I'm getting close to putting together my stroker engine. Just going with a simple 383 topped with Ai's 200cc heads along with their 232/242 108 cam. Lift is 0.615 on this cam. I already have a Scat forged crank. I'm looking at rods and pistons now and just wanted some input from those that have more experience with this in case I've overlooked something or am missing anything. The car is just a street car. I won't be drag racing it. I'll have fun with it from time to time of course and may even autocross it or due an HPDE event. Point being, I'm not trying to set the world on fire with my combination. I just want a solid reliable build.

Since I need rods and pistons and am an engineer, I've tried to put some thought into my choices. Or, I'm just over thinking this which is typical of engineers.

I'm looking at Mahle forged pistons for a stroker running 6in rods. They have been recommended to me as being a quality piston with good sealing and low friction. They are listed as being 406g too which is lighter than the 5.7in rod pistons from Mahle.

For rods, I'm torn between H or I beam. Scat's procomp I beam rods are 605g, $300, and rated for the power I expect to make. Scat also has H beam QLS rods that are 569g but $550 for the set. I'm not trying to be cheap with my build but my understanding is H beam rods can be more difficult to fit the block and clear the cam. Is this correct? Are they worth it?

Eagle also has H beam rods but they are much heavier than the QLS Scat rods and only a little cheaper. Are Eagle rods that much better than Scat's?

All the rods I'm looking at are 6in and forged. I see no reason to go with 5.7in rods due to cost and the components being heavier. I realize I might not being going with the lightest components out there but I figure I might as well try to put some thought into my selections.

Opinions? Suggestions? Anything you think is relevant is welcome.

Not sure if it matters but the block has had steel 4 bolt straight caps installed with ARP studs. I intend or hope to run the stock windage tray and oil pan.

Thanks

 

From what I've read, you're facing a compromise situation with rod length. Obviously longer rods give you a lower angular momentum but long rods put the piston pin well up into the ring pack. I believe the best choice is right around 5.85". Rieciprocating mass is important but the pistons have more influence than the rods...

 

OP

Forged Mahle pistons and Scat I or H beam 6" rods are good. I have Scat forged crank & rods and SRP pistons.

on stock pan & windage tray just use 1/8" washers between tray and nut to hold up the tray higher, no problem. Use the 3 stock extended studs or Miloden makes longer ones

Your stock pan should also clear but first put on with no gasket while motor is on stand and have someone turn engine over as you hold your ear to pan. You "may" hear a slight scrape from #2 rod bolt. It would leave a witness mark (scrape) on pan if there is contact. There was on mine and I just used a folded towel to place pan on and used the large end of a wood base ball bat to push out from inside. It took very little effort. Likely did not need to as the pan gasket adds about 1/8" between block & pan

 

Thanks for the information. One thing I did screw up is the crank I have is listed as being for 5.7 rods. I've been told it will work with 6.0 rods. I've emailed Scat to verified. I just wasn't sure if you or anyone else knows, too.

Do you happen to know what the power rating is on the Scat I beams? I know the H beams can handle the 500hp the engine should make. I just can't find a listing for rated power on the I beams. That was one of my concerns with using I beams in general.

 

IDK, but have the I bean 6". I only make 400 to the wheels so that is around 475 at the crank

 

Thank you!

 

Good Morning TA. Your putting some serious thought into this combo which I enjoy. Let me see if I can give you something to add to your considerations.

1. Weights
The weights of your rods and pistons are going to be more of a factor on the bob weight of the crank your using. Obviously if your piston/rod weight is lighter that your bob weight of the crank its not a big deal, the crank can be lightened to solve that. Lighter is always a bit nicer but cutting a crank down adds labor which adds up in costs. If your piston and rod weight is heavier, you may be forced with adding Mallory metal to the crank to make the bob weight heavier which is very common and honestly on a street car, its never going to become an issue. Top fuel where every run is money....diff story. If I have a choice I just try to get the two close to save some work on the balencing machine.

2. Rods
I-beam vs H-beam.....that has been a debate between manufacturer's for many years. typically in the past I-beams have always been more money and rated at a higher HP rating. I read a cross sectional analysis on the matter a while back comparing the typical I-beam and H-beam cross sections and metal strength. What was determined was that the cross sectional area was comparable but the metal strength of the I beam was about 40% higher. Now that would explain why I-beams are typically a lot more money, the material and production costs go up. So why are you finding I-beams cheaper now.... that is why I refuse to try one. In this industry reputation is starting to be used for capital gains. Example: Since the auto industry has a high regard for I-beam rods....I (Manufacturer of choice) will use cheaper labor and materials, make em a bit weaker but they will sell anyway and I will make a bunch of cash. Look at the roller rocker industry with manufacturers like ProComp or CAT....horrible failures across the board. A manufacturer that doesn't advertise an HP rating is something I would be weary of. On a budget build I typically use Eagle. Cost and quality, they do what they say. Eagle now has a microfinishing process now that leave the rod looking almost chrome. The surface is very slick to the touch and the manufacturer will provide you with a 1 year warranty from the date of purchase. Eagle rods have two different HP levels on many of their rods and the difference is the hardware used in the rod bolts. There are many other Rod manufactures that produce a quality rod with HP claims for similar budget.

3. Rod ratio with longer rod (without going into piston Dwell time at TDC)
With the 383 stroke of 3.75 the 5.7 rod is going to net you a rod ratio of 1.52. The 6.0 rod is going to net 1.60. Stock 350 is 1.64. General rule of thumb is that you want a rod ratio of 1.5~1.55 or better to minimize frictional losses and wear on the cylinder walls and piston. Higher the RPM the worse the damage will be and at some point you can actually feel it in the form of a weird vibration (extreme cases obviously). As mentioned above the compression height on the 6.0 rod pistons is going to be 1.140 which puts the wrist pin into the oil ring lands. Not a huge deal but it means a trade off. In my opinion at a .08 better rod ratio, your dealing with a partially exposed oil ring (which typically means a secondary support ring is also installed), the trade off is not worth it, your not honestly gaining much.

With all things considered, i don't think your gaining anything going to a 6.0 rod on a street car. At the same time either setup is going to work fine. Now one more thing I want to add, if your going to spend a lot of time in the upper RPM's (5500+) then I would go with the 6.0 Rod, if it reduces a tiny bit of wear, its good.

If you look at race team engineers today compared to yesterday, they care very little about rod ratio and they are turning 10000 rpm's at the blink of an eye.

Hope this helps just a bit.

Terry

 

Thanks for the detailed response, Terry. I appreciate it.

 

Heard back from SCAT. I gave them there expected power of the engine. They recommended their 6 inch I beam rods with 7/16" bolts. The rods will work with the crank, too.