What size single carb should I fit to this engine for trials driving. I have an HIF 1 3/4 in the garage that could be fitted, but is it a bit small or will it do the job?
according to http://www.classictruckshop.com/garage/shopmathcfm1.php you need a carb that does between 180 and 230 CFM. I am now trying to find some data for the HIF 13/4 carb, but I think it is in the region of 100 CFM.
this carb should be ok but only for grass and field type trials ,its to small for classic type trials with which you would be better off with a pair of dcoe type carbs (webber or delortos)which if properley set up will do both ,if petrol consumption is a concern then a fule injection set might be a answer (megasquirt ? )
SU's are extremely good carbs for trials car application. I successfully used a single 1-1/4 inch on VW Shorty, 1600 c,c but that was coupled to a very long inlet tract creating very high gas speed. Once the problem of icing was overcome the single SU performed remarkably well. My Troll had twin 1-1/2 inch SU's on a 1700cc Kent crossflow. Using FF tune crank/rods/pistons, a fully gas flowed but small valve head, and Piper 270 cam we had 110 bhp but the torque and power curves ran in an almost perfect parallel arc. No doubt with twin DCOE Webers we'd have had circa 140 bhp but at the cost of that incredible smooth and fast pick up. I used to run a 2 litre Fiat Tempra with the 150 bhp injection engine as a road car, smooth as silk and very torquey now that would have been lovely in a trials car engine!
Can you pass this information on to the gentleman with the single carb idea for the 2 litre twin cam.
I suggest he gets a copy of the book 'Fiat and Lancia Twin Cams' by Phil Ward with Guy Croft.
I quote from page 130 ' Changing from the asthmatic single carburettor fitted to most models to twin carbs yields very real and cost effective benefits. One choke per cylinder leads to quicker starting, improved throttle response and greater torque throughout the range. Not surprisingly, fuel consumption is improved for the same speed conditions.Inlet manifolds are readily available to permit the following conversions.
A single 1.75 SU will be excellent for torque and lower end power. Read David Vizard's book especially the generic sections, see the comparison graphs, and remember there will be no loss in power produced UNTIL the engine's instantaeneous airflow requirement exceeds the maximal airflow capability of the carburettor, AND even then it will not stop producing power, it will just produce a little less than could potentially be made if more air were able to be supplied. This will of course only happen towards the top end, which is not necessarily key in terms of what we need to do in Trials. Hence as David proved with his Troll, you can be very successful using SU's. They are also a lot more forgiving on an engine that is in an unknown condition.
So to have a torque and power curve running in a parallel arc is key for a good trials engine? And if so how is the best way to get this?? Cam, carbs, stroke, compression ratio??? HELP!!!
Currently running standard injection, is carbs really the only way forward for a good trails engine? I take it a set of twin DCOE Webers would be the only way to go for a standard 1600 p,205 engine. Or even a pair of SUs?
its a case of having the torque down low where you need it, no point having it way up the rev range.
if i was sticking with the 1600 engine i'd put a 16v head on which would let you try adjustments to the exhaust cam timing without needing to make a new cam each time. then i'd probably get some motorbike throttle bodies and put them on the end of a nice long inlet manifold and add some custom engine management to be able to tweak it all.
but thats if i had the money, on a budget i'd go the twin DCOE route myself.
well, actually i'd go the larger capacity engine route myself! but that wasn't the question :)
If the ATB diff rule comes in to place then will put a 2l 16v in it, if not will stick with the 1600, and try and get some more lowdown torque out of it. Thanks James
Thanks for your useful comments. I think I will be fitting the HIF6 SU carb. What are the parameters for a "long inlet manifold"? What is the optimum length/diameter ratio?
according to http://www.classictruckshop.com/garage/shopmathcfm1.php you need a carb that does between 180 and 230 CFM. I am now trying to find some data for the HIF 13/4 carb, but I think it is in the region of 100 CFM.
ReplyDeleteHS6 210 CFM HIF6 240 CFM Both the HS6 and HIF6 appear to be 1.75 inch carbs. So, do you know which 1.75" SU you have?
ReplyDeletethis carb should be ok but only for grass and field type trials ,its to small for classic type trials with which you would be better off with a pair of dcoe type carbs (webber or delortos)which if properley set up will do both ,if petrol consumption is a concern then a fule injection set might be a answer (megasquirt ? )
ReplyDeleteSU's are extremely good carbs for trials car application. I successfully used a single 1-1/4 inch on VW Shorty, 1600 c,c but that was coupled to a very long inlet tract creating very high gas speed. Once the problem of icing was overcome the single SU performed remarkably well.
ReplyDeleteMy Troll had twin 1-1/2 inch SU's on a 1700cc Kent crossflow. Using FF tune crank/rods/pistons, a fully gas flowed but small valve head, and Piper 270 cam we had 110 bhp but the torque and power curves ran in an almost perfect parallel arc. No doubt with twin DCOE Webers we'd have had circa 140 bhp but at the cost of that incredible smooth and fast pick up. I used to run a 2 litre Fiat Tempra with the 150 bhp injection engine as a road car, smooth as silk and very torquey now that would have been lovely in a trials car engine!
Hi Michael
ReplyDeleteCan you pass this information on to the gentleman with the single carb idea for the 2 litre twin cam.
I suggest he gets a copy of the book 'Fiat and Lancia Twin Cams' by Phil Ward with Guy Croft.
I quote from page 130 ' Changing from the asthmatic single carburettor fitted to most models to twin carbs yields very real and cost effective benefits. One choke per cylinder leads to quicker starting, improved throttle response and greater torque throughout the range. Not surprisingly, fuel consumption is improved for the same speed conditions.Inlet manifolds are readily available to permit the following conversions.
Weber DCOE/Dellorto DHLA or SK.
ISBN 0-947981-57-8
Richard Milne
A single 1.75 SU will be excellent for torque and lower end power. Read David Vizard's book especially the generic sections, see the comparison graphs, and remember there will be no loss in power produced UNTIL the engine's instantaeneous airflow requirement exceeds the maximal airflow capability of the carburettor, AND even then it will not stop producing power, it will just produce a little less than could potentially be made if more air were able to be supplied. This will of course only happen towards the top end, which is not necessarily key in terms of what we need to do in Trials. Hence as David proved with his Troll, you can be very successful using SU's. They are also a lot more forgiving on an engine that is in an unknown condition.
ReplyDeleteSo to have a torque and power curve running in a parallel arc is key for a good trials engine? And if so how is the best way to get this?? Cam, carbs, stroke, compression ratio??? HELP!!!
ReplyDeleteCurrently running standard injection, is carbs really the only way forward for a good trails engine? I take it a set of twin DCOE Webers would be the only way to go for a standard 1600 p,205 engine. Or even a pair of SUs?
its a case of having the torque down low where you need it, no point having it way up the rev range.
ReplyDeleteif i was sticking with the 1600 engine i'd put a 16v head on which would let you try adjustments to the exhaust cam timing without needing to make a new cam each time. then i'd probably get some motorbike throttle bodies and put them on the end of a nice long inlet manifold and add some custom engine management to be able to tweak it all.
but thats if i had the money, on a budget i'd go the twin DCOE route myself.
well, actually i'd go the larger capacity engine route myself! but that wasn't the question :)
I have a fiat twin cam manifold original single webber going on ebay soon
ReplyDeleteIf the ATB diff rule comes in to place then will put a 2l 16v in it, if not will stick with the 1600, and try and get some more lowdown torque out of it. Thanks James
ReplyDeletethanks for the comments.
ReplyDeleteI think I will fit the HIF6.
What are the optimum lenght/diameter ratios for a "long inlet tract"
Thanks for your useful comments.
ReplyDeleteI think I will be fitting the HIF6 SU carb.
What are the parameters for a "long inlet manifold"?
What is the optimum length/diameter ratio?