Well with the snow coming down outside, it seemed like a good time to write some tech articles. The aluminum rod thread has started what I think will be something of series with pix prior to the build, pix of the build, dyno results, and real world results. This is the next in the "series" that I wanted to do, and that is piston tech.

Obviously alot depends on the fuel being used and overall usage of the engine. Stock compression is 8.8:1 and looks like this:



They work well on pumpgas, racegas, E85, and any other combination you want to throw at them up to a point. On pumpgas the compression is high enough that 30 is typically pushing the envelope of what is possible without being knock prone.

Next up is an aftermarket lower compression piston. This particular one is 8.3:1 and on pumpgas (if that was all you really ever wanted to run) would allow for either more boost or more timing vs the stock 8.8 compression (stock or aftermarket). Pictured here:



As you can see there is significantly more dish than the 8.8:1 stocker.

Here is an aftermarket 9:1 piston and probably the most common compression ratio that is used when building a fresh motor:



There is still some dish, but far less than the 8.8 and the shape of the dish is also more pronounced vs the fairly open top of the stock piston. I had a set of 10:1 pistons that we use in our racecar as well as our E85 builds but unfortunately they got sent to the machine shop before I got a chance to get a picture. When they return I will update them. The 10:1 is a flat top piston with no dish, valve reliefs big enough to allow for our normal cam selection without worries of interference.

The 10:1 e85 combo results in significant increases in spool and these were the ones we used when in Lucas' motor that made 506whp. I would think that the normal domestic rule of 4% per full point of compression at a set level still applies. Everything I have read in doing research would seem to back this up, and I am sure that ones like Marco, David, Martin, Ted B, etc. have input in this category as well. In Paul's car even though it is "gas" we used 10:1 to help with the 4508 and 4202 spool and make maximum power. In my personal build that I have recently started I will be running 10:1 on a MaxRod 2.2 (4G64 with 94mm stroke and 162mm rods) and a ETS 4088 on E85. I will be offering what I have learned from that one in this thread as well.

This brings me to our last piston of this initial post. Having spent significant time with E85/E98 and knowing what it is capable of (how about 47psi from a 4202?), it became necessary to try upping the compression a little more than we had in the past. How about an 11:1?



and here is one of the piston hung on the 150mm alloy rod we use:



Methanol cars have run 11:1 and even higher for years with insane levels of boost, and while Ethanol isnt quite as awesome it does have similar properties that we can exploit to find the limits of power on any given combination. We will be testing these 11:1s in 2 cars in the near future and then in one of our racecars as well. Lucas' is going to use them in his stock turbo car and one of our DSM customers in his 3065 car. The DSM has already ran 10.09@142 so with a fresh build and 2 full points more compression do we have a 9?

What is the general consensus among both the professional builders and the DIYers about what you like to run? I am hoping we can get a good tech thread going to see how far we can push the platform.

Aaron

 

Very nice write up Aaron!

 

Agreed. Very nice thread here once again John

I wish this was around back when i built my shortblock as i would have tried out the alum rods, maybe go 2.3, and probably 9-10:1 on my motor seeing how the ethanol is working out well for you guys.

I'm very interested to see and glad that you guys are puching the envelope running 11:1 on the ethanol.

 

Seriously, why is your name Aaron, yet your screen name is JohnBradley? That deserves a tech thread of its own....

How do these higher compression setups run on the street, for day-to-day use? Is fuel efficiency greatly improved? Are these run on strictly AEM cars or has anyone run say a 10:1 on the oem ECU? I think pushing the envelope like this is awesome, 10:1 seems like enough of a push for me, but I am always Mr. Conservative and like to stick with what's proven to work. Running 11.0:1 on E85 and high boost seems like walking on water to me. Like anything else, I can't wait to see someone else do it

With that said, does higher compression actually increase power, or just improve spool time/responsiveness? If so, how much (in the real world)?

Also, thx for the nice pix aaron/john/steve/david!

 

The next thread will be a comparison of all the advantages/disadvantages of the 2.0-2.4 combos that can currently be built. Not purchased, but built

 

Lucas ran a 10:1 motor on stock ecu for quite a while. I think a little bit of that time might have even been on pump gas

 

Lucas ran 10:1 on the stock ECU with MAFT Pro when he made the 506whp and ran 10.82...The Aaron vs JohnBradley thread will happen after lunch.

 

I think there is still some left in the stock ecu as far as diff set-ups go just look at Mellon and his car. Sometimes i wish my car was still on the stock ecu.

Anyone doing stock ecu w/ speed density on an evo?

Sorry to get a bit off topic

I don't know why i keep assuming you Aaron are posting while using someone else's computer .......i'm probably just retarded from the x-mas shopping

We def need another thread for that

 

I am doing speed density on the stock ECU, but not with the ECU. Currently I am doing the same thing that Luke had been doing and using the MAFT Pro just to make the switch and the rest of the tune (other than when I had the 1680's in) has been entirely on the stock ECU.

I agree with you Patrick, there is plenty left in the stock ECU that we are just now really being able to do. Our dreams arent exceeding our grasp much anymore...well maybe a little but I am sure before too long it wont even do that.

Lucas ran 12.2 at 21psi on straight 92 with the 10:1s in the car much as Inneedof had pointed out. He also ran it on that build for 8-9 months on E85/E98 as well before switching to an AEM.

....and for everyone that wanted to know the story that doesn't already: Who is JohnBradley?

 

Do you guys have the 10:1 slugs setup for a stock bore engine?

 

I dont have any on hand right now but I can get them. Generally we were only keeping them for 85.5 motors. Give me a call and we can talk more

 

Interesting thread. Say you are running E85 with 8.8:1 compression at 30psi and it makes XXXwhp, and the same motor you put 11:1 compression pistons in it. With the higher compression you won't be able to run as much boost obviously, so which motor will make more power or have a better powerband?

 

We dont plan on running less boost, we plan on running the same or more and a bigger turbo so we'll find out. It will make more power and most likely better spool.

To put some numbers to your post:

My car with stock compression ratio and 28psi made 420whp. With 10:1 and some other mods the car made 480whp and went on to make 506whp with insanely fast spool. I am not sure what it will make as an 11:1 but I dont expect less

 

e 85 needs more compression to run well.

 

I see what you are saying. But what I am trying to say is, are you going to make more power by running more boost, or by raising the compression? Like if you were running 28psi and thats as much as you could run on the fuel you decided to use. Are you better off running a lower compression and higher boost, or higher compression and lower boost?