Friendly Freddie

I can't tell by your reply , which side of the fence are you on? Assuming fuel is not an issue and its an all out race app , where would your compression ratio be?

Adrenaline_Z

I'm a firm believer in letting the engine breathe and let the valve timing
fill the cylinder as opposed to raising the SCR to make up the difference.

There is more power available from more charge entering, than a smaller charge
which is compressed higher.

Fuel type is always a concern when selecting the variables, so I wouldn't
know how to answer in a general view.

Selecting your maximum SCR without knowing how well the engine breathes
and target DCR for a specific fuel is a shot in the dark. Even knowing those
variables is still a science.

I would be looking at the torque peak RPM and work from there.

SStrokerAce

iTrader: (2)

LOL, that "Bleeding off compression" thing with too much overlap scares me as well. I still want to know if they have even thought about that sentence and what would take for a motor to do all of that.

Freedie,

I would say the 13-14 range would be much better than 15.5:1. I think you can tune the compression with a new cylinder head with a larger chamber and settle most of your issues. You might also want to try different gasket thicknesses, maybe even larger than what you are running right now, and not just to control the compression ratio.

Bret

Friendly Freddie

In this app I kinda have a problem with "breathing" so to speak. I am limited by a small bore (4.030), and the fact that the engine is only 358ci. The cylinder heads flow mid 330's at 600 lift. If I go to a cylinder head like an ETP 4.0 bore LS7 (because it flows better than my existing head) will I have to spin the engine even higher to make use of the extra intake capacity? I am already buzzing this little engine to it's limit. The gearing , and converter already work very well with the power band I have now. I have never had the engine on a dyno , so I could'nt honestly tell you where it truely makes peak torque. Chassis dyno torque #s don't mean squat with a really large converter.

With my given situation I feel like I should get these AFR castings that I already own, finished up. If I don't make any more power than I have now, at least the thicker deck and better casting quality should bring me some reliability(and bring compression down a touch). Have my cam reground (or buy a new one) , this should net me a HP gain.

Adrenaline_Z

Talk about intimidation...posting behind Bret and Erik!

Seems to me you might have too much head for the displacement. What RPM are
you spinning to? What size are the ports?

THe cam specs that you have listed seem fairly decent. I would imagine the
overlap region is fairly high on a 110 LSA? Do you have the valve timing?

As for breathing, if you're limited with bore diameter, there's always power to
be found in the intake and exhaust lengths. What sort of exhaust setup
are you using, and what are the details?

Keep in mind, this reply is based on 69.9% theory, 20% application and, 10% dyno testing...the other .1% contains a little luck and bench racing! ha

Mike TexaSS

iTrader: (2)

Ditch whatever crankshaft you have and get a bigger one.

Friendly Freddie

I would have to get with my head porter to get an idea of the size of the intake port (I do think they are pretty large, 235cc give or take) . I need to pull the cam out of the engine to get the cam id # so I can get complete specs on the cam from LSM.

I have had the car on the limiter on a couple of occasions (9100). It pulls hard all the way there. I run a 1 7/8" stepped to 2" with 3 1/2" collector Kooks header , with a header muffler and then a short section of pipe with turn downs.

The long and short of it is this, I have to do some work to get the info everybody is asking me about. (I'll get to it, over the next couple of weeks).

Friendly Freddie

He he, shut up Mike! you know I would if could, without changing everything else. I wish I had built a big motor in the first place , but alas I had faith in the LS1tech series that is now defunct.

Adrenaline_Z

9100 RPM is not for the average valvetrain or cylinder head. I was under the
impression this was more a street/strip motor than a pure strip motor.

I bet the placement of that muffler will pick up some power. Is the muffler
connected dirrectly to the collector? Have you tried extending the collector
before inserting the muffler? Collector design, length and secondary length is very important.

Friendly Freddie

I have about 4 or 5 inches of pipe between the muffler and the collector and then maybe 24" after the muffler before I put the turn downs in place. What is the proper procedure for calculating these lengths?

heres a clip of the car.

http://video.ls1tech.com/search/8.73...72E1CACD51.htm

Ben R

Are you using a 5.3L crankshaft to make a 358 with a 4.030" bore?

1936FordPU

iTrader: (3)

Sean,

What ive always used for the folks that want header/muffler setups is the ole crayon trick. When the wax stops melting, i place the muffler there and then a short turndown at the end. It really depends on how well your collectors scavense as well. Poor collectors seem to lose exhaust velocity shorter and quicker compared the to the better versions. When tuning the headers on the Edelbrocks I shoot for around 32" total primary lenght before adding the collector (HVMC's at the end). Seems to be working on the cars ive used them on for making good all around power.

Mike

1936FordPU

iTrader: (3)

I thought its a 4.8 crank but could be wrong.

Friendly Freddie

Ben, it's 5.7l stock replacement lunati crank, but offset ground to reduce stroke. The Guys over at LME could better explain the exact specs. I might be full of poop when it comes to bore size, but I think its 4.030.

GrannySShifting

iTrader: (10)

Static compression doesnt work for much on a heavy nitrous motor. 15 hp doesnt go far when 50 is just another jet away.

Weve got cars going fast on 10.8 that was originally setup for 11.5

I always would err on the lower side for compression than higher - as per Erik and a few others that know well. Big nitrous motors are like Fuel motors than anything else in my opinion

Friendly Freddie

I agree , BUT I am already pushing this NOS bigshot plate to the limit now and the class I want to race will not allow a direct port system.

GrannySShifting

iTrader: (10)

Pm me, up the pimpness on the plate you can run more nitrous accurately through a plate system than an LS1 will keep its heads down on under any circumstances

Friendly Freddie

Done , any suggestions are very much appreciated!!

Adrenaline_Z

The crayon/paint method is much better than guessing, but according to
several tuners, the length is not optimum.

Where the exhaust heat stops burning off the paint, or crayon does not
necessarily represent the tuned wave length for a specific RPM.

I don't know of any programs that calculate the correct length.
Does "Pipemax" have such a feature?

I have used some empirical values suggested by Vizard to tune my exhaust.

CamKing

I can calculate it.

I just need the seat duration of the exhaust lobe(not .020" duration, but the actual opening to closing points.), the RPM that you want tho length tuned for, and the exhaust temp at that RPM.