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MG MGB Technical - mgb motor for fule mileage
| Would like some help from you guys that know motors, of what can be done to make things better for fule mileage. Am building a motor from parts, with 18v block with .020 over bore, 8.8 comp. pistons 3 comp. ring type. lighten con. rods (cut off ballance pads top & bottom), later type with wrist pin bush & ballanced. Am going to line bore the block & deck the top of the block, to make true to the crank. Thin bore the block, were the pistons are true. The head will be a 77-80 late type with stock intake valves & clean up the port webbing, the exhaust ports will be opened up & a 1.425 valve with 3 angle valve job. Will pollish the piston head & comb. chamber. Will have 9.0 comp & hope I can run on 89 oct. Have alu. flywheel & 280 Z 5sp. Will run the webber downdraft or Austin merina 1 3/4 S.U. with a exhaust gas temp./ O2 sencer. Will have cold air intake to the carb. The REAL QUESTION (Steve S. I hope you are out there!) What cam????? I need power BUT am after gas mileage! Will be building a very special set of header that will be jet coated inside & out. Is there other things I have over looked in the motor? I run my G.T. 30.K + a year & get 32mpg. a lot of the time, but would like to see more out of this old goat! |
| Glenn Towery |
| Glen, just have a look upon the EDIS ignition that is offered by Mat Kimmins. I think it would assist your intention to built a powerfull engine with good mpg results. An other point to considre is the selection of a suitable cam for your demands. More lift and more overlap will downscale the mpg readings compared to the results with the original cam. With the carbs, you should avoid the Weber if you haf good mpg readings high on your list. With the SU you will have to try some different needles, depending upon the cam you decide for. If you have a chance to pick a 3.7 rear axle from a auto B or from a C, it will aso help to save fuel. My engine is a 1868 (0.06 overbore) with flat top pistons (98 - 100 octane is available at the petrolstations in here neary everywhere), lightened crank, conrods, fly, valve train, ralley head, 285/2 cam, twin HIF 6 with BDR needles. Driving carefully it runs at an average of 28 mpg, driving just for fun 18 - 23 mpg is realistic. Hope this helps Ralph |
| Ralph |
| Ralph, yes I will look at the Edis seystem. I will look at putting the chopper on the flywheel like the rover (might use rover chopper) & the megasuqart ecu. I have read were the Kent 270 E? cam is a good cam for fuel mileage, has power & torq & 1 m.p.g. better than stock cams? I have 185/65/15 tires, .78 5th. 2150 rpm = 60 mph 2700 = 75 mph I think I am good with the gearing BUT I will swap it around for I have 3.7 & a 3.31. |
| G.T. |
| Glenn, David Vizard wrote an excellent book on the A series engines much of which applies to the MG B engine despite the difference in capacity since the principles really don't change. The title is :"Tuning the A-Series Engine: The Definitive Manual on Tuning for Performance or Economy" One point worth a look is finding a good rolling road dynomometer and more importantly a good operator. Small changes can yield large results but it will take time money and patience to get it sorted. Pete. |
| Peter Thomas |
| Glenn and Ralph, Remember that US gallons and UK gallons are not the same, I don't know which you use in Germany! I would think (based on my experience) that 28 miles per UK gallon is a good result for a big valve head and HS6s, so that's going to be about 20 per US gallon? Neil |
| Neil |
| Glenn, I can send you a distributor set up for fuel mileage if you like. I get 33 mpg in mine with fixed needle SUs, a Crane cam with 1.5 roller rockers, lots of (aluminum) head work and 10:1 comp. Email me and I can put one in the mail for you! |
| Jeff Schlemmer |
| Glenn, To answer your direct question, I think you would be hard pressed to find a better cam than the stock grind one, set at 108°. Makes a nice torquey engine, which helps fuel economy. Cheers, Paul K |
| Paul K |
| Peter, I have a book that David V. book called How to build an tune a car for Performance with economy & I like what he says & I will get the A series book. Jeff, I have the dizzy you did a year ago & I realy like it, I think you will find it hard to beat your earler work but I will get a dizzy off for the mileage. I will be sending the Buick/ Rover dizzys also. Paul, yes I think a stock cam is real good BUT it is 30-40 year old grind & I heard that a kent 270 cam will do real good with the torq. & give 1 + more m.p.g. The more I look at this old bag of bolts the more I see things that were ahead of there times, 1 long rods,2 hart shape comb. chamber,3 oil pump. I wish thay would have updated the ports on the head or a new to date head. Thanks for the bits. Glenn |
| G.T. |
| Good mileage is more about the driver than anything else. |
| Paul Hunt 2 |
| Paul, with a STOCK 12/71 BIG VALVE motor with 145,000 miles, that has NEVER had NOTHING pulled apart but the lifters changed every 45,000 miles, I think 32 m.p.U.S.g. is not bad at all!!!!! & this 32 m.p.g. is going 65-75! I do not baby her & I know what I have to do to get the mileage. I think a OLD OLD motor that can do this GOOD, with some up dates can do better. I think that someone has a cam out there that might help me out & I am open for other things that might improve the mileage. Will be lightening up the hole car at a later date. I think 36-??? is in reach. Will be neat to see this old boat do todays gas mileage. |
| G.T. |
| Paul, A true comment. There is an old saying that goes:- All those who are in favour of fuel economy, please raise their right foot ! |
| Owen McNeill |
| Glenn- Lightening and balancing the internal components of the engine will help, but I'd recommend using the last version of the connecting rods which had no balance pads. It weighs in at 760 grams. The horizontally-split connecting rods with balance pads used in the late 18GH, 18GJ, 18GK, and through early 18V engines were a notably heavier 845 grams. Match the volume of the combustion chambers while you're doind the polishing. I'd recommend the Piper 270 camshaft. It'll give good, tractable power output with reasonable fuel economy. However, the downdraft Weber DGV is a poor choice for use with the Piper 270 camshaft. Its adapter manifold has the airflow characteristics of a bathtub with a hole in each side. Properly set up, dual carburetors will do a better job in terms of fuel economy than the inefficient single carburetor designs due to their more effecient straight shot into the ports. The alloy flywheel is great for quickshifting on a racetrack, and might even allow a slight advantage in terms of acceleration in the lower gears, but won't help fuel economy. But, tell me why you want to go to an oversize exhaust valve? The North American Market MGB engine used four different cylinder head castings over the course of its career, all of which used variations of the same 1.344” exhaust valve size. This Original Equipment exhaust valve borders on being overlarge. This was a deliberate design feature made for the benefit of the factory race team so that there would not be any problems with the homologation rules of racing associations. |
| Steve S. |
| Steve, thanks for your input! I will do with the lighter rods, will be a big help BUT will put in the wrist pin bush, I have seen the wrest pins wear bad in a short time with the press in rods. The piper 270 cam were should I set the timming for the cam? adv. ? ret.? or line up the marks? Reading David Vs. book he says to open up the exhaust port & with the larger ex. valve for the better flow & with the type of header I am going to run I will not loose the mid range tork & will pick up the fule mileage, we have done this & proved it on my race bike. I am running a alu fly. & even with a 2,500 lbs. trailer it comes out of a stop no different than a stock fly. Am trying to get the weight of the motor down is another reason for the alu. fly. What do you think of useing the alu. rocker pillers like the MGA motors had? Will lighten the rocker also. Was going to use the composite lifters with this motor to help the cam life/ wear out but the man that was making them said that he can longer get the composite for it is all being used for the war tanks. Have composite lifters in a motor & I like what I see so far, but no can get anymore! Is there a better lifter out there? Steve S. & the others that have helped I thank you very much. |
| G.T. |
| If you are getting 32 with US gallons then I think you are doing remarkably well anyway, and to get any better you would have to be doing radical to the engine, ignition and carburation! It's even good by UK standards based on period tests, although I regularly exceed that and get the mid 30s just knocking around without creeping around. On several hundred miles through France on several tank-fulls I got around 40 on UK (OK, French) gallons, and on a trip back from Le Mans got 322 miles out of a tank in the V8. |
| Paul Hunt 2 |
| Paul - I agree. When I said 28mpg was 'a good result', I meant that it was something to be pleased about. Running a 285 cam and HS6s I'm lucky to get 23mpg. That's 'imperial' gallons of course! Steve - I don't understand why a lighter conrod would help fuel economy but a lighter flywheel would not? N. |
| Neil22 |
| Glenn- You can vary the timing of the Piper 270 camshaft by as much as four degrees in order to suit your needs. If you want to lower the weight of the engine, then use an aluminum backplate and an alloy head. The bigger exhaust valve may be fine on the engine of your racing motorcycle, but it's not powered by a BMC B Series engine. As a said before, the standard size exhaust valve is fine for a street engine. More flow does not automatically mean more power. In fact, an oversize exhaust valve and exhaust port will decrease velocity of the exhaust gases as they exit the combustion chamber, thus reducing scavenging and increasing pumping losses. Do not succumb to the temptation to install a set of aluminum rocker pedestals from the smaller version of the B Series engine used in the MGA. Because of the greater coefficient of expansion/contraction of aluminum, setting of valve clearances will be a problem. Aluminum being a soft material, these pedestals have a tendency to either collapse upon being over-torqued or gradually spread under load, causing inadequate clamping force to be exerted upon the head gasket. A blown head gasket will be the result. As if that is not bad enough, distortion of their bores also distorts the rocker shaft, leading to its eventual breakage. The top of the pedestal is relatively thin where it passes over the rocker shaft, making it prone to cracking. If a thin or non-hardened washer used, the top of the aluminum pedestal will be deformed with a slight depression, which in turn will cause small stress fractures to start in the aluminum pedestal, the result being that the pedestal will eventually break and allow the rocker shaft to move upward as the pushrods lift the adjacent rocker arms. This upward bending of the end of the shaft will dramatically increase the stress on the nearest pedestal, which is then very likely to fracture as well. Small wonder that these rocker pedestals were discontinued with the advent of the 1800cc version of the B Series engine. If you want a better tappet, then take a hard look at Arrow Precision's items. Both coatings have a friction coefficient of less than 25% of that of a standard nitrided tappet. The first type, Carbon-Slip, is an amorphous metal coating applied in alternating layers of carbon and tungsten carbide with only a 4-micron thickness, producing a very low coefficient of friction and good running-in qualities. More importantly, in a tappet application it offers greatly reduced sliding load in comparison to nitrided tappets. The second coating, Diamond-Like, is a single layer, pure carbon coating, and is harder than Carbon-Slip. It has even better resistance to wear, can cope with the higher sliding speeds common to radical camshafts, and has the same very low friction coefficient. Tappet/lobe interface pressures that would lead to seizure or cold welding in normal conditions are tolerable with this advanced coating, and even limited total lubricant starvation will not result in failure of a Diamond-Like coated tappet. You can contact Arrow Precision by e-mailing to enquiries@arrowprecision.co.uk . Neil- A lighter connecting rod requires less energy to reverse its direction of travel, thus Primary Vibration is reduced and more energy goes to rotation of the crankshaft. A lighter flywheel requires less energy to increase its rotational speed, which is why they're popular with racers. However, a lighter flywheel stores less kinetic energy to overcome resistance created by changing the direction of travel of the connecting rod/piston assemblies. Great for acceleration, bad for damping Primary Vibration. Also bad for steady-speed cruising for fuel economy because Primary Vibration is power that is lost (or should I say Wasted?). |
| Steve S. |
| Glenn- I'm just finishing a fly triggered EDIS, one of 3, from Matt K. Lets keep in touch on maps, eh? I'm fairly sure a proper timing map with the EDIS holds best potential for greater efficiency. Personally, I've only gotten + 30 MPG going downhill from Sierra Summit to sea level. 36 mpg will be an achievement ! Vic |
| vem myers |
| Glenn- It occured to me that I didn't address your idea of lightening the rocker arms. Removing material would be risky. Their surfaces are hardened, and their cores aren't so that they can resist the shocks of being slammed back and forth. Why not use a set of Crane's tubular chrome-moly pushrods instead? They weigh only 64 grams each vs. the 88 grams each of the Original Equipment items. |
| Steve S. |
| Steve, The primary forces - those generated from the pistons and rods going up and down - balance (if the weights are the same) in a straight four because you have two going up and two going down at the same time. Do you mean secondary forces? Neil |
| Neil22 |
| Neil- No, I mean Primary Vibration. There are two factors involved in balancing an engine, respectively referred to as Primary and Secondary Factors. The term Primary Factor refers to vibration that is induced by reciprocating components (Primary Vibration), such as piston assemblies and connecting rods. The term Secondary Factor refers to vibration that is induced by rotating components, such as the crankshaft and the flywheel (Secondary Vibration). Even if the the connecting rods are balanced end-for end to within .10 grams, and the piston/rings, wristpin assemblies are also balanced to within .10 grams, and the crankshaft and flywheel are independently balanced to with .10 grams (which is a very well balanced engine, indeed) their movement will not cancel each other out in an L-4 because whatever movement is created in cylinders #1 is duplicated by the movement in cylinders #2 & #3. For example, if #3 is decelerating, then so are all of the others. An L-4 will produce Primary Vibration, as will an H-4. This is why some designers of modern L-4 engines include a counter-rotating balance shaft to produce equal but opposite Primary Vibration to cancel out that produced by the engine. |
| Steve S. |
| Oops! Sorry, but I said that wrong in the last sentence. It should read: This is why some designers of modern L-4 engines include a counter-rotating balance shaft to produce equal but opposite Secondaryary Vibration to cancel out the Primary Vibration produced by the engine. |
| Steve S. |
| Stick to SU's!!!!! |
| allan |
| Steve, They are all decellerating in your example, but in different directions. Hence the forces (mass x acceleration) are balanced. The contra-rotating shaft is to balance secondary forces. Primary forces are so-called because they are the largest. Secondary forces because they are second, tertiary are third and so on. It's to do with the harmonic motion. As we aren't going to agree, shall we declare a stalemate? Neil :-) |
| Neil |
| Sorry, but Glen's target wars to get some information upon an engine that does not burn that much gas but is capable for performance. Sure, ballancing of ocsillating and rotating internals is essential, fuel performance and light wight are further poits on the list. For efficency the highest possible compression will help. This means to use flat top pistons and an optimised shape of the chambers in the head. A light alloy head would help to save further wight and will be more tollerant to higher compressions than a carst iron one and to the temperatures generated then. A lightened cam gear is also an advantage. If it is not top speed Glen is after, the stock cam is not a bad grid for torque but has to be set with care. Cleaned out ports and reworked stock manifolds also add performance when venting looses are minimised. The engine would not have to burn that much fuel to achieve the same power than an unrefined would have to do. There is nothing wrong with the discussion upon harmonic oscillation of rotating and reciprocating masses of the first or second or x...category, but there is one enthusiast who is willing to built an engine that is efficiant on gas and powerful enough to have driving fun still, as far as i understood this thread. So all the points that were left by the factory (for it would have been to expensive for regular production) are asked for getting an improvement and a personal reflection too... CR, cylinder head, valves, ignition, carbs and needles/filter, cold air intake, oil pump gear, valve gear and timing chain, water pump and pulleys, modestly lightened flywheel, radiator vent, size of alternator, light alloy engine parts and hood and, of cause, balancde crank gear, conrods (18V rods can be lightened to 570 gramms, balanced and polished), lightened pistons and pins, narrower size radial tires (155SR14 was factory strandart in the 1970's for roadster, GT's were delivered with 165SR14 sction wheels 185/70 or even larger do not help when you are after high MPG results), right (high) tire pressure, empty boot, single battery...and a little experianse upon driving economically. I can understand Glen's ideas very well. Living in a country where one litre gas is sold at @ 2 US$ (one litre is 1000 ccm, and there are four litres or so necessary to have a USgal.) you become more sensetive to these ideas how to save fuel but also keep driving fun. Think upon this situation in the US to come within a few years and be alarmed. Glen has understand this and is preparing his car for this moment and many others should wake up now. I hope i did not understand this discussion the wrong way?...noone should feel blamed by this, please! Ralph |
| Ralph |
| Neil- I really shouldn't write when I'm as dead tired as I was. Of course, you're right. In utilizing components that have been carefully matched for weight, the equalized oscillating dynamic forces produced by their reciprocal movement in cylinders #1 & #4 will be equal to those produced in cylinders #2 & #3, effectively canceling each other out and thus reducing primary vibration. As I said, a lighter connecting rod does require less energy to reverse its direction of travel, thus vibration is reduced and more energy goes to rotation of the crankshaft. Perhaps the real question is: Is the attendant vibration the result of the draining off of kinetic energy from the flywheel with its consequent deceleration in order to reverse the travel of the reciprocating masses that has resulted in a rapidly oscillating torque effect? Hmmmm...... I need sleep really bad. Ralph- Yes, this thread has wandered off on a tangent. It seems to happen more commonly as winter closes in. |
| Steve S. |
| Ralph, you SEE were I am GOING!!!!!! I like the idea of lighting up the cam gears, we did this on our race bikes. I will get the compression up as high as I can BUT I am going to run on 89 oct. I think the late head with a pollished comb. chamber & piston I can run 9.0-1. I am going to open up the exhaust ports, to try to get rid of the heat with a larger valve. Will run the cast iron head for you do not lose the heat transfer,like you will alu. Will jet hot the header to help with under hood heat. Will have cold air picked up infront of the radiator. Will try to get every bolt on part as light as I can alt., gear reduction starter, plastic horns, alu. hood/bonnit, no oil coller (have not run one in 20 years), on my V-8s or 4 cyl. Am thinking of making under the car air streamed as poss, like VW is doing for F/M. Am going to try & get down to 2200-2300lbs. BUT I will have a spare tire & comp. tool box! Had a 72 B with a Rover 4.8/T56 6sp. down to 2260. Steve I weighed the rockers we lighten, 25 years ago & there was a hole 5-6 grams differance from sock. Mild grind around were the adj. screw boss & rounded off the rocker above were the valve/rocker come together. I put 200,000 miles on the rockers, no break. And yes tires!!! & light wheels. The list goes on & on. I know earlyer I said 36 mpg BUT to stop you from ALL thinking I am NUTS I am realy after 40!!!+ |
| Glenn Towery |
| Glenn, You may want to give some thought as well to ceramic coating the piston and combustion chambers to increase heat retention. While you are there some attention to the aero side of the equation may also be worthwhile. Pete. |
| Peter Thomas |
| I remember a report some years back in which BMW (I think) did an expeimental comparison of high rpm (higher power) and lower rpm high torque engines. They found that the high torque engines gave better gas mileage. My supposition is that, since we normally operate the engine at lower rpms, at least in highway cruising, that a high torque build would give better mileage than an engine optimized for maximum power at hier rpms. Has anyone built a B engine to maximize the low-mid rpm torque and looked at the resultant mileage? FWIW Larry 72 BGT daily driver-commuter |
| Larry Hallanger |
| Larry, BMW did offer these car and by increasing the cui of the engine by 30%. They had the same horse power than the smaller ones but lots of torque. These cars had a higher price and were more expensive to service, so this modells were withdrawn soon. Modern engines make use of vcc and ecu to go there. Building an engine as Glenn is thinking about is surely possible. The only question that must be answered first is whether it is economical too. Two years ago i did some investigations upon pistons made of carbongraphite. Engines with this material for the pistons had been tested by different car manufacturers within the last few year and the results were very good. MPG was better, tollerances were smaller and the exhaust gas analyses were very green but the best offer i got for a set of these pistons for a B-Series engine was close to 2000 US$, not very economical for a car that only covers @ 5000 miles a year. Ralph |
| Ralph |
| "the high torque engines gave better gas mileage" They can also give better practical performance. In the 70s in the UK Ford and BL had an advertising battle over bhp and torque. Ford claimed a high bhp, but BL had a higher and wider torque curve which gave it better acceleration through the rev range. If Ford had a 6-speed box then they might have been better, at the expense of using the gearlever like an oar, but both only had 4-speed. BL cars also had better mpg but as well as engine design used SUs whereas Ford used fixed jet with accelerator pumps which can be very wasteful. BHP is just a measure of 'work done' and is largely irrelevant. It is torque that throws you up the road. |
| Paul Hunt 2 |
| Sorry guys, was laid up with a bad cold. Peter, yes I am thinking of going with ceramic coating on the comb. chamber & pistons, would someone know were I can find the people that supply this? Ralph & Paul, THIS IS WHAT I AM LOOKING FOR!!!!! Right know I have a tired motor that has a ton of torq., & not much go over 5,000 rpm, BUT it can go up a good hill in 5th.(or pull another B)real good. I am very happy with this motor & will ck. the deg. on the cam BEFOR it comes apart. With the datsun 5sp. I run 2,000 rpm at 56 mph, can mash the gas & it will pull. Am after the torq. & MILEAGE!!! not the H.P. Thanks. Glenn |
| Glenn Towery |
This thread was discussed between 27/11/2007 and 15/12/2007
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