Making the type four rev higher Options

[stugray]

Calculate the connecting rod ratio to determine what the projected RPM range should be.

Is there a "rule of thumb" for con-rod ratio for these engines?
I see that the stock ratio for a 2.0L is about 1.84.
It seems simple enough to get to 1.96 by buying 5.5" (~140mm) connecting rods and spacing the cylinders up by ~9mm.
That would reduce low end torque while decreasing forces at high RPM.

What is the downside of a higher con-rod ratio?

Stu

[messix]

weight...

the longer rod will weigh more.

the is a lot that goes into the science of designing an engine.



a short stroke engine

- has a slower piston speed compared to a longer stroke

- has a longer dwell at tdc [the piston doesn't move as the rod approaches and passes tdc]

-a short stroke will need a higher compression to get the best efficiency of the combustion

-the intake and heads has to flow very well while still maintaining high velocity [short intake pulses]

and there is much much more!

build a stroker that makes power all over. and stay around the stock red line.

[Trekkor]

More fun:

(IMG:http://www.914world.com/bbs2/uploads_offsite/i944.photobucket.com-1413-1371013449.1.jpg)


So, now if tach out the motor until the valves float, is that dangerous?


KT

[Trekkor]

That's probably my biggest complaint with the stock TIV motor, the low rpm redline.

Today's modern 4 cylinder sportscars rev to 6500 or higher.

My '99 Ford Escort does.

Also, I'm looking for a '69 VW Bug gear chart that shows speeds in each gear at the full rpm range.


KT

This post has been edited by Trekkor: Jun 11 2013, 11:45 PM

[Trekkor]

Dual Webers on the motor, BTW.




KT

This post has been edited by Trekkor: Jun 11 2013, 11:50 PM

[messix]

"floating the valves is not good!!!!

the valves don't "float" they bounce off the seat because the springs cant control the weight of the valvetrain any more.

this can cause spring failure, valve failure, lifter failure, pistons to meet valves... bad things happen if you keep it up.

[stugray]

they bounce off the seat because the springs cant control the weight of the valvetrain any more.

I thought that the problem occurred at the opposite end of the valve travel.
When the valve has enough momentum to "jump" off the top of the cam lobe and travel past full open.
This would cause the valve to travel farther than the cam is trying to open the valve.
The full open point is when the spring is trying to hold the valve back and the spring is at it's greatest force.

At the opposite end of valve travel (the one you are talking about) the valve is closing and the momentum of the valve is pushing against the rocker (and therefore the cam lobe).

Now IF the lifter has not come down to rest on the cam lobe from the overshoot at max open, then I could see that the valve train would be in "freefall" and the valve seat would stop the valve.

Do they really "float" so far for that to happen?

Stu - Maybe confused?

[r_towle]

You might want to consider a 915 tranny, or a properly built transmission for the type of racing you are doing.
Gears are better than higher rpm in these motors.....push rods have limits just cause...

Rich

[Mark Henry]

You might want to consider a 915 tranny, or a properly built transmission for the type of racing you are doing.
Gears are better than higher rpm in these motors.....push rods have limits just cause...

Rich

901 from a 911 is a better (easier) fit.

[messix]

they bounce off the seat because the springs cant control the weight of the valvetrain any more.

I thought that the problem occurred at the opposite end of the valve travel.
When the valve has enough momentum to "jump" off the top of the cam lobe and travel past full open.
This would cause the valve to travel farther than the cam is trying to open the valve.
The full open point is when the spring is trying to hold the valve back and the spring is at it's greatest force.

At the opposite end of valve travel (the one you are talking about) the valve is closing and the momentum of the valve is pushing against the rocker (and therefore the cam lobe).

Now IF the lifter has not come down to rest on the cam lobe from the overshoot at max open, then I could see that the valve train would be in "freefall" and the valve seat would stop the valve.

Do they really "float" so far for that to happen?

Stu - Maybe confused?

From the research I have done and what I have seen. It depends on the harmonic rate of the springs.

Yes the momentum of the valve train can and does somethimes by design continue to lift off the lobe. But the problem with the stock springs is age,low lift cams,poor cam design, and heavey valvetrain.

The stock heads don't even use spring dampers. So there fore I assumed the probable cuase of "valvefloat" on his engine to be poor harmonic response and inadequate valve control on a low lift cam.

[Trekkor]

Yes, maybe a 901 tailshifter with a flipped ring and pinion is the answer.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i944.photobucket.com-1413-1371091122.1.jpg)

KT

[DBCooper]

Just a general question, what's the history of aircooled fours in endurance racing? Sixes, obviously, but fours? 356's, T1's, T4's? And, again demonstrating my ignorance, what's the track record for finishing? Reason I ask is curiosity about effective cooling over long periods, not something I'm familiar with.

[brant]

Yes, maybe a 901 tailshifter with a flipped ring and pinion is the answer.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i944.photobucket.com-1413-1371091122.1.jpg)

KT

you don't have to flip it if you use a 911 model......

only the 914 version would need to be flipped.... a 911 car has the motor in back with the output to a transmission forward of it.... like a bug!

[Trekkor]

Just a general question, what's the history of aircooled fours in endurance racing? Sixes, obviously, but fours? 356's, T1's, T4's? And, again demonstrating my ignorance, what's the track record for finishing? Reason I ask is curiosity about effective cooling over long periods, not something I'm familiar with.

I don't know, but we turned 322, 3 mile laps in our 2012 24 hour race.
We only lasted 4 hours in our last.

Most air cooled fours do not do well at all.


KT

This post has been edited by Trekkor: Jun 12 2013, 10:03 PM

[Trekkor]

you don't have to flip it if you use a 911 model......

only the 914 version would need to be flipped.... a 911 car has the motor in back with the output to a transmission forward of it.... like a bug!

911 901's are not easy to come by.
914 tailshifters are being given away.


KT

[messix]

Just a general question, what's the history of aircooled fours in endurance racing? Sixes, obviously, but fours? 356's, T1's, T4's? And, again demonstrating my ignorance, what's the track record for finishing? Reason I ask is curiosity about effective cooling over long periods, not something I'm familiar with.

they still seem to do well in the Baja races....

[aircooledtechguy]

If I build a motor to rev higher these are some of the things I look at changing:

1. balance the rotating mass
2. H-beam rods. If using stock rods(!?), upgrade to ARP rod bolts (required).
3. stronger valve springs
4. Light weight lifters
5. lighter weight rockers and push rods.
6. Lightweight valves.

[messix]

and would you run it for 24hrs in race trim? only if you spent big$$$ on very high quality stuff!

[DBCooper]

You said "we turned 322 3 mile laps in our 2012 24 hour race", which is an average of about 40 miles an hour. That's not real fast, so did you spend time in the pits? How much? A 40 mph average speed won't stress your engine, so I guess the real question is what's your real average speed, when racing, the speed you'd need to maintain for 24 hours?

Reason for the T1 suggestion was cost. All the performance parts you need are cheap in a T1, while the same T4 parts are expensive. The question about aircooled fours in endurance racing was because you're doing something really rare and difficult, so it's really cool. But it's so cool exactly because it's so hard. And since it's hard to make a T4 live that long it seems that your priority is probably longevity before power or RPM's. Or no? And IF that's the case (lots of "ifs" here) then that suggestion to go big and mild might be wiser than smaller and stressed.

Did you chop up the back of the car, or was it converted to upright cooling? If so what are you using? Is there a thread somewhere?

[worn]

Reason for the T1 suggestion was cost. All the performance parts you need are cheap in a T1, while the same T4 parts are expensive. The question about aircooled fours in endurance racing was because you're doing something really rare and difficult, so it's really cool. But it's so cool exactly because it's so hard. And since it's hard to make a T4 live that long it seems that your priority is probably longevity before power or RPM's.

(IMG:style_emoticons/default/agree.gif)
My short experience, with a ton of explorative reading, has led me to the conclusion that the 914 was designed for a six and given a 4. And that 4 was pushed to and then past its design limitations. To make power you end up heating the heads which had already been increased in size progressively. By the time they got to the 2.0, which was born of necessity and I am glad that they did, they had reached a point at which they had to move the red line on the temp gauge and sell a car where the oil pressure light came on at about 3 psi, with no stock gauge! They also sold them in general to the same kinds of people who buy Porsches now. If there were problems they would pay the dealer.

Not a rant about the 914, because it is a thoroughbred chassis. I just think that if you want the power that the chassis deserves you are going to have heat or you are going to have a six (and heat). I drove my 914-4 to work today and loved every meter travelled.

What I think I am saying is that for power, I am not sure that the type 4 engine is the best example out there. Maybe if you have to have air-cooled, but even then I suspect there is more capacity in the Type 1. What is the icon for having said the wrong thing?