4.6 Stroker, Increasing Compression

[HttpWayne]

If you go here http://www.ajeepthing.com/stroker-motor.html I built the "4.6 Low-Buck Stroker" with Option 1, meaning I should be at about a 9.6 CR. So according to this phrase (it's on that page):

*For each 0.010" milled from the block deck (or taken from head gasket thickness) to reduce quench height, the combustion volume decreases by ~2.0ml and the CR increases by ~0.2*.

If I wanted to increase my compression so that I could run a higher octane gas (92 premium) in hopes of maximizing performance, I would basically want to raise my CR to 10.6'ish... correct? (mill 0.050 from the block) ??

I have it taken apart right now. Would milling 0.050 from the head be basically the same thing?


Wayne P.~

 

[HttpWayne]

Also, how much HP gains can one expect from the increased compression?

 

[HttpWayne]

I'm also reading this right now FWIW. http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

 

[old_man]

If you are going to up the compression, you would do well to take it fromt he block, not the head. It will improve the quench height. The ideal number is around .058". This will allow you to run lower octane without ping or detonation. I run 10.4:1 and run the cheapest gas available with not issues. Caveat....I live at 5k ft elevation which helps things a lot. I have almost 100k on my stroker.

Octane has absolutely nothing to do with performance. Compression does however.

 

[HttpWayne]

I understand it's the compression, NOT the octane. That's why I'm going for higher compression, NOT higher octane. But with higher compression you need higher octane. Maybe I mislead. I know higher octane is just to reduce detonation which comes from higher compressions.

My goal is to maximize compression (or almost rather) for 92 octane fuel (available in the states I have been through) in 100 degree weather (not normal weather for my location, but just to keep it safe) with a 180 degree thermostat. I also have the Flex-a-lite 440 series 2500 CFM (dual fans) that I will run. They are pushers, I know this. They are mounted inside the grille... with a little assistance from my good friend Tin-Snip.

I will be in Florida, so about... whatever is normal in Fla for sea-level. I assume pure sea level just to be safe. If the world freezes over like in the ice-age I want to be able to drive to the other half of Pangea in case of an emergency, so we'll assume exact sea-level.

Obviously 5000 feet is a huge factor in your situation. You might as well live on Big Bear mountain in California at that elevation. Not the case for me. I'd rather assume the worst case scenario and it improve if I went up, then build your situation and then come south and have problems. Then again all you need to do is upgrade to premium.

I want to know what the MAXIMUM CR is for me to run 92 octane fuel. I will detract from that what little I can, probably with the headgasket, just to be on the safe side.

Wayne P.~

 

[HttpWayne]

According to this I can gain about 3% efficiency roughly. That's from 9:1 to 10:1. I imagine 9.6:1 to 10.6:1 is the same gain. 3% doesn't really seem like much. Maybe I should just leave it be and piece together a supercharger over the next year??

If so... would I be safe with a 10.6:1 with a 5 PSI increase (as in I run higher octane, and don't change any internals) without having to worry about detonation?

 

[old_man]

I couldn't tell you without taking a lot of time to work the numbers and look at the all the parts but getting a good running system is complex and has tons of variables. Everybody seems to thing that getting the most from an engine is about just running some numbers and everything will be perfect. It it was that easy, NASCAR would always be a dead heat.

Going above 10 on compression opens up a whole other realm of issues and isn't simple. Building great engines is based on some formulas but for the most part it is trial and error. So in summation, there isn't a simple answer.

 

[HttpWayne]

I think you just enlightened me on what the "Formula" in Formula 1 Racing means.

 

[jeeperjohn]

Upping the compression alone may not provide the gains you seek. There may be alot you can do with shaping the combustion chamber to optimize air flow and atomization. You also may want to look at water injection to prevent detonation at a CR of more than10.5.

 

[HttpWayne]

Water injection? Why not just add water to my fuel tank and knock out two birds with one stone...

 

[jeeperjohn]

Water doesn't readily mix with fuel. It has to be atomized into the airflow to be effective.

 

[RWKHausSupply]

or one / two blue bottles?

 

[HttpWayne]

Awesome website RobertK. I found everything I pieced together that would have cost me over $800 on the interweb a couple of months back for only $633.

What are blue bottles. ??

 

[O-Gauge Steamer]

Water Injection is actually Water/Methanol and is used to cool the compustion chamgber. First used in aircraft... If you are seriously thinking about adding forced induction, the last thing you want is to increase the CR. It is easier to control the HP with the boost if you are dealing with a low compression engine.

Before anyone pops up and says "but top fuelers are high compression", TF engines usually get rebuilt between runs. Care to wonder why? There is a balance between HP and engine longevity and it is easy to sacrifice life for performance.

HTTPWayne commented on Formula 1. Those engines develop around 800hp, run at 18,000rpm (limited) and displace 2.5 litres. They do not have valve springs because the springs will shatter at that RPM. They use air cylinders to return the valves.

I had a Golen 4.6 with a modified 99+ intake and a 68mm TB from the 4.7 V8 that dyno'd 300hp at sea level (I'm at 7000') and while it ran, it ran very well. It also grenaded twice.

So, the big question is just exactly what do you want? I built a 2450cc (started as 1998cc) Triumph 6 cylinder stroker motor (3 Weber 40DCOE 2bbl carbs) that made 256hp back in 1972 . In a car that weighed 1850lbs, it was a screamer. It also grenaded on a pretty regular basis. On the other hand, I built a 347cuin Small Block Ford (based on a 289) stroker back in 1978 that, in so far as I know, is still running. Built to a different philosophy. HP gain by displacement but not trying to get every last bit of power. I sold it in 1984 running like a champ.

 

[HttpWayne]

I don't want my engine blowing up. I drive this regularly. It's not a guinea pig.

I just finally found a calculator that told me I would gain 4% HP (9 horses). that's not much. Not worth it. I'm going to keep it at 9.6 and research superchargers.

 

[jeeperjohn]

I don't want my engine blowing up. I drive this regularly. It's not a guinea pig.

I just finally found a calculator that told me I would gain 4% HP (9 horses). that's not much. Not worth it. I'm going to keep it at 9.6 and research superchargers.

I suggest looking at the Lysholm twin screw positive displacement supercharger for a couple of reasons. First, this unit is significantly more efficient than roots type blowers meaning you get more power for the pumping losses. Also the discharge air temp from this type of blower is lower meaning you could get away with not using an intercooler. I would intercool it anyways since you are already doing major mods, it never hurts to be sure. There have been superchargers installed on XJ's but it was by people who had the means to do lots of custom machining etc. It is a big investment in time and money. If you're going stroked and supercharged and you want your engine to live longer I highly recommend forged crank rods and pistons $$$.

 

[Porch951]

I guess it's probably too late for a comment like this, but why not just build a Chevy or a Ford motor to swap if you need power that badly?

I would not want to have a supercharger out on the trail...

 

[FunkRider]

You will net the same hp just advancing the ignition timing if you are set to stock specs. Granted you could gain even more power by upping compression and advancing timing.

If I was to build a low buck supercharger setup I would use an M90 from an L67 Series II 3800 aka GTP, SSEI etc. They can be had for 100 bucks all day long, are actually very dependable and draw less hp to turn than your alternator when the by pass valve is open. 6-8 PSI and you will have LT1 V8 power when you need it and the same fuel mileage when you don't.

 

[HttpWayne]

You will net the same hp just advancing the ignition timing if you are set to stock specs. Granted you could gain even more power by upping compression and advancing timing.

If I was to build a low buck supercharger setup I would use an M90 from an L67 Series II 3800 aka GTP, SSEI etc. They can be had for 100 bucks all day long, are actually very dependable and draw less hp to turn than your alternator when the by pass valve is open. 6-8 PSI and you will have LT1 V8 power when you need it and the same fuel mileage when you don't.

Thanks for the info. I'll look into that. I've been looking for supercharged vehicles online trying to see what's in the junkyards.