Which cylinders get the longer rods in a fathead hemi w/ roots blower on a 6" setback

Hi,

I have a question for all the guru's. Which Cylinders get the longer rods on the hemi with a roots blower on a 6" setback?

Is it possible to add some timing to those cylinders instead using the power grid? Like .5 degrees or something so all of the rods are the same length?

Thanks,
Trevor Sherwood

 

a roots blows the air forward so short rods in the front cylinders .. possibly the front 4 holes.. and don't mess with cylinder timing..

 

Or do it the proper way and move the blower back as far as possible. Brad sells a plate to move it even further back than what the manifold will do

 

How far back is far enough for a 14hhr over Big Dukes?

 

Hi Jay, We are already have a retro plate that is 6" back over the stock location, we could go 12" but then we get into snout supports and such and do not want to mess with that at this time.

Thanks,
Trev

 

timing

Hi Bruce, curious why setting the power grid to pull timing out of the hot cylinders is a bad idea.

Thanks,
Trev

 

Pulling timing makes blown engine run hotter. You would have to pull fuel of those cylinders as well, hince this is why efi is so awesome. Someone needs to get on this already. Petty told me that when they went from mechanical injection to efi they picked up 200 hp just in the switch over. The fine tuning was way more than they thought. My hogan manifold has a set back around 8 inches with a 2 inch offset pulley.

 

Two answer the question 1 & 3 have have around a .050 short rods even in some screw blown Hemi's with the opening in the rear. With chevys they usually just mill some off the dome. Mike Janis told me they take .030 off at with a belt sander at first and the .010 at a time till they get enough compression taken off.


Marty Creech

 

Temps

Hi Jay,

I was backwards on how I made the original posting, it should be shorter rods on the hotter cylinders so I would be pulling timing on those cylinders not adding.

I am under the impression that the point of installing the shorter rods was to de tune the hottest cylinders by effectively dropping compression to be more on line with the other cylinders, If I am wrong would someone please tell me what the purpose of the shorter rods is?

Assuming the de tuning of a cylinder was the goal then wouldn't retarding the timing on a cylinder fatten up that cylinder and accomplish the same thing as lowering the compression? Also with less timing the fatter mixture should run cooler I would think (assuming I don't lean out that cylinder more to compensate) the EGT's would probably show higher as with the retarded timing a little more fuel would be burning in the pipe instead of the chamber.

Again if I'm wrong please fill me in, I was trying to avoid having different length rods in the motor.

Thanks for the advice guys, I love these discussions and I love this website for this very reason. Over the years I have learned a lot on here.
Trev

 

You can change the timing and fuel all you want but the blower will still stuff the same amount of air into that cylinder, which is more than the other ones. Set back blowers do help, but you would still have to do an extensive amount of work inside the manifold to equalize the cylinders. Many time world champion in tafc ran 3 different size rods in his motor. That should tell you something.

 

Most legal blown promod engines have same rods and Pistons in each hole. Pay attention to set back and snout length. That will answer all your questions

 

You see a lot off pro mods with roots blowers moving them backwards but it's not possible with a srew?