Hi guys I have recently rebuilt my scooby sti version 6 rear thrust type with full forged pistons and rods and acl bearings and new roger clark crank I have noticed it is abit knocky first start up I am told forge can get slap when cold but the noise seems to go when warm what are your thoughts it maybe engine out again and to get bottom end back to the builder? I do hope not as it is all new what do u lot reakon??

 

Hmmmm!

 

From new my forged build clattered until it warmed up, not bearing 'knocky' though. 30k miles later it's still going strong. Take it to a specialist, they'll soon tell you if something's wrong.

 

i have a forged 2.5 built by zen and from cold it sounds awful,really clackety but quietens down when warmed up,the engine has covered around 20k with no oil usage so im not worried really

 

My 2.1 is a bit slappy when cold also. Quietens down once up to temp.

 

I have a 2.5 forged engine.
The first cold start I get piston slap until it's fully warmed up then it's quiet.

 

That answered my question thank god my forged 2.1 is not that quiet cold but is 100 times better when warmed up

 

I wouldn't go as far as saying mine is silent when warm,i dont think any forged lump is but it's certainly much much quieter

 

Mine sounds stock once warm. Less miles on it than yours though, mine is on about 14k.

 

Guys u don't know how much it helps to hear this I'm still not 100% happy but I think it is slap as u all have said it gets quite as it warms up not totally clear but bearable if u no what I mean do they all still clatter after they have done a few miles or still the same when cold could one of u send me a video of a cold start up of yours I think that would really put my mind at rest thanks again guys made me feel so much better ��

 

Mine has Cosworth pistons and is slappy when cold too, but from what I understand a forged piston will require greater clearance and as they heat up they expand and the clearance gets smaller hence the slap goes away when up to temperature.

If the noise doesn't go away when warm then that would be a worry.

 

It does go gets much better after warm but this slap on first start up surely isn't good for the engine is it? Also I have heard the bores need more tolerance due to expansion it don't smoke oil and bottom end defo not I've heard a bottom end on a scooby and it is a different sound but the slap don't sound great either eeek

 

True

Also if mine is left for a few weeks without starting I get a small puff of blue smoke as oil has passed through the bores I'm guessing. When using the car daily I get no smoke.

 

I've had bottom end failure on an impreza and it's alot more of a thud like sound compared to the clack of piston slap.

Bottom end rattle gets louder and obviously faster as the engine is revved regardless of engine temperature. Bottom end knock does not get quieter once warm.

I spoke with Paul from zen where my car was built and he said its nothing to worry about.

 

That is where it was mapped previously and licensed ecu of course it has different headers inlet front mount so I'm going to take it to him for a safe map to run it in what power are use lot running come on time to boast now boys lol thanks again guys I nearly cried when I heard that noise all that work for a clatter I thought :'(

 

I've not been on a dyno but I'd guess mines is around the 410+ region

 

On a forged build if you don't get slap when cold then it's probably not running enough clearance & you risk the piston seizing in the bore due to being too tight when hot. The builder will set the piston to bore clearance so it is correct only when the engine is at it's hottest hence they all slap like a b***h when cold. A little slap when warm isn't unheard of either.

 

Mine is running a gt30 making 440/440

 

Do they not bed in a little tho I still can't get over the fact piston slap on a fresh rebuild I had a c20xe corsa fully forged and never heard that slap I guess it's because it's a cast block

 

Nice power boys and these motors slap every single day on first start up ooosh

 

TRUE

on my 5 mile commute to work I use no boost as the engine only just reaches temp about a mile from work so my engine is still a little loud, on a long run with plenty of right foot action it's alot quieter

 

I'm sure that you are supposed to run in the new engine using specific oil for first 1000 miles and not go over certain revs etc.
Speak to the builder and see what they say.


The piston slap from cold will always be there no matter how old the engine is. Don't worry about that as its perfectly normal due to the clearances required from cold..

 

Good old boys thanks for all your help and comments much appreciated ;-)

 

Lol when I get to work and my engine still sounds clackety people say things like oh shrek your engine sounds knackered etc etc......then I take them out in it and show how much it isn't knackered lol

 

Ha lol ����

 

Lol

 

The torque on yours Shreksta must feel immense! I went out in a forged 2.5 the other day, was running about 370, but it was in a classic RA, and my god that properly threw me in the back of the seat! Dunno if it was because of being a passenger, but It felt seriously quick!

 

Yeah mine is awesome,it has 0 lag it just pulps and pulls in any gear..........it makes for effortless fun driving

 

Can u post videos on hear I just want u to hear my motor to see what u reckon to the sound?

 

Yes post up the youtube link