Compression ratio Question

[a91eagletalon]

long story short I want to run 20psi on pump gas is this possible I haven't bought pistons yet for the fact that I’m not sure what I’m going to end up with for compression. What is a safe compression ratio after boost is added to run. Will I have to go to e85 or will premium work. I do want to go to e85 sometime but not right now.

What piston brand Have you guys been having good luck with

 

[92AWDHX40]

Stick with pump gas grab a wideband, check out the upgrade path, set goals, for you car.Start there pick just about any aftermarket forged setup, again begin reading on your upgrade path.

 

[My1GLaser]

Do yourself a favor and go with 9:1! You will be very happy you did when u switch to E85. I didn't have any real issues running an 18g at 25 psi 18* timing and 10.8-11:1 AFR on pump gas with 9:1.

I did cooling mods to keeps the coolant temps at 170-180*. I ran non-projected BR7ES plugs. Ran a CAI to keep intake temps down. Make sure the cumbustion chamber doesn't have any sharp edges and keep the piston to head clearance (quench) as close to .035" as possible. All that adds up to more manageable tuning on higher CR.

I switched to E85 and I run 22* timing and 35psi with 12:1 AFR. I'm only running 60% E85. I'm actually about 9.3:1 after a couple head resurfaces and switching from the MLS HG back to a composite HG. I love it! There was a noticeable difference in off-boost reponse and spool up after the last head resurface and switching back to the composite HG.

 

[a91eagletalon]

What are the limits of the A'PEXi Super AFC 2 because that is what im using now i want to hold off right now befor i get a dsm link to tune with

 

[My1GLaser]

Sorry, I didn't check your mods first to see you didn't have ECMLink.

You are definitely going to want timing control with 9:1 CR!!! Probably even with 8.5:1. I am sure people run those CR without it, but I don't recommend it. You will probably want to stick with 8:1, especially with using an AFC which is already lying to the ECU about airflow and thereby lying about the engine load. You are already running 750s which is higher than the suggested inj to use with an AFC.

Look at the attachment. It is the stock 1G timing table the ECU uses. You are going most likely going to fight knock between 5000 and 6500 rpms unless you can pull back 4-6*.

My opinion is that the CR you choose is a long term upgrade/decision. Unless you have engine issues, you will most likely never change it again. My motor has been built for 6 years and never changed. I planned around my choice of CR.

If you switch to E85 down the road, you will regret not having at least 9:1...

 

[dsmcurse]

Id say run the stock 7.8-1 pistons. Are they out of life? How many miles? Did you do a compression test the proper way? As in pull the fuel injector signal so the fuel don't wash away the oil/cylinder surface? Please post your numbers. The factory stock piston/rod combination is VERY strong, even 20year old 180k mile factory bottom end will pump out some major power. The key is, "its all in the set-up and tune".

Since you'd have to ask such a question, it leads me to believe you are a novice mechanic, so a complete and major engine build is more than likely to goin to happen very soon. (No offense man). Learn the engine, break stuff, rig part combinations shitty, ITS ALL PART OF THE LEARNING PROCESS. That's okay man.

In all seriousness, the factory 1G piston and rod combination is VERY stout and can take a beating. If they're healthy, id say run 'em. If you are just itchin to do a build, out of experience along with many friends experience id recomend off the shelf regular Clevite engine bearings that you can buy at NAPA, good 'ol fashion regular Eagle H-Beam con-rods, regular 'ol ARP hardware (not L19, not needed, just regular ARP head/crank studs and rod bolts) and as far as pistons go.... the very best will be your favorite brand. Plain and simple. The actuall name brand pistons are all very close in terms of longevety and performance. Id say most of what you get out of piston life comes from the ECU tune. (Of course there's mechanical that comes into play to tho)

As far as compression goes, 9 to 1 is good, 8.5 to 1 is good. Keep it in that neighborhood tho, anything like 10-1 is kinda gettin greedy for a street car. If the car only drives a 1/4mile at a time than yeah, sure, but for everyday boostin stay lower compression as a means of "better safe than sorry". Why do you think the engineers used 7.8-1 right out of the box?

On my build I followed recomended advice from a friend that had been there done that, regular eagle h-beams, regular ARP hardware, and lower compression pistons. I used Ross Racing 8.8-1pistons. Just dyno'd 621 awhp in aapril, my build has 20k miles on it agin, ITS ALL IN THE TUNE

ID SAY PUSH THE STOCKERS OVER THE 400WHP MARK!

As far as cams for the cylinder head, that's for another forum, as far as E85 goes.... I personally say F that. Your limited on where you can buy it, problems with "geling" when it sits, the crap ain't worth it. You can use a properly matched water/meth system and blow E85 out of the water. I run a direct port meth set-up (every intake mannifold runner holds a 330cc nozzel) agin, I push over 600awhp on everyday 91octane pump. Another trick you can do to raise the octane value when the meth comes on is mix the shit spicy. I started out mixin it 50/50 but I'm now almost to addin just STRAIGHT meth to my tank and no water at all. ITS ALL IN THE TUNE MY FRIEND. Better get dsmlink....

 

[black97spyder]

Very well said alex! Lmao I need dsmlink really bad for both my cars ... been running great without it but I have been around the block a couple times when it comes to engines and tuning without a ecu (older cars). I promise I have lots of knock due to the boost level and mods I am running, and have no way to adjust. V3 is my next upgrade just sucks it costs so much... OP, dont in my footsteps. It is VERY easy to blow a motor up doing what I do. Do it the right way and get link v3 before you start your build that way you dont ruin a brand new and very expensive motor right off the start, dsmlink v3 will let you control every little detail to make that thing last and perform great!

 

[a91eagletalon]

Thanks for all the advise

Yes im novice when it come to the tuning of the car but i can turn a wrench with ease

i have had a bad engine faliure already i burnt up a pistion and jacked up he cylinder walls so i wanted to get a new block to start over again because that block was already .040 over now with my fresh block. I want to build a well respected daliy driver and not screw it up again

It Would be great not to have to go to E85 so i will have to look into the meth injection but it all sounds like i need to get me a ecmlink


How far are my 750cc injecters going to get me

Whats all involved in ordeing a ecmlink looks like there is alot of things you have to keep in mind before you order it

Thanks again for all you help
Matthew

 

[dsmcurse]

Oh okay, makes more sense now. The original motor was toast, and a differant build went to hell. (Wow, forty over? Yep, time for a fresh block) here's some advice to you my friend. Keep it clean! When you assemble the engine "everyone" has there own lil tricks and methods for puttin it together, no matter what you do, KEEP IT CLEAN. Don't have a engine opened up installing main bearings in a dirty dusty enviorment have a super clean dust free set up while working. Its all the lil stuff like goin the extra mile to do it the best you can that will make the differance on a build that will last vs's a half-assed one that will fail

My home garage was very clean when I assembled my engine, BUT, I was still paranoid. Believe it or not I assembled most all of it in my living room (had plastic down on floor to not get oil on carpet). Use LUBERPLATE 101assembaly lube. I swear, the best mechanics in the business use white engine builder grease.

The block, head and crank need to go to a reputable machine shop man that has lots of experience, go shop around, go to differant machine shops and just walk into the back to talk to the dude, look around at the enviorment and his work habbits, you'll pick up the right vibe when you meet a guy that's trust worthy. Get reputable machine shop work done, buy regular ARP hardware, regular Clevite engine bearings, regular Eagle rods and agin, as far as pistons go, the very best will be your favorite brand.

Stay in the 8-1 to 9-1 compression ratio, trust me. As far as E85 goes, (I know this is gonna start a war) the shits bunk. Its totally more trouble and hassle than its worth. Screw that. 91 or 92 regular 'ol gas station gas that you can buy ANYWHERE will work just fine. a water/meth system will alow you to do magical things dude.

Picture this, HX52 big dawg turbo pumpin 35+ psi boost, 20* timing on the top end and ZERO KNOCK all on gas station 91 octane fuel. Can gas up anywhere and not even worry about it thank you water/meth kit

I would argue anyone that a simple name brand water/meth kit will do better and go further than a E85 conversion for an actual street/daily driven car