SD2 tuning

[Steve Wood]

The one area where camshafts come into play is rpm.  The engine has to be able to turn enuf rpm to get to the desired mile per hour with the given rear end and tire diameter.  The converter slippage works against this. 

Many still try to think of a forced aspiration engine as a regular engine and choose rear gears accordingly.  Yet, in most cases, we find the higher the rear gearing (lower numbers), the better the car performs...3.2 5 is a good rear gear with a big turbo and good converter...al so helps to make launches more consistent

[Scoobum]

Over the years I've seen guys go to a looser convertor...as they say it won't spool quick enuf on the line. In general, a looser convertor will spool well...but lose some at the top of the track. I'd rather have a tighter convertor that couples better at the top of the track. Tuning low gear fuel/timing will loosen a tight convertor on the line. Erics chip is notorious for being rich in low gear fuel...as I've seen 02's as high as in the 870's in low gear fueling. The hotter you can get a turbo...the quicker it'll spool. Pull low gear fuel...add low gear timing...it ain't rocket science. Erics 5.7 alky chip also incorporates aggressive mode.

Vendors pushing their LU convertors claiming you can leave them unlocked for racing is becoming an epidemic. I read a post by Dusty Bradford from years ago. The higher you can shift an AC convertor...th e better it couples...and AC convertors can be had for a song these days. Shift my AC at 5800. 105 MPH through the traps tells me it's doing pretty well at only 25 PSI.

[Steve Wood]

Cannot disagree with that.  I am no converter expert, but, I can look at the log and see if it was doing its job.

Strange that over the years, the original Art Carr has consistently worked...and even more strange to me that the 911 seems to work well for most altho I broke one.  I think that was a fluke and not the rule.  In general, I like non lock ups for serious cars and I have noted that flavor of the months seem to often be hype and fade away.  Maybe success encourages sloppy, cheap work because some burst on the scene hotter than sliced bread and then the later versions seemed to not work well.

I guess it is one of those cases that you some times do not get what you paid for and you seldom get more than you paid for?

[nocooler]

Jason,


I commend you for sticking with this. At this point I'd think it'd be easier to swap cams than replace and re-shimming springs.

[Steve Wood]

I think Jason is like me.  He's gonna do it his way if for no other reason than to prove he can! I have more than one of these t shirts!

[daveismissing]

I think Jason is like me.  He's gonna do it his way if for no other reason than to prove he can! I have more than one of these t shirts!

As your offspring exchange knowing glances...

[good2win22]

Wow! Just checed this thread.  Been super busy with work. I have to agree on the converter being intricate in the recipe. I must also say that I have almost considered swapping cams with a known setup that will achieve my goals. I have been that frustrated with it.


Some of the biggest lessons I've learned from this is the selection of lifters must compliment the cam lobe on a hydraulic roller.  That being said, the spring must be selected and installed at the correct height and be closer to coil bind than my initial comfort level would like.  So many different theories about short travel, reduced travel and standard travel lifters. So many different theories on cam lobe and duration.  What I considered to be a reputable source for parts and information,  I find out that the fella is not well regarded amongst buick purists. Next lesson, probably not enough turbo for this setup but I'm gonna run it till I decide it's not enough. Next, my converter is probably too tight to get me off the line like some would like but there's something about running somebody down that inspires me. And changing a converter is easy.  Also, I have a converter guy just up the road who can cut this thing open and do anything I ask in a single day.


Huge learning lesson here to be sure and to be honest, I could throw it all back together and drive the car just fine. It just wouldn't be what I wanted it to be. And Steve is right, I'm gonna get this solved with this cam.  I have a great belief that this cam with its lobe selection, lift, and duration is going to surprise some folks.

[Steve Wood]

Hydraulic rollers are a big compromise at the best of times in this type of application.  Adding boost behind the intake valve certainly does not help.

If I were going to build a serious engine, I would use solid lifters so the cam could do what it was designed to do....it's so easy to pump up a hydraulic roller lifter and also easy to collapse it.

In the end, the turbo is going to trump theory and make the power...all the cam has to do is open and close the valves reliably.  Spooling the turbo is largely the responsibility of the converter and a static compression ratio high enough to offset the thermal inefficiency of the aluminum heads where combustion is concerned.  More heat thru more timing will get it started.

The one thing that a cam does is to extend the rpm range.  We reach a point pumping more air thru the valves with a good turbo that we must have more top speed if we want to still be gaining speed at the finish line even if the converter is slipping only 2% (we wish)

This gives us two choices.  The first is a combination of taller tires and a taller rear gear-say 3.23/3.25 which gives us more speed fora given rpm.

The second is a longer duration  cam lobe profile which allows more rpm before the valve train ceases to be able to follow the lobe shape properly and bad things occur.  Roller cam profiles tend to reduce the top allowable rpm while increasing the amount of area under "the curve" which is not as beneficial on a turbo'd car as it is on one that is naturally aspirated.  This is particularly bad on a hydraulic lifter which is not only much heavier than a solid lifter but it also introduces pump up, etc.

On a stock block car, this is not always bad because we know our blocks are not built for high rpm as they are basically grocery getters from the onset.  Wise men used to tell us that we are playing with fire if we turn a stock block past 5600 rpm.  They were probably correct other than no one could predict how many times we could get by with it.  Stock cast cranks have been failing at 35 mph for 15 years while others are still giving us run after run.  The mickey mouse rods have hung in many times longer that most would have thought in many cases,  Better cranks and rods are available and band-aided blocks have helped but we are not dealing with things that were meant to make 700-800 hp reliably.  That is why we have Stage blocks and the TA blocks that were built to handle high rpm and high hp.

That puts some contraints on our engine designs...at least if we have any sense at all.  IN my opinion that limits rpm to around 6000 rpm which is about what a good roller design in hydraulic can handle for short periods.  That rpm and the effective rear end gearing tends to put a fuzzy ceiling on how fast the car can go theoretically. ..

Harsh hydraulic roller lobe design tends to work against us in getting all we can get out of it whereas the turbo does not care about stuff like that.....turn the boost up and get out of the way.  Might help to pray for the block to stay in one piece but that is part of racing.

[good2win22]

Steve your thoughts on lifters, I believe are spot on.  The whole reduced travel, short travel thing got me confused which is why I had to dig deeper to understand mechanically what goes on with these different type of lifters. Ill get it sorted and no, I'm not trying to win the rpm challenge with this build. Just want to get to 56-5800 for a shift.

[nocooler]

Like a old wise man once told me - combination, combination, combination. That led me to seeing how far I could push things, I broke stuff - but that's part of learning. 

[Steve Wood]

Like a old wise man once told me - combination, combination, combination. That led me to seeing how far I could push things, I broke stuff - but that's part of learning. 

Lawrence once told me that if I would simply tell him how much money I could spend, he would tell me how fast I could go...and then,he would try to tell me how often I would have to come back to get it fixed...

these days, I pretty much understand what he meant.

I'm still interested in theory....but, I have learned that with regard to turbo'd Buicks, the turbo and the converter are king and the cam is almost insignificant except for determining top end to a degree if one has a good converter.  Think about it.  How many logs have we seen where the car is trapping 120 miles per hour at 5600 rpm, but, when we compute the converter slippage, it is shown 25% or more?

Like you say, combination is everything but somethings count more than others   If we are class racing, then hundreths can make a difference, but, in a bracket it can also beat you but it cannot help you win..only consistency counts.  Then there are guys like me that sit there and think is it on green yet?

everything I say is contrary to what a vendor will tell you or what a magazine will write but I have nothing to sell but experience.

[TexasT]

LC was/is a pretty sharp individual.
I'm just glad you aren't charging us to partake in the experience sale.

[reality]

Why do BUICK guys complicate it so much?
A good fuel supply and spray the hell out of it
Don't have to worry about converters and such and dial up HP

[Steve Wood]

Lawrence and Janace are some of the nicest people I ever met.  Janace is suffering a battle with cancer which is very sad but she's a fighter.  Lawrence, Duttweiller, and Dan Strego brought a lot of brains to the table.

When Lawrence was going to run Tweaked in Houston, he would be dialing it in at the shop on Saturday morning.  He was at the end of a row of shops and he would get out in front of the shops and launch the car.  There was a Mustang shop a couple of doors up and he would almost suck those guys out of the shop when he went by.  they got no work done on Saturday because they were all standing in the door watching him.

He ran a Powerglide with one of those bolt together converters and he would spend a couple of hours getting it to stall at 5000 rpm.  He said even a couple hundred rpm off would destroy his times.  He was running 7's in those days and very few cars of any kind were doing that.  I don't recall if Dan Strego was in on the engine building then, but he was for Tweaked II

[good2win22]

Guys I really do appreciate all yalls input. I do not take your thoughts lightly.


The problem with my engine would not exist had I done my homework a little better with regards to the selection of parts for my combination. As Steve mentioned, vendors only want to sell parts. That's their livelihood. I should've done a better job of exhausting my research and deciding who's info I chose to trust.  Is my combo undriveable?  No. Just not what I was hoping it to be...yet. I have a few things to measure when I get off work and then I can get a couple of part numbers on order that will compliment my combination. A costly experience? Not at all and I know that's relative.  I've lost more money to lousy sellers/vendors advertising bogus parts and paying for parts that I've never received.


Is my build complicated?  I don't believe it is.  Perhaps my explanation of things makes it sound more complicated than it actually is. Chasing your tail is easy to do when you're the valedictorian of the school of hard knocks