teething Problems with rebuild 1275

[williamt]

Right heres the problem and a long story lol... had an engine built its in and going well now.. but accelerates well up to 75 then nothing not even down hill makes a difference... im sure i should be fit to hit 100 given the spec and that i had a 998cc in it could do 90..

Its a 1275 bored out to 1330 low dish pistons 3 ring 6cc dish i think..
ported and polished head and skimmed
fast road cam
high lift rockers
lightened flywheel
gt Manifold
hiff44 carb
full stainless big exhaust

it goes really well and hard up to 75 then it just like it has no power to keep going Its not spluttering at 75 just like a car that has reached its max.. But im sure it should be capable of more.. A guestimate of power by Engine builder was 90-100 bhp I believe this is kind of what that engine usually achieves after a good rebuild..

Doesnt seem like the carb is icing up as its not spluttering from a fuel Cut.. anyone got any ideas as its a bit of a let down to accelerate so well then just bog at 75.. its an a series out of an Allegro 1300 super it kinda feels like when you bury it in first and it reaches its limit just wont accelerate any more.. I thought the max that box was capable of was 104mph? in 4th.. just doesnt make sense

[woody]

You haven't mentioned what gearbox and final drive your using. I did a quick search on the allegro and found a final drive of 4.1 and max speed 80mph ( on larger wheels) so that is one possibility that would tie in with your description . Fuel starvation at the top end, have you fitted a high flow fuel pump or is there restriction in the fuel supply( crushed pipe under car, I've had that one, fuel filter). What dizzy are you running?

[williamt]

You haven't mentioned what gearbox and final drive your using. I did a quick search on the allegro and found a final drive of 4.1 and max speed 80mph ( on larger wheels) so that is one possibility that would tie in with your description . Fuel starvation at the top end, have you fitted a high flow fuel pump or is there restriction in the fuel supply( crushed pipe under car, I've had that one, fuel filter). What dizzy are you running?

Sorry Ya Allegro Box that was with the engine.. ratio is for 13 inch wheels id have to go check what it is exactly.. just a search i did on allegro said 104 mph in 4th.. Im fecking Baffled.. ya seems like Maybe the box is holding the engine back.. Im going off me head with this Yoke.. No didnt change fuel pump and dont know what dizzy to be honest.. but I woldnt imagine its a kinked pipe as it starts and runs sweet
and acceleration is good right up to 75 when it literally just stops accelerating.. ill have a look at drive ratio and Google Thanks

[williamt]

You haven't mentioned what gearbox and final drive your using. I did a quick search on the allegro and found a final drive of 4.1 and max speed 80mph ( on larger wheels) so that is one possibility that would tie in with your description . Fuel starvation at the top end, have you fitted a high flow fuel pump or is there restriction in the fuel supply( crushed pipe under car, I've had that one, fuel filter). What dizzy are you running?

Sorry Ya Allegro Box that was with the engine.. ratio is for 13 inch wheels id have to go check what it is exactly.. just a search i did on allegro said 104 mph in 4th.. Im fecking Baffled.. ya seems like Maybe the box is holding the engine back.. Im going off me head with this Yoke.. No didnt change fuel pump and dont know what dizzy to be honest.. but I woldnt imagine its a kinked pipe as it starts and runs sweet
and acceleration is good right up to 75 when it literally just stops accelerating.. ill have a look at drive ratio and Google Thanks

[williamt]

You haven't mentioned what gearbox and final drive your using. I did a quick search on the allegro and found a final drive of 4.1 and max speed 80mph ( on larger wheels) so that is one possibility that would tie in with your description . Fuel starvation at the top end, have you fitted a high flow fuel pump or is there restriction in the fuel supply( crushed pipe under car, I've had that one, fuel filter). What dizzy are you running?

Sorry Ya Allegro Box that was with the engine.. ratio is for 13 inch wheels id have to go check what it is exactly.. just a search i did on allegro said 104 mph in 4th.. Im fecking Baffled.. ya seems like Maybe the box is holding the engine back.. Im going off me head with this Yoke.. No didnt change fuel pump and dizzy is Lucas.. but I wouldnt imagine its a kinked pipe as it starts and runs sweet
and acceleration is good right up to 75 when it literally just stops accelerating.. Diff ratio I cant find now only a casing No.on Box 22g1832 and ano on side of shaft into diff 13/3 ill have a look at drive ratio and Google Thanks

[woody]

Allegro 1300 Super Final drive is 3.95 and top speed 82 mph. I ran a 3.66 before that top out at about 90mph. A restricted fuel flow won't stop the car from starting or running normal its only when you want more power and more petrol that it becomes a problem.Very important to have the right dizzy for the engine spec.

[williamt]

Allegro 1300 Super Final drive is 3.95 and top speed 82 mph. I ran a 3.66 before that top out at about 90mph. A restricted fuel flow won't stop the car from starting or running normal its only when you want more power and more petrol that it becomes a problem.Very important to have the right dizzy for the engine spec.

Seems to be similar final drive quoted for them ive found several that say 3.94 but the factory quoted top speed is 87mph and a top speed of 97mph also stated as i said earlier I have seen 104 for 4 speed but I dont know how to work out the max speed of a 3.94 drive.. What would the best option be a replacement box with different Ratio.. or has Anyone on here ever Bought a 5 speed box from Mini spares they are different ratios and all seem to be A+ boxes and exchange basis will an A+ box fit an A series engine.. What would be seen as the best Ratio for Acceleration and Top speed.. What I was Aiming for was a car that could pull fast from the lights and keep going to surprise Much younger cars

[keith]

what RPM are you running at 75mph?
is the cam timed correctly? also is the spring/needle correct? could be that the carb-piston is fully up (open) when you get to 75, so wont give more - in that case you might need a heavier spring.
see this thread: http://www.theminiforum.co.uk/forums/to ... ot-spring/

also, dizzy specs are vital as Woody said

[williamt]

what RPM are you running at 75mph?
is the cam timed correctly? also is the spring/needle correct? could be that the carb-piston is fully up (open) when you get to 75, so wont give more - in that case you might need a heavier spring.
see this thread: http://www.theminiforum.co.uk/forums/to ... ot-spring/

also, dizzy specs are vital as Woody said

what RPM are you running at 75mph?
is the cam timed corre
ctly? also is the spring/needle correct? could be that the carb-piston is fully up (open) when you get to 75, so wont give more - in that case you might need a heavier spring.
see this thread: http://www.theminiforum.co.uk/forums/to ... ot-spring/



also, dizzy specs are vital as Woody said

All should be Spot on as I got a guy who Knows them inside out to do the work.. I suppose the Biggest Problem is Maybe he Misunderstood what I wanted out of it as it has been back 3 times as wasnt happy how she was runnning.. was Using old carb and manifold with a race needle said it would be fine.. but there was too much back pressure she couldnt breathe so went hiff 44 gt manifold and big stainless exhaust.. Ill have to talk to him as I know nothing about changing needles or messing with carbs etc.. im fine changing brake pads servicing bolting parts on and off but no real experience on minis so dont know.. Its just I dont want to be pestering the Guy if 75 is the limit of them Boxes then thats it.. just so many conflicting views on the performance of 1275 engines and boxes.. I thought surely would outperform my 998 by a mile..

[dayoungfella]

We need to know what revs the engine is doing at 75mph. No point speculating on diff ratios otherwise!

[williamt]

We need to know what revs the engine is doing at 75mph. No point speculating on diff ratios otherwise!

Ya sorry no idea im afraid its an 81 mini with a single clock no rev counter im afraid.. ill just have to check fuel line and filter and failing that have look at dizzy set up and Needle choice.. Maybe go to someo one with a rolling road and a selection of needles and good knowledge of these Engines.. Thanks V much for the replies..

[williamt]

So Engine Out Today and was a 4.1 drive in it.. Was keen on a 3.21 for top speed but been Advised to go the 3.44 so I have Decided to compromise and go with the proven Drive used by fellow mini`s.. My thinking was that at 3.21 used in the metro turbos i had the same power anyway and would be a good choice.. but then the top speed difference is 10mph and if Acceleration is going to suffer just for that 10 mph then i suppose its pointless.. it would be interesting to see the differences on the engine of 3.21 and 3.1 although expensive and time consuming

[woody]

Don't forget to change the speedo drives to suit your setup.Calculator at link below
http://www.guess-works.com/Tech/ratio.htm