So I snapped a timing belt and messed up a few pistons on my track car. I have done my reading on CR and e85 but figured I would post up what I plan to do for the Evom critics incase I might have over looked something. I'm stating with the stock crank and will be having it lightened and balanced as well as cleaned up if it needs any deburring etc. I'll be using Manley H-beam rods which IMO should be plenty as the largest turbo I would run would be a RED. For the pistons I haven't decided exactly what to use but would like about 9.5:1 CR. My thought process behind this is that a stock varient turbo tends to blow a lot of hot air at higher psi soon going up in compression I'll be gaining some response while not needing to push the turbo to make the power yet letting the turbo still live in it's efficiency range. I'll be running the kelford 272's with supertech singles and Ti retainers and will be running the CBRD upgraded turbo(both compressor and turbine hopefully). The goal is to keep the car completely reliable and easy to drive. From what I have seen this should be a solid setup without braking the bank. So... What's your guys take?

 

bump... Anyone?

 

That sounds interesting Steve, and may not be a bad idea. I'm not the most knowledgeable about technical details on the CR, except that by going up will limit
1) the amount of boost you can run and
2) the kind of fuel you can run

If it were me, I'd keep the CR relatively low, and add more boost, and keep more flexibility in my build. You can change turbos and fuel relatively easily to your heart's content, but a bottom end is something I wouldn't want to have to do again, or work around with the other two.
Granted, E85 tends to keep your EGTs relatively low, but higher CR is generally more prone to detonation, and if you are road racing on a hot day, you'll want to combat this as much as possible. I understand your motivation for not wanting to blow hot air, but that's what an efficient FMIC and E85 are for

I'm interested to hear what more informed people have to say on the subject.

 

I agree with hokiruu. For someone not trying to build the highest HP car and wants to build a track car that will last, I'd go high boost low CR. Much easier to change boost levels if necessary with different turbos and other parts than it is to change the CR. Obviously if you change other parts and have a higher CR you pick them based on that or tune accordingly, but why limit yourself.

 

In my mind at least I would assume that a higher CR while lowering the boost would generate less heat. I would think that pushing in cool efficient air would be more important then the CR seeming that that's what controls how dense the charge will be. Sure e85 will help but e85 can't really cool the air. With e85 being $3.40 a gallon and garbage 91oct being $4.00 I really don't see a need to keep it overly flexible. The car rarely gets driven on the street and the only thing I would run other then e85 would be 104 or higher if I was forced to for the class or possibly if I run an event and it's not possible to bring that much e85 with me. In either case it seems like the better route.... At least in my mind. Hopefully others can chime in though.

 

Why are you so concerned with heat? A good IC and it really is a non-issue for the most part. With a higher CR it isn't so much the heat but the stress on the engine itself.

 

that's not true at all IMO. On the track heat is usually the biggest issue. Plus with a small turbo it's fairly easy to get outside of it's efficiency range. For instance, I had a friend do some testing for me and we were able to hold 27-28psi till 8000rpm with a stockish turbo on a 10.5 hotside. But, when the the tune was finished we ended up making over 20whp with 24psi and more timing because the turbo was just not efficient enough to keep up and was just blowing hot air. That was in decent weather in front of fans and with time between runs. Imagine if that was on the track, in traffic at 105deg for 20-30mins. There really isn't a ic that can keep up in those conditions. Sure it can help a lot but if your just blowing hot air through it all the time itwould have just been better running less boost and more timing. So by uppi g the compression a bit I take that factor out. As for wear unless there's detonation there really shouldn't be a real big difference since there's not much more sustained cyl pressure since you run less boost.

 

There are guys having great results running higher compression motors on E85 making mid 120mph traps on the stock turbo..Go for it!!

 

yeah ill for sure be doing a little higher compression I just don't exactly know how much more...?

 

The problem is I don't think there are a ton of guys running E85 on the track. Not a lot of experience there. I would think you'd be ok with a slightly higher compression ratio with the cooler burning e85, but that's only my totally uneducated opinion on things.

 

If you wait about two weeks, your build will be done, only in my car.

Mine is going to be around 9.5/9.7:1 because I had the machine shop take a
little more than normal off the deck surface of the block.

Basically, a quick rundown, going to be run 100% on E85:

9.5:1 CP Pistons
Eagle Rods
No Rear Balance Shaft
Front Balance Shaft Counterweights Machined Off.
Fully Knife Edged Crank (Lost 6.28 lbs.)
Fidanza Lightened Segmented Flywheel
ACT 6-Puck Unsprung Center Disc

And a TON more stuff to keep heat out of the "engine assembly"

I took a TON of steps to try and get the coldest AIT's into the manifold
as possible. It was a VERY particular build...

If you want to chat, feel free to PM me. Soon I am going to post a big
build thread with a ton of pictures.

Erik@MIL.SPEC - That's not a totally uneducated opinion. I am doing it because one of the reasons you listed.

 

I am definitely interested in the 9.5:1 builds. That is the CR i have been investigating to go to.

 

nice tkklemann. Look forward to seeing how it all turns out. What ecu are you running?also if you have any pics of your crank I would be real interested in checking it out.

 

For realibility I'd recommend a conservative CR combined with a bigger, more efficient turbo.

On track your temps go up bigtime, meaning that knock could become an issue if you're running alot of boost with a high compression ratio on a stock or upgraded turbo. I'd guess that E85 or race fuel would extend your knock threshhold significantly but why risk it?

No shame in giving up a few hp for reliability IMHO.


BTW sounds like a very nice set of parts you're aiming for there.

 

yeah I'm thinking 9.5:1 is a fairly decent compromise. I spoke with JE and they said they could make me some 9.5:1 pistons with no over bore for $170ea. Which $700+ seems a bit rough. Anyone have any suggestions on what my other options might be for what I want?