[charlie66]

I decided to change the compression ratio in my 4cyl in attempt to help the low end low rpm torque/power to spool the motor sooner. This has been the biggest problem I've had in getting it tuned for drag racing . I had it spooling ok up until I had to tighten the converter do to the power level im looking for. So in turn this is where im at. I bought some custom flat top Ross pistons to replace the Ross 24cc dish tops that was being used. My old compression ratio was 8.4:1 now it will be 9.8:1. I know there will be more objections to this then anyone agreeing with doing this but I think it will help with the characteristics of a 8.4:1 4cyl with 254 .050 duration. Its like stepping into the mud when stepping on the gas until boost.. I have a lot of data with my old pistons. So I know the safe boost levels and a/f ratios as well as timing settings. I have never burnt the motor so I feel good about using them to refer to as I go forth as a guide line for what im trying to do, design a safe tune .. So with this said I have gone an done some calculations to kind of try to get a grip on what to expect with boost and timing setting with the new pistons. So all of my psi setting that I use to use (different tunes for what I was doing in any given day) I compared to the new 9.8:1 static ratio that I now will be using . So first off, the old volume to pressure index of 68 will now be 83. Im hoping this doesn't work against me with detonation, but I think it will help the low rpm torque/power for spooling. The second thing is dynamic compression comparison between the old ratio to the new. The old was 7.15:1 with my present valve closing timing and the effective stroke of 3.12 inches from the 3.75 stroke .The new will be 8.32:1 . basically 1.17 more .
Then I went and figured the effective boost compression ratio, reflecting static c.r., cam timing, altitude for both ratios to see what they are to compare them . The 8.4:1 at 20 PSI = 16.88 :1 . The 9.8:1 in comparison = 19.64 :1. knowing the tune for the old 20 psi I figured out what the new psi will be to match it . So 15 psi at 9.8:1 will yield all most the same at 16.81:1 . So the old 20 is now the new 15psi. This is all theatrical of course but it is all I got and it makes sense to me.. So im thinking ill be able to use my old tunes settings for my high and low boost levels with the lower psi's of the 9.8:1 that matches the higher old psi's.. I made a graph to reference for different levels of boost. I use to drive around with the PSI set at 26 . So if I want to match that for tuning it the same the new psi will be at 20 . And I will set the timing lower and learn where it wants to be..

Any way I just wanted to share this and see what everyone thought. Feel free to give your opinions good or bad I will appreciate it in any form ... its all good...

[Tom Vaught]

Good Luck with it Charlie.

You are well past the "Boost Greedy" Phase so I know you will sneak up on the tune-up again.

The Engine makes power by pushing down on the piston. About as basic as it gets.
So if you can get the same cylinder pressures with less boost but more bottom end driveability and close to the same power at the lower rpm points then you have a better overall package. The OEMs will give up some HP on the top to improve the lower range and mid range HP and satisfaction of the customer.

Keep us in the loop. You will still be running on e-85 so you should have more room with the compression ratio. Timing is another story.

Tom V.

[charlie66]

Thank you Tom.

What are OEMS?

I have a safe and effective way i have learned with turning up the timing on this motor . So I think ill get it to where it wants to be right away. The spring in the waste gate is a 25 pound spring. But I think over the years its lost its ability to be all it can be. I only get 18 psi out of it now . So my starting boost will be 18 psi. I have no doubt tuning it at that level with be a breeze. When I used to turn it up with the dish tops I was as high as 45 psi. That tune was stable and never had a burnt piston or even a burnt plug. But that was where the crank couldn't handle the power any more . Point is, if I could tune it at that level an not burn it up , I think ill be able to get it figured out with 1.4 higher ratio of compression with less boost. So the old 45 psi if I ever wanted to try it again will be the new 37 psi. Now I don't plan on trying this, im just talking about the comparison here. So if I did try it I would just have to find out where the timing wants to be.
So because my spring in the gate yields 18 psi that's where I will be starting out and stay for awhile . So 18 PSI at 9.8:1 is my old 8.4:1 at 23.4 psi. This level of boost will still have the hp up over 600 . So if that's where it winds up staying , that wouldn't be all that bad for a street car...

[Tom Vaught]

Sorry Charlie and others reading the post.

OEMS = Original Equipment Manufacturers (FORD GM CHRYSLER FIAT TOYOTA etc)

The Guys who make the Street Boosted Cars.

Tom V.

[charlie66]

So I've been driving the car now for 2 month's with the new compression ratio. To my surprise it doesn't really spool much faster maybe just a tad. But I will say its faster with less boost. Cranking cylinder pressure went from 140 to 170. I've been basically using the same tune as I used with the old dish tops on the top end, but had to change up the idle and midrange cell numbers for more fuel. It was not as hard as I thought it would be. I am battling problems with the cold cranking starting as well as even after its warmed up. Starting it is a pain in the butt now. Its now basically 5 psi lower with the same power output then the old boost level now from the previous pistons . It does seem to be more sensitive when adding boost as It goes higher in pressure. So in other words , the gains seem more per psi from say 24 psi to 27 psi then say 20 psi to 24 psi. With timing I backed it down 1 or 2 degree's at full boost but it doesn't seem like I really needed to . But im keeping it down till I have more experience with the new change . Over all I think I made a good decision but I know now that I really didn't need to. Only way to know is to try right? I have to say that Wallace calculator really helped me out with comparing different compression ratios . It was dead on with what it told me to what actually came to reality . I whish I knew who to thank for that .... I made a graph of the old pressure to the new pressure projections and I followed them in parallel very carefully for tuning for what I will have to say was with great success.....

And I want to say Thank You for all your advice Tom Vaught ..

[Stan Weiss]

Originally Posted by charlie66

So I've been driving the car now for 2 month's with the new compression ratio. To my surprise it doesn't really spool much faster maybe just a tad. But I will say its faster with less boost. Cranking cylinder pressure went from 140 to 170. I've been basically using the same tune as I used with the old dish tops on the top end, but had to change up the idle and midrange cell numbers for more fuel. It was not as hard as I thought it would be. I am battling problems with the cold cranking starting as well as even after its warmed up. Starting it is a pain in the butt now. Its now basically 5 psi lower with the same power output then the old boost level now from the previous pistons . It does seem to be more sensitive when adding boost as It goes higher in pressure. So in other words , the gains seem more per psi from say 24 psi to 27 psi then say 20 psi to 24 psi. With timing I backed it down 1 or 2 degree's at full boost but it doesn't seem like I really needed to . But im keeping it down till I have more experience with the new change . Over all I think I made a good decision but I know now that I really didn't need to. Only way to know is to try right? I have to say that Wallace calculator really helped me out with comparing different compression ratios . It was dead on with what it told me to what actually came to reality . I whish I knew who to thank for that .... I made a graph of the old pressure to the new pressure projections and I followed them in parallel very carefully for tuning for what I will have to say was with great success.....

And I want to say Thank You for all your advice Tom Vaught ..

What you are seeing is although the higher compression ratio is producing a higher peak cylinder pressure, it will decay quicker on the down stroke and the engine will have very close to the same cylinder pressure @ EVO.for both cr's.

Stan

[Tom Vaught]

Originally Posted by Stan Weiss

What you are seeing is although the higher compression ratio is producing a higher peak cylinder pressure, it will decay quicker on the down stroke and the engine will have very close to the same cylinder pressure @ EVO.for both cr's.

Stan

X2

If the engine "drives" better with the higher compression ratio but you made the same power or slightly less power then the overall 'happiness factor' is probably better.

But you understand Charlie, that you changed a bunch of stuff: NEW CALIBRATION BASICALLY
Cranking cylinder pressure
Idle and midrange cell numbers for more fuel.
Timing I backed it down 1 or 2 degrees
Starting it is a pain in the butt now
5 psi lower with the same power output then the old boost level (not racing boost Charlie)
The gains seem more per psi from say 24 psi to 27 psi then say 20 psi to 24 psi.
(which it should be at higher boost and higher new non boost cylinder pressures.)
Tom V.

[charlie66]

Originally Posted by Stan Weiss

What you are seeing is although the higher compression ratio is producing a higher peak cylinder pressure, it will decay quicker on the down stroke and the engine will have very close to the same cylinder pressure @ EVO.for both cr's.

Stan

Can you explain this a little more please...

Not sure of what I said that you're comparing this to.

[Stan Weiss]

Originally Posted by charlie66

Can you explain this a little more please...

Not sure of what I said that you're comparing this to.

The increased peak cylinder will push harder on the piston during the top portion of the power stroke (increased HP / Torque). The same cylinder pressure @ EVO means that there should be no more exhaust pressure to help you spool faster.

Stan

[Tom Vaught]

That is why Charlie instead of delaying the exhaust valve opening with conventional valve timing opening points, you might as well open the exhaust valve as the exhaust pressure has basically flat-lined and will not drive the turbine wheel any faster than the energy you have at that point.
Heat is the big contributor for driving the turbine wheel.

Tom V.

[charlie66]

So what you guys are saying is , I should grind a new cam so to open the exhaust valve sooner so that you have more energetic exhaust? an then the closing events would be at the same place as they are now?

[Tom Vaught]

Have Mr Computer whip you up a simulation Charlie on what the effects are when you play with exhaust opening events and leave the rest of it basically the same.

Some interesting things happen. Get that info before you race out to have a new camshaft made. You will probably be reading/providing exhaust pressures in the cross-over pipe again but no big deal for you.

Tom V.

[Stan Weiss]

Originally Posted by Tom Vaught

Have Mr Computer whip you up a simulation Charlie on what the effects are when you play with exhaust opening events and leave the rest of it basically the same.

Some interesting things happen. Get that info before you race out to have a new camshaft made. You will probably be reading/providing exhaust pressures in the cross-over pipe again but no big deal for you.

Tom V.

Must be talking about yourself here Tom. Since you were the only one who has talked about valve timing points.

Charlie, sorry but I done, otherwise I will just pull your thread off topic.

Stan

[charlie66]

Originally Posted by Stan Weiss

The increased peak cylinder will push harder on the piston during the top portion of the power stroke (increased HP / Torque). The same cylinder pressure @ EVO means that there should be no more exhaust pressure to help you spool faster.

Stan

Stan

Addressing the no more exhaust pressure issue.
I did make a test while trying to spool the motor on the trans brake and on the foot break. What I did was compare the EGT's 2" off the head in the primary header tube and compared that reading to a reading took in the A/R housing right at the flange. The difference was the primary egt's were 1250 and at the turbo was 750. and @ idle was, primary 1050, turbo flange 450. So maybe most or some of the problem lies there? But also may have to do a little with having to tighten the converter up to handle the 800hp. That's a hard situation to address because on its own the motor is lucky to make 250 hp. So getting it to flash to 3500 rpms which is where the turbo really starts to ramp up, it becomes too lose to hold the round about 800hp, and Being im not spinning the motor over 6500 rpm's is where the problem lies. If it was spinning to something like 7500-8000 it would most likely tighten up enough to hold the power. So there you have it, my little 4cylindr dilemma.... I shoulda built a 8 cylinder... haha. So if you have any advice im all ears....

P.S. Don't worry about the thread.. Its not that popular, so go off topic if you like , its cool. lol...

[charlie66]

Originally Posted by Tom Vaught

Have Mr Computer whip you up a simulation Charlie on what the effects are when you play with exhaust opening events and leave the rest of it basically the same.

Some interesting things happen. Get that info before you race out to have a new camshaft made. You will probably be reading/providing exhaust pressures in the cross-over pipe again but no big deal for you.

Tom V.

I guess I comprehended what you were saying wrong. Sorry..

[charlie66]

I forgot to say that I have decided to go a head and build a new intake manifold . It will have a 2.3 to 1 ratio with my motors ci's. Right now the manifold plenum on the motor is 100 ci. The new one will be 455 ci. And it will be a bottom entrée type.... I have the lower portion mocked up just need to finish the plenum design now....

Question about runner length and shape. does it make a big difference when going real short and straight . Runner will be inside 1 1/8 wide and 2 1/4 high with 3/8 radius corners..

Thanks...

[Tom Vaught]

Super Flow has in their Flow Bench manual on page 33 an explanation of Dynamic Flow Effects. In basic terms this means that you could design a intake manifold that could tune in a given range of rpm points. The Harmonic Pulse Strength would be higher or lower depending on which Harmonic you were to choose.

So if you picked the 2nd Harmonic Wave to use for tuning:

You take 132,000 and divide it by your rpm point you want to tune for.
Say 5500 rpm: 132,000 divided by 5500 rpm = 24 inch long runners

If you picked the 3rd Harmonic Wave to use for tuning:
97,000 divided by 5500 rpm = 17.6 inch long runners.

If you picked the 4th Harmonic Wave to use for tuning:
74,000 divided by 5500 rpm = 13.45 inch long runners.

You can keep the 132000, 97000, and 74000 numbers and just type in a different RPM
number (say 6500) and get a new runner length for each Harmonic.

Example: 97000 divided by 8000 rpm = a 12.1" runner length. This length is from the Intake Valve Head to the Radiused Entry of the of the Intake Runner.

All that being said, the tuning is less on either side of the rpm point so it works well on a Indy car at max RPM or a NASCAR vehicle at a typical lap rpm but not so good on a street engine.

Now if you are boosting the engine, the wave tuning is affected by the pressure from the Boosting device so the tuning effect is minimized. Most ignore Harmonic Tuning with boost unless it is a Mercury Race engine with twin turbos that races at a fixed rpm point most of the time on the water.

In your case Charlie, Package is more important vs being off a bit on the runner tuning BUT the plenum volume DOES make a difference.

Tom V.

[Stan Weiss]

What is really nice about a computer is if you have a cam lift profile and cylinder head flow information you can generate the numbers from the graph at the bottom of page 34 without counting all of those squares.

Now if you are looking to help spooling, I would be looking at the exhaust system side if it was me.

Stan

[Tom Vaught]

So you have some good info from Stan and I look forward to seeing posts about your new bottom feed intake manifold design, Charlie.

Tom V.

[charlie66]

So what is going to be an effective method of getting the turbo to spool sooner with the set up that I have, or modifications I can make to the intake manifold or exhaust? If I make an intake then do I have to worry about a loss of performance once the motor is at an rpm out side of the harmonic resonance it was tuned for. It was never really clarified about the question I asked about a change in exhaust vale timing events, longer exhaust duration by opening it a few degrees sooner. What modifications to the exhaust system, shortening the run to the turbo, wrapping insulation from the header to the turbo inlet?