two are definitely not better than one on a 4cyl engine.

I agree that I wouldn't do twin turbos ... but disagree that two are not "better" than one.

Porsche did sequential turbos in the 959, then changed to parallel for the newer cars, with very good results (and some very careful engineering). Are they wasting time? Surely they could have fit a single turbo instead.

And of course the top Ferraris used twin turbos. A lot of work, careful design, but apparently worth it.

The RPM range of the turbo is not tied directly to the RPM range of the engine ... with only half the exhaust of an engine per turbo, say two turbos usually used on 150hp engines would still give better top end than a single tubo for 200hp engine. Or at least it seems (OK, I admit I'm not a turbo engineer and where the line is crossed is probably why us mere mortals shouldn't try it ... )

I was talking to Vince about a street car project of mine and he like myself would not waste our time with twin turbos on a CA

Quote:

No. They will still run out of puff at high RPM. You will have a better torque spread but top end power will be compromised. You can have 4 turbos but they are still T25's and are designed to work within a certain rev range

For good bottom end response AND top end power use twin sequential turbos.

But you're right...it would be a fun project. Just use a better motor than a CA18

why not one big and one small so you have no turbo lag at all but that would take a bit of work wouldnt it i dont no much about turbo systems weel i no how they work but nothen much more than that

Rigoli wouldn't care about turbo lag, as he runs a drag car. Top end power will have no difference between one big turbo or two smaller.

Twin turbos appropriately sized result in less lag. Two big turbos would probably be a mistake.

If you run twin turbos, you go with smaller turbos and get better low-speed response ('cause they are smaller), AND more flow ('cause there are two of them). If you make a really clever piping system with butterfly valve you could have dual-path intake (short and long) to improve it further.

Far easier and probably more reliable to use a single. But if you do your own work ... might be a fun project.

My thoughts on this are if you sell the turbo that came with your CA you will only be $600 - $700 short of buying a S15 turbo. This would be the best budget option short of spending the $ 2600 on the big sucker garrett range.
My reasons are :
1.The S15 turbo will bolt onto your manifold
2.The S15 turbo will more than likely have less kilometres and be in better condition than most T25's
3. S15 Turbo is ball bearing so it spools up fast for minimal lag.
4. You will have to find a T25 of similar condition to use
5. The S15 turbo is ball bearing and is capable of 200rwkw+ on a S15
6. I assume this is a CA18 in a 1200, you may struggle to fit them between and around the strut tower.
7. You will need to fit two exhaust dump pipes then into one large pipe in the bay before the exhaust levels out and travels the length of the car, this would need to be done to clear the steering and the road. This could be done Toyota soarer style to reduce room needed, i guess.
8. Twice the plumbing no real disadvantage just a pain in the ass.
9. Lots of lag, by using two turbos that is alot of air to push, basically a T25 you are running a GTR sized set up on a 1.8. It would be laggy but you could always try and drive around it.
10. The money spent on extra piping, exhausts and clamps etc, will be similar money it would of cost to by the S15 turbo in the first place with a lot less brain damage.
They are just my opinions and 10 things i could think off the top of my head. It may be cheaper in intial outlay but more expensive in the long run. I ran this subject by Vince Rigoli not that long ago for another project he had in mind and he replied "twin turbo, twice the trouble".
Although if your budget can stretch to the bigger garrett range (like on Dattodude's CA in his avatar) then that would be the best option.

Hey,
Ball bearing cores do not affect a turbo's flow capabilities. If you went twin T25's on a pissy little 1.8L motor I reckon you would have to go ball-bearing. And even then I'm not sure it would be able to spool them up. Although, I've never seen it tried so I could be wrong.

What turbo you choose will depend on how you want the motor to behave. A smaller T25 will come on boost earlier but won't make as much power up top as a larger T28.
A bb T25 will make the same power as a normal T25, but will spool up quicker again. That is generally speaking of course.

And with the twin T25's, I think you'll find you will get bucket-loads of flow down low, but because they are still T25's they still won't be able to hold it up top.

I would try and find a BB T28 off a S15, GTI-R...etc. They're cheap and ( I think ) will bolt straight up without hassle.

Anyway thats MY thoughts on it...

Hi folks, I have been looking at what other turbos I can fit to a ca18det. looks loke the options are
S15 t28 bb starting from $1000
Gt25/28 starting from $2600
Rb25 bb starting from $600 ceramic turbine (can only handle 1 bar)
Vg30 starting from $2200
OR................

............Why not put on two t25 turbos , they are very cheep in comparison, all I would have to do is make up a manifold, change the oil returns and change the intercooler piping.
I guess they are not ball bering but wouldnt they flow more than the others, and would only really cost a lot of time? not so much money
What are your thoughts on it??