(almost) No Cut K20 Swap

Wheels are 15x8 0 offset. Tires are 245/40/15 Hoosier A7s- approximately 23 inch overall diameter.
 
As large an OD as reasonable. Do consider a wider tire will increase rolling resistance and the wider track will affect the dynamic roll center.

There is a wide spread belief that wider-larger tires produces more grip. In reality, tire size depends on actual tire loading. Might try going to a smaller width tire on that 8" wide rim, about 215 rather than 245.

What is the ride height, spring rates, weight at the rear RH & LH, front RH & LH?

Stability bars, front - rear?

Dampers and damper settings?

Location of the lower control arm relative to road level?

Current wheel alignment settings. These numbers must be accurate to 0.5mm or 0.02" for toe, 0.10 degrees for camber, 1 degree for caster. Chassis loaded to ride height?

The commonly used 'computer alignment rack' is not accurate enough due to the simple fact the sensor are placed directly on the wheels. Run out, and related wheel tolerances absolutely limit the accuracy of these systems. This is why the majority of race teams including the F1 brigade use string with precision floating wheel-hub stands.

If the exxe chassis is lower too much, the dynamic roll center will go below road level causing the tire to dive into the road with cornering load. Tires do not like this at all. Lower is NOT better, there is an ideal ride height for any given suspension.

One of the gravest errors of the PBS x1/9 FP race car was to lower the chassis around the suspension with spring rates that were FAR too low. This single error made that chassis severely dynamically limited.

Try curing rear wheel spin with spring rates before trying a LSD. On the LeMons racer with similar power to weight ratio as this K20 conversion, there is ZERO wheel spin power full on out of any corner with no LSD and that chassis is on DOT 180 Dunlop Direzza, 195/50/15 performance street tires.

The challenge will be getting the chassis to behave, easy part of adding power appears to be mostly done. Getting a chassis to behave properly, predictably meeting the driver's needs and optimized for a given course is a FAR greater challenge than adding power. This is where lap time reduction really happens.


Bernice



Dennisrh said:
Wheels are 15x8 0 offset. Tires are 245/40/15 Hoosier A7s- approximately 23 inch overall diameter.
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Pete Whitstone said:
But wasn't sure that was the case because of this line:

"Its an interesting balance and the lesson to be learned is: don't floor a K20X during a corner"

Seems to indicate it's a 2.0.

Pete
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Of course we can get it from the horses mouth, but if it is a k20a2, rev limit is 8100
 
I believe it is a k24 and 7100 sound about right if he did not change
the oil pump to a k20a2 or k20z1 style,if he did change the oil pump
he could bring his red line up to the 8100 mark,the k24 has a lot more torque on the bottom to mid range so I can see the tires letting loose.

Rick
 
It is now a K24a2, it was a K20a2 before. I have been calling it a K20X since before I finished the conversion and still do now, I guess technically it is a K24X. I have changed to the K20a2 oil pump and oil pan as the original K24 oil pan doesn't fit with Matt's engine subframe. I have not tuned the ECU, still running the stock map for a K24a2, so haven't increased the rev limiter yet. I will wait for the professional to determine how high to rev. I look forward to reving to around 8100 rpm though.
 
Ideal red-line is based on the dyno curve. Where red-line should be is just over the peak of the HP curve bump. Idea is to get as much area under the curve as possible for a given power curve on that given engine.

Example, if HP peak is at 6,800 RPM with the HP falling off at 6,900 RPM red line should be a few hundred RPM beyond that, say 7,000 or 7,100 RPM where the rev limiter should be set.

There is a LOT of paranoia about grenading an engine due to over-revving, this depends a LOT on the specific engine, if an race motor cannot tolerate a few hundred RPM above it's HP peak, it is defective in every possible way. Any race or performance engine worth it's oily bits must be able to stand being run at red line, flat out-wide open throttle continuously for it's rated service duration before rebuild.

This does not mean over-revving the engine by 1,000 RPM or more past it's rated red line which can often result in damage.

Bernice



Dennisrh said:
It is now a K24a2, it was a K20a2 before.

I have not tuned the ECU, still running the stock map for a K24a2, so haven't increased the rev limiter yet. I will wait for the professional to determine how high to rev. I look forward to reving to around 8100 rpm though.
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I would think there would be a lot of other factors to look at

Rupunzell said:
Ideal red-line is based on the dyno curve. Where red-line should be is just over the peak of the HP curve bump. Idea is to get as much area under the curve as possible for a given power curve on that given engine.

Example, if HP peak is at 6,800 RPM with the HP falling off at 6,900 RPM red line should be a few hundred RPM beyond that, say 7,000 or 7,100 RPM where the rev limiter should be set.
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for setting redline. Gearing and torque peak would be in that mix too. When you change up to the next gear after running to redline, you would want to fall into a favorable rev range as far as torque production, in order to provide the best acceleration. I'm sure there are many other considerations also.

Pete
 
weights

Still haven't gotten my engine tune yet, the tuning shop is very busy lately. But I did lower the car more and somewhat corner balance it as well. Here is the corner weights with me in the car and about 1/4 tank of gas. I weigh about 185 lbs.



The xcel Spreadsheet that I use says I'm at 50.5 wedge to 49.5 corner balance, which I suppose isn't too bad. Still looking to lighten the car a bit more, so the corner balance will need to be done again after I get racing seats and battery. I am also still looking for lightweight rims.
 
More suspension help please

Did a track day and a couple autocrosses since the last post and the car is handling much better than before. Handling is balanced front and rear, but now I am having a different problem. Previously, before lowering the front a lot and the rear a little, I was lifting a front wheel when cornering hard. Now I am lifting a rear wheel around hard corners. I have an LSD, but I am still getting some wheel spin when the inside rear wheel lifts and it is slowing me down. Not sure exactly what to do since the car is feeling pretty good. I don't want to lower the rear or go with stiffer springs as I believe this will cause my car to understeer again. Any ideas or suggestions?
 
*What are the spring rates front & rear?

*Does this chassis have front, rear or both front&rear stability bars ("anti-roll" bars)?

*What is the camber front / rear.

*What is the toe front / rear.

*What are the tires and pressures front / rear?

Understeer / oversteer can be adjusted in numerous ways.

LSD will not and does not always correct or eliminate wheel spin. It can add difficulty in setting up a chassis and cause wheels spin (improper chassis set up. This is a complex interaction between power train, chassis-suspension-wheels& tires) if there are tight corners involved. It is simplistic to believe that forcing torque to both driving wheels stops wheel spin. What is happening dynamically as weight shifts around a chassis from cornering, braking, accelerating is FAR more complex than simply both wheel are delivering driving torque to the wheels-tires-they should not spin.



Bernice



Dennisrh said:
Did a track day and a couple autocrosses since the last post and the car is handling much better than before. Handling is balanced front and rear, but now I am having a different problem. Previously, before lowering the front a lot and the rear a little, I was lifting a front wheel when cornering hard. Now I am lifting a rear wheel around hard corners. I have an LSD, but I am still getting some wheel spin when the inside rear wheel lifts and it is slowing me down. Not sure exactly what to do since the car is feeling pretty good. I don't want to lower the rear or go with stiffer springs as I believe this will cause my car to understeer again. Any ideas or suggestions?
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What are the spring rates front & rear? 600 lbs front and rear

*Does this chassis have front, rear or both front&rear stability bars ("anti-roll" bars)? No stability bars

*What is the camber front / rear. Front camber 3 Degrees, rear about 2.8 Degrees

*What is the toe front / rear. No toe in the rear, front slight toe out, don't have the exact measurement, but I will be going back to the alignment shop this week.

*What are the tires and pressures front / rear? Hoosier A7 - 245/40/15 all around. Tire pressure is 26 lbs cold all around.
 
Dennisrh said:
What are the spring rates front & rear? 600 lbs front and rear

Those are pretty high spring rates for a road work. On a track car, pretty typical.

600 lb/in front, try 500 lb/in rear, +/- 50lb/in or when the rear wheel spin on corner exit stops or greatly reduced. Rear wheel spin is likely due to excessive rear stiffness.

Dampers will have an effect on this too. What are they and where are they set?

Chassis height also has a significant effect. Begin with setting the ride height by the position of the lower front control arm. This should be about parallel to level ground with the car loaded. DO NOT lower the ride height more than this as it will cause the suspension camber curve to go the wrong way and cause the dynamic roll center to go below road level on bump causing the tire to dig reducing mechanical grip. LOWER IS NOT BETTER.

Once this is done, corner weigh the chassis to achieve near 50% cross weight similar to what it is now.


*Does this chassis have front, rear or both front&rear stability bars ("anti-roll" bars)? No stability bars

*Good. Key to getting the chassis-suspension to work well with no bars is spring and damper rate.

The alternative is to use lower spring rates with F & R bars, this tends to do better on bumpy roads trading off independence of wheel movement and gaining load transfer from side to side wheel (left to right, right to left). At some point of lower spring rates with BIG bars tend to make an independent behave more like a solid axle suspension. There is a balance and trade off.


*What is the camber front / rear. Front camber 3 Degrees, rear about 2.8 Degrees

*Performance radial tires tend to produce highest grip between 2 to 4 degrees of negative camber. The ideal setting depends partly on front to rear grip ratio needed. This affects understeer-oversteer balance and over all mechanical grip available.

Once the spring rates and damper rates have been some what adjusted to a workable range, optimize camber with a tire temperature gauge. The ideal would be the same tire temperature across the tire on all four corners. Typically, tire temperature across the tread is going to be about 10 to 20 degrees F higher on the inside. 10 degrees higher on the inside is OK, 20 degrees is running HOT. Temperature differences more than 20 is trouble.


*What is the toe front / rear. No toe in the rear, front slight toe out, don't have the exact measurement, but I will be going back to the alignment shop this week.

*Toe front-rear is seriously important as it affects chassis-suspension behavior and tire wear in significant ways.

The exxe chassis-suspension does not like front toe out. Initially set the front toe to zero or slightly toe in, about 1mm or 0.040". Same with the rear. From there, the rear toe can be adjusted to toe in for rear stability or toe out for slightly improved turn-in (OK and used by autocross folks, not always OK for a track car).

Front and rear toe MUST track and be aligned together. The chassis-suspension will behave weird if the front-rear toe are NOT parallel. The rear track on the exxe is wider than the front, once this has been accounted for the toe can be set accurately. Imagine the exxe chassis-suspension placed into precision rectangle. From the center of each wheel, measure the distance from the center of each wheel hub to the inside edge of the precision rectangle. Adjust the distance from each wheel hub to the inside of the precision rectangle until they are equal side to side. Once this has been achieved, toe can be measured as the difference at the wheel rim's edge. This set up can also check for chassis-suspension condition as a bent chassis-suspesion-wheel hubs/uprights often does not line up inside a precision rectangle. If there are questions to chassis condition, there are specific chassis measurement check points in the Fiat-Bertone service manual. These are basic to getting the chassis-suspension to function properly.

Accuracy of setting toe is a must. IMO, modern optical alignment racks are NOT as accurate as they appear due to the optical alignment sensors being mounted on the wheels. This adds the tolerance of the wheels and attachment to the alignment setting. To deal with this, racer folks have been using alignment wheels and stands for quite a while now. like this:

http://xwebforums.com/forum/index.php?threads/26077/

http://xwebforums.com/forum/index.php?threads/25043/

*The Mazda rotary powered LeMons exxe has precision aerospace grade spherical bearings in the suspension along with new Fiat ball joints where used.. This makes for high precision and stable suspension alignment settings. We can dial in a chassis setting, put the car on the track to test, put the car back on the set up rig and be within 1 degree or less of set camber and 0.010" or less of the toe setting.


Precision string set up IS often more accurate than the common optical-digital alignment rack due to the direct connect to the hub. This eliminates the tolerance problem with the wheel (side to side run out) and connection between optical alignment sensor to the wheel.


*What are the tires and pressures front / rear? Hoosier A7 - 245/40/15 all around. Tire pressure is 26 lbs cold all around.

*26 psi cold is a start, what are the tire pressures hot? Typically, 30 to 32 psi hot is OK. Hot tire psi also gives a clue as to running tire temperatures and how the chassis-suspension is behaving on a given course. The over worked tire is going to have higher pressure due to the higher heat involved from working harder than the rest. Work to correct this if this issue appears.


Bernice
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I was wondering if you could send me the pick of your work I am getting ready to do a swap now. I hit your link and the won't come up.
 
no one wants to cut there cars , but that engine is bigger and when you want to service it it harder and harder without cutting ,transmission will not fit anyhow

firewall to the intake is hell also i can go on and on for little more lol , when doing K CUTTING is a must lol !
 
Agreed. Be brave - get out your angle grinder with cutoff wheel, file, MIG welder and do it right. It's fun and very satisfying...
 
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