What's stopping this engine from having a 8000 rpm - 8500 rpm powerband?

[IDailyDriveABean]

After the obvious is done like a much larger turbo, ported head, aggressive camshaft (mountune/piper stage 4) and upgraded valve springs what's next?

Is the stock rotating assembly strong enough to handle those kinds of rpms?
I would think the rotating assembly would have to be removed and precision balanced before spinning that high. The forged rods and pistons as far as I know are a bit more dynamically balanced than the oem components but heavier... And with that i was wondering could your run of the mill machine shop come close to the balance of a aftermarket components

Lastly a lightweight crank is also available and I'm sure that will help too.

I'm just curious as to why 8k rpm Fiesta's are exceptionally rare. If i could i would definitely try my hand at building one.

 

[Capri to ST]

One reason you may not see them, besides the obvious extra cost of modifying the drivetrain to handle such high RPMs, is that the car with its turbo setup is clearly designed to make more power and torque down low.
When I think about cars with an 8,000 RPM redline, I think about cars like my NSX, which had exactly that redline. It's fun as hell having that and it's thrilling as you approach redline, but the difficulty is then you have designed a car which has to be way high up in the RPM range to make its power.
Honda and Acura mitigated that somewhat with VTEC, but an earlier Acura I had with VTEC and a 7000 RPM red line, a '96 Integra GSR, pretty much had to be flogged to death to make any power and didn't have much down low.

 

[Dpro]

One reason you may not see them, besides the obvious extra cost of modifying the drive train to handle such high RPMs, is that the car is clearly designed to make more power and torque down low.
When I think about cars with an 8,000 RPM redline, I think about cars like my NSX, which had exactly that redline. It's fun as hell having that, but the difficulty is then you have designed the car which has to be way high up in the RPM range to make its power. Honda and Acura mitigated that somewhat with VTEC, but an earlier Acura I had with VTEC and a 7000 RPM red line, a '96 Integra GSR, pretty much had to be flogged to death to make any power and didn't have much down low.

Funny you mention your NSX and the 8K redline , that was one of things that made people feel the cars were underpowered.
Compared to the inline 6’s and Nissans V6’s of the day that usually came turbocaharged but also had gobs of down low TQ, RB’s,2J’s, S50, S52, would just pull on the NSX . I remember toying with an NSX in a RB25DET powered to 240sx . He just could not keep up with me.

 

[Capri to ST]

To the OP, one interesting fact about the design process of that NSX that has relevance to your question is that to get to the power level that they wanted, which entailed letting the car be capable of an 8,000 RPM red line, they had to add titanium connecting rods to the engine.
They are very light and strong, but high $$.

 

[IDailyDriveABean]

One reason you may not see them, besides the obvious extra cost of modifying the drivetrain to handle such high RPMs, is that the car with its turbo setup is clearly designed to make more power and torque down low.
When I think about cars with an 8,000 RPM redline, I think about cars like my NSX, which had exactly that redline. It's fun as hell having that and it's thrilling as you approach redline, but the difficulty is then you have designed a car which has to be way high up in the RPM range to make its power.
Honda and Acura mitigated that somewhat with VTEC, but an earlier Acura I had with VTEC and a 7000 RPM red line, a '96 Integra GSR, pretty much had to be flogged to death to make any power and didn't have much down low.

I find it funny that the V4/stage camshafts for the Fiesta are pretty similar to the B16A/B16A2 of the GSR and civic si

With the GSR having identical lift and less duration and the SI having marginally more lift but still less duration than the Fiesta Race cam.

Is there are design constraint within the cylinder head that prevents having a cam with 11mm or 12mm of lift?

Fiesta ST Piper Race cam
Int-276 dur. / 10.67mm lift
Exh-264 dur. / 8.91mm lift

Integra GS-R
Int-230 dur. / 10.6mm lift
Exh-227 dur. / 9.4mm lift

Civic Si '99 Spec
Int-240 dur. / 10.7mm lift
Exh-227 dur. / 9.4mm lift

Seeing things like this just makes me think 🤔, puts things into perspective.

And it seems that both stock GS-R and old civic SI's tip out at 7.5k rpms with a small dip at 8k rpms

 

[Capri to ST]

I find it funny that the V4/stage camshafts for the Fiesta are pretty similar to the B16A/B16A2 of the GSR and civic si

With the GSR having identical lift and less duration and the SI having marginally more lift but still less duration than the Fiesta Race cam.

Is there are design constraint within the cylinder head that prevents having a cam with 11mm or 12mm of lift?

Fiesta ST Piper Race cam
Int-276 dur. / 10.67mm lift
Exh-264 dur. / 8.91mm lift

Integra GS-R
Int-230 dur. / 10.6mm lift
Exh-227 dur. / 9.4mm lift

Civic Si '99 Spec
Int-240 dur. / 10.7mm lift
Exh-227 dur. / 9.4mm lift

Seeing things like this just makes me think 🤔, puts things into perspective.

And it seems that both stock GS-R and old civic SI's tip out at 7.5k rpms with a small dip at 8k rpms

I was thinking that '96 Integra GSR had a red line of 7,000 RPM as I said, but I believe you're right, I believe it was 8,000 RPM.

 

[Intuit]

From the ground-up perspective and stating the obvious, it isn't a dedicated racing engine.

This is an absolutely fascinating article.

https://lambdageeks.com/gasoline-engine-bore-and-stroke-ratios/




For such a small engine, the fuel efficiency... well... it's an insult to use the words fuel and efficiency at the same time... but it's more optimized for racing.


The FiST engine by comparison...

 

[IDailyDriveABean]

I noticed this too B16A's 81 mm × 77.4 mm, but I guess why these ecoboosts make pretty good torque for what they are. But on contrary the B18C(x) series is simply a stroked B16 identical bore sizing but an 87.2mm stroke and those engines rev high all day long.

 

[M-Sport fan]

What Intuit posted above also hints at that an over square setup (larger bore diameter than stroke length is more capable of higher revs because of the structural physics involved (slower actual piston speeds at TDC) than an under square setup (smaller bore than stroke, like ours is) due to our higher actual piston speeds at TDC.

Of course many other factors come into play; valvetrain efficiency/spring pressures, rotating assembly fine balance and weight/'knife edging' of crank counterweights, etc. as well as valvetrain weight, and oil slinging/all other frictional losses.

If I got any of the above wrong, I hope that the engine builders, engineers, or any others on here who have much more knowledge than I will ever have on the topic will weigh in and PLEASE correct me on the above!

 

[Dpro]

Longer stroke engines tend to be higher lower hp and do not rev vs short stroke engines will produce more hp less tq amd rev to the moon . The balance is a perfectly square engine like Nissans SR20DET which has 80mm bore and a 80 mm stroke which with the proper valve train will spin up high . The problem with the SR20 is the valve train is semi rocker. Which gets valve float at 8500 rpm . On the other Nissan CA18DET which was basically 4 cylinders of Nissans famed RB26DETT had bucket follow cam valve train and indeed revved up like no tomorrow those engines could see 9k with out breaking a sweat . They were also very expensive to build hence Nissan going to the SR20DET for Silvia’s and 180sx’s as well as Pulsar GT’ir’s ( AWD Japanese Hot hatch we never got to see stateside circa 91-92). Funny thing is the KA24DE that we got stateside in 91 up 240sx’s had a bucket follow cam head that flowbenched among the best for a factory 4. cylinder head. Too bad Nissan stuck it on a Long struck 2.4 liter bottom end that did not rev for beans. Though Turbocharged those engines dropped gobs of TQ people just had a habit of blowing them up due to improper fueling and rudimentary tuning capabilities . Standalone ECU or go home. I always wanted to get a Japanese KA diesel crank and destroke that engine. Rarer than hens teeth I might add😂