Hi everyone,

This winter my father and I are rebuilding the engine of my '99 Tib. We are taking it all apart and cleaning it out, but we are also sending the head out to a machine shop to be acid washed and shaved for a higher compression ratio. Now I don't know a whole lot about this, but I hear people talk about LOWERING the compression ratio when you want to boost a car (for obvious reasons). My question is, if I am running at a HIGHER compression ratio than stock, is it still possible to install a turbo kit sometime in the future? I ask this because I intend to keep the car for many years and eventually (hopefully) get to boost the crap out of it once I have a good job and another car as a daily driver.

Thanks,

Nick

 

What I say doesn't count for a lot in the boosted world since I only mess with the theory, but if I remember correctly it'll increase your chances of detonation and force you to run higher octane fuel, possibly pushing you out of the range of fuel you can get at a gas station (if you took the compression high enough).

Now I'll let those who have boosted talk about it.

 

The main reason to lower the compression ratio (and most other things people do to tune a turbo setup) is to avoid detonation. If your setup is *properly* tuned (read: $$$ of dyno time with a professional tuner) then you can probably get by with as much as 5-7lbs of boost on a slightly-higher compression ratio. Stock CR, 8-10lbs. Lower compression ratios you might be able to run 20+PSI.

The other thing to consider is: when you have a better job, you can buy a different engine, rebuild it with stronger internals, and drop in a turbo-prepped engine after x years of running around on a nice naturally-aspirated engine. Then you don't have to rush the engine build when you finally have the money to do a proper turbo setup. Or, if down-time isn't a problem, rebuild the same engine with lower CR and forged internals etc.

Some people are highly skeptical of the whole concept, but do your own research into the merits of Singh Grooves, especially if you are thinking of boosting the static compression in an engine that started at 10:1.

 

"Properly" tuning a car means to spend money at a dyno? I disagree. Anyone with the knowledge can tune a car with a wideband. There isn't a difference other than your car sits on a dyno versus driving and logging, fixing and driving again.

Gaining the knowledge is as simple as researching what you are doing.

Lowering compression allows you to run higher boost psi while lowering the risk of detonation, but at the cost of lower power output do to the lower compression. By lower power output I mean compared to a car at the same boost psi with a higher compression. It's all in the tune. A safe tune is the best thing to avoid detonation.

 

So your wideband tells you when a change alters HP or torque output? Wow.

You can get close with a wideband.

 

of course, a car can be tuned on the streets but only to a certain extent. you have to pay very close attention to timing because detonation can't be very much heard on the streets. that, and of course the power issue stated previously. so in short, a dyno helps the tuner optimize the tune of a car.

to answer the question, you can have your head shaved for higher CR but later on (or better get them now) and get forged internals (with a lower comp piston) when you will be boosting it. it'll be slow right now but once you put on a turbo it'll be a different story. smile.gif

 

Optimized, but my argument was that it is still proper.

 

Yes, you can street tune the fuel map based on the wideband and logs while using a conservative, safe ignition map.

A dyno would allow you to tune the ignition map as well which would give you more power.

Bottom line - Is dyno tuning worth it? Yes. Can you get decent results without it? Yes

 

Street tuning with the aid of a chassis ear is about as close to a dyno tune as you will get, but STILL not as good as a dyno tune. On the dyno, the tuner can put the engine in various loads and stress tests, heat soak vs non heat soak, subtle changes to spark timing, sublte changes to fueling and boost. They get instant results to see where the gains ACTUALLY are according to actual computer numbers, not just your "butt" dyno. Well, WELL worth the money, especially if you are going higher compression.

My car is street tuned to 10 PSI. We are shooting for 15 PSI. The next 5 will be done in a controlled environment on the dyno with my HIGHLY qualified tuner.

More On Topic, you will be able to run boost, just not as much. Really depends on what you are shooting for. Sounds like a great track or autocross setup! I LOVE my high compression setup (well, stock, but higher then most folks running FI) because it launches great and has NA throttle response off boost, and then loads of power when the boost kicks in. I'd say go for it! BUT....might wanna get some beefy forged components. You will run a much higher risk of detonation then most of us on here. forged pistons should help tremendously to keep your high comp. FI monster running long and reliable.

Also.......you will want to DEFINITELY consider an E85 conversion! Its like running race fuel on pump gas prices. You will need to plan accordingly if you do this. This would significantly help reduce risk of detonation. You will need to make sure the entire fuel system can handle E85. I am considering this as well. Things I am still researching to see if its E85 compatible is: Fuel tank, lines(hard and soft), o-rings, fuel pump, regulator, and injectors. Will most probably need to go stand alone ECU for this setup. Maybe not though, I think dmdicks might be running a piggyback on his E85 setup. Maybe He'll chime in. I gotta pick his brain anyways!

Hope that gives you a little to think about. I'm sure others will chime in as well. smile.gif

 

I would highly recommend against shaving the cylinder head unless you really know what your doing. Even a few thousandths of an inch can raise your static compression ratio by a half a point or more. Plus it will jack with your camshaft timing so an adjustable cam gear is a MUST if you want to retain stock cam timing. Now if your head is warped then you either need a new head or deal with the side effect of increased compression.

The stock pistons are plenty strong if you know how to tune. So you either need to learn how to tune or find someone that knows how to tune and then figure out what tuning method your going to use, whether it be a piggyback or standalone ECU like the megasquirt.

As far as E85 is concerned it will go a long way towards staving off detonation but there are a couple things you MUST consider before doing the conversion:

1) E85 takes approximately 30% more fuel to maintain the same Air/Fuel ratios required for safe operation under boost. I can go into why this is, but I wouldn't want to bore anyone. You WILL need to take this into account when selecting fuel injector sizes

2) You WILL need a new larger flow rated fuel pump to handle the increased needs of E85. All walbro pumps are certifed to work with E85 so I would start there. I myself run a 190lph pump and have had no issues.

3) Its recommended to change out any part of your fuel system that has rubber lines. On my GK tib this was the line from the firewall to the fuel rail. I've been running E85 for almost 3 years with zero fuel problems.

4) E85 is not a 'Fix-All' magic fuel. You will still NEED to know what your doing to keep a stock block from exploding from too much "boost". Will it help? Hell yeah as its octane rating is 106. smile.gif

5) You don't need a full standalone ECU to run E85. A good Piggyback ECU will work fine.