Bhp/Torque - whats 'enough'?

[SlickV8]

Hi all, This is part me thinking out loud and part me being inquisitive but I'd appreciated your thoughts... 

I've a '67 Mk3 Spitfire which I've been slowly doing up over the last 24 months or so. Its got a rebuilt GE 1300 engine with a fast road cam. I've just had it converted to Efi  - as in literally just and as I write I've not yet picked it up but the tuning co have rung through the rolling road figures....

Before i tell you the results I ought put my thoughts in perspective; I'm not building a race car but rather I want a quick, fun road car and I occasionally think doing the odd hill climb might be a great way to spend a day out. There seems to be a lot of internet talk of 100bhp 1300's being but an afternoons work, so with that figure in my mind I got busy.

So my engine spec is;

GE small crank engine , plus 20 pistons, minus 10 big ends and mains tri metal bearings, pistons and rods balanced, New timing chain, tensioner oil seals gaskets , uprated oil pressure release valve. new swept back oil  pump, lightened flywheel (approx 5 kg ), TH5 fast road cam with new followers, big valve head with competition high lift  twin valve springs lightweight alloy caps.

I'm pretty sure converting to Efi was never going to increase the hp, but I cant decide if i'm disappointed or If i'm looking at a piece of paper rather than waiting and feeling through the seat of my pants;

80bhp and 95lbsft @ 5100.... at the flywheel.

i'm no expert but wikipedia suggests the car would have left the factory with 75bhp and 75 lb-ft @ 4000rpm [albeit 53 years ago], so my mods seem to have given me 10bhp and 20 lb-ft.....but then look again and thats bhp +12% and torque +28% assuming triumphs figures were also quoted at the flywheel.

Thinking out loud, those percentages dont actually seem too bad and doing the same calculation to get to 100hp would mean an increase of over 33%; I'm reasonably sure the internals could take 100hp but to get there would seem to be significantly more than the proverbial afternoons work?

So am i looking at a glass half full or is something not seeming quite right with my engine?

Many thanks

[NonMember]

That's probably not a bad figure, TBH. The myth of "easy 100BHP" 1300s assumes "optimistic" measurement and a completely undriveable torque curve. you said you have a "fast road" cam, not a "full race" one.

First thing to note is that you need to know what your tuning company mean by "at the flywheel". They will probably have obtained that by measuring at the wheels and correcting for the drag measured on run-down with the clutch disengaged and/or gearbox in neutral. This is a fair and reasonable method which gives results similar to the "DIN" measurement method used to quote the Spitfire 1500's 75BHP. It's not the same measurement as the Mk3's figure. The industry changed the standard, in about 1970, from "bare engine" to "with standard ancillaries" (i.e. your water pump and alternator connected up).

You're correct that an EFi conversion isn't going to magically give you loads of extra BHP. The power you get is all down to how much air you can pull through, and the standard twin-carb arrangement was pretty good for that. What you will find with a well-set-up EFi is that the power is delivered more consistently, more smoothly, and more reliably. The piece of paper won't show any of that but you will notice when driving.

[Mjit]

EFi will give the same BHP as a race-tuned carb/dizzy engine but will normally give a slightly better figure than a road-tuned carb/dizzy engine.  Not down to magic, just the fact that the carb/dizzy combo rarely give you the perfect amount of fuel and spark advance for any running condition while EFi can.  In the race case it's all about full throttle running, so you can tune to be perfect under those conditions and just accept a 2000RPM tickover.

Peak RPM isn't where you win with EFi though, it's the fact that rather than being spot on at 2 or 3 spots across the rev/load range and within 10% the rest of the time you're spot all the time, everywhere, so the torque line's a little higher across the graph and the power line's a little straighter, with fewer/smaller peaks and troughs.  And that's the day to day power you can actually use on the road.

[SlickV8]

Thats great guys thank you. The more i think about it I dont suppose that Ive done much beyond the cam that would really increase HP, and certainly not by 30+%. I guess i just got that nice round 100 number stuck in my head

There seems to be a general lack of printed results for these engines so I'll try and get a print-out and publish it for future reference too....although interestingly the rolling road guy did suggest if i took it to a.n.other place he knows not too far away their equipment would probably show an extra 10-15hp. Theres nothing simple anymore!

Mines running 50mm trumpets [for clearance] - they did do a run with 90mm trumpets and that gave 82hp

I'm collecting the car thursday so hopefully I'll get some miles in friday / saturday and can offer some feedback on the actual driving experience...

thanks again

[Colin Lindsay]

8 minutes ago, SlickV8 said:

I'm collecting the car thursday so hopefully I'll get some miles in friday / saturday and can offer some feedback on the actual driving experience...

thanks again

That will be the proof of the pudding and you may not need anything further. Let us know how it goes.

[Clive]

Did anything else happen to the head? Any porting, raised compression? That would hold figures back.

Also the revs, I would expect more power at 6000rpm. Not sure what happens after 5100 with yours? Maybe I need to look at the TH5 cam power band again. (had one in my 1500, not bad, with 10:1 CR and std inlet/exhaust it made 91bhp) I remember the TH5 suits the 1500 as it is not a screamer cam profile.

 

I have a mk3 spit, pair of dellortos and megajolt. TH7 cam but matched head. I have understood it it be in excess of 100bhp, probably nearer 110 and I would happily believe that. Torque curve is amazing too, pulls nearly as well as a 2 litre (from my hazy memory). And it will rev to 6500 and beyond.

[SpitFire6]

"80bhp and 95lbsft @ 5100.... at the flywheel" suggests to me that you have restricted gas flow with the TH5  2200-7000 Cam.

 

 

[NonMember]

What exhaust system have you got? The standard single-downpipe cast manifold is OK for a 70BHP engine but may be restrictive with the fast road cam and big valve head.

[Clive]

21 minutes ago, NonMember said:

What exhaust system have you got? The standard single-downpipe cast manifold is OK for a 70BHP engine but may be restrictive with the fast road cam and big valve head.

And that includes exhaust manifold....

[JohnD]

Thought of taking it to rolling road for an estimate of what it's doing?   Perhaps to have the operator adjust timing and mixture, becasue that's easiest when ythey can run again and see any improvement, or not?   That will optimise it, and then you'll know, more or less, what you have.

 

[Nick Jones]

There are some unanswered questions in you original spec list - most notably (as Clive says) whether the head has had gas flowing work and what the compression ratio is. Also what form the the injection manifold and system takes and what exhaust manifold/ system you have.

We do have a multi-point injected 1300 Spit here based on a slightly weary Mk3 engine with standard internals. It’s reasonably lively, very tractable and economical, but no monster. Dunno what power as it’s never been on an RR. Probably 75 - 80 bhp.

In contrast, many years ago I built a small crank 1300 for my Herald. That had a fairly standard bottom end. Just lightened and balanced, a Kent TH3 cam and a horrifically expensive head by Silverstone Engineering. Fuel fed in by twin SU HS4s and exhausted with a TT 4-2-1 manifold. The rest of the system was made up of motley rescues but fairly large bore and straight-through.  Had a very un-Herald like bark...... No idea what the power was - it never saw a rolling road  - but it did go well.  It would genuinely out-drag a Volvo 360GLT an XR2 and an XR3 (had mates with all of those and it made them unhappy - which me me happy). It could just about stay with an XR3i and Rover 216GTi, to the surprise of two of my colleagues.

The down sides....... it wasn’t at all economical, it could be politely described as “crabby” below 2000 rpm and “very crabby” in traffic. It was not ideal as a daily driver, which is what it was. But between about 3000 rpm and “Smiths” it truly flew.  Would have loved to try and civilise it with injection, but those days were still in the future.

Nick

[mpbarrett]

my experience of going from twin SU's, tubular exhaust, 1500 engine straight to EFI and wasted spark mapped ignition is that the EFI/fuel and  ignition means thats you get a smoother engine. Not sure there is an overall gain in max power but instead of a couple of sweet spots in the tune its nice over the whole rev range. And so much nicer to drive...

This was on an engine with 3 good compression cylinders and one very poorly! 

Mike

[Colin Lindsay]

13 hours ago, Nick Jones said:

But between about 3000 rpm and “Smiths” it truly flew.  

Lo that reminds me of my first Daihatsu Charade, it was only clocked to 95 so used to go right off the clock and I drove it by the rev counter... 5500 rpm in 5th was around 100.

[SlickV8]

Theres not been anything done to the head in terms of compression or porting - maybe thats worth a look. It has a [arguably too loud]  'sports' exhaust with tubular steel manifold. The RR guy has suggested that the cam timing may be out a little or it could have been deliberately adjusted to give more torque? Its all witchcraft to me so i dont quite understand that or how that would make a difference. I'm intrigued by the restricted gas flow suggestion; how would that manifest and what the solution - is that the porting / raising compression?

thanks all

[Clive]

Yes, you need to start by checking the cam timing is correct. Also the valve clearances, they are something like 18 and 22 thou (but check!) compared to 10 thou std.

With a warmer cam you will need increased compression. No idea what you have, but if a herald head maybe 9:1, where as with that cam nearer 10 would be a benefit. 

Did the power start to drop after 5100rpm? As above, that is low and indeed cam timing is a contender. But if you are (a) unhappy and (b) unsure of the build spec, you willneed to properly investigate.

[SlickV8]

really grainy pic RR guy sent me. Not sure why it stops at +/- 5800 but Ive a number of questions to ask when i get to pick it up so I can decide on what to do next...

[Nick Jones]

3 hours ago, Colin Lindsay said:

Lo that reminds me of my first Daihatsu Charade, it was only clocked to 95 so used to go right off the clock and I drove it by the rev counter... 5500 rpm in 5th was around 100.

The tacho was a 1500 Dolly one calibrated to 7k.  Used to go well past that....

RR plot stops at 5,800 because that’s where he lifted off. Power/torque had been dropping for a while anyway. Something strange about the torque curve anyway. Peaks very low at 2700 ish and then declines gradually all the way to about 5k, where the rate of decline accelerated.

Not really what I’d expect from a 280 degree cam. I wonder if it is significantly advanced. Will probably drive nicely though so I wouldn’t make any rash decisions until you’ve got acquainted with it.

Compression ratio needs to be at least 9.5:1. 10:1 probably better. Presumably the ignition timing is also controlled by the ECU?

Would love to see a pic of the inlet/injection arrangement.

Nick

[Nigel Clark]

Another question to consider is the accuracy of the rolling road, as they are probably not all calibrated the same. A few years ago I had my TR6 on a well known rolling road in the Midlands. It's a 1970 Lucas injected model with skimmed head and sports exhaust. As we know, the factory claimed 150bhp for this engine, though 135 would probably be a more reasonable figure.

My car peaked at 126bhp on the rollers and the experienced operative commented it was the best near standard TR6 he had seen, as most make 110-120 on his rolling road. The car goes very well and never seemed down on power.

I've also had my GT6 Mk3 on the same rollers and that showed a peak of 80bhp, though the factory suggested around 100bhp. Again, the GT6 goes just as well as expected of a near standard car.

I feel the way to view a rolling road is as comparative testing tool. If the mixture or ignition timing is changed, the rollers will tell whether the engine made more or less power as a consequence, but unless it's a calibrated engine dyno measuring direct off the flywheel the absolute figures may well be misleading.

Nigel

[Nick Jones]

Absolutely right....

[SlickV8]

Yes I’m definitely not planning anything until I’ve driven it. These were pics they sent last week showing initial install. I’ll take and post some better ones once it’s back home. 

[Steve P]

Who built the engine?,i would certainly question any builder who bunged a cam in,big valve head with competition double springs(not required imho) without improving flow and upping the compression ratio?.

Steve 

[Nick Jones]

Presumably the TBs are from a motorbike?  I see a Ford coil pack on the bulkhead too.  Do you know which ECU?

This is ours

Nick

[SlickV8]

Me221 ECU was mentioned on the quote. Looks like I’ve got a fair bit of cable tidying to do going by your engine bay 😀

[Mjit]

On 16/06/2020 at 12:05, SlickV8 said:

really grainy pic RR guy sent me. Not sure why it stops at +/- 5800 but Ive a number of questions to ask when i get to pick it up so I can decide on what to do next...

On a power run most RR operators will stop once the power starts to drop off and it's clear it's not just a flat spot.  If you think about it, if the power is dropping all continuing to increase RPM is doing is increasing the stresses on the engine...to get the same BHP you could get by backing off the throttle to lower RPM.  I mean, why run the engine at 5800RPM to get the same power you could get running it at 4300RPM?

Personally I'd be more interested why the track only starts at 2500RPM...  Ideally you want to start from idle in 4th (1:1) gear and run all the way up to the red line/power peak, to help theRR with it's drivetrain loss estimation - though in a 1300 Spitfire that's usually asking a bit much and you need to get it going in 1st and 2nd before slipping in to 4th.  Last time my car was on the RR to map the MegaJolt timing we were able to trace from 1500RPM (getting 60 at the road/estimated 75 at the flywheel).

Peak power/RPM was limited because my car started running either rich or lean at higher RPM and the tuner didn't have suitable needles in stock but why change them.  I mean I'll soon get on with the rest of the swap to EFi... Just looked and the RR chart's dated 2007 😶

[SlickV8]

So as the rain cleared I sneaked off to my Unit to have a first drive this afternoon and found there’s no brake lights, no indicators and no wipers. FFS!!

No idea what’s happened and wiring is not my strong suit so having to call in an auto spark next week....disappointing but typically mirrors most of my experiences of putting projects out; 1 job sorted but 3 more created.