Maximum Compression Ratio w/Pump Gas
- Thread starter fe4snake
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Martin
Enthusiast
I was wondering what would be the maximum compression ratio on 93 octane fuel before you need to start using racing fule?
I have an N/A motor with a 10.66 CR and wanted to increase the CR to around 12:1 CR.
What year car and engine and how many miles on it? Depending on cylinder head material, spark plug heat range and location, timing, etc., you're right about at the limit at 11:1 with 93 octane (maybe a bit over the limit after you get some carbon build up). With 12:1, you'll definitely need to blend in race gas. Or, you could look at water injection. If done right, it can help a lot with detoonation and keeps your cylinder heads nice and clean.
It's an 02' GTS with only 6K miles on it. I just did the motor 500 miles ago with new C&C ported heads, cam, lifters, R&R rockers, and a split second computor. Also, would I need to change the injectors if I increase the compression?
Martin
Enthusiast
You wouldn't need to change the injectors - when you increase compression ratio you're increasing engine efficiency, so you're making more power with the same amount of fuel. Honestly, if it were me, I'd leave it as it is now. When you get up into higher compression ratios things get much more difficult to keep running right - as plum said.
What kind of power are you getting with that setup? And, to beat 1BADGTS to the punch 
...what is your ET/trap speed in the 1/4? <-- I don't really care about this but I know a certain someone will ask. Who did your heads and what are the cam specs? I've been thinking about doing something similiar but the advice I've received has always been to ditch the cream puff pistons (at least) when going to higher compression.
...what is your ET/trap speed in the 1/4? <-- I don't really care about this but I know a certain someone will ask. Who did your heads and what are the cam specs? I've been thinking about doing something similiar but the advice I've received has always been to ditch the cream puff pistons (at least) when going to higher compression.
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Car dynoed 575 rwhp and 571 rwtq on a 93 F. day. As far for the 1/4 I do not know yet beacuse the track has been close for renovations. The heads and cam where done by Greg Good. The install was done by me. I did not change the pistons due to I was undecided about what kind of stroker motor I would like to do in the future plus it gives me an excuse with the wife to do something else with the car. I know a lot of folks over here that are runing cream puff motors with force induction and NOS without any problems yet. I guess it depends on how hard you get on it and how often. But I will tell you this, any of these engines will outlast any of those rice cookers wanna be.
EllowViper
Enthusiast
VERY Respectable N/A build. Probably very reliable as well. Not sure if the cost/benefit equation is going to be working in your favor for much more out of that set-up. Heck, I bet my current ROE set-up isn't much more than 100 additional HP than yours...and that has been a long row to *** up to this point. Good job!
The myth that cast pistons and HP don't mix should really come to an end. The only time it can be an issue is with forced induction. The cast motors (2000+) have lighter pistons, longer rods, and tighter clearances which add up to more horsepower. If I could get 11:0-1 out of my stock short block, I'd do it in a heartbeat. I just don't think it's possible without piston to valve clearance issues with my heads. I'm thinking it would be good for another 40+ rwhp. 12:0-1 should add at least another 40+ as well. I really don't think you could tune it safely at 12:0-1 on pump gas either. I believe that the cast pistons would show their ugly side the first time you rattle the motor on cheap gas. This is where knock sensors (if the car had them) would help save the motor.
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I agree Camfab, That is why I did not change the stock cast pistons for just an N/A setup. So if I understand you correctly I should not increase the compression anymore unless I change my rods and pistons? Let me explain better what my goal is. My plan is to try to achieve around 675 - 700 rwhp using pump gas. I do not want to discourage force induction cars. Is just a personal goal of mine to go N/A. The way I see it is that a Gen II motor makes about 56.25 hp/liter and I think that it should be able to around 85.00 hp/liter. There are many stock N/A engines out there doing more than that with out a problem. Does this sound logical?
I think you and I are on the same wavelength. I think at 675 -700 rwhp your going to have to make big steps. I've got Striker heads and could possibly go smaller on the chambers by milling, but I think piston to valve clearance would be an issue. I'm not certain about your heads (I'm assuming they are ported stockers). I wish I had the resources to test out the possibilities, like how much porting of the stock intake is necessary, header optimizing, comp ratio, etc. Seems like comp. is your only hope, I know spinning these motors up is a bad recipe. Clearly it's doable as Lingenfelter has made amazing power with it's stroker motors, but your talking about a whole different playing field.
britospeed
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700rwhp is not going to happen NA on pump gas easily, possibly at all. You'll need the largest ci bottom end with Striker Race heads with further portwork and a custom intake. The cam will have to have a lot of overlap. So much so that it would make the car no fun to drive on the street. I think that if you remove the pump gas limitation then you can meet your hp goals with a better driving combo.
Either way good luck and keep us posted on your results.
Either way good luck and keep us posted on your results.
VENOMAHOLIC
Enthusiast
The old Lethal 750 GTS from C&D 2002 was bored and stroked to 550ci and was claimed to have 750hp 800ftlbs at crank. Every now and then it is for sale on EBay. The article never went into detail on CR but it ran on pump gas in the test.
Thank's for the input everyone. I even spoke to Mike with Mitech Racing Engines
who even makes a custom racing intake for the Viper but the intake runners are too short for use in an A/N motor he mentioned that their intake is better suited for force induction. I found that they make some good stuff at a very reasonable price, check them out. I guess, I will keep doing some more research but it looks like I need to stroke and bore this motor to achive what I want.
who even makes a custom racing intake for the Viper but the intake runners are too short for use in an A/N motor he mentioned that their intake is better suited for force induction. I found that they make some good stuff at a very reasonable price, check them out. I guess, I will keep doing some more research but it looks like I need to stroke and bore this motor to achive what I want.
Martin D
Enthusiast
Over 700 N/A here. 512 CI, 11:1, Greg Good heads, Ported but stock intake, Solid cam - .723 lift.
Pleasure to drive, not hard at all. With right combo and setup, 700 is possible.
gl!
Martin that sounds like a wicked combo. A few questions if you don't mind me asking.....
What Gen is your motor?
If Gen II, did you go with bigger throttle bodies?
Did you maintain the stock fuel system architecture? Bigger pump and enlarged stock injectors or complete retrofit?
Bored and stroked? If stroked did you off set grind or go with a complete new crank.
Cam duration @ .050 and LCA?
What size and who's header?
If you don't want to disclose the info. I understand, and or if you prefer you can PM me
What Gen is your motor?
If Gen II, did you go with bigger throttle bodies?
Did you maintain the stock fuel system architecture? Bigger pump and enlarged stock injectors or complete retrofit?
Bored and stroked? If stroked did you off set grind or go with a complete new crank.
Cam duration @ .050 and LCA?
What size and who's header?
If you don't want to disclose the info. I understand, and or if you prefer you can PM me
Joseph Dell
Enthusiast
Martin's car is one of the oldest and nicest NA vipers on the streets of Atlanta. I won't steal his thunder, but he's probably had more fun with that car than just about any other viper owner i've ever met. well, except for the fact that he hasn't put it on a formal race-track...
I hope Martin chimes in... He isn't on the boards as often as he used to be... *c'mon out of hiding Martin!!!*
Joseph
Martin D
Enthusiast
AS for disclosure, I dont mind - but I have been asked from varous people in the development of the car to keep things to myself. So, I respect thier wishes.
I do have bigger TB's - port matched to the intake.
The fuel system has been totaly reworked. (no intank pumps and it is return style) 50lb injectors.
Stroked - mild mild mild bore. Offset ground stock crank
Cam is well... the big secret! - (as are the heads flow numbers)
The headers are from my original Venom 650R package.
I will also mention that we had to modify the block to use the cam/lifter combo. This car is certailny a one off and has hours and hours of R&D. Essentially, nothing is stock anymore.
It's a red 98 RT/10 -- with a 300 shot!! And other than sounding like a top fuel car it is a pleasure to drive. no bucking etc, responds well under low RPM, and pulls like a freight train to 7k.
britospeed
Enthusiast
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Martin, sounds like a great setup. Do you have any dyno sheets that you would be willing to share? I'd love to see the power curve.
Randy Forbes
Enthusiast
Where can I get more information about stroker crankshafts? I have a (loose) crank that might be one, but I'd want to measure the throws to know for sure.
I'm pretty sure it's been narrowed down to a GenII engine, based on partial part number:
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Also have a raw forging, if you really want to get adventurous on offset grinding the crankpins...
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Any insight (or interest) will be most appreciated. TIA.
HIGH resolution pictures of the above (sorry for anyone that opened this before I linkd the smaller images) can be seen at: Gallery :: Viper_crankshaft
Martin D
Enthusiast
I am at my Florida beach house so no, I dont atm. I would have to dig around to find one. I do haev a framed one from a few years back that did 630/630 BEFORE the GG super saturday night special heads! (added 50+ cfm more)
JD - Email is a problem here at the beach.. but I got yours, just cant repsond.
Neptune's Retreat is my beach house - 10% off for any viper owners!!
l8r - MD
99 R/T 10
Enthusiast
Problems, problem................... nothing but problems.....................................
2001 GTS
Enthusiast
Martin is my hero
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