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Discussion Starter #1
So I killed the 2.5l Mumm Bros Motor finally. After years of 8,200 rpm revving and hours and hours of full throttle pulling, it hung a valve and tore itself up.

Now, I finally get to put together the spare motor I have had sitting in the corner of the shop for about 8 years. Don't worry, the rotating assembly and bits and pieces of the Mumm Bros motor will be reborn as a high revving, high compression, big cam 3.0L, but that's for next year.

The cool thing about the Mirko motor is that it actually made substantially more power than the Mumm Bros motor. There is a ton more porting done to it, it has very different cam specs, the combustion chambers have had more work done to them and the pistons are the wackiest pistons I have ever seen. Great big squared off domes with sharp edges on the piston everywhere. I have never seen pistons like this before. Also, the Mumm Bros. motor made peak power at 7,250 rpm (265 hp), the Mirko motor makes peak power at over 700 rpm more and the HP number starts with a 3.

I am going to make some changes to the Mirko motor. First, I am changing the stock springs over to some Supertech Beehive springs with a little more compressed pressures, changing the headers over to the stepped Kinetic headers I have on the car right now and using all of the intakes and everything I presently have. I am also going to use a programmable ecu from SDS and a different coil and plug wire setup. Its going to be a very different engine. I will also be using my 5 lb flywheel and 7 lb clutch assembly, paired with the Quaife dogbox. It should be a blast to drive. I am hoping for a couple of seconds a lap at CTMP.

Now some cool shots of the pistons.

Eric
 

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Welcome back! Can't wait to read about the progress on the new motor! :thumbsup: HP number starts with a three, huh? Niiiiccceeee!
 

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Discussion Starter #4
wtf pistons :confused: what compression are those?
I totally hear you. I have never seen pistons like those before in my life. Big squared off domes, 2 bath tubs on each side. Piston crown, fully machined. I had no idea.

After talking to the guys at Nautilus last week, I may have gotten an idea as to what Mirko was thinking. The guys at Nautilus brought up a very good point. It seems that one of the major issues with these motors is rod bearing weakness. They think that it is critical to get the flame front centered over the piston to reduce side thrust on the piton/rod and thereby the rod bearing. The cylinder heads have the casting teardrop thingy, machined away so that there is nothing to stop an even flame front from going right across the piston and filling the chamber. Also, the bathtubs may hold the pressure closer to the center of the piston top as well. All of this was theorized to promote better thrust vectors and focus the energy release over the center of the piston and reduce sideways thrust waste. Improves the life of the pistons and bores, keeps the rod thrust centered over the bearings and maybe reduces piston friction.

I don't know, but Mirko had a reputation for doing things differently and this is an example. And the compression is 11.8:1.

Eric
 

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I don't think that design is a good one. Flame front skips over the piston regardless of the design, all sharp edges and recessed areas do is allow fuel to puddle and can cause pre-ignition problems. Seems like they were in a hurry and didn't finish them properly. It is possible they were trying to get lower compression from machining the tops also. Just a weird design. Look on line at piston tops, none look this way.
 

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I don't think that design is a good one. Flame front skips over the piston regardless of the design, all sharp edges and recessed areas do is allow fuel to puddle and can cause pre-ignition problems. Seems like they were in a hurry and didn't finish them properly. It is possible they were trying to get lower compression from machining the tops also. Just a weird design. Look on line at piston tops, none look this way.
Not that i am going to argue with design, but they make them like that. Not uncommon

https://www.google.com/search?q=high+compression+pistons&num=40&source=lnms&tbm=isch&sa=X&ved=0ahUKEwifquelycbWAhWCsFQKHfwADiEQ_AUICygC&biw=1920&bih=949#imgrc=I4DTE85GHbsibM:
 

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Discussion Starter #8
Actually, I completely agree with your assessment. They are the oddest pistons I have ever seen. The headers were strange as well with all kinds of anti reversion cones, big pipe steps and conical merge collectors. Mirko had some different ideas. The one thing is that the motor made some massive jam compared to the more traditional Kinetic Race engine. Almost 20 hp more with the same compression and rules.

I was cleaning up and found this. I thought you guys might like to see a clue as to why I need to build up this motor.

Eric
 

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Discussion Starter #9
Update....

I have taken the heads from the Mirko motor in for a checkover and maybe a slight decking to true everything up. They are also going to look at the valve sealing and clean that up as well. Two concerns with the heads. First, the cam towers on the exhaust cam for the front head have some metal transfer and grooving. I hope the rebuilder can do some magic to build up the metal and line hone it smooth again. The heads have had the combustion chamber smoothed out to allow for the huge domes on the pistons. If the heads can't be resuscitated then I will need to build up a new pair, which I don't want to do as they have some funky porting done to them. The second issue is that the cam that was in those towers also has grooves on it from running out of oil. I need to take the cam in to see if it can be saved. The local cam grinder said that they should be able to build up the metal with welding and then machine it back down. It may be cheaper for them to grind me a new match from another cam. I will need to hear back from them as to what they want to do.

Big issue in that I don't think I can swap the cams from the Mumm Bros. motor into this motor as the domes are entirely different and there may not be enough room for the valves. Issues, issues... Finally, some good news. In cleaning up my other shop, I found a complete set of beehive springs. These are the uprated custom ones used in the Mumm Bros motor. This is very exciting as that could save me almost $400 if they are still good. I am going to get them checked to see if they still measure out to correct spring load. All I have to do is get new retainers. This will be interesting as the retainers from the Mumm Bros. Motor are still good, but I am missing one...grrrr. Might only need to order a single retainer. Anyone know how to determine if a metal is aluminum or titanium?

Eric
 

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Discussion Starter #10
I checked using the remains of the broken retainer and it looks like it is aluminum. I believe that it should be okay depending on the spring rates, but I am going to go a bit beefier for the rebuild. Right now I am looking at tool steel or titanium retainers. I am also having all the springs checked for fatigue so that I don't have to worry about possible failures again with both of the new motors. The hard part is that I am working sorta blind on this as the motor was built by Kinetics Race Engines and they aren't giving me any information...

Eric
 

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you slide someone a 50 and youll get all the information you need... lol
 

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Anyone know how to determine if a metal is aluminum or titanium?
Non destructively,? piece goes on scale, weight is noted. piece goes in water-filled beaker, volume is noted. weight is divided by volume, specific weight of alum vs Titanium gets looked up, beer gets uncapped.

Matweb says 7075 T6 aluminum is 2.81 g/cc, aka 2.81 grams per mililiter, or 0.102 lb/in³.
I don't know what allow titanium retainers would be made of, but matweb also says pure titanium is around 4.50 g/cc or 0.163 lb/in³ . should be a large enough difference to tell accurately without using an insane-high dollar scale.

Also, readings your posts? nevermind college. I need to start sweeping your floors and cleaning up your race shops. Great stuff!

EDIT : late to the party with that idea. my bad.
 

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Discussion Starter #13
Some updated information. I have checked around and the original retainers are aluminum. They should be fine with the relatively low spring rates the car runs. The big issue is their longevity and I am going to look at replacing them with tool steel retainers or even Titanium ones. The car has to be able to rev hard to 8,200 rpm and make power at that level without valve float. The Mirko motor runs different cam timing as well as a stand alone ecu setup from SDS. As well, it runs 3 LS coils to spark things and a very interesting circuit board. I have a couple of companies that could possibly get some new ones from Supertech, but I may just order a complete new BeeHive spring and retainer setup from Supertech.

I will be going to PRI in December and I will be speaking with a number of valve spring and retainer companies while I am down there. My goal is to get as close to 300 flywheel horsepower as possible in an N/A 2.5l motor. After I build this one to start the year with (and after I have the 13b Rotary rebuilt for my RX7), then I will start the race 3.0L and go for 350 HP.

I want both little pigs to be ready to rock and roll again.

Eric
 

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Discussion Starter #15
can the standard roller rockers withstand 8.200 revs
Yep. The Mumm Bros. race motor and the Mirko Race Motor, both were using stock rockers and lifters. The only things non-stock were the valve springs, cams and retainers. The SVT motors were running to 7,000 with all stock stuff, so 8,200 rpm is usually fine. I can tell you that over 9,000 rpm, the springs allow the valves to float and they do contact the piston and cause all kinds of fun stuff to happen.

Eric
 

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So I may be able to run a little higher than the 7.600 I have limit set . Forged 3 l st220 engine with k1 rods and cp pistons and running svt cams . Lot of porting of heads and manifolds with 70mm mustang tb . Hp still climbing at 7.600 . Have been told the st220 heads run a stronger valve spring also
 

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Hi,
i'm currently also building a 8k+ 3.0l ST220 engine. But that really needs a lot of work with balancing and optimizing stuff to get higher rpm's on long term.

What i have done:
  • grinded and optimized Jaguar oil pump (no edges, flow optimized and widen where possible)
  • Modified crank (oil hole chamfering), highly balanced
  • Professionally laser-measured and grinded ST220 heads
  • high-temp bronze valve guides
  • High-RPM Beehive springs with Titanium caps
  • Professionally balanced and lightened H-Beam rods made by K1
  • Custom pistons by Diamond Pistons, all balanced to +-/0.1 grams
  • Balanced complete crank trunk with clutch and light flywheel
  • Tri-metal Clevite TR77 bearings (main & rods)
  • Noble specification "hot" cams to enable high-rpm power
  • ....and many more
I have made some gallery if you're interested here.

... and running svt cams
Are you running SVT cams on oval port engine or do you have hybrid 3L?
 

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Discussion Starter #19
Okay, a quick update and some questions. I took the heads from the Mirko Motor and the Heads from the Mumm Bros Motor over to my rebuilder. I feel really dumb in that I never noticed the difference in the combustion chamber shape between the 2 motors. The Mumm motor had an open and round chamber that totally works with the piston used in that motor. The Mirko motor had a ver closed chmber with a squared off chamber at one end. This explains the very odd piston shape as it is designed to fit the chamber. Both sets of heads are saveable and getting done right now. The question I have is what car/ year does the closed chamber head come from and what car/ year does the open chamber head come from? I need to purchase head gaskets and I need to know what ones to get? I just don't know enough about these motors yet to guess.

Any help would be appreciated.

Eric
 

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the only thing i heard of is different oil passages between the years. not sure if different chambers ever effected the head gasket design. only thing i have is a few pictures of an 04 3.0 head if that helps
 
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