Rod Slots???

[Ryan140]

Ive heard some mention to modifying rod slots and was wondering if one of you gurus could tell what is done to the rod slots, how it is done and what advantages and disadvantages there are to these mods.

[Rusrog]

You can dop quite a bit on the 2.5 litler motors to help the flow situation and there is room for improvement on 2.4's just not as much to be gained. Also you do not want to do too much as you can actually lose velocity if you go too far with them. On 2.4's what you need to do is know all the casting flash down around the slot and take off the edges closest to the bottom of the intake ports. Give the incoming charge a path to follow and direct it at the port. That will be your best bet. I have done this with good success but I do not have a pic to illustrate it. Sorry....

Russ Rogers
Ft Worth TX.

[Burke Kilgour]

Heres a good pic of a 2.4 rod slot.

[STV_Keith]

Just had the ones on my 2.4 BP done by Jim Ruck. Here's what it looked like:

[Rusrog]

That will make you some horsepower and help out with the torque.

Russ Rogers
Ft Worth TX.

[DaveR]

This a print I came across

[DaveR]

Sorry - I guess it's too bad a shape to read.

[Ryan140]

Does this mod help all parts of the power band or is it just a mod for high rpms?

[us1]

It does wonders for midrange power.

[T-REX]

Dave, I no what it said, and no who it cum from too!!!...I got one sumwhere...It wuz dun by an ugly PUSS;)

[DaveR]

And after I went to the trouble of blocking out the name in case it was a secret :D

[DaveR]

Rex, you what? HA. I think I got from you a couple years ago!!

[STVRacing]

i thought it would help if you stuff the crankcase more rather then take away metal and open it up.am i doing the wrong thing by milling the front half to put the reeds further in the block?

[Superdave]

By cutting the front half and moving the reeds closer you are, in effect, stuffing your block. The rod slots improve flow. Notice the "double" rod slots shown. The angle of the cut is constant with the rotational disturbance in the block and the reciprocating rod/piston combination.
DAVE

[Talon2.5]

good thread!! i'm glad this one finally came up in this fashion :cool:

hey rex is that a treasure map you drew? :D

[T-REX]

If U call HPa treasure, then it's sorta a treasure map!!!...But, I kan't take tha credit fer drawing it, I juss benifited from the ole GURU that did draw it!!...

[ShorePounder]

Looks like I'm addin another page to my 2.4 notebook. Thanks for the info

[CompKing]

Found this looking around in some old threads



Re: Rod Slot Porting - questions
From: Prof. OB
Rig:
Email:
Date: 05 Jun 2000
Time: 00:43:34
Remote Name: 216.79.207.165


Comments
WTrip, your inquiry concerning rod-slot porting is one of the most relative questions an performance enthusiast should be asking of his engine builder in regards to modifying his engine. If he doesn't have the right answers, move on. The three basic questions I understand you to be asking are: (1) why port or "Flare" on the intake side of the rod slot area (2) doesn't this intrusion into the block reduce primary crankcase compression and (3) Is this reduction in crankcase compression justified by the loss of the "negative" pumping loses as the piston makes its attempt to return to T.D.C. I will address each question in a paragraph form below.

I will answer questions #1 and #2 together - Any intrusion into the rod slot area by porting reduces crankcase compression which is bad, period. Therefore any such intrusion must be justified by an increase in charge flow sufficient enough to overcome the crankcase pressure loss. Any engine builder is always faced by this delimma. Is the cut he is fixing to make in the rod slot area, (or any other area for that matter) going to sufficiently increase flow to negate the loss of crankcase compression. I will say this, and many out there are going to disagree with me, but the only cut justified in the rod slot area is the one (1) made in one corner to better expose the behind-the-liner ports. Now I expect to take some flak about this statement, so fire away. The reason I say this is simple, the behind-the-liner ports in an engine are the only true "velocity" ports in the engine. The flaring into the rod slot area of any other three corners is not only nonproductive, but shows a lack of understanding of how the large transfer ports (the two largest ports adjacent to the exhaust port) really work. These transfer ports are "volume" ports, whose performance only truely comes on their own with the increase of RPM (and the accompaying increase in crankcase compression in PSI) at mid, upper-mid and top end RPM. Then and only then, is there enough pressure sufficient in the crankcase to truely load these ports to achieve proper charge velocity and volume to effectively utilize these ports. Any reduction in crankcase area only delays the RPM at which this will occurr, and invariably minimizes their effectiveness. These are "floor" fed ports (via pressure being exerted during the down stroke, and all the flaring in the world will not increase their effectiveness in a behind-the-liner engine. I will make exception, that being on 2.4 LTR motors that do not have behind-the-liner ports. Since these are "piston ported" motors, correct "flaring" will provide "direction" of the charge into the tranfer port area as it emerges from the crankcase area and better scavenge the charge out of the crankcase. This "directioning" on the 2.5 LTR engine is not worth the loss in crankcase compression and the reduction of charge velocity through the behind-the-liner ports and ultimately all the ports. One particular thing that makes this effective on a 2.4 LTR is, is that not only are the transfer ports larger on the 2.4, they are also deeper, so any attempt to augment flow is usually justified. The reduction of velocity through the finger and booster ports are a justifiable loss in an attempt to feed the two primary ports of the engine.

(2) The reduction of crankcase compression could never be justified by a reduced "pumping" loss. If you wish to reduce pumping losses do it at the expense of compression ratio and ignition lead timing. What we are after is maximum charge delivery into the combustion chamber, by about any means. Not to be ludicrous, but thats why we utilize turbos, and other superchargers. Charge delivery will always overcome any other attempt to increase horsepower, compression and timing are merely variables to "capitalize" on the available charge..................OB

[DaveR]

Yep, that ones in my file too. Excellent call for you to post it here. Gotta organize my stack of printouts one of these days!

[CompKing]

Does anyone have a number on how many cc of cranckcase volume are gained when you cut the rod slots?I know it depends on who and how they are done.Mine were done by Jim Ruck and look like the ones STV_Keith posted a pic of.

[CompKing]

Didn't get a reply on my question so I did some math and came up with a increase of 2.3 cc per cyl .I also figured that the .050 I milled off the front half reduced the volume by 4.2 cc.So I have 1.9 cc less crankcase volume than stock now.

I was wondering if any of you Guru's know what the total volume of a stock 2.4 is and what is the C/R in stock form?

[Ryan140]

Dave I like to read some of the archives from time to time. The other night I saw a post between us1 and trex and few others about a crankcase stuffer kit. I think they said it was made by Chuck Goodman. I have never seen it and I am not sure how it works. See if you can get the gurus to bite on this post.

[us1]

I have heard it has its problems such as needing to be remover to bore, hone or resleeve the cylinder. Also when one comes loose from a minor blowup it can destroy the whole motor.

[Cycix]

I noticed in the pictures that Burke Kilgour's slots differ from STV_Keith's even though the block appears to orientated the same. Can someone throw me some insight as to wich way they should sit, in relation to a port or how a side is in comparison to the other side. Also, what are you guys thoughts on milling the front half to compensate for the gain in case cc, good or bad? If good how much.

[Cycix]

Have you done the milling yet on your front half yet??

[us1]

They are both the same, pone is the port view and the other is the starboard.

[CompKing]

Yes I did,I cut off .050 and if it's a carb motor thats about all you can take or you start cutting into the bleed valve holes.

[Cycix]

Is there a very noticable difference, and did you do the milling in conjunction with the rod slots to compensate for the gained volume of the ported rod slots?

[CompKing]

I have no idea what the gain is.I've had people I trust on both sides of the fence on crankcase volume.I figued it wouldn't hurt with small rods and rods slots and didn't cost anything.

[us1]

There is a huge difference.