Compression ratio
- Thread starter Rick V
- Start date
-
MOPAROFFICIAL
Oogliboogli
Not so much the compression as it is the RPMs.
But I probably wouldn't go over about 14.1, since you're asking . hehe
But I probably wouldn't go over about 14.1, since you're asking . hehe
ChargedDart75
Well-Known Member
A truly stock bottom end isn't going to yield as much compression as you'd think. The pistons are too far down in the hole, and it would take some seriously (maybe even impossibly) small chambers to get true 9.5:1 and up.
I am planning on zero decking the block and running worked magnum heads
ChargedDart75
Well-Known Member
With stock pistons? You'll be cutting alot off the deck, some pistons have been measured .120" down in the hole. Why not get some pistons with a taller compression height, then you can zero deck those pistons.
I do plan on getting pistons, just wondering what the stock crank and rods will handle. Trying to get the most out of it on a small budget and looking for any suggestions or advice.
ChargedDart75
Well-Known Member
Ok, just wanted to clarify. Like MOPAROFFICIAL said, it's more about RPM that they will take. Factory rods and cranks are pretty good, but with the rods they might have to be resized, then you might want to upgrade the fasteners, so you're pretty close to a set of Scat I-beam rods which are really good for the money.
I will check out the Scat I- beams, thanks for the info RammerJammer75
ChargedDart75
Well-Known Member
Not a problem.
yellow rose
Overnight Sensation
The higher the CR, the tighter the tuneup window. E85 is a bit more forgiving, but I wouldn’t use any more CR than you think you can tune.
This is all new to me
This is all new to me as I've never had a high compression engine so I'm interested in what the difference is in tuning higher compression
I'm currently running 13:1 compression with my 408 on e85. The pistons are 5 thousands out of the hole with a 57cc Edelbrock head (ported). I also use Scat I-beams (great rod for the money). I have heard that you can go a little over 14:1 on e85...but I have no idea if you would have head gasket issues at that level (I'm using Felpro 1008's). My engine does seal up well with studs (also a good idea for high compression).
One thing you will need if you are going to run e85 is a wide-band O2 sensor. e85 burns so clean that it is VERY difficult to read plugs. The wide-band is about the only way to get a safe tune on the carb without guessing. I run my car between 0.77-0.82 lambda at WOT.
With that said, you can make pretty stupid power with the right setup....my Barracuda is running low 10's on e85 and can drive most anywhere...except past a gas station
.
One thing you will need if you are going to run e85 is a wide-band O2 sensor. e85 burns so clean that it is VERY difficult to read plugs. The wide-band is about the only way to get a safe tune on the carb without guessing. I run my car between 0.77-0.82 lambda at WOT.
With that said, you can make pretty stupid power with the right setup....my Barracuda is running low 10's on e85 and can drive most anywhere...except past a gas station
.
Krooser
Building Chinese Free Engines since 1959...
My small block race motor ran reliably with 13-1 on alky in a dirt modified.
Mopar 340 rods and a Mopar billet steel crank. Stock parts are tuff enough that its unlikely you will break either.
The issues you will have with HIGH RPM is with the oiling system. Get that right and you are golden.
Mopar 340 rods and a Mopar billet steel crank. Stock parts are tuff enough that its unlikely you will break either.
The issues you will have with HIGH RPM is with the oiling system. Get that right and you are golden.
I'm currently running 13:1 compression with my 408 on e85. The pistons are 5 thousands out of the hole with a 57cc Edelbrock head (ported). I also use Scat I-beams (great rod for the money). I have heard that you can go a little over 14:1 on e85...but I have no idea if you would have head gasket issues at that level (I'm using Felpro 1008's). My engine does seal up well with studs (also a good idea for high compression).
One thing you will need if you are going to run e85 is a wide-band O2 sensor. e85 burns so clean that it is VERY difficult to read plugs. The wide-band is about the only way to get a safe tune on the carb without guessing. I run my car between 0.77-0.82 lambda at WOT.
With that said, you can make pretty stupid power with the right setup....my Barracuda is running low 10's on e85 and can drive most anywhere...except past a gas station
I'm currently running 13:1 compression with my 408 on e85. The pistons are 5 thousands out of the hole with a 57cc Edelbrock head (ported). I also use Scat I-beams (great rod for the money). I have heard that you can go a little over 14:1 on e85...but I have no idea if you would have head gasket issues at that level (I'm using Felpro 1008's). My engine does seal up well with studs (also a good idea for high compression).
One thing you will need if you are going to run e85 is a wide-band O2 sensor. e85 burns so clean that it is VERY difficult to read plugs. The wide-band is about the only way to get a safe tune on the carb without guessing. I run my car between 0.77-0.82 lambda at WOT.
With that said, you can make pretty stupid power with the right setup....my Barracuda is running low 10's on e85 and can drive most anywhere...except past a gas station
I greatly appreciate the great information flyfish. I am definitely going to be going with the Scat I-beams and studs for the mains and heads. Looking hard at the KB 167 pistons and will definitely go with wide-band O2 sensors. What carburetor are you running? Again I greatly appreciate the helpful information.
ChargedDart75
Well-Known Member
I would have the mains line honed with studs just to make sure they're true.
Thanks for the info Krooser, I will definitely research the oiling system.
Thanks RammerJammer75, I was planning on that as well.
yellow rose
Overnight Sensation
When I said the tune up window gets tighter as the CR goes up, I mean to say that you have less room for tuning errors. Let’s take 3 different compression ratios. 10.5:1, 12.5:1 and 14.5:1 and look at them.
At 10.5:1 you may be able to be off two heat ranges on plugs on not kill it. At 12.5:1 you may get lucky if you are off a heat range, and at 14.5:1 you will do damage right quick if you are off a heat range.
Same thing with ignition timing. You can play around with total timing and the actual curve at 10.5:1, but as you go up in CR, that “window” you have to get the timing correct starts getting smaller, and by 14.5:1 two degrees can be the difference between big horsepower and big piles of broken parts.
And so it is with most tuning aspects as CR goes up. The higher the CR, the tighter your crap has to be wired together or the consequences can be expensive.
B3422w5
Well-Known Member
my question is if its going to be race only, and you seem intent on pushing the compression, why in the world would you risk your health and the guy in the other lane by running stock rods, etc.
Sorry, it makes zero sense to me.
And i say that as a guy who went 11.20-30’s with a stock bottom end 360 the last 4 years. But i babied the heck out of it. 6k shifts, and it was balanced professionally and put together with attention to detail. All fresh.
I just retired it, not wanting to push my luck. I got lucky.
Didn't drive over it. Due to some health issues i didnt race a ton most of those years.
My carb is a something I pieced together from ~ 4 old carbs... it's a bit "Frankensteined" carb....The important parts are a 750 Proform main and an e85 conversion kit I got off ebay from Rob Mix. After a whole lot of tuning, it is the one that stays on my 408 because it is fast and consistent. I also have a new Holley 950XP carb that is ~ 0.5mph faster, but it is unreliable for a foot brake racer like me. It has an occasional hesitation at the hit of the throttle that has cost me a few races...now it sits on a shelf for when I switch to leaving off a button.
-
