For the 'natural aspirators' - How tuned is your engine?

[williredale]

Kozy said:

AW111 said:

Interestingly, the old RAC (taxable) horsepower was calculated in a similar manner -

RAC hp = bore^2 x cyl / 2.5, with bore in inches.

= bore(mm) ^ 2 / 1612.9

RAC hp = bore^2 x 0.62 x 10^-3
Kozy max hp = bore^2 x 9.694 x 10^-3

So in 1910, the RAC assumed a PI of 64, if my maths is correct

Edited by AW111 on Sunday 13th October 14:55

Interesting... What was this calculation used for?

Tax.

The amount of road tax / VED you paid depended on the RAC horsepower rating.

This was all prewar. I can't remember when they changed it but it was affecting engine designs

Edited by williredale on Sunday 13th October 18:13

[ArtVandelay]

619 for an early V8 Vantage.

89mm bore
380bhp (or there abouts)

4.7l has a higher rating

[otolith]

k-ink said:

Kozy said:

C.A.R. said:

Unfortunately for me extortionate rent and other bills have forced me into a dull old diesel, but the old 2ZZ-GE engine in the Celica I used to drive had an 82mm bore and gave 189bhp - scoring an impressive 725 on your calculator.

Those engines appear to be extremely under-rated!

Why oh why did they not put that VVTLi system in the GT86!!

Re: 725

Cracking engines. 8300rpm on the second cam is a thrilling experience. Place it in the kart like handling chassis of an Elise 111R, or Celica T190 and they are wonderful fun. Amazing value in the Celica T190 too. Easier to live with than a DC2 anyway. Now the ratio of 725 v the cost of a Celica T190 (£3-4k for a real minter) is good value!

I'd still rather I had a Honda K20 in the back of mine, though. It's not a bad engine, but the Honda is a better implementation of that sort of thing.

[msduk]

M113 engine in various states of tune...

l    bore   stroke  bhp   pi
4.3  89.9   84      279   445 
5.0  97     84      306   419
5.4  97     92      367   503 

Edited by msduk on Sunday 13th October 18:45

[Grahamr123]

My Celica T sport with a bore of 82mm and 190bhp gets a rather solid score of 729!

[Kozy]

williredale said:

Tax.

The amount of road tax / VED you paid depended on the RAC horsepower rating.

This was all prewar. I can't remember when they changed it but it was affecting engine designs

Edited by williredale on Sunday 13th October 18:13

I see, so it didn't matter what the engine actually put out, only what it should have put out according to the bore size?

As fair as any other tax I guess..

[havoc]

X959 said:

Thanks for taking the time to write that up.
Quick question after reading that then, so mine has the 2.5" 4-1 manifold and full 2.5" system with decat. If the standard airbox is that good then the expected gains from the induction side can be pretty much disregarded, so expected power as it stands should be c.210?

The ecu remains untouched so the limiter is still at the standard point and I haven't fitted a vtec controller. After reading up on them, they just seem to make the vtec come in earlier and make more noise without any real benefit.

The power delivery certainly seems peaky, but I can't compare to a standard one having never driven one.

And if it makes any difference it is a genuine JDM B18C Type R, and not a UK spec B18C6.

I'm not a tuner, just a numbers guy going off a too many years reading stuff on itr-dc2.com among other places, but that sounds about right. A 4-1 manifold will emphasise peak torque at higher revs (and hence peak power) at the expense of 'a thicker midrange', so your comments make sense. Only real way you can know power gains is to do before- and after- runs on the same dyno, ideally on the same day.

VTEC controller - agreed, their main use is to get rid of the 5,800rpm 'kick' - the crossover point between the two cams is actually closer to 5,000rpm, but they engineered the kick in there to make the car feel faster/more involving, apparently.

UK / JDM engines - very little difference once you strip the manifolds off. JDM cars were measured on 100RON fuel, so on UK RON they're probably low-190s (which would make yours real-world ~205-ish*)...but then the 187 for the UKDM car is quietly considered to have been 'the best seen', rather than typical - low-180s is probably more representative, and probably less now for most machines.


* A true 205, not a rolling-road stated 205, note!

OP - apologies for the digression...

[Kozy]

No problem!

Looked up the LSx engines...

LS1 - 99mm - 345bhp = 454
LS2 - 101.6mm - 412bhp = 515
LS3 - 103.1mm - 430bhp = 522
LS7 - 104.8mm - 505bhp = 593 (good for 842bhp NASP! )

One thing I am interested in is the costs of tuning various engines. If anyone posting here has actually tuned their engine, an interesting one to know would be the before and after PI score and the cost to upgrade!

Obviously, this will be a bit sketchy as we all know rolling roads can be dubious, but I'd still be interested to hear about it, I image there is probably a strong trend in cost per point as the scores go up...

The website is only a few months old and doesn't have much on it at the moment. So I should mention the obligatory 'follow on facebook' if you like the gist of the article, as I'll be doing a lot more.

Edited by Kozy on Sunday 13th October 22:51

[Talksteer]

TVR 4.3l 96mm bore 430bhp comes out as 818

[davepoth]

Kozy said:

williredale said:

Tax.

The amount of road tax / VED you paid depended on the RAC horsepower rating.

This was all prewar. I can't remember when they changed it but it was affecting engine designs

Edited by williredale on Sunday 13th October 18:13

I see, so it didn't matter what the engine actually put out, only what it should have put out according to the bore size?

As fair as any other tax I guess..

Except it became a nonsense because the engineers found ways around it however, it was responsible for most mass-market British engines being built rather undersquare for many years.

https://en.wikipedia.org/wiki/Tax_horsepower#Brita...

It also explains why so many cars of that era had a number as a name in the UK - it was the tax bracket.

[XJ Flyer]

Kozy said:

No problem!

Looked up the LSx engines...

LS1 - 99mm - 345bhp = 454
LS2 - 101.6mm - 412bhp = 515
LS3 - 103.1mm - 430bhp = 522
LS7 - 104.8mm - 505bhp = 593

To put it another way in the real world you've got around 4.1 hp per mm of bore with the LS3 and 4.8 hp per mm of bore with the LS7.The LS7 has made a 75 hp increase in power with just a 1.7 mm increase in bore.Which seems to show that you can get more power out of every mm of bore size by increasing the stroke measurement at least so long as you avoid making it an undersquare engine.

Edited by XJ Flyer on Monday 14th October 05:17

[Bibbs]

I'd read it's more of a limit of torque per litre (as you can move this about for BHP).

I read on some bike tuning that 85/90 lbft of torque per litre was about the peak for NA applications (race bikes).

And I've had two engines at the opposite ends .. an F20C (s2000) and an LS2 (HSV GTS)

Edited by Bibbs on Monday 14th October 06:44

[Camaro]

fk sake!

1991 Chevrolet Camaro LO3 5 litre V8 Max HP Output when new: 170hp

Stroke: 88.4mm

PI Score: 281


No wonder it nick named the boat anchor!

[pimpchez]

Kozy said:

C.A.R. said:

Unfortunately for me extortionate rent and other bills have forced me into a dull old diesel, but the old 2ZZ-GE engine in the Celica I used to drive had an 82mm bore and gave 189bhp - scoring an impressive 725 on your calculator.

Those engines appear to be extremely under-rated!

Why oh why did they not put that VVTLi system in the GT86!!

Ive just got rid of my corolla t sport .Major engine for sure

[stevesingo]

Kozy said:

One thing I am interested in is the costs of tuning various engines. If anyone posting here has actually tuned their engine, an interesting one to know would be the before and after PI score and the cost to upgrade!

2467cc BMW S14 238hp as standard PI=680

Pistons £750
Head work £1000
Cams £800
Airbox £1200
Exhaust £600
EMS I spent £3000, but you can get away with £1500

TOTAL £5850

Result is 280 hp on the Dyno PI=800

800-680=120
5850/120=
£48.75 per PI

Ouch

[Don1]

Talksteer said:

TVR 4.3l 96mm bore 430bhp comes out as 818

Can you update this thread please? Modified Speed Six wiki
That's a very good result for a 4.3...

[My Evil Twin]

My old XFlow Caterham @ 1700cc = 592
Current Caterham HPC C20XE = 669
My old 1998 Primera wagon = 457

[Kozy]

Talksteer said:

TVR 4.3l 96mm bore 430bhp comes out as 818

6 cylinder? I get 802?

[Iroquois Plisken]

skyrover said:

Chevrolet Corvette ZR1 LS7

pi 593

Supercharged, not NA.

Clio 200 F4R832

Bore 82.7mm
Stroke 93mm
Max Power 197BHP

PI: 743
Max RPM: 8,065

Edited by Iroquois Plisken on Monday 14th October 09:23

[Kozy]

stevesingo said:

2467cc BMW S14 238hp as standard PI=680

Pistons £750
Head work £1000
Cams £800
Airbox £1200
Exhaust £600
EMS I spent £3000, but you can get away with £1500

TOTAL £5850

Result is 280 hp on the Dyno PI=800

800-680=120
5850/120=
£48.75 per PI

Ouch

Excellent start thanks for that. Going to collect as much info as I can and put together some of graph to see how much of a trend there is in the cost of tuning across a wide variety of engines.