I'm contemplating putting in a set of brand new Wiseco pistons, flattops, in my 383 that will yield me 12:1 compression, with 9" deck (0 deck height) and 58cc chambers on the heads. I will be using 6" rods and a 3.75" stroke crank with whichever pistons I run. My other set of pistons are the used SRP pistons which came w/ the car. They look simialr, but they actually have a small step that divides the piston in two. IOW, half the piston is about .050" lower than the other half. These SRP pistons make up 11.2:1 compression. The thing is, one of these SRP pistons got damaged when the engine came apart, thank *** the heads didn't get damaged. To run these, I'd have to just buy a new piston, a set of rings, and make sure all the other pistons are okay. What do you guys think about this? Should I run the old pistons to be on the safe side, or should I run the new ones and experiment w/ timing, and the possibility of having to run race gas some of the time? Remember I have AFR heads and the comb. chambers are flawless, they've had additional work done to them besides the near-perfect AFR cnc job.

 

I hope its not a daily driver because gas is not going to be cheap. Anything with less octane is going to kill your engine. What octane are you running now? Might have to get some jet fuel eventually to prevent it from knocking.

 

This is true to a point. Then again I'd like to know how certain guys, namely John Beck, in the PHR engine masters challegene ran between 12to 1 and 13 to 1 on pump 93oct gas, with carbs! I know combustion chamber design, quech area, and other factors play a part in this, that's why I mentioned my comb. chambers. My quench is also .040" w a .039" head gasket. .035"-.045" is an ideal quench range for maximum perf.

The engine will be together within a month. The only pump gas I'd consider would be Sonoco Ultra 94 oct.

 

You may want to try and contact him. I always contact those guys doing amazing things and they always seem helpful and willing to tell you their secrets to a certain degree. At least you can get a better idea.

 

Yeah, that would be a good idea. I know that cam overlap and valve timing play a big part too. I remember in the PHR mag. that Beck said that he was experimenting, w/ a bunch of camshafts to see how that would affect compression on pump gas. What does everyone else think?

 

If your run an aluminum head, you can ran about 1 point higher compression than with a cast iron head. If your cam has a large lobe center, like 112 or higher than that will bleed of some cylinder pressure to, so with aluminum heads and a cam with a big lobe center, than you can run 93 octane all day long. But make sure you have your timing down, to much advance will cause it to detonate and run like crap.

 

Hot Rod did a high compression big block awhile back. They used a lot of the same tricks you are, unfortuantely its been too long to remember the details. The aluminum heads, fuel injection (I hope), all that jazz. Your rod/stroke ratio looks decent too. They did use one trick I have not seen before. Some sort of coolant called Evans' coolant or some such thing. I guess its pretty expensive, but helps to control detonation somewhow. Anyway, if it were me, I would stick with the lower compression ratio. Less hassle, and, potentially, less $$$.

 

I think you'll need to run a bit tighter quench than that, and pray the cam is enough to keep that thing happy on pump gas. I think its going to be unhappy personally... but stranger things have happened.

 

I agree this idea could get very expensive and create a big hassle. I have read into many of these types of projects and when you get into detail all the cheats they do you head will be spinning. You also have to realize these guys are probably testing on top of testing so to get this result probably was many $ later and lots of rebuilds. Thats why I suggest you try and contact the man who is doing it and get the lowdown.

 

http://purplesagetradingpost.com/sum...%20engine.html

 

Very interesting reading. Go for it. Only thing is I could probably build a 383 for less than what they say and still run on pump gas and have similar numbers. Also my compression would be alot less and the engine would probably last twice as long.

 

Thanks for the replies guys. Have any of you know about those 104 octane boosters or lead additives you can find at AutoZone or Wal-Mart?

 

I just realized that the motor in the article had 6.209" rods!! This is definitely a plus for running higher compression. The higher the Rod/Stroke ratio the better for running higher compression and power. Any experienced engine builder will tell you this, regardless all the crap you read on these boards. Get the longest rod you can. Anyway tell me about those additives guys, please.

 

Everything you wanted to know about compression and more

http://www.boyleworks.com/ta400/psp/compression.html

Dynamic CR calculator

http://cochise.uia.net/pkelley2/DynamicCR.html

Of course there are many variables but one of the reasons they were probably able to run 12-13 compression was because of a large duration camshaft. Another could be simply that the engine wasn't in a car. I know the dyno puts a load on the engine but it's not the same as being in an actual car.

I'm not saying it'd be impossible but I'd think it'd be hard to accomplish.

As far as additives go............ My dad had a 62 Nova 406 SBC with camel hump heads and something like 11.5-12.0 compression. It would NEVER EVER run right with an additive he always had to buy the real stuff. That's the only experience I have on that.

 

Useless.

Thats my .02

 

I agree with your title, your nuts!

In my book anything over 11:1 for the street is risky business. Imagine building and balancing the motor for 12:1 and then not being able to run it on anything less then 100 octance. You would be so pissed all the time that you had to fork out 4$/gallon just to pleasure cruise, and forget about road trips.

I prefer about 10.25-10.5:1, even 11:1 invites octane fits on road trips where all you can buy is 91 octane, like here in AZ.

But it is your baby, what ever makes you happiest.

 

Ominous, I figured I'd take some crap for being nuts, but for some reason I'm leaning towards using the new pistons. I don't know about reusing the SRPs even though they are good forgings and only one is bad. I'm sure I could get away with mixing 93-4 oct. with a half tank of racing gas. I'm not some idiot who would just decide to run high compression, with brand new 4340 forged parts for the hell of it without doing research. Trust me, I've done my fare share, I'm just looking for someone who runs high comp. on the street and what they do as far a gas. I don't mind spending $3.00/ gallon average per tank, if I can get on it while cruising. I'm willing to accept that if I'm putting 450hp to the wheels. I don't drive my perf. cars much, I reserve the cross town trips for the beater. My concern is that I may want to take a long trip once in a blue moon, maybe to FL, but I want to know if it can be done? I know there are several timing retard ***** or systems out there. I want to know if anyone has had success with these? I don't really care if I have to kill my timing or hp on a long road trip, I just don't want to damage the engine on pump gas, whatever it takes. Basically I'm looking for guys who have run 12 to 1 on the street w/ fuel injection. It seems I'm charting new waters compared to most thirdgenners.

 

I was in the same boat when I built my motor. My stroker kit actually included flat tops for ~11:1. When the shop was boring my block there was a tooling error and they hung a bit and scored a cylinder wall. They were very apologetic and willing to do anything to make it up, find new block etc.

We ended up going .40 Vs. .30 over to clean up the wall with a new -12cc dish piston traded for my -7cc and a new balance on the assembley at their cost. They also threw in the stroker clearancing of the block for free and the final cleaning and plugs.

When it was all said and done I was kinda happy it happened as I was able to bring my compression to 10.3:1 Vs 10.9:1. Now I get away with 91 octance all day long , I couldnt be happier.

Your probably best off searching at corvetteforum.com or camaroz28.com. Thats where I did all my digging when I was planning on the higher compression.

It can be done, I found alot of examples of people doing it. But to run on the street they had to pull timing and keep the rpms down to run pump gas. You are not going to get away with 12:1 comfortably at all. You will be fighting detonation forever.

 

Hey Camaro Joe,

I would just buy a new set of pistons. I think of pistons as one of those things that you buy in a set. Not worth the risk if one is damaged, possibly others are damaged or stressed and look okay. Not worth it right?

I like low compression motors personally...but have fun with 12:1. My 383 was about 11.2:1 before I rebuilt it and I had some detonation problems, but they weren't too bad. I had to run 93 though. Just once I filled with 87 and it knocked so bad at 3500 and up. Good luck..

 

Its all in the camshaft design. massive lift and duration bleeds off
compression at low rpms. Until it reaches high rpms then Hold On!

 

You might want to invest in a wide band o2 sensor. That way you can run leaded gas with out problems. Unless you still have your cats on. Please tell me you don't.

 

Of course I don't have cats! The car has true dual 2 1/2" that run to flowtech mufflers and dump at the rear axel. My exhaust is the exact same as 11SEC91Z, I think Leathal told him about the setup. I hear you about the wideband, just when $$$ permits.

Hey Ski, where the heck are ya at, man? Help me out bro! I'd like to know what you're running for gas and how much toulene you run in a tank?

 

Camarojoe,

Sorry it took me a while to get back to you.

I am at 11.8 compression on my motor, and can advice you based on that.

On the street, I have no problem running 93/94 octane all day long on long trips whatever. You just have to practice a little self control. I tend not to go over 1/2 -3/4 throttle when running that lower octane gas. This is not a huge concern, since I either blow the tires off of it when doing that, or face a nice fine anyways from the nice state trooper. So its not a big deal to me. I can do anything an LS1 transam can do at WOT to my 1/2 to 3/4 throttle to put things into perspective.

On the strip I shoot for 100 octane. I'm sure I could get it down to about 96-97 octane with no problems, but I figure why risk it and error on the side of caution. I have gone at times after resetting my valves to a tighter spec, WOT with 94 octane and did not hear it ping. But as I said, I would rather error on the side of caution. I suppose the tighter lash setting just let a little more pressure bleed off. And maybe I could get away with 94 octane, but its not worth the uncertainty.

12:1 on good heads with a properly built motor is not what outrageous. The gains from it are worth the risk for me. At the strip I talk to guys running lesser parts in all out race cars with 14-15:1 compression year after year, and some dumping nitrous on them also.

As of lately I have just been having Corky pick me up race gas that is around 102 octane and mixing it 1/2-1/2 with 93 octane. So the last two times at the track I have been running around 97-98 octane.

Its not as big of a deal as people make it out to be here on this forum. The same people that make a big fuss about it, turn around and get in their Supercharged /Turbo /nitrouos equipped cars and drive them into the sunset without a bit of hesitation.

To me there is 10x the risk with running one of them.

But to each his own, and its your car so do with it what you like.

 

Thanks Jesse, your reply was well worth the wait. It even furthens my decision to run the 12 to 1 wisecos more. I'm planning on running the MSD adjustable timing control module where I can adjust the timing from the drivers seat 15 degs either way. This way, I may lose major hp, but on the street I don't care, I just don't want a bunch of holes in all my new parts. Thanks again everyone.

 

Your welcome....

These things are not the fragile eggs people make them out to be, "When built right".

Quick (funny) story. Buddy of mine, ran a 6 cylinder in a beater car for almost 3 years with not one drop of coolant in the motor!!! Heat of the summer 50+ miles each way, cold of winter; didn't matter. He went to check the oil in it one day, it was a quart low(understandable) for a motor with 175K beans on it!!!! And abused beyond belief daily. Anyways. He added one quart, nothing on the dipstick. Ok maybe he let it go a little too long between checkup....(Over 1 year! since the last it was checked) So he added a second, still nothing....a third quart, still nothing...I actually got down on the ground and looked underneath the car assuming that is was just pouring out the bottom. lol. Nothing down there. He added another then it was almost at the full mark!!! lol.

I said there can't be any oil pressure left in this thing, since for the years without the coolant, he prided himself on the oil pressure it maintained.. I took the liberty to turn on the car, to view the gage. 60psi after a few seconds of run time.

Took it for a ride and to my surprise the old girl ran quite well. Squieled the tires on takeouts (front wheel drive)!

I suggested a check of the tranny fluid while we where at it, but he said he did not want to "spoil" her with too much new fluid. That was ~4 months ago and it still tooling around strong as ever. lol.

While I would NEVER condone such actions myself. It sorta makes me laugh when I change my sythetic oil every ~5 race events. Which is about every 1000 miles on the car.

So I think a well built motor will take the demand you ask of it with 12:1 compression and a little ping here if you get overzelous when on the lower octane.

 

Running any sort of leaded gas with an O2 sensor will kill it...Just like silicone will kill an O2 sensor as well...

 

I'm running 11.3:1 on my 355, it likes 93 octane and a pretty conservative spark map. I'm running AFR heads w/ 58cc chambers, and 0.032" thick copper shim head gaskets.

While compression is good, that's about as high as I'd go just for economical reasons. 100+ octane gas is friggin' expensive, and when I'm driving my Z I like to work the gas pedal. The extra few hp just isn't compelling enough to up the compression further.

 

Good info, guys. Kevin, did you zero deck your block so that the pistons are even with the surface? This and the intake charge temp are the two most important things to fight off detonation. I guess these AFR heads have about the best chambers of any heads you can buy. It seems like people who run them and 11+ compression ratio have good luck with no pinging. My heads have had the chambers polished on top of the already almost-perfect job AFR does on them. I'm hoping my car makes as much power as Ski's, which means I won't have to push down very far on the gas in order to get moving fast. I do know that it won't have quite the low end as some of you guys with superrams and ltr setups.

Ski, good story, you're right about people acting like our blocks our made of paper mache. I also wanted to ask you if you're still thinking about tring a different intake? I do like the miniram more than I thouhgt I would, but I do miss the mid range burst of tq that the superram gave me. I still think the SR is a better street intake and I'd probably put one back on, except my new heads just seem a little big and flow too much to be restricted by a SR. It really is fun to wind the car up high, but everyone knows that stuff breaks easier this way.

 

Camaro,

Absolutely! I was just talking with the manufacturer. He got behind on some of his work that he was doing and needed to catch up. Should be here next week if all goes as planned.

Its working out well, as I have my entire underside of the car out! I pulled the TC for a stall speed upgreade ~4000 stall. And also have the rear end out for a rebuild/refreshening.

Read about it on the Corvetteforum is you like. So the timing should be perfect for the testing.

Should be some other exciting stuff going on as well. The fun just doesn't stop

 

Nix. Pistons are still 0.025" in the hole, the machinist checked the deck surfaces when I was having the block prepped, said they were true so no decking for me.

I don't feel good zero-decking unless I'm running really good rods, just kinda paranoid. In this current engine I reused the stock L98 rods, with ARP bolts and had the shop resize them.

Sure, I gave up some squish in the quench area, but at 0.057" total (0.025" deck height + 0.032" gasket compressed) running 2VR flat-top pistons nothing's complaining.

 

Swapping head gaskets sux.

 

Marine gaskets is the answer to that

 

I haven't checked the vette forum in a while, because of my slow dial-up at home. Ski, The guy who sold me the 91 used to have a 4k stall, he said it slipped too much vs. the 3200 stall so he ended up with the smaller stall in the end. He said the 4k stall cost him 30-40rwhp vs. the 3200 stall even though it produced a bigger tq spike down low.

Kevin, thanks for the info. You're really doing good to run the quench area you do with that comp. ratio. You're also right about the rod length. My 6" esp eagles helped me with my decision to run a zero deck.