I would like to continue the previous discussion. First let me say the IF I had an auto trans I would go w/383. Since I have an M21 w/3:55 gears, the longer stroke 383 would wear too much and burn too much gas. The question for me was "Could a 350 put out similar power as 383 w/o the fuel comsumption? In my 360 sb the 6" rod allows more compression 10.25, the pocket porting, backcutting valves and Hyd Rol cam should make things almost equeal, except just off idle. W/4 sp my motor does not need to run as low as auto trans. I am looking for LONG TERM durability that I don't think I will get from 383! I am trying for the 12 sec 20 mpg club. Let the discussion begin!

 

???

 

Quote:

"I am trying for the 12 sec 20 mpg club. Let the discussion begin!"

That is called having your cake and eating it too! You will need Superram and 700R4-3.07 gear for that.

Assuming you have a carbed motor and GM heads,your best bet will be a 3.48 stroke and 5.7 rods with that gear.You don't have enough cylinder head to support the 6.0 rod use through mufflers especially.Again,only assuming.Much info is left out.

The debate over rod lenght will always be just that.Debated on street strip cars.Have posted before that we don't race dyno's.Real world is what depicts the proper rod lenght for a given combination/usage.I suspect that the GM Engineers new that when they chose to use 5.7 rods in the early LT1 near 3600 lb Corvette.Think about it.Their pride and joy.

Throw the auto out and use 2 4spd Vettes side by side using marginal GM heads.Exact same internals except the 2 different lenght rods.These cars are rolling at 1500 rpm in 1st gear.The 5.7 rod motor will leave on the other.How much?Depends but still will leave on it and the 6.0 motor will have to run it down.You want long motor life?Spinning them up is not the best for that.E/T is where it's at.Equates to drivability on street also.MPH is bragging rights.First to trip the win lite has done his homework

Piston ring stack is an issue as well on a long life 383 w/6.0 rod as well.
Typical 500hp small block shows around 10 hp difference between these 2 rods.I am not desparate to have that advantage over the car down the street at a loss of low end power with moderate rear gear.

Rod lenght and side load/longetivity? A 400 small Chevy will run 100k with the 5.565 rod.I don't know about you but I would not with 100k on a hi performance motor want to be say 300 miles from home on that weekend trip bang shifting that buddy.Motors need freshened up on occasion.

A 2700 lb 67 Camaro or a 2950 lb 62 Vette would change my thinking on what rod to use.But only if I had cylinder heads to support as in 230cc 23 degree heads with good exhaust port and 4.10 + gear

Someday let's talk of Lake Racer Boats.Jet drives in particular which not only is a water dyno as in rpm/hp conversion with Berkley impeller chart but acts much like a heavy automatic drag car with 4500rpm stall and how a .250 long rod Big Block will get smoked by a stock rod engine running 6300 RPM

I am a no typer so be easy on me! I guess,.......It's time to click the button and let the flames begin!

 

Mountainmotor: I have seen your responses before and I respect your knowledge. I can't argue w/anything that you have said. Take those two cars you mentioned and give the 6' rod an extra point of comp. What then? In my orignal post I mentioned 10.25 cr w/TFS heads. That was my main reason for the long rod! I wanted the extra 10lbs+ tq and mpg that the extra cr would give. I agree w/you tq is king. When I spoke to rep for Comp Cams I made clear that I was interested in tq for the street. The 270 HR he suggested is not an rpm cam, 218-224 @.50. I hope to peak tq @ 3800 and hp @ 5800. I was concerned w/good combustion. Dished pistons was not an option. I wanted a good flame front "flat top pistons w/.40 quench" Hp is just frosting on the cake! My car came w/3:55 and M21. It was easier and cheaper to build motor to match what I already had. I agree that EFI and OD would meet my goals, it would also cost as much as my whole engine! I know that my exhaust system is holding things back. I still have to pass smog again in 2003. After that, headers, X-pipe and better muffelers. That should free up 25-40 hp! To make sure the extra comp didn't overheat my system, I went to 4 core rad and dual spal fans. My power is going to wheels, not in the fan or up in excess heat. This is a street engine was ment for daily driver. The 12 sec 20 mpg was just for braggin rights. The air gap and Demon 750 vs are there to make sure that this combo doesn't "lay down " on the top end. So far I am very happy w/tq curve. This motoer just keeps on pulling! Fine tuning is all that is left. Thanks for the response, let the flames begin.

 

No flames.Just friendly conversation.

On the "dished pistons was not an option" I would like to ask who has quantified this theory and actually has the numbers to back it up and what the actual measured or other "quantifiable" differences/advantages would be?Not "guestimation".Real world comparison is in need here.No doubt I would prefer a flat top with a small combustion chamber to reduce the need of excessive ignition lead and am not at issue with your statement..Just would like to know where you get this from.By chance would this be from a magazine article?


Not aimed at you "really not" but would like to pass this along from a reader that sent to Car Craft .


(Mindless striving for the latest in technology is no better than irrationally clinging to the past.)

I have seen the octane/quality of gasoline on a steady decline.I recently saw in a forum post that best gas available in CA is now 91.Don't know if true.But the fact that Oklahoma had oxygenated gas last summer"reserved for large cities and winter months" makes me wonder about the future of a street motor with a carb living on the ragged edge compression wise and what is actually pumped into a car from gas station pump these days.

Life is uncertain and I have taken that into consideration in the process of building my Son's newest TPI motor.It must last 100K plus miles which equates to 10 years or so.I set it at 9.45 with Iron heads,dished pistons and good chamber design for ultimate durability with A/C and heat issues and header bolt hole repeated use/ strenght ect.All in an effort to out guess what's next or rather take into consideration the trend towards gasoline and the fact that I might not be around to "redo" this motor in a few years.

Some of this is off your original topic.Most is not. Good luck in whatever you chose.

 

I don't think you'd see a significant difference in fuel economy between a 350 and a 383 that were equal in power. The extra cubes of the 383 would permit it to make the same power as a 350 while in a slightly milder state of tune that would, possibly, allow for more efficient use of fuel.

I don't think that the longer stroke would have much of an impact on long term durability, especially if we're talking about comparable power levels. Despite the longer piston travel, I haven't heard of any related durability problems being associated with many other engines that have similar or longer strokes as a 383. 396's, 427's, 454's, plus many non-Chev engines come to mind. The larger engine can make the same power at a lower rpm which puts less wear and stress on the rest of the engine also. While one combination may have an advantage over the other in economy or durability, I suspect that that difference would be small. It's your car and your money so, if you have a preference for a shorter stroke engine, then that's what you should build.

 

Still a little off topic from original post but Vetterodder hit it pretty good about milder state of tune with 383.Many over cam the 383.It is not that much larger.I have though seen stroker motors get pitiful gas mileage in an effort to gain all out low end torque.Can get too strong a signal from motor to the carb in some combinations.
Much to it all.Wish for a device to speak into and out come printed words :)

Ricasan I can see where you are coming from though.Been there before.Fun to build a "creation" of compatible parts.To each his own.No doubt your knowledge will show in what ever you create in that you are on the right track and will run well regardless of subtle differences internally.Dissing the norm can be a good thing if one is prepared to be on top of it at the end.I beat to my own drum as well! We only go around once in life and have fun while you can. Wade through all info recieved then build it your way would be my suggestion.As Vetterodder said and I agree,It is your money.Most of all have fun with it.
Later

 

Mountainmotor. Still no arguement from me! I have been waiting for back to back testing of rod lenths, for some time. You hit it when you said compression on the edge and 91 octane do not mix. Here in Ca 91 is all we get. I felt that the 6" rod was insurance against problems w/detonation. In my SWAG I decided that the 10-15 hp & tq was not worth the 10%-15% less mpg. Remember my previous posts "3:55 gears and M21 4 speed". Given the givens, the 6" rod was cheap insurance! Even if the long rod wasn't worth any hp, the extra comp is!

Vetterodder. If I had a blank sheet of paper and blank check, a 5-6 speed trans and bigger motor would be happening. Gears can make all the differnce in the world. Having 3:55s and 4 speed reality rears it's ugly head.Like you I live in Stockton and want no problems on a hot summer day driving up the Altimont! To have to turn off a/c because of overheating is UNACCEPTABLE! I am striving for a true GT machine. Something that does everything acceptably w/o specialising. If I spun the 383 at 3K @ 70 mpg, I believe that wear would become a factor down the road, not to mention mpg. Like mountainmotor my engine will have to last 100K or 10 years, whatever comes first. The better rod angle can't hurt.

CFI-EFI, Why did you even post? Question marks, what do you not understand? If you are going to take people's time, say something!

 

The longer the rod you run the more detonation sensitive your engine will be in general not the other way around. Just run the apprpriate compression and be safe. The rod ratio is too small a thing to affect any of this anyway. There are a lot of rod length tests where they keep CR and reciprocating weights the same and the shorter rods usually make a little more power and have less detonation due to their lower pumping losses. In reality the long rods will usually show a little more power due to the slightly slower instantaneous air speed at the same rpm and the lighter pistons longer rods let you run cutting down inertial losses.

 

Quote:
"Even if the long rod wasn't worth any hp, the extra comp is!"

That is where proper cam selection comes full circle back into play.Not just duration either.
On the hiway what will your average cruise RPM be?Need that thing running efficiently at that speed .So with those gears might need to cam it up a little or tighten the LCA.

If you have not bought a cam,now is the time to do the homework.I think I can get you closer to what you need than what was suggested by Comp.


[Modified by mountainmotor, 12:39 PM 3/5/2002]

 

Mountainmotor: You asked me if I was getting my info from a mag and you were right. My reading list includes the usual car mags, 3 motorcycle rags and books by the usual published "experts" Lingenfelter, Vizzard, Yunick, Cameron, Muzzy, Yoshima and a few others. I too have been around fast boats '625 Hp drag hydro" low 10s in 1/4. I wish we could experiment w/differnt combos. Not having a lot of $ I tried to get things right the first time. I noticed the article "The 350 Chevy should have built" Hot Rod. Running 11-1 on 87 gas got my attention. Your right, lack of low end can be made up w/cam. Mine is 218-224 on 110 lca. The 1.6 rrs bring ex to .539. That should get things moving. I talked w/reps before I bought anything. My combo is as coordinated as I could. Nothing radical. I told my mech to build a car for his Wife and child to do trip accross the country and back. Right now I think my stock "beat up and flattened" ex is holding things back. After 03 come headers and X-pipe!

 

If you really want gas mileage go with 114 lsa or higher. That keeps the dynamic compression ratio higher over a broader rpm. Keep your motor water temp about 210. If you have aluminum heads use thermal coating.

Also in reality gas mileage is determined not so much by c.i. But by how efficient a motor is at a given highway speed rpm.

Crane cams are rated in C/R required and cruise rpm

 

Yoshima as in the old Ontario Motorworks, Ontario CA? Kaz Yoshima? If so it is a must see for me! What is he doing these days?Well I can imagine what he is doing but is he on his own or a factory tuner?

Just caught you are running a 750 Demon and Airgap but passing emmisions in 03 is an issue concerning exhaust now?


[Modified by mountainmotor, 4:36 PM 3/5/2002]

 

What I didn't understand, is the passage I posted as a quote. I didn't realize that I was that "mysterious".

I am sorry that my question marks consumed so much of your time. I am also, sorry for this post, but You asked me a question and I thought it deserved an answer.

At this time I'll elect to continue to stay out of the discussion.

Again, I'm sorry for having wasted your time. Both with the question marks and this response.

 

I didn't understand that part either, but I saw that you'd already covered that base with the "???."

Jake