," it's a threaded boss -- a blind hole. The Chrysler ECU doesn't use a knock sensor, but there's not need to plug to hole.

 

Thank you! Makes my life a tiny bit easier :) 

[Sevik]

So I'd start to save money on a ported Edelbrock head and SC kit, rather than on a stroker kit. Looks cooler anyway, SC can be actually seen in the engine bay.

[cruiser54]

I'm not sure those knock sensors are so sensitive Impulse. 

 

Many cars use the same one. Even on my supercharged Miata they just had you use the hole for a motor mount bracket. It worked fine. 

[Megadan]

It's not really the sensor, but the ECU.  They have a "range" that they are set to ignore.  Like I said, older vehicles probably aren't as sensitive as most modern ones, so it may not make much difference.  Just stating it as something to keep in mind.

[DirtyComanche]

As I understand it, the later blocks still have the boss for the knock sensor, you just need to drill and tap it.  Not that it really matters in this case.