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MG MGB Technical - Dyno
|I have been on dyno last week but am pretty disappointed with result that showed 108 HP @ 5429 rpm flywheel (or 93 HP at RW) and 175 Nm (129 ft lb) @ 3236 RPM. Ok it was pretty hot day (35 C) so maybe I could see 110 HP on cold day but for 1950 ccm engine with MSX crossflow head and 4 ITBs (EFI) I was expected to be in 120+ range. Camshaft 390 @ 106, duration 280 with 28 deg overlap.|
Anyone with similar engine and dyno
My engine has a Derrington crossflow head, a Piper 285 camshaft, a recurved distributor, dual Weber DCOE 45s, and a Maniflow exhaust system, so I feel that such real-world performance with your specification is indeed pathetic. Allowing for the fact that your Dynometer numbers are incorrectly calculated (a four-speed transmission will absorb about 22 HP, making for 86HP at the flywheel in your case), it is obvious that something is very wrong either with your fueling, ignition timing curve, or both. It is also possible that your exhaust system is too restrictive, but with such low power output, I believe that the problem lies in more that that alone.
I'm no expert but if you've got 93 at the wheels and transmission losses of 22, then actual output is 115. This doesn't seem to be too far away from the expected performance of a 'straight-out-of-the-box' MSX cross flow head - I think Webcon used to estimate around 105-110 for their injected cross flow set up on an otherwise standard 1.8 B-series engine. From what I have read about the MSX cross flow head, it seems to benefit from some porting prior to installation with significant gains in flow reported. Other things to consider will be the compression ratio (CR) of the 1950 engine. Increasing the capacity without skimming the head will have lowered the CR reducing the potential for power.
|"Increasing the capacity without skimming the head will have lowered the CR "|
Assuming the size of piston dish is the same, increasing the swept volume will also increase CR.
|Dave O'Neill 2|
|Thanx for input. I own some additional explanation. Engine was built (with SU carbs) by Mr. Cameron Gilmour. CR is 10:1, head gas flowed and ported (fast road spec), dynamically balanced,.. I have big bore exhaust with performance tubular manifold from Moss.|
I basically just swap two HS 6 with 4 ITBs each 38 mm ID and Megasquirt MS2. One thing that is strange to me are losses in transmission. Dyno operator told me that are measured during runs and that should be 15 HP spot on. Comparing to data I found on internet should be more in range of 30 HP?
I didn’t made dyno with SU carbs so difficult to compare but car runs pretty same as with carbs, only sounds much better.
|Toni Did you do any tuning on the dyno ? There is something not right with the graph. The power and torque curves should be the same and cross at 5252 rev|
when using horsepower and foot pounds, otherwise one or both are wrong. Denis
|Tend to agree with Denis on this|
The figures (graph) look a bit weird
Specially that sudden drop at the end
Fuel pressure maybe dropping off under load
|regarding the 5252RPM, one RR I've used has the x-axis accurate on road speed, but clearly scales the RPM off this somehow rather than measuring directly from ignition pulses as the scale not only fails to correspond with the actual rpm, but the variation factor is wildly inconsistent. So road speed is the only meaningful scale along the x-axis. (OK for repat sessions with the same car on the same RR, but no good for comparing with anything else!)|
So perhaps this is the explanation for that particular feature?
|Tony, I took my S/c car to a well known RR here in the UK where it gave the performance figures of a standard car. As I was a guest I just left it at that. Before tearing into your system, I'd be inclined to try another RR, or if that is not practicable, discover how it was calibrated.|
|The figures will not cross over at 5252 as the torque is in NM not lbs ft. If you take Nm at 5250 to be around 145 then lbs ft would be 107 which looks near enough to bhp at 5252.|
We get 15-22 bhp transmission losses depending on box etc. Ford five speed give less losses.
I am thinking the engine has not been tuned on the rollers? I have known Cameron for ever and a few days and I am sure the bhp if it is a Fast Road cam will be nearer the 140/150 mark or 120/130 at wheels.
Drop off will be due to lifting off prior to ceasing recording probably.
I attach a graph of Cameron 1950 turnkey dynoed 1950 MGA engine with cast iron head, once we got it sorted we were seeing similar figures to Cameron. We think it gave 138 Lbs ft at engine ( remember losses are very low below 70 mph for tyre losses and gear losses are very low even at high speeds) max engine bhp we reckoned was 128 bhp. You will note I wrote ignore flourish at end, this is the way I stopped the run and it confused the laptop for a second!
You will also note peak bhp lower at wheels than on engine dyno. Usually we record around 500 rpm less than engine dyno. I have always thought this is due to tyre losses increasing and masking the max bhp rpm/figure.
|Peter Burgess Tuning|
|Those numbers are final result of rolling road session. I am able to do only basic programing of Megasqurit so I hire service from tuner to remap fuel and timing on rollers. He made many attempts but that was the best at the end.|
I don’t know nothing about RR so difficult to make any comment all I can say is that is this particular RR unit Made in Italy (soft-engine.com). All runs were made in 3th gear, that is the reason why if final velocity only 120 km/h. I been told that in 3th gear engine faster reach top RPM.
Gearbox (3 synch) and diff are standard units but rebuilt. Since I had some issue with fuel pressure already during building I installed fuel pressure gauge and it shows steady 50 PSI at all RPMs.
Dyno figures aside, how does it feel/perform on the road compared to when it was on the su's
|Toni, if you can get them to run in 4th gear/direct top as the gear losses are easier to measure on coast down. We do tend to get a higher reading in third but lower losses so end result similar.|
Do you have ignition curve and the afr graph?
|Peter Burgess Tuning|
|Well it brings you smile on your face but comparing to twin HS6 I don’t see much difference in performance. On the other hand I wasn’t had chance to drive it past 2 years, so maybe memories faded a bit. It performs best between 3 and 4000 RPM - if you push further it revs but you can fell that there is no power behind. Huge difference is sound. In many articles you can find that is in performance no much difference between SU and Weber/Dellorto but engine sound so much better with 4 throttles as with 2 SU. At bottom line it feels like real sports car and yes I love to drive it.|
Regard second run on RR with top gear I will have to wait a bit tuning shop just close for summer holiday or I should find another one. I attached picture with AFR and ignition table. It is a bit small but hopefully you can read it.
|What ignition advance were you seeing at wide open throttle 2000,3000,4000,5000 and 6000?|
|Peter Burgess Tuning|
|"The figures will not cross over at 5252 as the torque is in NM not lbs ft. " Haha, well spotted Peter, the rest of us were caught napping!|
|Must be getting old but do not see a composite graph often, usually one or the other. Tony did you dial in the cam ? If using an adjustable gear is there, any chance it moved when tightening the bolt? |
|Hi Stephen Strange (and all),|
I am interested in the tune of your car with the Derrington head. I have similar engine in my MGA (1950cc GB, HRG-Derrington head, twin 45 DCOEs, etc) that I recently destructed due to my own doing and am now looking to rebuild the engine (advanced the timing to 32 deg BTDC @ 3,500 rpm and destroyed a section of N0 4 piston - ouch! and have also found the camshaft and followers badly worn that I suspect was due to a lubrication problem - too thick an oil - all this with only 2,500 hard kms on the engine!)
Do you have high ratio roller rockers with your Piper 285 cam? Do you know what the actual valve lift is with your setup? Have you had any wear problems with your cam/followers? How many kms on the engine?
My valve / spring arrangement limits valve lift to 0.510" - installed was bit less, (1.625:1 Titan roller rockers)
Detail of my cam are show on attached image. Looking at my cam valve timing it looks like it might be equivalent to a Piper B929?
My engine failure and rebuild might need it's own thread!
I don't understand too thick oil? Was your cam a billet from Piper or a repro? I have only seen cams fail when they have been run at low rpm from the start and not run in properly. We put moly past on the lobes and lifters/followers to aid bedding in. Repro cams tend to wear fairly quickly depending how deep the case hardening is after regrind. I have seen cams fail from turning the engine over without slackening off the rocker screws and getting coil bind or hitting valves on block and destroying the top of the lobe!
With regard to ignition timing, get it on the rollers and leave well alone afterwards unless you need to revisit the rollers.
|Peter Burgess Tuning|
|Thanks for your comments Peter. |
Originally about 3 years ago I busted a cam follower - it broke in half through a side wall oil hole. Cams were a little worn and 3 or 4 other followers were pitted so I had the camshaft reground by a local camshaft specialist and he supplied new followers (radius ground rather than flat). I am not sure of the origin of the camshaft as it was in the car when I acquired it - I assumed it was good quality to match Carrillo rods/Venolia pistons (no name on it but stamped AEH 770 and local specialist said it was a #398 - not sure if these numbers have a significance, it is all machined so don't think it is a chilled cast iron - billet maybe?). When I assembled the engine I degreed the cam as per the cam card spec (vernier timing gear), used Comp Cams Pro-Cam Lifter Lubricant http://www.compcams.com/Company/CC/Products/Default.aspx
and ran for 20 minutes at 2000 rpm in the garage, no load, to bed in, then did about 300 kms of road driving to run the engine in (new rings also) up and down the rev range - stop start.
You might be right about the cam being too soft after the regrind but I would have expected the local cam expert to warn me if this was the case (he has been in the business for over 40 years). Also I am sure I didn't damage the cam lobes originally as I fitted new adjusters to the Titan rockers and had new push rods made to ensure that the rocker geometry was correct (packer installed under the pedestals). Also you will see running clearance were bumped up to 0.021" because of the high ratio rockers.
My comment about the too thick oil also has a story. At an MG national sprint competition back in April (before the current failure) I noticed a loss of oil pressure on a couple of corners (I have a low oil pressure warning light that comes on at 42 psi - normal runs at 60 psi on the straight 2000 rpm upwards). I have a baffled sump and run about 1 cm over High level. Added another 1 litre of oil and the light didn't come back on. Then prior to current failure I changed oil from Penrite HPR30 to HPR50 thinking this might lessen the surge problem and boost the oil pressure a bit when hot at idle. In retrospect maybe this oil was too thick to lubricate cam surfaces and distributor/oil pump drive (these gears are also badly worn)
When I say the cam is badly worn a couple of the cams are 0.045" small in diam than the only undamaged cam!!!! (Recent failure was also on the track after about 3 x 5 lap x 3.1 km lap sessions.
Interesting to note the oil hole failure in the follower, we have seen this many times and have never fitted or advocated having the holes!
|Peter Burgess Tuning|
|Table shows total advance for different loads – it is not represented as line like we are used for standard dizzy. At WOT is vacuum very low so to see total advance at that positon you have to read bottom line or two (50 – 70 kPa): 6000 rpm shows 41,8 - 44,2 deg, for 3000 rpm approx. 38 deg. Hope that helps.
|If you are pulling a genuine 38 at 3000 and 42-44 at 6000 I think you have way too much advance. I would be looking around 28-32 max depending on individual requirements on the rolling road. In fact I would expect pinking and holes in the pistons if used hard with the figures you give.|
Have you asked Cameron for an idea of distributor curve?
|Peter Burgess Tuning|
A bit late here and I'm a bit knackered but here's a couple of initial comments:
AEH770 is original BMC race profile, aka 648 or 649 in A series application, used in Le Mans spec works cars IIRC. The lobes were a bit wider than the std MGB lobes, which make it an easy identifying feature. This profile was a good race profile in its day, there are better ones now but it's still quite a driveable yet grunty cam. In my experience it works well with 1.6 rockers.
If it is that profile (and your spec sheet indicates it likely is, though the inlet timing has been shifted a little), then the 21 thou running clearance figure is wrong even after allowing the rocker ratio difference. 21 thou was in fact them timing clearance for that and other BMC cams. The timing clearance (the point at which the valve timing duration was measured) was set to be well after the end of the ramps - at a point where the valve was lifting much more rapidly. This made for much more accurate measurement than the vague slow lift rates around the ramp, and is taken a step further these days with a lot of cam grinders who list timing/duration at .050 lift for the same reason but as a standardised figure across a range of manufacturers to be clear of those whose opening ramps extend to well over 20 thou clearance.
BMC specified a running clearance figure which was quite different from and not to be confused with the timing clearance. In the case of the 770 profile, it was 16 thou. Even at 16 thou, it is 1 thou off the end of the ramp, so starting to move quite quickly as opening acceleration is quite rapid. I have explained more on this in a current thread "valve clearances on aftermarket cam" in midget Technical.
So where all this leads to is:
If it's the 770, then 21 thou is too muh clearance. At that point, the take-up speed has nearly double from what it was at 16 thou. So the impact on the follower and cam lobe would be nearly doubled too, which transaltes directly into accelerated wear. Follower wear in my experience is the weakest part of the engine, which is why I keep the clearance on the ramp when using the car as a shopping basket.
Regarding the oil, I have had issues with the Penrite 20W-60. It's viscosity when cold is well in excess of other 20W oils - like treacle when pouring it in winter. As a result I ended up with oil starvation when the engine was cold in mid winter on a really frosty morning: it just wouldn't pick up much more pressure than 20psi for a couple of minutes on a new engine (well, new+250 miles). I stripped the bearing shells out immediately after this and they showed classis oil starvation damage. I fitted new shells, refilled the engine with 20w-50 that poured like normal, and the problem went away.
|No, I didn’t talk to Cameron yet but originally engine come with 14844 dizzy without vac. (Moss item TMG10773). Thank you for advice and effort. Will visit tuner again when he will be back to work.|
|Moss USA has that as a 101BR1 so I am guessing it is the same as the Aldon 101BR1. We use these on fast road engines and race engines. Usually we are around 26/7 max for race and 28/32 fast road to suit each engine. We set the timing max at 4000 rpm.|
|Peter Burgess Tuning|
|Just out of interest-|
Do any of you guys use a simalation dyno on your pc
I had a couple a while back and found one that was quite accurate - Good for a guide of what to expect and very good for choosing a new camshaft to compare graphs
I'm desperately trying to think of the name of the real simple one I had that was quite accurate
I can remember loading the specs of our Chev in it and it came up with 609hp at 7100
When it went on the it peaked at 612 @7050
|We used to play with DesktopDyno for a laugh.|
It is difficult to simulate real life engines from most simulators, the one I know works really well is Ford's own one. It develops as the engines develop but there is so much information available from Ford the feedback for the simulation is stunning. I guess it would be crap at sorting a B though! I suppose we will have to rely on a small band of enthusiasts around the world to further the B. There is nothing like winning races to know what is working but even more can be learned from what loses then move forwards. We move forwards a little, move back when we find another problem then creep forwards again.
Our lastest 'discovery' in the high revving FIA engines doing 40+ minutes racing is cavitation damage around number 1 bore and water pump vanes!
|Peter Burgess Tuning|
|Peter, Sounds like you need an electric water pump with thermatic variable speed control. Our MGCC have recently seen a demonstration on what these guys can do - very impressive. |
Not allowed on FIA.
The website link is good, they look like good pumps. A lot of them we see fitted seem too weak to do the job! My friend uses a BMW ecu controlled one on his V6 Alpine engines.
|Peter Burgess Tuning|
I might be way off here, but the Ford Cleveland V8's have a cavitation problem on engines that get revved a bit-- They eat the w/pump impeller and housing and the steel plate behind the pump
The fix for them is to remove every second blade from the impeller
Also there is a coolant additive available from Ford for the 7.3 diesels that will stop the coolant vibrating
In the diesels, because of the high combustion pressures the sleeves get pin holes in them from the vibrating coolant and this additive is good enough to stop the damage---might be worth a try--or not
|Thanks for the info William, I'll look into it.|
|Peter Burgess Tuning|
I to have have been busy and a bit knackered! Thanks for your comments on the cam running clearance - I will read your article on the Midget site with interest and will contact you direct if I have any queries. Originally when I had the cam reground the cam card said running clearance of .019" but when I said I had Titan roller rockers (1.625:1 ratio) he adjusted this by dividing by 1.5 (std ratio) and multiplying by 1.625 to get the 0.021 running clearance (I assume this is the correct way to calculate).
Anyway I need a new cam and am looking at a Piper replacement based on Peter's recommendation for longevity. Do you have a recommendation for a replacement? The current cam was quite grunty as you say and was amazingly tractable with the Derrington head and twin Webers. Use is for hillclimbing and sprints and I do drive the car to the track when they are reasonably close by.
I agree with Peter's comments about your ignition timing being too far advanced after my recent experience.
I have had my engine out a few of times in the past and always remove the distributor to make it easier. I just mark the location of the distributor with liquid paper and put it back in the same place. The last time I thought I would be smart and check what the timing was at full advance (ie 3,500 rpm) with my dial back timing light - to my surprise it was only 25 deg BTDC, no worries, I wound it up to 32 deg. Took it for a quick test drive to check whether it pinged when laboured in top gear mid range, all appeared fine. The next week on the track after some sustained running around 6,000 rpm, kaboom (see attached image).
When I get the engine rebuilt I will get it set on a rolling road dyno and not play with it!
|With cams I find it's very subjective as to what people like. What A calls amazingly tractible, B finds horribly ropey!|
In general, if you have a cam with the characteristics you like, then stick to it unless you want a bit more power.
I have a Piper 755/756@104 in my B, set up principally for special stage rallying (so a bit more tractible than an out and out sprint/race cam) but also used in anything else against the clock :-) I have found it better overall for what I do than the 770 and equivalent profiles: similar midrange, better top end, but a bit less (but still fine for me) tractibility.
It has more lift than the 770 (352 thou at cam v 325 thou) and a bit more duration (260 deg @ .050 lift). It pulls strongly right through and is tractible enough to handle our 1 in 2.5 driveway without drama, and to autotest if you don't mind a bit of clutch dump and tyre smoke :-) In detail: power is really good from 4000 to 7000; under 4000 it still pulls well from 2500 on full throttle (very good for being caught in the wrong gear in a rally stage) but you are better off down a gear to get the best. Under 2500 it wont accept full throttle but will pull away cleanly on part throttle over 1500.
It has a long ramp and needs a running clearance of 22 thou (1.6 roller rockers), giving a valve lift of .541".
Looking at your earlier post it might lift a bit much for your head?
I have just read back through this lot and see a problem that you have there
It is more than possible that your camshaft is being eaten by the lack of available valve travel
Cam card quotes .328" lift
=.328 x 1.625 = .533" minus .021" clearance = .512"
But you mention you are limited to .510"
Have you got sufficient clearance (extra lift) left at the full lift position
If it's too tight here, that could be causing the worn lobe problem or too heavy valve springs
What seat pressure and specially full compressed pressure you have effect cam wear enormously
Also your camshaft interests me- The 770 cam which as Paul mentions is the old factory cam
This cam had .315" lobe lift and ran at .018"clearance
Most aftermarket cam grinders stamp the end of the cam when they regrind them
Has your cam got #398 stamped into it
The regrind No. for a #770 copy from your cam man ( if it's who I think it is ) would be #176
I think you need to confirm the cam you have matches the card you have by looking for a stamped number on the end
It's just interesting that they are so close but different and that it has the inlet timing pulled back on it when these engines respond better to angrier inlet timing--
well it is not so easy to compare EFI timing with dizzy advance. Dizzy depends only on RPM (and few extra degrees if is equipped with vacuum actuator). Looking to EFI it is pure vacuum because it depends only on engine load – how much vacuum is made at throttle.
Will have to dig a bit more in theory to be shore if was my statement in previous mail correct. Maybe would be best to read timing during drive – that way will get exact numbers. Will come back.
Do you have any contact of Cameron I sent him few e-mails but no replay. Maybe is on holidays?
|"Looking to EFI it is pure vacuum because it depends only on engine load"|
Surely not. Centrifugal advance compensates for the fixed speed of the flame front during combustion. Unless you advance the timing as the revs increase the burn occurs further and further into the expansion stroke with more and more energy being lost as heat. Whilst load does vary timing because the likelyhood of pre-ignition or detonation increases as cylinder pressures go up with increasing throttle, cruising at a light throttle is still going to need changes in timing with revs. The engine itself is exactly the same whether you have a distributor or an ECU, and both have to be doing the same job.
Far from a few degrees, distributor vacuum adds anything from 6 to 24 degrees to timing depending on distributor spec.
you could try contacting Cameron via his FaceBook pages, send him a private message on it, he usually answers pretty quickly.
I recall reading a comment on his Facebook pages from a guy in Holland with a 1950cc crossflow unit like yours but with two DCOEs that Cameron built for him a few years ago and he was delighted with it. I seem to remember him quoting bhp figures of somewhere in the region of 140 to 150.
I think the Cameron Gilmour engine that Peter published the dyno results of is mine in my MGA which I took to Peters about a month ago.
It has a 5-port cast iron head and a Newman PH1 cam, single Weber 45 DCOE with Maniflow inlet and exhaust manifolds.
The power of this engine is awesome it has tranformed my MGA, now that Peter has set up the Weber for me.
The engine pulls incredibly strongly even from 30 mph in 5th gear but is also just amazing if you change down ,it will rev to well over 6000 rpm but to be honest, you just dont need to do this. There just doesnt seem to be a powerband as such.
If I were you I would try it with the SUs back on and see how that goes, the problem must lie in your induction system.
The second thing I would do is bring the car over to Peters Dyno and let him sort it out, he is just so good at this stuff.
|This is a video clip I uploaded onto YouTube of Peter at work on my car.|
|Paul, just want to pint out that is with dizzy much easier to say how much advance you have at certain RPM (at least looking to diagram). I am not expert so don’t want to go deep in debate but looking to ignition at EFI is that function of RPM, engine vacuum and air and coolant temperature (at normal conditions). If you look to distributor you have only advance in function of RPM (presented as centrifugal force).|
Regardless of theory I made few runs with connected laptop and it looks that I have to correct myself. I been a bit misled with table that goes to almost 2 bar and not to 1 what I would expect (will have to ask tuner why he choose that scale). So ignition at full throttle never goes beyond 30 deg what is on table row with 100 kPa. It is a couple deg more as Peter suggested but that shouldn’t eat 20 HP.
Colyn, thanx for input but I am one of those that do not participate in social networks – maybe is on holidays if not will try to call Cameron.
|Check the TDC is zero for your timing and you are actually pulling 30 degrees as stated on your software.|
Back on the rolling road drop the ignition 2 degrees everywhere foot flat and check bhp. If better try a little less advance. and work your way to the best bhp with the minimum advance. tappet settings need to be spot on for best power, check they are set to what Cameron told you in the spec sheet you got with the engine. AFR, do you have a graph of afr against rpm wide open throttle?
Is your back box hollow? Get these things sorted and you may find your bhp. Do you know what a standard MGB makes on the rolling road you use? Did you get a reading on your sus?
|Peter Burgess Tuning|
|Thank you for advice, will try to convince tuner to repeat session with less advance.|
Regard timing and valve clearance I checked it 2 weeks before dyno but will do that again better to check twice. According to tech spec should be rocker clearance 0,016” inlet and 0,018” exhaust so I set 0,40 mm for inlet and 0,45 mm for exhaust (I have only metric feeler gauges). Unfortunately I don’t have AFR/RPM graph from dyno run, I got only printout of BHP&torq/RPM but I have wide band AFR meter on dashboard and can confirm that is engine on rich side during acceleration.
Before EFI conversion I didn’t made any reference measurement and engine itself also was not on dyno so difficult to compare.
|It is good you can read the afr, what sort of numbers are you getting when you work it up a hill? Tappet clearances sound fine. Don't forget to check rear silencer, tap it with a socket extension and see if it sound hollow.|
|Peter Burgess Tuning|
|I checked ignition timing and it is 3deg off so at 30deg is really only 27deg. Will have to compensate that in Tuner Studio.|
Also AFR looks ok. At WOT gauge shows 12,7 and during acceleration newer drops below 13,2.
Valve - rocker clearance in at correct value but it was set at clod engine. Is that OK? I never understood what difference between running and timing value is.
Rear silencer is OK, I recently removed it because I had problem with rear LH shock absorber and have to remove it to get access. It done only 13 thousand km with that exhaust system, looks as new and I can confirm that is not jammed, I can see trough pipe.
I will go for holidays next 2 weeks and when I will be back will appoint new dyno run.
Would like to thank to all of you for input.
|Toni, tap the silencer box and listen if it sounds hollow, nothing to do with being straight through.|
Maybe the car will respond with more igniton advance, the dyno should tell you.
|Peter Burgess Tuning|
|Silencer box does not sound hollow it sounds very solid. But I have new problem, so I open new thread – white smoke.|
This thread was discussed between 25/07/2016 and 12/09/2016
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