overboring - worth it?
Discussion
As some of you may have gathered I'm deciding on spec for this season...
Engine in 1500 Midget hillclimb car needs a rebore. Currently has standard size pistons to give 1491cc.
I have assumed that a 20thou oversize piston increases the radius by 10thou. Is this correct?
According to my calculations, if I go for 20thou oversize capacity will increase to 1512, 40 thou 1532, 60 though 1553.
I'm not sure the 60thou pistons are still produced but, assuming I could find some, would an extra 62cc and an increased piston area be noticable? Everything else (valve sizes, cam timing etc) is as standard except for better exhaust manifold, air filters and jetting) and must remain so by class rules.
If it didn't cost much more to rebore wider then I'd do it for 3bhp. 3bhp from the pistons and 3bhp from the removal of the fan is a 10% power increase!
Engine in 1500 Midget hillclimb car needs a rebore. Currently has standard size pistons to give 1491cc.
I have assumed that a 20thou oversize piston increases the radius by 10thou. Is this correct?
According to my calculations, if I go for 20thou oversize capacity will increase to 1512, 40 thou 1532, 60 though 1553.
I'm not sure the 60thou pistons are still produced but, assuming I could find some, would an extra 62cc and an increased piston area be noticable? Everything else (valve sizes, cam timing etc) is as standard except for better exhaust manifold, air filters and jetting) and must remain so by class rules.
If it didn't cost much more to rebore wider then I'd do it for 3bhp. 3bhp from the pistons and 3bhp from the removal of the fan is a 10% power increase!
Hi Chris,
I have seen you have put a couple of posts about squeezing a few BHP out of your car, and when the regs are tight on modifications every little helps.
I was just wondering if you had considered weight (BHP per Ton) not your personal weight :-)
I don`t know how much it currently weighs but scrapping underseal, and removing door locks/windows, etc... can make a huge difference espically when there sounds like very limited engine mods.
Its just a thought, I use to do the 205 rally challenge again where mods are very limited and weight helped me squeeze a bit more out of the car.
I have seen you have put a couple of posts about squeezing a few BHP out of your car, and when the regs are tight on modifications every little helps.
I was just wondering if you had considered weight (BHP per Ton) not your personal weight :-)
I don`t know how much it currently weighs but scrapping underseal, and removing door locks/windows, etc... can make a huge difference espically when there sounds like very limited engine mods.
Its just a thought, I use to do the 205 rally challenge again where mods are very limited and weight helped me squeeze a bit more out of the car.
Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would.
John
John
No room for weight reduction except underseal (good idea!) everything else must remain as standard including carpets etc. Bumpers / trim removed where allowed. Infact my car has full cage and is therefore probably heavier than standard! I can change driver's seat but I can't find one narrow enough to fit between the cage's door bar and transmition tunnel. I am working on this.
When I'm taking it seriously I do run with hardtop on and soft top removed as slightly lighter and more slipery (I expect).
Front suspension lowered and stiffened and rear lowered but not stiffened (for traction) and fitted with uprated dampers (but still lever arms). This is all that is allowed (even bushes must be as standard)
Pads improved which is all that is allowed for brakes
Reason I'm chasing every last bhp is that my car holds most of the class records which were set using this set-up but with the old engine. Target system sets targets at 98% of record. Hopefully I am improving but if I could get even 7 more bhp (ie 10% more power) it would make a big difference. Traction is not really a problem so a lot of the run is spent with foot flat down. Its an extreme example, but at Silverstone I recon I was something other than flat for about 6 seconds on a 60 second run - heavy braking for chicane and tiny dab for Stowe and the next one (forget its name). Even at narrow twisty Prescott I recon it is probably not much more than 10 seconds not flat out.
I have raced club level sailing boats for years. I never spent much money on boats / sails / setting up etc. I don't do very well but never know how much is becuase of a lack of talent and how much is becuase my boat is slower than other peoples'. I want to know for sure with car.
Having said that- if the engine hadn't broke I would have carried on but since it needs rebuilding anyway...
Only other area for development is tyres (wheels are as big as allowed) and, of course driver who has a lot of improvement left in him!
When I'm taking it seriously I do run with hardtop on and soft top removed as slightly lighter and more slipery (I expect).
Front suspension lowered and stiffened and rear lowered but not stiffened (for traction) and fitted with uprated dampers (but still lever arms). This is all that is allowed (even bushes must be as standard)
Pads improved which is all that is allowed for brakes
Reason I'm chasing every last bhp is that my car holds most of the class records which were set using this set-up but with the old engine. Target system sets targets at 98% of record. Hopefully I am improving but if I could get even 7 more bhp (ie 10% more power) it would make a big difference. Traction is not really a problem so a lot of the run is spent with foot flat down. Its an extreme example, but at Silverstone I recon I was something other than flat for about 6 seconds on a 60 second run - heavy braking for chicane and tiny dab for Stowe and the next one (forget its name). Even at narrow twisty Prescott I recon it is probably not much more than 10 seconds not flat out.
I have raced club level sailing boats for years. I never spent much money on boats / sails / setting up etc. I don't do very well but never know how much is becuase of a lack of talent and how much is becuase my boat is slower than other peoples'. I want to know for sure with car.
Having said that- if the engine hadn't broke I would have carried on but since it needs rebuilding anyway...
Only other area for development is tyres (wheels are as big as allowed) and, of course driver who has a lot of improvement left in him!
Engine can (and will) be balanced (but not lightened though I'm not sure when balancing becomes lightening!). So will at least be smoother which might reduce friction losses a tiny bit, I suppose. It would allow higher revs but since it has the standard cam this isn't a gain.
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
I think the weight taken off in balancing is so negligible that I don't think it could be considered cheating. But the balancing is well worth it, especially if the engine is apart anyway.
There's all sorts of lotions and potions, but how good they are I don't know.
Talking of hidden bhp, I remember an article in CCC years back where they were prepping a Rover Tomcat racer and found an extra 5 bhp (or similar) by running at min oil level rather than max. Don't know whether I would want to risk it myself!
Don't forget to keep your hair short and go to the loo before the start....
There's all sorts of lotions and potions, but how good they are I don't know.
Talking of hidden bhp, I remember an article in CCC years back where they were prepping a Rover Tomcat racer and found an extra 5 bhp (or similar) by running at min oil level rather than max. Don't know whether I would want to risk it myself!
Don't forget to keep your hair short and go to the loo before the start....
cold air intake?
Probably not allowed to build a complete air box set-up but could you route some fresh air upto the carb's? I'm thinking along the lines of some of the heater ducting, cut short and run upto the air intake?
An article in enjoying mg recons there's HP hiding in the heater, with it running they measured engine compartment temps, was a good few degrees lower with the heater & fan switched on!
Probably not allowed to build a complete air box set-up but could you route some fresh air upto the carb's? I'm thinking along the lines of some of the heater ducting, cut short and run upto the air intake?
An article in enjoying mg recons there's HP hiding in the heater, with it running they measured engine compartment temps, was a good few degrees lower with the heater & fan switched on!
thisisnotaspoon said:
An article in enjoying mg recons there's HP hiding in the heater, with it running they measured engine compartment temps, was a good few degrees lower with the heater & fan switched on!
On the same lines what about running a cooler thermostat? It's reckoned to be worth doing in the Alfa twin cam and a mate with a hot Mini (A-Series) thinks the same. Incidentally the Mini 'stat fits the Alfa, and I presume the Midget too? QTH101 is a 74 degree one.Out of interest, what championship/regs are you following ? Maybe you can send us all a link and we can take a look.
I know with the Pugs that everything had to run standard, but there were 3 or 4 different standard cams, and they did two different standard heads, Im sure you get the picture, so maybe mix and matching engine parts is also worth while.
Also I don`t know if you have to use standard wheels, but if they did 2 or 3 different types weigh them as on the pugs you could save 1kg a corner. Not much but it all helps.
I know with the Pugs that everything had to run standard, but there were 3 or 4 different standard cams, and they did two different standard heads, Im sure you get the picture, so maybe mix and matching engine parts is also worth while.
Also I don`t know if you have to use standard wheels, but if they did 2 or 3 different types weigh them as on the pugs you could save 1kg a corner. Not much but it all helps.
If the 1500 is the same back axle the earlier 1275/1098/948 Spridgets then the half shafts are very weak. Back in the 60's I used to carry a spare in the car. You can get stronger ones now, not the sort of thing a scrutineer would spot. I'd use a top quality synthetic diff oil. Try the Redline website.
BMWChris said:
Engine can (and will) be balanced (but not lightened though I'm not sure when balancing becomes lightening!). So will at least be smoother which might reduce friction losses a tiny bit, I suppose. It would allow higher revs but since it has the standard cam this isn't a gain.
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
I carry a spare driveshaft and diff. I'm not allowed to upgrade any transmition components. Stronger driveshafts are availiable and of course nobody would know, but that would not be in the spirit. Anyway, this would just put more load on the diff. It is always in the back of my mind though, especially as I drive to and from events. I don't spin the wheels to warm the tyres, for example.
Re cold air intake: I'm researching this but can't find a picture of the standard Midget 1500 set-up. If it is the same as Spitfires had then it could have a cold air intake with 2 tubes running to the front of the car. Currently my car has trumpets with sock filters. I'm thinking of changing this as I use the car in off road events (such as rallies) too and I don't want to suck dust into my new engine. But I did find a sock filter that claimed better filtration than standard paper filters. I am not keen on taking the air from directly above the exhaust manifold, as I currently do, but I'm not sure how much warmer this are gets when the car is at speed - it is pretty open infront of and below the engine and there is a heat shield between the two manifolds.
One option might be to fit the trumpets into the standard airfilter housing with the trunks going to the front to bring in cold air. However, assuming it is the same as the Spitfire, there wouldn't be much depth in the box so I'm not sure where the filters would go. A compromise might be to put the trunks back on (assuming it had them - adding ducts is not allowed) so that they supply cold air in the general area.
Not sure there is much point on carbs as the car will not be able to adjust fueling to take acount of denser cold air, though I suppose if thats how it is set up on the RR then it should be fine.
quote=AJAX50]If the 1500 is the same back axle the earlier 1275/1098/948 Spridgets then the half shafts are very weak. Back in the 60's I used to carry a spare in the car. You can get stronger ones now, not the sort of thing a scrutineer would spot. I'd use a top quality synthetic diff oil. Try the Redline website.
Re cold air intake: I'm researching this but can't find a picture of the standard Midget 1500 set-up. If it is the same as Spitfires had then it could have a cold air intake with 2 tubes running to the front of the car. Currently my car has trumpets with sock filters. I'm thinking of changing this as I use the car in off road events (such as rallies) too and I don't want to suck dust into my new engine. But I did find a sock filter that claimed better filtration than standard paper filters. I am not keen on taking the air from directly above the exhaust manifold, as I currently do, but I'm not sure how much warmer this are gets when the car is at speed - it is pretty open infront of and below the engine and there is a heat shield between the two manifolds.
One option might be to fit the trumpets into the standard airfilter housing with the trunks going to the front to bring in cold air. However, assuming it is the same as the Spitfire, there wouldn't be much depth in the box so I'm not sure where the filters would go. A compromise might be to put the trunks back on (assuming it had them - adding ducts is not allowed) so that they supply cold air in the general area.
Not sure there is much point on carbs as the car will not be able to adjust fueling to take acount of denser cold air, though I suppose if thats how it is set up on the RR then it should be fine.
quote=AJAX50]If the 1500 is the same back axle the earlier 1275/1098/948 Spridgets then the half shafts are very weak. Back in the 60's I used to carry a spare in the car. You can get stronger ones now, not the sort of thing a scrutineer would spot. I'd use a top quality synthetic diff oil. Try the Redline website.
BMWChris said:
Engine can (and will) be balanced (but not lightened though I'm not sure when balancing becomes lightening!). So will at least be smoother which might reduce friction losses a tiny bit, I suppose. It would allow higher revs but since it has the standard cam this isn't a gain.
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
Like the batery idea - will research.
I have to keep transmition absolutely stock which is a shame because the axel is week. I broke two half shafts and a diff last season. Did there used to be a Slick 50 type additive that was supposed to reduce friction? Might look into that too...
Re cold air intakes: I'm not completely convinced of their value after doing some tests with an MR2 turbo I used to own. I was always wondering about this and the engine bay air temp (around the air intake) only increased much more than ambient at less than 25mph and that took a little while to rise anyway, so I decided not to bother spending the money.
Whats this got to do with midgets? well im still trying to get my own 1500 finished for hillclimb/sprints. Its +040 with peaned rods and all balanced etc, when its all back in the car and been on an RR i can report back as to power etc. I thought about cold air intakes but remembered the test i'd done with the MR2 and dcided not to bother. Was hoping to get it al done this year , still hoping thats the case so perhaps I'll see you at an event or two.
Neil
Whats this got to do with midgets? well im still trying to get my own 1500 finished for hillclimb/sprints. Its +040 with peaned rods and all balanced etc, when its all back in the car and been on an RR i can report back as to power etc. I thought about cold air intakes but remembered the test i'd done with the MR2 and dcided not to bother. Was hoping to get it al done this year , still hoping thats the case so perhaps I'll see you at an event or two.
Neil
Dart said:
Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would.
John
Got to be enough cheap Triumph 1500 blocks around for this not to be an issue surely?John
agree with Dart...
"Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would."
"Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would."
v8250 said:
agree with Dart...
"Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would."
I agree too. Unfortunately appart from driver there is no room for development in the other components (please see previous posts for explanation). As is sensible everyting that could be improved has been. Engine left to last. "Don't rebore to max oversize because if you are racing you are more likely to break something and then need to rebuild it. You will have another 1 or 2 rebores in the block before you need to get a whole new engine. Sorting the weight, brakes and suspension and spend money on tuning your ability will get you faster lap times than even 10 bhp would."
neilr said:
Re cold air intakes: I'm not completely convinced of their value after doing some tests with an MR2 turbo I used to own. I was always wondering about this and the engine bay air temp (around the air intake) only increased much more than ambient at less than 25mph and that took a little while to rise anyway, so I decided not to bother spending the money.
Whats this got to do with midgets? well im still trying to get my own 1500 finished for hillclimb/sprints. Its +040 with peaned rods and all balanced etc, when its all back in the car and been on an RR i can report back as to power etc. I thought about cold air intakes but remembered the test i'd done with the MR2 and dcided not to bother. Was hoping to get it al done this year , still hoping thats the case so perhaps I'll see you at an event or two.
Neil
#Whats this got to do with midgets? well im still trying to get my own 1500 finished for hillclimb/sprints. Its +040 with peaned rods and all balanced etc, when its all back in the car and been on an RR i can report back as to power etc. I thought about cold air intakes but remembered the test i'd done with the MR2 and dcided not to bother. Was hoping to get it al done this year , still hoping thats the case so perhaps I'll see you at an event or two.
Neil
Which championship? I'm going in MGCC Luffield. Rules here (I'm in standard class) http://www.mgcars.org.uk/mgccsc/
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