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Dyno run on 18V engine. Comments?

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MGB65B Avatar
MGB65B Gold Member Thomas Aczel
Sydney, Kurrajong Hts, Australia   AUS
1962 MG MGA MkII
1965 MG MGB "Dad's Little White Car"
Hi performance guys.
I thought the dyno chart below might be of interest to some of you.

My MGA Mk II was rather limp in its performance when I purchased it compared to my MGB Mk I that I was very used to. I'd thought the MGA Mk II with its better breathing "16" head, higher compression, lighter flywheel (compared to earlier MGAs), lighter weight (than an MGB) etc should be not too far shy of an MGB.

A dyno run confirmed my impressions of an engine significantly down on power; it made a mere 53.5 HP at the rear wheels.

Investigation revealed a number of problems. Awful previous head work with massively oversized inlet ports in particular, plus combustion chambers taken out so far the head gasket overhung into the chamber edges, and dished low compression pistons giving 125 lb/sq in compression seemed to be the main culprits.
Flat top pistons got the compression up to 185 lb/sq in so the 40 oversize 1622 engine (so about 1670 cc, roughly) now was very significantly more lively than it had been. It even sounded better, crisp. But it didn't really come on song till about 4,000 rpm (hi lift cam also fitted by a previous owner).
The lack of low speed torque was amplified in particular by the fact that the Ford T9 gearbox I fitted had the tall first gear option of 2.98:1 (vs standard MG and Ford 3.65:1 first).

In the end I decided to start all over again with a standard bore 18V engine, modified for my own tastes.

Specs:
Standard Cam (for torque and good power spread)
Ported head, with manifolds matched to the ports.
9.8:1 compression.
MGA H4 carburettors.
Stub stacks.
K & N filters inside the original Vokes air cleaner housings.
Jet coated MGA three branch exhaust manifold (mainly to reduce the heat around the fuel bowls).
Piston/con-rods and flywheel/clutch balanced.

With this I now had a lovely eager smooth torquey lively engine with real bite and response. Above 4,500 rpm or so it starts to make more noise than more power, but since it's purely a street car, I was very pleased.

Yesterday, to get rid of the points, but reliably, (I've had three pointless ignitions on my two MGs fail, so far), I had a 123 distributor fitted.
To optimise the advance curve, (about fifteen different curves available), I had this done using a dyno. (Curve C proved the best).

Attached is the dyno curve which looks very much the way the car feels to drive.

I've been advised by guys who really know their stuff to fit a VP12 or Piper 270 camshaft, and to lighten the flywheel (it's the 18V flywheel ground down to MGA/MGB Mk I diameter to take the MGA diameter, so it's already a touch lighter than the 18V flywheel, though, very surprisingly, despite the smaller diameter and drilling to balance it, the now smaller 18V flywheel still measured 8 ounces MORE than the MGA flywheel!)
I'm sure the cam change would get things happening where they presently start to taper off above 4,500 or so, but as a purely street car, I wonder if this really matters?



Edited 1 time(s). Last edit at 2019-02-02 04:04 AM by MGB65B.

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mgblestyle Avatar
mgblestyle Philip Shave
Olympia, WA, USA   USA
Thomas, nice looking combustion chambers, shouldn't have any pre-detonation issues even at 9.8:1. I think a cam change would extend that RPM range. I recently built a similar 18V with 10:1 compression, prepped my chambers much like yours, 1.625" intake valves, D9 grind cam (much like the VP12, 292" lift, .050" duration of 228, lobe center of 108), ported new County head, HS4 carbs, stock exhaust.

I timed the cam at 104.5 degrees ATDC. While the idle is up a little and smooth at 1100 RPM, there are no off-idle or low-end problems; no lack of power or torque. In an 1980 MGB, heavier car, it will lug around as low as 1500 RPM. The torque from 2000 on up is just amazing. This engine pulls quickly to 6400 RPM in the lower gears. Here's what many would not expect--around town from idle to 4500 the added torque feels like twice the stock motor. I find myself using only the first 1/2 inch of throttle because it pulls so well. So, I wouldn't be afraid of a little more cam if you time it properly and it should match well with your compression.

Oh, you mention possibly lightening the flywheel. I did use the Fidanza, 8.5 lbs. I think it helps the motor spin up quickly in the lower gears. I see this cam choice as a win-win: Much stronger in normal driving, much more torquey and another 2000 RPM and a bunch of HP on the top end. Phil

Perdido Avatar
Perdido Gold Member Rut Rutledge
Tuscaloosa, AL, USA   USA
Thomas,
Nice build and like some people I like a little higher end oomph, so I used the VP12 cam on Haps recommendation. Like Philip I’m using an Fidanza aluminum flywheel and while it ads nothing in the way of power, it really lets the B engine spin up and it’s one of my favorite mods. My engine has a slightly lumpy idle at 900 rpm and it pulls great without having to feather the clutch when starting off, flat or uphill.
Good luck, Rut



1960 Bugeye undergoing restoration, 1275
1970 MGB, Pale Primrose
1967 Triumph TR4a
1966 Triumph TR4a
When I went to school, they asked me what I wanted to be when I grew up. I wrote down 'happy'. They told me I didn't understand the assignment, and I told them they didn't understand life. John Lennon

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B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
A lot of people post the HP/TQ chart but not the AFR chart. I find that's more important data for tuning. You appear to have achieved very typical results for an 1800. The "rough lines" of your dyno graph speak volumes, but the AFR chart would confirm what I'm thinking.



jeff@advanceddistributors.com

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
48 RWHP and 150+ ft-lbs of torque?

Doesn't make sense to me...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Dick, you need to stand upside down when looking at the chart. 90 ft-#s and 77RWHP.devil smiley


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Dave Headley, dba FAB-TEK offers full service race car parts and preparation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Guess I can't blame it on color blindness... confused smiley

Dave, don't the curves typically cross at about 5,200 rpm? Is this rule of thumb different for chassis dyno rather than engine dyno?

Dick



In reply to # 3884762 by fast-MG.com Dick, you need to stand upside down when looking at the chart. 90 ft-#s and 77RWHP.devil smiley



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

MGB65B Avatar
MGB65B Gold Member Thomas Aczel
Sydney, Kurrajong Hts, Australia   AUS
1962 MG MGA MkII
1965 MG MGB "Dad's Little White Car"
Thanks for all the comments everyone. Most helpful and educational.

Given that I started from 53.5 RW HP, and now have about 78, I’ve gotten a 50% increase from where I started. No wonder it feels much better.
I’d heard that a good, completely standard MGB makes about 62 RW HP. If so, I’ve gotten about a 25% improvement on that, though that seems a bit far fetched for what the rise in compression and some careful porting and flow work should achieve. So maybe a good but standard MGB is more like 65-68 HP?

I’ll try to get the AFR graph. The dyno guy told me it was a bit rich at idling which he leaned off, so presumably he has the AFR curve on his computer.

I’ll also put up the original dyno graph, which was accidentally left at the workshop, if I can get it back. I’d taken it as a reference for the operator, so he could compare the new and old curves for interest.

BTW here’s a photo of one of the stub stacks. An MGA doesn’t have these though the MGB does. I’d read these little things are worth 3-4 HP !
I bought these from Rimmer Brothers and would have been presumably for a Triumph TR application. They were originally much taller but for the confined MGA Vokes air cleaner housings I had them machined down.



Edited 1 time(s). Last edit at 2019-02-02 02:01 PM by MGB65B.


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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Dick, Some of the dyno operators here in OZ use a split graph where the HP an torque are on a different scale. If they they use Metric they dont cross until 9549 revs. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Thanks, Denis. Other than my obvious brain fart, it hadn't occurred to me that you would be using metric units of measure. Do you use Watts for horsepower and Newton-meters for torque?

Dick



In reply to # 3884858 by Denis Dick, Some of the dyno operators here in OZ use a split graph where the HP an torque are on a different scale. If they they use Metric they dont cross until 9549 revs. Denis



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

twentyover Avatar
twentyover Greg Fast
Lives in SoCal, Resides in the Burbs of Detroit MI, USA   USA
In reply to # 3884864 by dickmoritz Thanks, Denis. Other than my obvious brain fart, it hadn't occurred to me that you would be using metric units of measure. Do you use Watts for horsepower and Newton-meters for torque?

Dick



In reply to # 3884858 by Denis Dick, Some of the dyno operators here in OZ use a split graph where the HP an torque are on a different scale. If they they use Metric they dont cross until 9549 revs. Denis

In the photo shown, torque is in ft=lbs on the RH Y axis, and hp on the LH Y axis. Scale between the teo is 2:1, so the torque/hp curves cross @5252/2, or 2626 rpm

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Dick The dyno operator I use still uses HP and foot pounds, and although we use metric for everything else most motor heads use SAE for power output ( It just doesnt look right in metric)

Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Thomas Your engine has a nice flat torque curve and should be nice and flexible. Dont expect huge leaps in HP, as the stock cam will still produce its power at much the same revs, no matter what else you did to the engine. Mid range should be sweet.
Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Got it. Thanks...

Dick



In reply to # 3884894 by twentyover
In reply to # 3884864 by dickmoritz Thanks, Denis. Other than my obvious brain fart, it hadn't occurred to me that you would be using metric units of measure. Do you use Watts for horsepower and Newton-meters for torque?

Dick



In reply to # 3884858 by Denis Dick, Some of the dyno operators here in OZ use a split graph where the HP an torque are on a different scale. If they they use Metric they dont cross until 9549 revs. Denis

In the photo shown, torque is in ft=lbs on the RH Y axis, and hp on the LH Y axis. Scale between the teo is 2:1, so the torque/hp curves cross @5252/2, or 2626 rpm



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

MGB65B Avatar
MGB65B Gold Member Thomas Aczel
Sydney, Kurrajong Hts, Australia   AUS
1962 MG MGA MkII
1965 MG MGB "Dad's Little White Car"
OK, I called into the Dyno shop today. To my great surprise, the dyno they use doesn't have the facility to record the air/fuel ratios! eye rolling smiley So that's a big disappointment.
I did however pick up the graph of the earlier dyno run on my MGA with the previous 40 oversize 1622 engine that was in the car when I bought it.
The bottom blue line is what the car did as they received it from me. The second, red, line is a run after playing with the advance curve. As is patently obvious, it was a very poor performing engine, and confirms that "bigger is not always better" (such as the hugely oversize inlet ports and high lift camshaft).
For easier comparison I've reloaded the more recent graph with the 18 V engine fitted along with the earlier run with the previous engine.

And Denis, you are absolutely correct, the engine is "nice and flexible". It is a lovely smooth responsive engine, with great torque and "bite" between 2,000 and 4,000 rpm; a really sweet street engine. It does run out of its eagerness above 4,500, but frankly I don't venture up into that range often.

Oh and by the way, it was "Curve 3" (and not "Curve C" ) advance curve setting on the 123 distributor that gave the best all round result with my 18 V engine.



Edited 1 time(s). Last edit at 2019-02-04 05:28 AM by MGB65B.


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