3.8TransAM

Recently begun serious tuning work on friends car. Was a former 92 SD 5 spd 305 tpi car now has a 350 w/ 6 spd conversion.... All pertinent sensor are working (VSS etc)

My biggest concerns are the timing curve and partially the VE curve. In all stock tpi manual bins i see what to me looks like an enormous amount of advance at a given rpm.. Is this do to poor tuning on the side of GM(thought 305 were prone to detonation in the first place)? The VE curve also tends to have the same design to it more of a flattened curve , instead of a rise and then peak then a slight fall like in a 350 SD bins i use. I have quite an amount of time and broke the multi hundred chip barrier on my own prom developments (3 diff SD cars).

This whole manual deal is really starting to give me fits.
I searched "manual" "stick" "tuning manual" and anything else i could think of. I never found any information as to regarding the actual reasoning for the timing and VE curve, at least in relation to an auto aplication. I dont see how the car could pull that kind of timing and not knock, even when stock.

Anyone have any information that they are willing to share and/or know of another resource that has material on this subject? I also did a good amount of digging at diy-efi and i did not uncover anything else new in relation to it that i didnt dig up here.

Im basically looking for the differences in tuning a manual app than my usual automatic platforms.

If anyone has a version or is willing to share a bin , im more than willing to share anything i've gained and any of my bins (i have lots that work and lots that dont lol). Im just trying to figure out if im approaching it wrong since its a stick or maybe the car has an underlying issue or 2(dont believe so, but u never know)
thanks
Jeremy
PS im really hating manuals right now

RBob

iTrader: (1)

AXCN is a Vette TPI 6-spd bin. May be a decent starting point.

RBob.

Grumpy

It's 3/4 about getting cars thru the EPA test cycle. I'm not sure how concervative the shifting is for the test, but I'd venture it's alot more granny like then the average guy doing chips for a 3rd Gener.

Manuals, ie 5 Spd vs a 4 Spd auto also can keep the engine in a tighter operating range. The more speeds the narrower the power band can be.

You also have to remember, that at speed an auto trany shifts faster so there is more load after a shift then a manual, since the manual had the **breathing** time, and got a shoot of AE during the shift. So the manual can tolerate more timing.

And below the stall speed of the converter, you just don't need or want much timing.

Then also with additional torque multiplication of the converter the VE stuff will be different.

Not to mention the cummulative effect of all this stuff.

And at times it's just alot easier to listen to what the engine's tellin ya, rather then thinking about what it should need or want.

FWIW all things being equal a small bore engine is less prone to detonation then an engine of the same size with a larger bore.

3.8TransAM

Many thanks for the replies guys

Grumpy what u state about the auto shifting quciker and the manual having some breathing room makes definite sense to me..

I was thinking along the lines of a narrower powerband due to the addition of more available gears, but im still kind off in shock at the timing values i see at the higher load points(kpa)... guess im going to have to dig in and see what she likes best... im just kinda tryign to walk slowly and gain some steam i have zero experience in playing with a manual car and actual chip burning lol

Is it still best for me to work from a F body bin? or due to the modification and 6 sd should i head for a corvette bin? I've searched thru the board and come up with a 50/50 split on the issue and currently working with a 5 spd bin(91 f bod).. Im aware of the differences from vette vs. F bod bin(used f bod bin for that reason) and did some experimenting on my Formula. Just this stick shift has me spooked, i hate being blind lol
thanks
jeremy

funstick

you would think that wouldnt you ?? would make sense ?? it doesnt. long stroke small bore engines. very intolerant of lots of spark lead. at least form the cars ive tuned. now a 302 SBF there a knock resistant motor. big 4 inch bore with a short stroke.

id bet it has to due with compressive preheating of the combustion charge being higher in a smaller bore.

Grumpy

All things being equal, it is true.
If your going to hit reply how about trying to stay on topic, or if you want to go off on a tangent, start a new thread.

When you swap over to an entirely different engine kind of kills the all things being equal. Cutting apart a Ford head will show some interesting differences from what GM does. But that's even getting more tangent to the original posting.

RBob

iTrader: (1)

I can't really say which bin is best for you (Y | F body). If staying with the f-body bin can use the calibration of AXCN to help give you an idea of what a manual cal looks like.

One major difference between a manual and auto is when pulling out from a standstill. When letting out the clutch it is easy for the RPM to dip down and the MAP to go to 100 Kpa. This makes the SA & VE need to be tuned in those areas.

May need to tweak the stall saver to get it to not effect the pulling-out too much.

RBob.

funstick

i was just stating that its not all equal and bore relation ship. the real key is piston speed.