where should the power be?

[fastman614]

W/W,
I am going to study this for a bit later on tonight.... you pose an interesting question (or two... or more...)

[SPARKY]

WW what is your final drive ratios
trans ratios
Tire size
speed are you are targeting

[kiwi belly tank]

Well Gogg's, It looks like everybody's talking about their stuff & you are probably interested in your stuff.
Short stroke engines like your 3.8 are never going to be a stump puller so you've gotta RPM them & that means more speeds in the trans to keep it on the boil.
You can over cam a low compression engine, you really can't over compression a mild engine assuming you have the octane to support it.
Too much cam & porting on low compression will actually cause an over scavenge situation. If you are running an ECU, you will also most likely be getting a false O2 sensor read as well. The ECU will lean it out due to the seeing the over scavenged fuel firing in the exhaust. Pretty good chance your plugs are always a little ghosty.
If you want to wake it up, show it some compression.
I really like the crap out of my 3.8 but then its got a blower parked on top of it.
  Sid.

[fastman614]

This goes back to the original question about power curves.

The dotted curve is for a pretty much standard engine that originally had a torque curve shaped like the one at the top with 50 lbs-ft torque, maximum.  Intake and exhaust tuning with some spark advance curve tweaking was used to take away some of the torque from  the left side of the hump and move it towards the right side.  The dip in the torque curve around 5,200 rpm shows where I removed it.

The engine before the intake, exhaust, and advance changes pulled hard up to 6,500 rpm and then it started to go flat.  The motor was sorta flat until around 6,000 rpm and then it pulled hard until about 7,500 rpm after the changes.  It was was much faster and a lot of fun to ride.  I just had to make a quick shift around 6,500 rpm to make it work.

The solid line is the torque curve for the 865 cc engine.  I have done the spark advance curve and intake tuning.  The exhaust tuning will be done this week and the dyno session is scheduled for the 14th.  Just like with the little 790 cc motor, I am trying to bias the torque curve toward higher rpm.  The curve I am trying to get will be good for LSR and lousy for everything else.

Do not abandon your long block until you have done this sort of tuning. 

Okay... it would be nice to see a horsepower curve as well....and then based on the torque/horsepower curves, some educated assumptions could be made.... I think that your biggest problem will be not having gear ratio spacings in at least your top two and preferably three speeds to make the best use of your peak area. When you "overlay" your physical RPM drops for each gear change, how does the highest RPM in the lower gear relate to the lower RPM actually obtained at the point of either re-engaging the clutch or getting back on the throttle (depending, of course, on if you shift with or without the use of the clutch)?

Perhaps this is "hijacking" the original thread tho'.... although, the principle remains the same....

[fastman614]

Well Gogg's, It looks like everybody's talking about their stuff & you are probably interested in your stuff.
Short stroke engines like your 3.8 are never going to be a stump puller so you've gotta RPM them & that means more speeds in the trans to keep it on the boil.
You can over cam a low compression engine, you really can't over compression a mild engine assuming you have the octane to support it.
Too much cam & porting on low compression will actually cause an over scavenge situation. If you are running an ECU, you will also most likely be getting a false O2 sensor read as well. The ECU will lean it out due to the seeing the over scavenged fuel firing in the exhaust. Pretty good chance your plugs are always a little ghosty.
If you want to wake it up, show it some compression.
I really like the crap out of my 3.8 but then its got a blower parked on top of it.
  Sid.

Kiwi - you are talking my kind of talk on this concept... more speeds in the transmission is the way to go... and much closer ratios too!...Failing the ability to get more speeds though, much closer ratios still has a noticeable net benefit.

[Milwaukee Midget]

 

I started before the last two responses but that's what I'm lookin for.....

straight as an arrrow.....and short stroke motors....sound familiar Chris?

yeah

Well Gogg's, It looks like everybody's talking about their stuff & you are probably interested in your stuff.
Short stroke engines like your 3.8 are never going to be a stump puller so you've gotta RPM them & that means more speeds in the trans to keep it on the boil.
You can over cam a low compression engine, you really can't over compression a mild engine assuming you have the octane to support it.
Too much cam & porting on low compression will actually cause an over scavenge situation.

Which is one of the issues I discovered in North Carolina - along with a few other problems.  Had I not spent the first 1/4 mile just getting the darned thing up on the cam, I suspect I'd have been in striking distance of the old Maxton record.

I've seen the pictures of your heads - you can drive a truck through those ports.  The valves are big with respect to the cylinders - so unless there is some issue with the valve bowl area, flow should not be an issue.  But you are leaving horsepower on the table by not jacking up your compression.

I know Jack Dolan suggested the parameters, but at this point of the game, I feel pretty confident that you can maintain the durability you're looking for and that was initally designed into the build, and still wring some more ponies out of the new donk by upping your CR.

The problem is - and I'm quickly becoming aware of this - is that with a small displacement, short stroke engine, it's tough to make up CR without looking at either shaving the heads a LOT, and in my case, to the point of the ragged edge of reliability, popping up the pistons above the deck height, using a domed piston of some sort, or a compromise combination of all three. 

When it comes time to put the REALLY short crank in that I sent you, that is when you'll start enjoying the Technicolor, panoramic nightmare I'm encountering with widened lobe center angles and other such mathematical voodoo.  It's not for the faint of heart, so come that day, keep many sharpened pencils handy.

At Gairdner, you have a huge advantage in that you actually have some air to work with.  Bonneville is 4200 feet above sea level, you'll have 14% less air density to fill those little cylinders come that glorious day the SOS is shipped over and arrangements are made to tow it to Wendover.  It's been said that the lower air density is often a wash because you wind up with less aero drag, but that only works on cars with bad aero.

You've nowhere near maxed out the rev potential of the 3.8, and it's not likely that you will with the new diff gears.  Get the CR up, buddy - carefully and thoughtfully build up the torque curve, and the power will follow.

[wobblywalrus]

The post with the dyno curves was missing the thing I wanted to say.  The bigger 865 cc engine is torquey in the midrange similar to your drag racing friend's suggestion.  It is the upper curve.  The little 790 cc engine is the middle curve.  It has much less torque overall.  Its torque is more oriented to the top end of the power band.  Note the vertical line which is the target RPM I try to run at.  The big motor has only a little bit more torque than the little one at the target rpm.  This shows in the timing slips, too.  The big one is only a few mph faster.

The point is, the shape of the torque curve is important.  Note how much more torque I can get at target rpm if I can somehow shift the big motor's torque curve hump a few hundred rpm higher.  This is where intake and exhaust tuning can make a big difference.  

Sparky, this is Goggle's thread and I'll post the Triumph data on the Team Go Dog, Go build diary in a few days.  I am kinda tired from getting up early and working on the bike.  Big progress is being made.    

 

[SPARKY]

WW  you are being most kind to Dr. G  but in defense of we hijackers---his brain is sorta like a sponge it soaks up knowledge as well as brewskis 

[fastman614]

WW  you are being most kind to Dr. G  but in defense of we hijackers---his braind is sorta like a sponge it soaks up knowledge as well as brewskis 

Sparky, Sparky, Sparky..... we will ALL talk nice to "Uncle Sam's Men" at the border  - yet again -.... and bring enough brewski's so that you can, after looking us up, try one that is like soaking up a whole 1 1/2 at a time....!

[Dr Goggles]

Ok. I started this thread because this site is full of opinionated people, mostly those opinions are backed by either strong theoretical knowledge or plain experience and grit.

Some people know why something works, some people know what works.

In this sport though you can choose your filling, you can trade money for time....or knowledge.If you don't have much money then you have to gain knowledge, the more knowledge you have the better choices you can make.

Continuing in this game isn't a case of budgeting for me, I just scrape what I can.

My skills in the auto world are almost entirely self taught, and my knowledge in the landspeed game is from considering things logically. I am a thief, there is no two ways about it, I listen and try to sieve what I hear through a logical process. It is , after all physics, there is no magic.

I am the guy in the middle between the Reverend with his design and engineering skills, and the Colonel with his vast experience of making things run. I am the producer, the guy who said it will happen, the guy who tried to excite the Colonel and calm down the Reverend.......trust me that's what it was like.

I started this thread to see ideas collide, to try and reaffirm some things I thought and to refresh what I thought was important. I'm not contributing because I'm not arguing anything.I am watching, checking whether I have my head in the right place...if I just asked a question to solve a single facet problem I would learn little but there is stuff already in this thread that is valuable. I will chart our shift points after we dyno next time and by then I will have a realistic idea of whether what we are trying to do is achievable with what we have.....

For our car with which on our budget we could always have more power and a higher redline it has been pretty obvious that we need the peak power to be near the top of the rev range because the power we are making isn't that much more than we will need to travel at that  speed. We need to accelerate to that speed within  a given distance....as anyone who has done it knows, you don't really "have ages to get up to speed".... if we had some room in the car we'd have a different transmission....we don't and therein lies at least some of the rub......we built a car with what seems to be very good aero, and severe packaging problems. Our engine choice was dictated by the room we had, the engine parts dictated by the cash we had...sound familiar?

By the way, I'm a stirrer too and moments after I posted the topic I received an email from one of the good friends I have made here who said...." what are you up to, sh*t stirring again"?......

Thanks to all of you who have chipped in.

[Stainless1]

Doc, sorry didn't get into this one earlier.... my answer... applied to the ground 

If you can, gear to what you have, if you can't drive to what you have... then try to make more the next time.

[Tman]

Doc, sorry didn't get into this one earlier.... my answer... applied to the ground 

If you can, gear to what you have, if you can't drive to what you have... then try to make more the next time.

Must be tha great minds thing.................I was going to smart off with the same reply!

[Dr Goggles]

Steele , you and your smarty-pants mate there ...out! go on ,

when we dyno the motor again we will have a curve that hopefully runs up to just under 8 grand, from there we can work out the drops at the changes. From there we will be able to get an idea of the power applied, that will give us a better idea of whether we can do enough work to get in the region of the speed that we want to do....if we had ten miles we would be fine........we don't. I am pretty confidant that we will be able to raise the capability of the valve train to handle the <8k and that the car has enough power to haul at that speed, I'm not so confidant we have enough power to do that work required between the start and the four mile.....

The ground, good on ya.

[Rex Schimmer]

James,
I used your target top speed, 240 mph and your estimated hp, 400@ 8000 rpm and did a little "pie are square three bags full etc" and came up with some numbers and maybe some thinking regarding gears, hp curves etc. As I do not remember or know what tranny you are using I will assume that the 3rd gear is probably around 1.28:1 and that to run 240 at 8000 with 28 inch tires you will need about a 2.78:1 diff gear. Using these "guesses" it shows that your max speed in 3rd gear @ 8000 is 187 mph and using the rule that the aero hp increases with the cube of the speed increase and again assuming that your 400 hp is what it takes to make your car go 240 then at the top of 3rd gear, 187 mph, you will need about 190 hp. Now your engine when you shift 3rd to 4th @ 8000 will drop to 6250 rpm so you need to have over 190 hp @ 6250 rpm and more hp you have available at that rpm the faster you will accelerate toward 240. Again remember that if you had an absolutely flat torque curve between 6000 and 8000 rpms your hp curve would be a straight line but the aero hp curve is a curved line that is increasing in slop at a cubic rate. So if you only had a small amount of power surplus at 6250 you may not be able to accelerate to 240 as the engine hp curve will cross the aero hp curve below the 240 mark. So what does this say, 1. You want as much surplus horse power at the 3rd to 4th shift rpm, 6250 in this case, as possible to ensure that you can get to the targeted 240. 2. If the engine hp curve crosses the aero hp curve before 240 you can either wind the engine tighter in 3rd which raises the position on the engine hp curve to a higher rpm or you need to reduce the ratio of 3rd to make the rpm drop smaller. Horse power makes speed, if you have a narrow power band engine you need lots of gears and the progression through the top 2 or 3 gear ratios need to be approximately: each ratio change should be about 1/2 of the previous.  If you are bound to the existing transmission then I would highly recommend plotting your engine hp curve vs the aero hp curve and I would also make sure that you can over rev you engine in 3rd gear by 3-500 rpm to bring your available hp at the 3 to 4 shift as high as possible.

Rex

[Dr Goggles]

Rex I just lost a long reply that I'd written.

I will go home tonight and work out what ratio 3rd is.

We have been running a 2.77:1 rear end but are swapping to a 2.41 or 2.56 . The 2.77 had us at 231mph at 8k the 2.41 has us at 7250 @240.

Here is the dyno sheet from the early incarnation of this motor.


We are addressing the rev limit which we figure was valve springs.