2 seasons ago I melted a piston in my 383 lt1 which ended up requiring a sleeve. While it was down I bought a 355 lt1 from a friend (the engine out of "the spool bus" if anyone has heard of it) so I could run at a yearly event we put on for lt1 cars. It did well in his setup, went 10.0 @130 through a t56 at around 3500#. I used it mainly to cut my teeth on blowthrough carb tuning and work the kinks out of the setup and see what I could do to improve on before building and swapping the 383 back in. My best time was 11.03 and my best mph was 139 at 3700#. I know that a big issue I had was not being able to build any boost off the line but I was hoping someone could look through these parts and see what they think could improve its efficiency.
After looking though the build parts it's all a bunch of off the shelf parts, nothing fancy. Here's the specs...
355ci lt1 splayed mains
Eagle 3.48" stroke forged crank
Eagle 5.7 " h beam rods, arp 2000 hardware
Srp 4032 alloy -24cc dish pistons
Compression ratio 9:1
Como cams 08-303-8 cam (actually a nitrous grind?)
Duration: 288/315
Lobe Separation: 113°
Duration @ .050" Lift:236/248
Intake Centerline: 108°
Valve Lift w 1.6 rocker: 0.555/0.578
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=205&sb=2
Edelbrock performer lt1 heads, untouched. 170cc intake runners. 1.94/1.5 valves
https://m.summitracing.com/parts/edl-61905

My hotside consists of...
1.75" forward facing headers
2.5" outlet to 3.5" merge
T6 flange
Turbonetics Y2K 88/101 turbo 1.32 a/r (I believe)
4.5" downpipe to dual 3.5" that dump before the rear tires.

Coldside is 3.5" to the carb, no intercooler.


The 383 is also fully forged,
Mahle 2618 -31cc pistons. With a zero decked block and smaller chamber heads the most compression I'm going to be able to get out of it is 9:1

About the best value for lt1 heads is a set of ported trick flows that will end up with about a 210-215cc runner and 2.08/1.6 valves, but I don't have them bought yet. I'm kinda wondering how/why the edelbrock heads did so well with such a small runner and valve.

I'm wide open on cam selection.

The car is an 85 monte ss, around 3700#, 4l80e (if I keep this trans I'm getting a brake), 3.50 gear, 28" tire.

Let me know what you guys think. Thanks

 

Nitrous Camshaft is not helping you in my opinion. Cam probably would have worked ok on a belt driven supercharger.
What is the actual flow of the heads?

Y2K turbo is a great turbo if you are running PRO Mod with a 700-800 cid engine and have 600 cfm intake ports.
Not so well on stock heads combined with large pipes to the system that also destroy any real exhaust energy to the turbo at lower speeds.
A thing to remember is: If you are on the line with the engine at 4000 rpm and no load on the engine, the exhaust flow volume is actually pretty
small and the exhaust temp is fairly low due to the lack of load.

So to get the thing to spool quickly off the line you need a way to load the engine on the line and a clutch car has a hard time doing that easily.

Think those things over a bit.

Tom V.

 

Thanks for the reply. I know I've got a lot of mismatched components here. My main focus isn't so much on the 355 as I feel it's served it's purpose.
Now that you mention it, the previous owner had originally ran a Procharger, so I'm sure it was speced out for that, not the turbo he was running when I bought it. I had a feeling the cam was definitely the weak point of the setup with the heads being a close second.

Here is the flow of the heads (I should note that many side by side tests guys have done with these heads vs stock castings shown little to no gain and were certainly not worth the money)
Valve Lift-Intake-Exhaust
.100"61/52
.200"117/100
.300"174/140
.400"220/167
.500"242/184
.600"232/192

I'm completely aware that the turbo is gross overkill for even the 383 that I had originally intended to run it on. The 355 was just mainly to make an event and get some experience tuning the carb.

Knowing what I know now I probably would have ran 2" pipe off the headers with a 3" merge to keep velocity up. I'm wanting to move the turbo to behind the bumper anyways so I may use it as an excuse to redo the system.

I'm running a 4l80e with a small stall, the previous owner was the one with a t56.

 

A smaller diameter turbo header system has run 6.27 @ 228 mph with a 482 (small engine same as Big Chief's but not Big Chiefs) cid engine when the big boys run 600+ engines.
A 350 chevy 1982 style engine with ported heads and a good twin turbo match in a Monza chassis ran 8.60s so the 350 size engine is not necessarily the bad character either.

You just need to get to a Turbo specific package designed for the exact engine you want to run.

Tom V.

 

Thanks

 

So I got a trade offer for a forced inductions billet S484, 84mm compressor, 96mm exhaust with a 1.32 A/R divided flange. Has about the same run time as mine. If I trade him I'd be looking at changing a few things to make it work so it would be a good time to change the piping. Was thinking of going with 2.25" from the headers to the turbo. I notice there's also some 2.13" piping available that may be more for me as I'm only after 1200 horsepower max. Any thoughts on the trade or piping size?

 

Tubing is an interesting subject. Tubing is sold by the outside diameter. So a 2" pipe will be 2" outside diameter and then depending on the wall thickness .060" or .090" the inside diameter will be 1.880" or 1.820" inside diameter.

What is the wall thickness of the 2.130" pipe?

Tom V.

 

It is .065 wall (16 gauge)

 

I've had success footbraking my 4L80E with it in 3rd gear. I made a launch from 5000rpm and 13 lbs of boost out of a converter that stalls 3500rpm before building boost. I run twin 67's with 0.68 p-trim T4's fed by 2 inch (16 gauge) pipes on my cammed 5.3L. I've also had success placing the wastegate as early as possible in the system, either just after the header/manifold or right at the merge.

 

I have ran the "sloppy brake" with much better success than just a 1st gear footbrake alone. But mine releases very slow for some reason and it's a lot of my issue with slow 60'.
Here are some pictures of where I put my wastegate at the merge. I tried to place it at a point where it would be in the path to receive exhaust from both points. Looking at it now I recall that I ended up needing to place it farther away from the merge and almost to the point where it may not be getting enough flow from the passenger side. Maybe this is the reason it overboosts?
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I've herd of people modifying the valve body/bleed hole in the transmission to help speed up the 3-1 shift for the launch, although I'm not sure of the details. I've seen worse wastegate placements, but where it's placed on that setup can only really bleed off air from the one bank of the engine. I'd think it should still function decently well though given the size of pipe/valve that are there. I mention the wastegate placement mostly in relation to rear mounting the turbo. I'm making a rear mount set-up on my S10, and have placed the gate at the merge and reduced the pre-turbine/post-gate pipe to a 2" diameter that is still more flow area than the nozzle/restriction of the turbine.
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Yeah it's a 66mm wastegate and 2.5" pipe. I see what you mean about only getting half a banks worth of bypass though. If/when I redo it I'll try to make the merge longer so both banks flow into the wastegate piping better. The other turbo I'm looking at has a divided flange so I may end up with a different routing altogether. I'm still looking for info/suggestions on whether that billet S484 would be the better for my goals vs the turbonetics.
What do you guys think would be easier to spin, a 101mm turbine with a 1.23 ar or a 96mm turbine with a 1.32 ar?

 

It doesn't matter so much if one bank or both are vented. What matters is that you remove the pressure from the whole system. If you can bleed enough right off of one header that the turbine doesn't see enough pressure to drive it, then the boost will be controlled. Think of it like a water hose running a sprinkler.

 

Yeah that's a good analogy, didn't think of it like that.