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Bomb Proof Turbo.

1K views 46 replies 11 participants last post by  RDS 
#1 ·
Ive just started building a bomb proof 20LET. The LET i used was a late type post 93. So far i have replaced the crank for a knife edged early type 20xe, Flat type flywheel, alloy front pulley, shot peened and polished rods, arp's, copper lead bearings and looking at a oil spray bar(PRICES OF SUPPLY AND FITTING OF ONE PLEASE).

I want to use the early type cam belt as i have heard bad things about the later type. I have all the parts needed to do this but was wondering if anyone else had done this?

Also i have 2 different heads i can use. One early and other late type. Both KS type(dont give me any bull about coscast as there both pressure tested to 40psi in boiling water and the fine!) What i need to know is r the later type bolts any better than the early shorter type?. Also i think the only difference is the heads? am i right or are the threads in the block different as well?

Cheers.
 
#2 ·
re:the head and your comment about them

iirc a thread posted by gary with pics showing where the porous fault happens, but more importantly why it happens. iirc it was found to be the torqueing sequence that caused a crack between the oil and water ways. i had a head all refurbed and pressure tested but whn i fitted it it was still porous so dont over look it ;)

a question..whats the difference in the cranks?

rodgerq
 
#4 ·
Didnt mean to sound like a know all when i said i did need any info about the KS vs COSCAST head thing but i get feed up with hearing how every KS head will go porous and the people telling me would not know what porous was if it fell no there head!
As a quilfied service engineer for MTU/DETROIT DIESEL building engines day in and day out day i was applying the methords i know and have been taught to test the heads. I have NEVER been told to apply 100psi presure to a any part a cooling system as there is no need to and will prob cause damage. 40psi is 4x working pressure, + boiling the head = more than enought of a test.

I Would like to be corrected on this if u can point me in the direction of where u got this info from as i alway am interested to learn more.

I can how ever understand how the massive load and forces applied wilst torquing would cause a weekness it the head to come to light. I will try to fing the coments made by gary as i here he a bit of a god in the head department.

Still would like to know why vxl changed the lenght of the head bolts?
 
#5 ·
unsure on head bolt quey mate. but when you see the pics you will see why it goes "porous", not even an accurate description of the problem. the casting actually cracks right underneath where the head bolt torques to which causes the crack to occur.

rodgerq
 
#7 · (Edited)
rodgerq said:
re:the head and your comment about them

iirc a thread posted by gary with pics showing where the porous fault happens, but more importantly why it happens. iirc it was found to be the torqueing sequence that caused a crack between the oil and water ways. i had a head all refurbed and pressure tested but whn i fitted it it was still porous so dont over look it ;)

a question..whats the difference in the cranks?

rodgerq
Difference in crank is the weight. The early one was far better finished and as a result much lighter. Cant remember were i read it to start with but a blind man could see the difference.
Early type 16kg
Later type 18kg

Both measured in a clean envrioment and 20c and my "old dears barthroom scales"
 
#8 ·
wouldnt have bothered knife edging it personally, can weaken the crank if not done right

also, the cooling system runs alot higher than 10 psi, most coolant temp pressure testers run at 90 psi

also, your rods, do you mean de seamed then shotpeened?
 
#9 ·
im gonyleave the late(heavier crank) in. dont want things too light with it being a turbo engine, same kinda effect with not lightening the flywheel too much. holds some momentum so you dont lose too many revs during change up, keeps lag down.

rodgerq
 
#10 ·
rodgerq said:
im gonyleave the late(heavier crank) in. dont want things too light with it being a turbo engine, same kinda effect with not lightening the flywheel too much. holds some momentum so you dont lose too many revs during change up, keeps lag down.

rodgerq
Weight dose mean more wear. Besides i cost me nothing and if u had both lying there which would u fit?
 
#12 ·
yeah same here. i do have bth sitting here, an ealry xe block and a late LET. didnt know there was any difference but now i do im still fittin the LET crank :)

you can get stupidly lightflywheels anyway, if you want to take the weight down.

rodgerq
 
#13 ·
region17rc said:
wouldnt have bothered knife edging it personally, can weaken the crank if not done right

also, the cooling system runs alot higher than 10 psi, most coolant temp pressure testers run at 90 psi

also, your rods, do you mean de seamed then shotpeened?
With the pressure thst thing like i side it what i been taught be im willing to learn more.

Rods where sent througt a cosworth engine builder to a company how shotpeen engine and transmission components for race and rally teams including F1. Only cost me a £10 so i got to keep it close to my chest.

Knife edging was a freebee as well. So couldnot say no.
 
#14 ·
rodgerq said:
yeah same here. i do have bth sitting here, an ealry xe block and a late LET. didnt know there was any difference but now i do im still fittin the LET crank :)

you can get stupidly lightflywheels anyway, if you want to take the weight down.

rodgerq
Lag can be fixed Holes in the side of blocks and cant, vxl stoped using the early crank cus it cost more than the late one. Same as the coscast head, like u said in your earler reply "dont over look it".
 
#15 ·
have you ever heard of a crank breaking? i've only ever sen one let go, and that was in a 10k revving racer,
so the rods, did you have em deseamed then polished?
and i would have said no to the knife edging, it might be worth 2 bhp, and if anything it'll weaken the crank, i would have had it nitrided/tuftrided instead
 
#16 · (Edited)
region17rc said:
..also, the cooling system runs alot higher than 10 psi, ..
yeah, up to 15psi.
the cap should relieve any excess pressure, or else you're looking at things breaking.
Don't know where you got the 90psi figure, it's waaaay off:beer:



By the way, the most important factor in a bombproof LET is to control cylinder pressures. Cranks don't break, as others have mentioned.
Over-revving damage is also avoidable, since there is no need to rev higher if you tune it properly. It helps, but you don't have to tune for 7Krpm, except if you aim for silly bhp figures.
 
#17 ·
i can't see the crank breaking mate! mine'll be gettin nitrided anyway which im goin to see about today. hopefully the engineering place can either do it or know someone who can while they have that and my block for boring etc. i have every confidence in it even with the high spec im aiming for.

rodgerq
 
#18 ·
JohnA said:
yeah, up to 15psi.
the cap should relieve any excess pressure, or else you're looking at things breaking.
Don't know where you got the 90psi figure, it's waaaay off:beer:
from the testers i used when i worked for british airways in their ground fleet garages, and the one that bernie at novatech uses
 
#21 ·
region17rc said:
have you ever heard of a crank breaking? i've only ever sen one let go, and that was in a 10k revving racer,
so the rods, did you have em deseamed then polished?
and i would have said no to the knife edging, it might be worth 2 bhp, and if anything it'll weaken the crank, i would have had it nitrided/tuftrided instead
I have seen a broken crank in a 9 litre 2 cycle diesel which revs to 2400rpm. And it was still runing.
shoot peened rods. Not sure of the actual process used they have been shoot peened for sure. But the rods also have a poilshed look about then. Sort of like a shiney orange peel effect. The seem has gone as well so i guess there deseamed. Will ask the guy if im aloud to give out info on the company who did um and put out a post on it lated. They do look the dogs And for a £10 a rod im happy.

Place near me in southampton can still tuftrided the crank for me so cheers for the idea.
Knife edging was carryed out by a company near me who have been doing the process since forever. Its not to make the crank stronger its to help it help reduce drag. And when done propley it should affect the strength(fingers crossed).

Just read the post from gary and i can defo see what he means. Think ill go for a service ex from vxl.
 
#23 ·
MADVALVER said:
I have seen a broken crank in a 9 litre 2 cycle diesel which revs to 2400rpm. And it was still runing.
never seen a let one let go though, and i would think that would be more relevant tbh
Not sure of the actual process used they have been shoot peened for sure. But the rods also have a poilshed look about then. Sort of like a shiney orange peel effect. The seem has gone as well so i guess there deseamed. Will ask the guy if im aloud to give out info on the company who did um and put out a post on it lated. They do look the dogs And for a £10 a rod im happy.
so, de seamed and shot peened then, so why the big secret?not like other people dont do this
Place near me in southampton can still tuftrided the crank for me so cheers for the idea.
Knife edging was carryed out by a company near me who have been doing the process since forever. Its not to make the crank stronger its to help it help reduce drag. And when done propley it should affect the strength(fingers crossed).

.
no worries, tuftriding will give you more benefits than the knife edging
 
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