Hi Peeps

I have been offered a GT35/40 (roller bearing) Turbo for very little money brand new and never used (external waste gate type)

right here goes I know that the Gt35 isn't any good a for a 2.0 litre bottom end because they do surge and has been proven that they do on a 2.0 !! and to make them work properly you have to have more cc's to stop the surge !!

do i buy it and do a straight swap with a GT30 what do you recon ??

I'm going to go more power anyway late next yr (if everything goes well) but i want to buy all the bits first so i am undiced to buy this turbo or not

Marco

 

how cheap are we talking

 

Marco if they surge on a 2.0 then the engine builder knows fuck all

Beleive me with correct specs no surge.

Sorry to dissapoint the "other" camps

 

On a 2.0 YB the surge issues with GT35's can be improved with the correct selection in cams and the use of a suitable tubular manifold and large throttle body. However after having mapped around 15 engines with GT35's (May I add most NOT built by myself) all surge to some degree. The worst spec engines surge all the time with any boost over 26psi up to 5500rpm, where as the best spec engines only surge when running max boost at part throttle up to 5500rpm. Either way they're a surgetastic turbo!!!

 

i dont really unerstand the question, but a GT35/40 is just another term for GT35s that most people use TBH, as they have a GT40 compressor.

Kinda like RS500 turbos have a T4 compressor but not a T4 turbine side.

Why do 2litre YBs surge with GT35s and so many other 2litres etc dont then?

 

Can I just ask as well. Karl? What is surge? and how bad is it to have it?

lookin at a gt35 on a 2litre engine

should I really avoid it?

Thanks

 

Steve, the issue with GT35's surging is related to the YB efficiency. The YB seems to improve considerably in its VE over 5500rpm and as such below 5500 is the surge zone when using a GT35. If you also look at the compressor map for the GT35r you will see that at pressure ratios over 1.6 bar the surge line is rather shit!! As such it is not uncommon to have to cap 2.0YB's to around 25psi until after 5500rpm.

As I've mentioned above this situation can be improved with other parts, but Ive yet to see an engine spec that has no surge at all with a GT35r as even the best ones still surge when running full boost at part throttle under 5500rpm.

I'm looking forward to a ride in Ade's car at full boost and part throttle as Rod says it has no surge at all!!!

 

how can you tell when your car is surging then ?

 

Don't know Marco, but it'd make more than 350bhp with that turbo

You really need more power?

 

GT35/40 is a pretty vague description too, there a fair few configurations possible.

Trouble is that things that you do to minimise lag generally, like a smaller exhaust housing increase the chance of surge.

Still possible to get good results from them on a high revving motor though.

If you are building to 8500rpm anyway then reasonable power from 4000 and monster power from 5500rpm is a not bad bet, so even working around the surge you can still make a very quick car, but for a road going car i would sooner have a GT30R really myself on a YB, so i reckon you would be best to swap it if you do get it.

 

Good post chipster

 

Marco - personally i would go with a decent t4 - rev limit to 7800/8000 and a pair of karl's cams, a new inlet - either an nms item or the swedish one. And some 1000cc injectors

MUCH less hassle and all you need is a turbo/cams/inlet/injectors and a remap...

Your noise will not be as much of an issue and you don't have to have all the noise of a screamer.

 

Marco, If I was you, I'd go with an internally or externally gated GT30.

 

Aint that a T4 with more issues porkie LOL

 

marco, I would go with a nice T2

 

For all those people who think a GT35 Surges on a 2Litre, i believe Ades car will be proving differently on Thursday at the Daddy Thrash.
Martin & Karl have been invited to attend i believe they have excepted. That will put an end to these type of posts. If the Engine/Head/Cams are correct THEY DONT SURGE.
Rod
ps. Getting Blue in the face saying this.

pps. Marco Perhaps you are asking the wrong people & if you wish to fit this Turbo you should know by now who to ask.

 

No idea about these turbos on YB's but... As chip said - Gt35/40 is a useless description, it only tells u that it has a 68mm turbine inducer. So unless you know the compressor details, u cant look at a map to see if it's going to work!

 

Don;t know about surge, but here'e a proper 500hp turbo, unlike the T4 being more of a 440hp turbo - GT3076R

 

Basically what you are saying is like saying "ive been told esorts arent any good for rallying, im getting one cheap, should i use it or swap to a sierra"

But at no point mentioning if its a WRC escort cossie, or a 1.1 popular plus.

 

Before you slag the T4 too much, find a graph for that and check out its surge line!

T4 just will not surge no matter what you to do it basically!

Lot to be said for reliable old technology sometimes!

 

A T4 can surge Chip.

As Stu once put it, a T4 is the mayor of Surgeville, or something like.

 

Marco im currently stuck with the same dilema, have gathered most my parts for a rebuilds but unsure what to use. Shall be speaking to Reyland in regard to rebuild and spec etc.
The turbos pictured are gt28/35 and gt35/40. Also hks external wastegate
May have to sell one or the other depending on outcome.

 

I'd disagree based on T4 YB lumps ive seen in action, but obvioulsy like anything else it depends on getting the right T4, as thats also a vague desctriiption really, difference is, more cossie tuners seem able to spec a T4 than a GT35!
Get the correct T4 and it wont surge, even if you make bad choices on cams and headwork etc, a GT35 though, seems to be VERY fussy about all aspects of the engine to avoid surge.

 

can someone PLEEEEEEASE explain what surge is then? and why its so bad to have??

 

Dom,

an the most hated of phrases, surge sounds like "wastegate chatter", in that instead of getting it when you let off the throttle, the "chatter" is there under load.

the engine cant consume the air that the turbo is pushing quick enough, hence the noise iirc. I think, but trust me, i'm probably wrong, that the turbo is also trying to stall too.

Remember tho, wastegate chatter doesnt exist, and its turbo stall - happy Rainbum? LOL

Its bad cos it can fuck your turbo iirc LOL

 

T4 is only a 440bhp turbo - afpmsl....

mine made more power than that with out being remotely close to its limit

 

Mike, cheers mate

does this mean the engine/acceleration hesitates?

 

The RS500 turbo is a hybrid unit and not a "real" T4, but its good for over 500 bhp and then some..

 

Dom,

More of a stutter LOL

 

lol, cheers mate

damn surge

 

You say that dingy, doesn't Paul Bailey's Mk2 make something like 560bhp using a T4? Obviously I don't know the spec but would agree their good for more than 440hp

 

Chip and your experience of a T4 is?

They surge mate been there...even on a lightly ported head above 25psi and its a nightmare....open ports right out and use correct cams then its fine just like the GT35

Also to Rick a T4 is a genuine 500bhp turbo..providing you have a good spec engine @ 2bar boost..reliable all day everyday

 

T4:
After around 440bhp a T4 is a restrictor. We can push the air harder and harder and make more power, whilst generating more heat, but we are fighting the turbo itself and would be better fitting a bigger more suited turbo, end of story. Peeps in the Ford scene would do well to remember that having to use 2bar of boost is not actually a good thing

Surge:
Surge is caused by the stall, which is worsened by surge, its a vicious circle...

Imagine the way our turbocharger's compressor is driven, right back to basics: The turbine wheel is spun by exhaust gas, utilising also the energy stored in the exhaust gas as latent heat.

This force on the turbine shaft generates torque at the compressor end as they are physically connected. Remember that part as its the key element, Torque

Ok,
Now lets imagine our turbocharger compressing air, forcing it into the engine, the engine is utilising it.. what happens then? Ok, The engine expells it, and our turbine housing pressure goes up accordingly, the torque applied at the turbine wheel increases, increasing the spin speed and compressor efficiency at the other end. Great chain of events!
End Result? boost is climbing nicely.

Ok,
Now imagine this scenario:
The turbo begins to spin, as above, but the compressor wheel is generating more air than we can move and the torque required to spin that huge compressor is not being met? Remember that unless the air is processed by the engine, and expelled as hot, rapidly moving air into the turbine housing, our turbine shaft torque will not increase to spin the compressor faster, and it may well diminish.. our compressor is slowing, braked massively by the compressed air its trying to overcome and increase.....

Result? Compressor starts to slow a little.. (beginings of a compressor stall)

Ok,
So now what?
The engine is still rotating and consuming air, but the turbo has stopped producing an excess, so our engine has now had chance to consume what excess was available and the inlet pressure is now diminishing, the turbine torque is now increasing again...

VERY IMPORTANT:
Remember also that at same time, compressor resistance to spin has also dropped due to housing no longer being as pressurised and as a result, the torque required to spin it has dropped massively..

Boom.. Suddenly the Turbine wheels torque massively exceeds the compressors resistance and the turbo spins to speed in an instant!! Sounds great, rapid boost climb!! The compressors acceerating at over 2G

BUT:
We just hit the same problem again, our huge compressor has made so much boost, so fast, and is trying so hard to push the massive volume or air, that our YB cant use it.... so we start to slow again........

So we went: Fast, slow, fast, slow, or in other words: The turbo is Surging.
As you can imagine, it continues this cycle until it hits the revs your engine consumes all the air.. then your away!!

Downsides to this surge are pretty obvious:
We can have serious bearing wear, due to the excessive loads imparted on the shaft supports.

Compressors have been known to simply explode!!

Worst case scenario, the compressor being slowed rapidly with a turbine still trying to accelerate it can simply do as expected, part company.

Hope this helps to explain in as simple terms as i can put it, the phenomena known as "Turbo Surge."

More info and a big argument, here:
https://passionford.com/forum/viewtopic.php?t=34511

 

Phil/Dingy- whilst i agree the T4 can make a lot more than 440bhp (proved countless times), it's not designed as a 500hp turbo, simple as. You are way off the compressor map, which is why u need massive massive intercoolers to try and combat the stupid charge temps.

People have different concepts of reliability, but if i wanted a reliable 500hp engine, i wouldnt use a T4.

 

Marco what HP/TQ will you be after when you finish it,
The GT30/40 or 35R is a 600hp+ tubo,
The GT30R is good for around 530hp,

Mark

 

Rick i disagree 2bar is the correct max boost for a T4 and with a good spec engine you should acheive 500bhp shouldnt you?

 

Thats a bloody good post Stu, made good sense to me!

 

Phil - max boost is difficult to define - max for what exactly? The way you SHOULD define the capabilities of a turbo is by looking at it's compressor map. I don't have a T4 one to hand. The example of the GT3072R i gave above is a turbo designed for 500hp. Im pretty sure u could push it harder for more power, just as you can push a T4 to over 500hp.

My point is that if you are speccing an engine, and want 500hp, it makes no mechanical sense to fit a T4.

 

T04B or T04E and what spec, there's quite a few "T4's"......

 

very cheap not saying


Richard

not really no!!. in all honesty i don't think i ever had a 400+bhp engine allthough did have a graph to prove it to say it was ... it went ok on track but was never 400+bhp or anywhere near that ....

it would be good to have the extra power on tap if you know what i mean not knocking anyone on here but 500/600+bhp on track theres no way that i could use all of that bhp on track with out lowering the boost some what i would find it totaly hard to drive flat out being honest



Steve

I understand what your saying and that is a good set up see what i don't like about the T4 it's laggy in Sierra .. ok in your car it isn't.. but your only pulling 1000 kg so it does help

I know you can bring a t4 in earlyer say at 3.5k thats all well and good but then i'll lose out the 500 rpm at the top end .. so it's a catch 22

Mark

I want to run about a gen 530/550 bhp but i want to the turbo to start making boost at the same as my T34.63 does now

so basically same type of boost just with more power so i can use it when needed

I'm happy with my 350bhp because the rest of the car is sorted and thats why it might seem good for 350 bhp it's just that i want more power on tap for next yr

Marco