Piston Noise...

[superstingray77]

So stroker #2 has what sounds like piston knock when cold. I know it cant be the bearings as all that is new, cranks new, polished, new rods, bearings etc. The noise is on all 6 cylinders so I am trying to decide if its just me not being used to the Solid Lifter Cam or if its the pistons slapping a little until they expand into the bores. They are the Racetec 505 .060 forgings with the 4340 Forged rods. Press fit pins. Once the engine warms up its solid strong and normal. Havent noticed it get any worse since the initial fire up which was about 2000 miles ago now. On my third oil change. Joe Gibbs Driven Break in oil, first 300, then swapped to the Brad Penn 1 for the last 2 changes. Oil is clean still looks new after 500 miles and has no metal in the filter (cut the last 2 open to look). I have the block honed to .0045 piston to wall clearance which was for the KB ICON 944's even though Zac @505 told me the Racetec's will be fine with that PW clearance I think it may be the culprit. Do I need to worry? Naturally i warm it up and dont hammer a cold motor..

[Cheromaniac]

Cold start piston slap is normal with forged pistons simply because they have a greater thermal expansion rate and need a bigger clearance from the bore. As you said, as long as you take it easy while the engine's cold it'll be fine.
Don't be surprised if the engine sounds like a diesel on first start-up when it's a very cold winter's day.

[superstingray77]

Funny you mentioned that it sound EXACTLY like a marine diesel. Thanks for the reply man I was worrying as I just sold my BMW 3 series over the weekend and need/want my Jeep to be reliable. She runs awesome but I expected a fully balanced engine to be smoother in the upper rpm range guessing I am used to the manual trans in BMW/Vette vs. the 42re whine box.
Just curious how large of an exhaust will a 4.7 making an honest 400hp require? I have a dynomax single 2.5" and it just feels like it needs to breathe more.

[superstingray77]

Oh yah, have the dual outlet header with that goes into the dual cat Y pipe (cats are hollowed out) 02 sensors are disabled in the PCM as i am tuned for open loop mode. That goes through the factory Y down to a 2.5" Dynomax cat back. (no 3rd cat either) I am going to install a 3rd cat because I do care about the air we breathe and cannot stand the stink of the non-catted motor. Should I redo all this as full 3" or dual 2.5 from the header back to a single 3"
Frankly I love the sound as is quiet on the road but you know its not stock at idle..cam is nasty

[SilverXJ]

What is the true piston to wall clearance? If it was .0045" for the KB's and you didn't hone or bore I doubt its the same for the Racetecs. I doubt a NA 4.7L is making 400hp.

[superstingray77]

Motor Specs...
CNC ported Head bowls,etc full race port not just a cleanup/match job.
LS valves 2.02/1.60
Lunati Solid Cam .515/.525 lift 226/237 @.050
Nitrided the cam
4340 Forged Rods
Racetec Pistons .060 w 20cc dish
Scat Forged stroker crank
ARP everything, head / intake
9.24:1 with the MLS head gasket
Banks Torque Tube header
#24 Motorsport disc 4 hole injectors- flow matched
Shaft mounted adjustable roller rockers.
Trick flow 3/8 pushrods
Peak power feels (no dyno yet) to hit around 6200-6300 range.
SCT custom tune, open loop only still tinkering with AFR to get it flattened out but 12.8-13.1 @WOT From 4k-6500
The 2k-4k range is still in the 12.2-12.4 range which I really think needs to be leaned out a bunch..

Honestly 400 hp I would also be shocked to see that kind of # out of a <300 inch non cross-flow headed engine. Considering all the technology in my 400hp LS2 Vette or the massive cubic inches in my 496 Stroker Stingray. However all these builders like 505 performance keep telling me I should see numbers between 375-400... i am skeptical, and if it felt like 400hp I wouldnt be thinking it needs larger exhaust rofl..

I built the engine to sound mean make decent power and ultimately be strong, the plan is to start fabbing up the single turbo/intercooler setup next. So coming off that Im curious if I can get away with the 2.5 system or if i need to spend the 1k on a custom 3" or larger. I really don't want to hear it while cruising the freeways only when on it the pedal hard or windows down idle.

[superstingray77]

PW clearance is .0048 which Zac at 505 said was optimal for the Racetecs.
It was .0022 with the IC 944 but after the catastrophic cam failure in that engine I had it loosened up with a hone to the .0048 per Zac's instruction. Also supposed to provide more clearance for the turbo use.

I also did file fit rings gapped for turbo use.

[SilverXJ]

Just to put that 400 hp claim into perspective, the current Ford Mustang GT 5.0L makes 420hp @ 6500 rpm. That is a modern engine with DOHC, 4 valves per cylinder, cross flow, V8, etc. With a turbo I can see a 4.7L making 400, but no way NA.

What alloy are the Racetec pistons made out of? That .0022" was definitely to tight on the KB944s.

[superstingray77]

Were on the same page, i agree with you.
I had a 4.6 32v with a T-Trim on it fully forged etc modmax valves/springs ports cleaned up all the normal crap... stuffed in a Lincoln Mark 8 back in the day. I laid down 640 on the boost @15psi.
That engine made 257.6 to the wheels N/A and was like 290 rated. The displacement is not the issue but the intake runners/head design etc. It will be interesting to see what this lays down on the rollers once i get the damned fuel curves right.

[superstingray77]

BTW nice work on that Airbox fab!!
Im still running the stock box on the WJ with a paper filter, I have the bored TB and port matched intake. Did you notice a difference with a conical filter?

[jsawduste]

2 comments

Most anything that comes out of 505 I am VERY skeptical of. Be it product or tech.

Have a date with a chassis dyno this week. My stroker is set up a bit more aggressive then most. Be interesting to see what the numbers are.

[SilverXJ]

BTW nice work on that Airbox fab!!
Im still running the stock box on the WJ with a paper filter, I have the bored TB and port matched intake. Did you notice a difference with a conical filter?

Thanx. Going with a conical filter was one if the first modifications I did. Back in 2001 or 2002 I went with Rusty's intake tube with a 6x9" K&N filter. It really improved the responsiveness of the 4.0L all over. The airbox setup wasn't that great on the later XJs. The air box's intake use to be through a hole in the header panel. At some point the removed the hole so the air box opened into a closed header panel. Maybe 1.5" away from the panel. Not the best design.

Most anything that comes out of 505 I am VERY skeptical of. Be it product or tech.

x2. I've spoken with a few people that have purchased products or had dealings with 505 and all but one were less than thrilled. I was considering one of their "roller" cams a while back, but pre sales tech info was pretty weak.

[Cheromaniac]

Just curious how large of an exhaust will a 4.7 making an honest 400hp require? I have a dynomax single 2.5" and it just feels like it needs to breathe more.

I can't see your engine making anywhere near 400hp naturally-aspirated. I'd say ~300hp NA and 400hp with forced induction. If you do add FI, I suggest you do a dual 2.5" exhaust. If NA, a 3" single system will suffice.

[superstingray77]

I am speaking of crankshaft power not rear wheel hp. I would be shocked with 300 to the wheels N/A rofl.
The turbo setup I am planning will be around 12psi max, just love the TQ curve of an FI setup.

I had the head reworked and flow tested at 291 cfm intake and 184 cfm exhaust @.500 lift. It was first done at 505 then David Kropp at the cylinder head shop here in Austin went back through it all for me because I too had some "experiences" with 505 and did not trust the work. David has since passed away he was awesome his shop is now closed, RIP David .
Head started life as a new casting from Alabama cyl head.

At times I wonder what a full on custom intake would do with perhaps E46 M3 style TB's... one per cylinder.

I need to find a dyno here in Austin to run this on once we get the AFR a little more flattened out just to see how it turned out. It is significantly more powerful then my 01 Limited 4.7 V8 WJ (non-HO), and that one has a 5 speed auto and only 2whl drive.
Not certain what the Chyrsler 4.7 v8 head flows but I know the stock 99 up Ford 4.6 2v heads flowed around 180 int/150 exh @.050 and with mild cams/TB we could pull 300hp+ out of it at the crank.

[superstingray77]

Short clip of engine idling...

http://www.youtube.com/watch?v=41GwpdqqGt0