speedjohnson

I'm purchasing a stroker kit from Lunati. I just figured that bigger was better, however, the Lunati tech favores the 4.000; citing a more favorable rod ratio.

I know the conceptual theories of how a long rod engine will effect time spent at TDC, efficiency gains, ... etc.

?? BUT WHAT ABOUT REAL WORLD EXPERIENCE ?? Has anyone got a solid basis for favoring a 383ci vs. 395ci.

The rest of the engine is: GM CNC LS6 60 cc chambers pn#: 88958622
Ls6 intake and valley cover
Lunati cam 237/242 595/600 112 pn#:55008
Spring pn#: 74600lun 130# @ 1.800 /320#
LPE header/ off road
02 Ls6 clutch cover/ plate
Ls1 edit

Mopar Jimmy

I did a alot research on this exact topic before i pulled the trigger on my brand new MTI 427 ironblock motor which only has 325 miles on so far, which utilizes the big 4.125 crank and 4.060 overbore on the LQ4 ironblock. So far, my engine is a dream come true and the power i am making under my peak numbers make my car a TORQUE MONSTER!

Many claim that the 4.00 crank is more favorable b/c of a better rod ratio but many run this big crank that i have heard of without any problems and i have also heard that WADE at ARE is also a big fan of the bigger crank for LS1 Superstrokers.

In addition to my having 100% faith in MTI abilities to put together a bullet proof motor for me (which comes with their unconditinal 2 year warranty if not F/I or spray), the final deciding factor in my having 100% confidence with the bore/stroke ratio utilized by my MTI 427 motor as set forth above, came from what SHIRL DICKEY (MR ERACER), who has been building and drag racing SBC motors for many years and who also is an aircraft engineer. He really know his stuff and also recently built MICHAEL (AUSTRIAN VETTES brand new 422 ironblock using the bigger crank). Here is some info that SHIRL DICKEY recently provided to AUSTRIAN VETTE in regards to this exact issue you post about here. Giving credit where credit is due, SHIRL DICKEY was the original engine builder who recommended that i go with my 4.060 overbore and 4.125 crank to acheive 427 cubes and i am the only C5 that i am aware of on this forum who is running this exact combo on a ironblock, and only time will tell how durable my motor will be and i have full confidence that it will not let me down.

Anyways, I think that you will find this very informative and helpful in giving you confidence with the 4.125 crank. I would also talk to WADE at ARE and see if he thinks it would work well for you exact application. HERES THE POST from SHIRL DICKEY:

"Hi Michael,
Neither the piston speed or the rod angle has anything to do with the bore size. In the case of the 4.125" stroke and
a 6.125" rod length (your combination), the rod ratio (a measure of rod angularity) is 1.48. I have been running this
rod ratio for years in my nitrous 406 cid small block '79 Corvette. It had over 10 years of hard drag strip and street
use on it before it finally swallowed a valve. This car ran 132 mph in the quarter and took uncounted shots of NOX up
to 225 hp and never failed a rod or a piston... During that period I put over 40,000 miles on the car and the piston
skirts looked like they were new... This had more to do with the Mobil 1 oil that I used than with piston angularity...
Lower rod ratio's have some very highly desirable features that are overlooked by most tuners... With a lower rod
ratio, the piston moves away from the top at a faster rate than it would with a longer rod (higher rod ratio)... On the
intake stroke, this results in a much higher intake impulse (more suction sooner) than is the case with longer rods.
This helps the intake charge to get moving into the cylinder earlier and with more energy... This (increases
volumetric efficiency) and makes the engine breath much better. As a consequence, it generates more low and mid range
torque and far more area under the HP curve... For a street driven car there is nothing better than this. This is
especially true with an LS1 which could use all the help it can get on the intake side...
With regard to piston speed, a longer stroke will generate higher piston speeds at any given rpm. At 6000 rpm the
piston speed for a 4.00" stroke is 4000 ft/sec. and for a 4.125" stroke the piston speed is 4125 ft/sec. which is only a
3% change... Not enough the bother with... Another way to look at it is; a crank with a 4.00" stroke has the same
piston speed at 6000 rpm as a 4.125" crank has at 5820 rpm. Piston speed does not become a concern until it exceeds
5000 ft/sec... With a 4.125" stroke, that occurs at 7273 rpm... As you can see from all this math, piston speed is not
a concern for the strokes and engine speeds used in a stroked LS1 street driven Corvette...
As far as the bore size is concerned, this only effects valve shrouding in a very small way... With a 4.030" bore,
you are .130" larger than a stock 346. A 4.10" bore is .200" larger than a 346... I think you will see that built 346
engines are generating more hp per cubic inch than the big bore strokers... That being the case, I don't see where the
small bore size on a 346 has hurt it much using essentially the same heads... The reason the big bore engines are not
able to match the 346 in power per cubic inch is because of intake limitations, not bore size limitations... In regards to using a smaller bore size...(4.030 or 4.060 LQ4) The benefits of the lower rod ratio 'way more' than offsets
any possible valve shrouding on a smaller bore...
Hope this helps...
Shirl

HOPE THAT HELPS YOU,

MTI 427 Roadster :smash: :cheers: :cool:


:flag GOD BLESS AMERICA, OUR PRESIDENT AND OUR TROOPS! :flag


[Modified by MTI 427 Roadster, 10:18 PM 3/19/2003]


[Modified by MTI 427 Roadster, 7:06 AM 3/20/2003]

NEPTUNEBILL

I'm with you, Wade is building my stoker now with the 4.125 crank, it is very encouraging to here Shirl's point of view as he is certainly very respected among our group and others, I feel much better about my decision. Good old NA torque, can't wait and heres to ATI :U :U :U

God bless our boys in Iraq and F Saddam and his F sons

TEK WARRIOR

The Lunati tech is right.On an LS1 motor you want more bore than stroke,Go with the 4.00 crank,I guarantee if you built a motor with a 4.125 bore and a 4.00 stroke as opposed to a motor with a 4.030-60 bore and a 4.125 stroke,the 4.125-bX4.00-s will make more power,the bigger bore is what you want,an all bore motor will be faster down the track than an all stroke motor.Cartek uses the 4.00 stroke on there bigger motors with a bigger bore,they don't like the 4.125 crank in the LS1 motors,I think they built one motor like that,they prefer the 4.00 crank.Granted the 4.125 stroke will feel good driving around town,but if you go up against a bigger bore motor your most likely going to be looking at his tailights.


[Modified by TEK WARRIOR, 2:05 AM 3/20/2003]

Mopar Jimmy

[QUOTE]The Lunati tech is right.On an LS1 motor you want more bore than stroke,Go with the 4.00 crank,I guarantee if you built a motor with a 4.125 bore and a 4.00 stroke as opposed to a motor with a 4.030-60 bore and a 4.125 stroke,the 4.125-bX4.00-s will make more power,the bigger bore is what you want,an all bore motor will be faster down the track than an all stroke motor.Cartek uses the 4.00 stroke on there bigger motors with a bigger bore,they don't like the 4.125 crank in the LS1 motors,I think they built one motor like that,they prefer the 4.00 crank.Granted the 4.125 stroke will feel good driving around town,but if you go up against a bigger bore motor your most likely going to be looking at his tailights.


TEK WARRIOR/STEALTH:

Although i generally agree with what you state and most tuners probably would to, i do think however the real issue presented in this thread is that once your bore is choosen for your engine build and everything else is 100% equal, is it bettter performance wise to go with the 4.125 crank vs the 4.00. No question, when given a choice to get bigger cubes in a drag racing motor ideally you want to achieve the bigger cubes by going with the biggest bore size you can and its better to get the big cubes with bore vs a bigger stroker, primarily b/c the bigger bore unshrouds the valves and makes the heads breath better and b/c of the faster revving of the engine when faced with an all bore vs. stroker.

FOr purposes of this thread though, the issue really appears to be once your bore size is choosen, what crank works/performs better (4.00 vs 4.125). In other words, in my build once i new i was stuck going with a 4.060 overbore on my ironblock, i put alot of energy, research and decision making whether to run the bigger crank and get 427 cubes or the 4.00 crank which would have given me 414cid. Everything else being equal in my build i was convinced by a couple of extremely knowlegable sources such as SHIRL DICKEY who i quote above, that the bigger crank and more cubes in my case would make consistently more horespower under my peak horsepower & throughout the entire rpm band and therefore, would out dragrace my same motor with a 4.00 crank. Again, the old expression there is no replacement like displacement. I know other major tuners such as WADE at ARE is also a big fan of the bigger crank to obtain bigger cubes and here is the key, everything else being equal, including bore sixe.

For instance in your new ironblock motor where you are running a 4.04 overbore, would your car on motor only perform better ifyou were running a 4.125 crank (423 cubes) vs. the 4.00 crank (your 418cid). I am no expert, mechanic, SBC engine builder, aircraft engineer, racing engine builder, etc. but SHIRL DICKEY is and he pretty much convinced me that although in my examples (where the bore size is already determined and everything else is equal) that the bigger crank yielding bigger cubes will out perform the smaller crank b/c of more power(torque) being made throughout the whole rpm range under the peak numbers and as most knowleagable folks know (thats where a drag race is truly one).

MTI 427 Roadster


[Modified by MTI 427 Roadster, 8:07 AM 3/20/2003]

MattG

I do agree that the more bore the better on an LS1, or any motor for that matter. However the stroke, in my opinion, depends on what you plan on using the car for and what you want out of it. If you are looking for a quicker reving, high rpm motor with its main focus being dragracing, then I too would recommend the 4.00" stroke crank. If you are looking for a torque monster street car that will make its power at a slightly lower RPM, then I would recommend the longer stroke 4.125" crankshaft.

My car's main useage is for street driving, a bit of autocrossing, a few roadrace lapping events each year, and a few runs down the 1/4. For this reason, I went with the 4.125" to get maximum displacement and torque at lower RPMs.

So again, it is all a matter of what you will be using the car for, and what you want out of the car.

marco383

Now for some real world numbers. My 4.00" stroke 427 has made 520 RWT. with 440 at 2500 rpm, this with 11:1 C.R. on 93 octane. Anyone out there with the long stroke setup that has done as well?

NEPTUNEBILL

My driving is pretty much like Matts and I am very happy when I look at his dyno chart and see 400lbs torque at 2200 that stays above 400 and close to 500 all the way to redline. 95% street use and looking for torque, the only thing I liked about my viper was the torque, I never get to go 200mph but I go 0 to 60 a lot. I'm very pleased Matt is building my 436 and can't wait to bolt it in.

kromberg

If the two versions of the setup make the same rwhp, what does it matter where the peak is located?

Keith

EuG

Here’s a comparison of 4.0” crank vs. 4.125” crank in a motor with same identical heads/cam/exhaust etc.

It’s an old mild setup running cats, etc, but that’s not the point.
It’s just to illustrate the difference.


(click to enlarge)


I think for drag racing set up with 4.10 gears, more aggressive cam that peaks higher and causes you to shift close to 7K rpm or higher it’s better to go with 4.0” crank.

For anything else I’d prefer 4.125” :yesnod:…
My $0.02



[Modified by EuG, 11:30 AM 3/20/2003]

Shinobi'sZ

Great comparison Eug..its nice to see some back to back numbers.

Austrian Vette

My reason to go with the bigger crank but not to bore the maximum was to spray the poopie out of that engine without getting problems with the cylinder walls.

So now I have a torqui street car that can go fast at the tracks.

For me and my needs that´s best of both worlds. :yesnod:

Michael

Mopar Jimmy

EUG:

Great post man and right on point for this thread. I think this illustrates that everything else being equal (except for miniminal bore difference of 4.08 vs 4.1) that the 4.125 crank is the optimal set up for this engine/set up.

MTI 427 Roadster :cheers: :chevy :smash:

vstella

I just ran across this neat website with a cubic inch to litre conversion calculator...Try it ..It works!:thumbs:

http://www.mtv411.com/auto/Cubic-inc...calculator.htm

speedjohnson

Great info guys!

The intention of the car is for an occasional roadrace event in SCCA ITE.

I have already made the transition from a production class to a GT-1 car, however, the GT-1 car just sucks the life out of me. It is a thrill to drive, but I find myself going to fewer and fewer events (= less fun?). It is an expensive weekend: race gas and lots of it, brakes, slicks and tweecks. It's unreliable: especially the valvetrain issues. Sure it revs, but the springs only go for a little while, titanium wears quickly and the spring pressures kill the guides necessitating full scale rebuild after approx 7-8 events. When it rains you get wet. No heater to defog the windscreen and you can't use wipers on lexan.

It was alot more fun when I raced the production car. Gas was cheap. I ran on DOT tires for the entire season, instead of rotating the slicks in and out after two events. The thing didn't have valvetrain issues because engine speed was kept under 7000. When it rained I had a real roof, windshield and defroster.

That's what I would like to do: work back towards the production car concept (fun, cheap, reliable) with the C5. It already handles more nimbly than the GT1 C4, minus the stick from the slicks. I would like to match the engine to the gearbox/ track. Since the gears are realitively wide spaced I will need a torquey engine. I will need to reach at least 6800 RPM's or I will have to hit 5th unnecissarily on the front straight, but will still need enough grunt to pull in 5th for awhaile at the upshift on the backstraight. sj

Mopar Jimmy

Given your use of the car, everything else being equal with your engine build, i think you will be better served with the 4.125 crank as the torque will RULE SUPREME and even though you will probably make peak horsepower around 6300rpms like my 427 motor using the same crank, the car will still be pulling strong up to 6800rpm (as my motor is) and you will be good to go.

MTI 427 Roadster

TEK WARRIOR

Torque doesn't win races,horsepower does,just look at the HP to TQ ratio of an Indy car,Winston Cup Car,C5R Lemans car uses bigger bore less stroke,I rest my case.If you like the seat of the pants feel of a little more torque under street driving conditions while your in traffic,go with the bigger stroke,when you get to the track,drag or road race you'll place second to the bigger bore cars.

kromberg

Yeah for those little girly races that go around and around in a circle. Torque is the thing that gets you up and going. Why do you think all the ricers what to race from a roll? Because they have no torque. Sure they might have 700 fwhp, but they only have about 300 fwtq :D

Keith

Mopar Jimmy

MIKE:

I generally agree with your statement but i believe this post is more about once the bore size is determined, i.e.-Let's assume a 4.125 bore, then will that particular motor perform better at the dragstrip, or make more power (HP/TQ), if it is matched with the 4.125 crank or 4.00 crank. Alot of evidence seems to support that the bigger cubed motor, with the 4.125 bore and 4.125 crank may in fact outperform the the same bore 4.125 match with a 4.00 crank (and smaller cubes) on the track, be it a dragstrip, a autocross or roadrace track. I guess the only way to really tell would be to match up the same car with the different cranks (all other varialbes with the engine and car being the same) and see which crank outperformed the other, for its given application, i.e.-Dragracing, roadracing, street racing, etc.

MTI 427 Roadster

MTI 427 Roadster

NEPTUNEBILL

I thought the expression was that "hp sells cars, but torque wins races". Ferrari uses a big bore short stroke engine and with good balanced gear ratios overcomes the lack of torque (relative) with quick revving run through the gears at high rpm, but you don't see them setting any records at the drag strip, if you run around in circles at 200 mph than hp would play the part and torque would not be as important as long as you keep your revs up, I would think that 60' times etc would depend on torque and the inertia it produces, in any case I think we all go zero to sixty a lot more often than we go 200mph, typically I would take a shorter stroke and bigger bore for competition, but as MTI states, If my motor would only take a 4" bore and I had the option of adding more ci with a longer stroke I would do it, if I could go with a 5" bore and had the same option I would take the 5" bore and still going with the longer stroke.