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bbcchevelle
01-16-2006, 11:50 AM
anyone try using two turbos from a grand national? what kind of hp could you get out of them? with a 350? thanks

jakespeeds
01-16-2006, 12:12 PM
They would be a little laggey. Without getting into air compressor mapping and all basically with a twin turbo small block you have 2 4 cylinders. What you want is a set of turbos like off a Celica Altrac turbo (CT-20) if you are trying to do it on a budget. They would work very well.

ProStreet R/T
01-16-2006, 12:51 PM
They would be a little laggey. Without getting into air compressor mapping and all basically with a twin turbo small block you have 2 4 cylinders. What you want is a set of turbos like off a Celica Altrac turbo (CT-20) if you are trying to do it on a budget. They would work very well.

I think your a little off base here, stock GN turbos aren't very big at all. I would have no problem running a pair on a street small block.

Better yet look at the stock turbos like a HX35 from a CTD ram.

jakespeeds
01-16-2006, 01:05 PM
You're right they are not very big but the airflow map for a stock GN does not fit well to one side of a SBC. There is just not enough exhaust gas energy coming out of a SBC to get two of those spinning under pressure until almost 4K RPM. That's not so good for the street where I am concerned. Two CT-20 turbos on the other hand would be spinning under pressure around the 2800 RPM mark. I have no experince with the HX35.

shmoov69
01-16-2006, 08:01 PM
They make great power! :headbang: The power #'s out of a good set up with those turbo's would be anywhere from 450-600ish RWHP. The TQ would be around another 100 higher. The turbo's that I have are VERY similar to the late GN turbo's and believe me, there is no spool up problem if you got a decent converter. Yes, they are probably not IDEAL, but what is in the hot rodding world? They might be spinning a little hard at the big #'s, but they will work fine on a budget. Remember, you feel the TQ, not so much the HP. And the TQ curve on a turbo engine is pretty much vertical and then horizontal until you shift!
Go for it! :twothumbs

Disclaimer-I know nothing about turbo maps and such, just what works on my car in the real world! :drive:

jakespeeds
01-17-2006, 05:51 AM
Glad to hear it. That's the way it should be. Actually with technology leaps in turbos over the last couple of years there are some hybrids available that are hard to believe. But not for the person on a budget. At what RPM do you start to feel the boost? Turbo maps are not pinpoint accurate by any stretch of the imagination and are based on conditions that are not generally found on the street. They are just used to get you in the ballpark.

bbcchevelle
01-17-2006, 03:53 PM
thanks for the info

shmoov69
01-17-2006, 08:12 PM
I can start getting boost at around 2500 or so and by the time the converter locks dead up (3200) the boost is really starting to multiply! I have never understood, or taken the time to understand the maps, I just got a couple turbos' and a buddy and I went at putting it together. This is when "it couldn't be done!" on the cheap or without fuel injection. Well, it was. Not perfect, but quite impressive none the less!

jakespeeds
01-18-2006, 05:51 AM
The boost map I was looking at was using 7.5:1 compression for its baseline. What compression is the motor running in your car? Sounds like it is setup right where it needs to be.

ProStreet R/T
01-18-2006, 05:55 AM
The boost map I was looking at was using 7.5:1 compression for its baseline. What compression is the motor running in your car? Sounds like it is setup right where it needs to be.

Curious, why do you want to run such low compression? The car is going to be a dog off boost.

If you guys have any questions on reading compressor maps feel free to PM me and I'll be glad to explain them. It's really just a simple efficiency map based on air flow (in #'s of flow) and pressure. You just need to figure your boost range, airflow requirements, and find an efficiency scale that will meet the full range, while trying to stay out of surge and keeping egt from melting the top end.

Simple enought right :hammer:

jakespeeds
01-18-2006, 10:26 AM
Its just the map that I had access too at the time of looking into doing this myself. On my Supra I run 8.7:1 compression. But with the ITS GT51 turbo there is almost no lag and it certainly is not a dog. The LS1 TT setup I am working on for my Nova will be using something closer to 9.5:1.

shmoov69
01-18-2006, 07:42 PM
Those turbo's on my engine is ok for the hp levels that I stated above. They may not be in their most efficent range, but still work great. Now if you are talking power levels like Charlie has, those turbos may work if you add another two of the same to the mix! :drool:
The compression I have in it now is 8.0:1, I had around 8.7:1 in the last engine. They were both dogs without boost. But I have no computer and the timing to stop advancing at 24*. So, lets see here, no timing, fat carb, low compression.........= Pig off boost! With it set up like that, I would bet that it has around 200hp. If it were set up (tuning wise) like a normal N/A engine, it would prolly pull another 50 or so, my guess at least.
But in another sense, after feeling it with boost, anything without it feels like a pig anyways!

jakespeeds
01-18-2006, 07:51 PM
Well you can add more timing but you will need to add a boost referenced ignition retard unit. Actually the GT51 turbo would be way to big with two on the LS1 but a couple of T3/T4 hybrids are going to do quite well.