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What boost are stock LET conrods and crank good for?

804 views 24 replies 11 participants last post by  chip 
#1 ·
Tried searching the archives but found nothing. Basically is it worth doing "half a job" doing just the pistons? I'm running 1bar at the moment on the standard turbo.

If I get a hybrid, what boost can I run with standard pistons?

And with forged pistons and standard rods and crank?

Cheers :beer:

Tricky
 
#2 ·
Its not just about what boost, its also about how much torque you are making and what revs you are using it at.

As a rule of thumb though the standard are good from 350bhp at least if used with ARP rod bolts and new bearings, in fact TFS was running 400BHP plus on his with worn bearings and standard rod bolts and it still took over 18 months to die (but that was running nitrous, you cannot get the same power from the same bottom end as safely without nitrous, as nitrous power is gentler on the engine)

Compression ratio will also make a difference, the actual pressure the pistons are subject to for a given level of boost is lower and over a longer time period on a lower CR motor, so a thicker head gasket or lower CR pistons will allow the rods to take more bhp than standard as well.

Personally iwouldnt bother changing the rods on a LET unless you are going for more than the 400bhp ballpark if you are building the rest of it sensibley.


Chip
 
#9 ·
the boys are correct in the whole boost issue.

The load's are not the problem its the cycling. A rod fails after so many cycles.

It could probbaly take a compression load of a few tons for a million years, same if it had a few tons clinging on to it.

But when your doing both thats when the trouble arises, thus aftermarket rods etc usually come with a cycle life, like 10million cycles at an equiv of 7krpm.

Some rods will go and go, others will fail sooner.
 
#10 ·
0ddball said:
is it mentally draining mentioning nitrous in every single one of your replies ? lmao

A little bit, im just waiting for one of the non-nitrous users on here with a cally turbo to do tens of thousands of miles with 400bhp+ though, and then ill have some examples of cars that dont use nitrous.

As it is though, as far as im aware no one else on here at the moment can match TFS's time so his car is a good exmaple of what works and what doesnt.

If he had just done the rod bolts and bearings like i told him to his original engine would still be fine, so it shows the rods are good for 400 easy.


Chip
 
#13 ·
[idle comment]
Waaaay to many preachers on here these days...... :rolleyes:

Not many people seem to be able to put their point across without being condescending.
Shame, 'cos some of the points are worthwhile.
[/idle comment]


Sorry, please resume normal service.....

;)
 
#16 ·
12.9 seconds up the pod in a non stripped out car (including stereo and that bottle you keep going on about being so heavy) very clearly puts it in the 400bhp ball park, timing slips are a far better judge of power (given a consistant driver) than imaginary figures from rolling roads which vary so wildly.


Chip
 
#18 ·
RDS said:
Above 350ib/ft and the rods start snapping. Brian has never had a rolling road confirm his car at 400bhp either;)


Just for anyone who doesnt know how to do the maths and would rather think in BHP than LBFT

350lbft=
367bhp @ 5500rpm
400bhp @ 6000rpm
433bhp @ 6500rpm
466bhp @ 7000rpm
500bhp @ 7500rpm

So claims the standard rods are good for 500bhp are backup up by what RDS is saying about the amount of torque they can withstand.

Chip
 
#25 ·
Sorry should have put more detail in my post there for the pedants who wont bother looking at the rest of the facts themselves

i should have said something like

"making a 12.9 still despite blowing up the intercooler before the line and coasting accross in a standard weight calibra after getting a pretty average 60ft time due to crap tyres clearly puts it in the 400bhp ballpark"
 
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