Syty vs blazer 4.3

[ghettogmc91]

Hello everyone,
I've been on the board for a while now and have come to the point I'm having issues getting a straight forward answer on the questions I have.
I currently have a 1997 GMC Jimmy that has a 4.3 with marine intake and I've been tuning with HP Tuners and an AEM UEGO on a 0411 pcm. I used to have a powerdyne supercharger on it that I boosted to 7-8psi with an A2A intercooler. When the suoercharger bearings failed I swapped to a turbo setup: syty manifolds, garrett T04b turbo, syty downpipe, turbonetics deltagate external wastegate. I started with a 3psi spring just to make sure the tune was right and have gone up to a 5psi spring and still no knock issues. Next summer I'm going to up it to 7psi then 9psi if there is no knock. Motor and truck currently have 150k. Only mods are 1.6 rockers, 255lph Walbro pump, and ls1 tb.
Here's my issue. I currently have a 4.3 stock rebuild with less than 2k ready to put in the truck when the time comes so I'm using this motor more for testing and tuning to get everything sorted out for the new motor. I'm having issues finding out the specs for a syty stock engine though. From what I've read the stock boost is 13.8psi and the compression ratio is 9.0:1 is this accurate? I'm not looking to run a lot of boost but I want a bit more than it has currently. Just trying to figure out what all changes GM made to be able to add boost to the 4.3 safely. I'm guessing most if it was the fueling system and tuning which I've got covered but wanted to verify the stock boost/ compression before attempting more lol.
Thanks in advance for any help!

 

[Captain Morgan]

Re: Syty vs blazer 4.3

I forget what the stock max boost pressure was, but the compression ratio was 8.35:1, not 9.0:1

The main changes to the stock 4.3L internally were dished pistons, different head gaskets and nodular iron main caps. Thats about it.

 

[bigmileage]

Re: Syty vs blazer 4.3

If your fueling is good and you're not seeing knock I don't see why you can't safely run 10psi on a stock block 4.3. My brother has a 01 S10 with a Vortech blower and a custom W2A IC hat (cam and headers too), I tuned it on a stock pump with an aftermarket upgraded injector spider with HPT. He's been running 10-12psi on a regular basis with it. I have it tuned at around 18-20* of timing at WOT without any knock on 93. If he didn't have a cam the boost would be higher (boost= backpressure).

In the 3800 Series III engines there are plenty of guys running 20psi on stock blocks. I run 18psi with my Eaton and have been for years.

You have the best thing going for you know, HPT and you know how to use it.

 

[dgoodhue]

Re: Syty vs blazer 4.3

I forget what the stock max boost pressure was, but the compression ratio was 8.35:1, not 9.0:1

The main changes to the stock 4.3L internally were dished pistons, different head gaskets and nodular iron main caps. Thats about it.

:stupid: The ECM programming was set to control boost to 13.8 psi. Because of poor boost control its usually looks like a roller coaster. Its more like 13.8 +/- 1.5 psi over a run. So you often see peaks of 15psi but valleys in the 12's over a 1/4 mile run in normal good running SyTy motor.

 

[dgoodhue]

Re: Syty vs blazer 4.3

My Syclone uses a later higher compression motor. I am in the 9.2:1 range. I was able to run 13 psi with Vortec heads on pump gas and low timing and no knock. I didn't push that tuning combo and have since added alky.

 

[Jimmy]

Re: Syty vs blazer 4.3

:stupid: The ECM programming was set to control boost to 13.8 psi. Because of poor boost control its usually looks like a roller coaster. Its more like 13.8 +/- 1.5 psi over a run. So you often see peaks of 15psi but valleys in the 12's over a 1/4 mile run in normal good running SyTy motor.

Huh. I always saw a straight line. Max boost ---------- done .

Not stock though. Stock was blown up had to upgrade.

 

[Snoman002]

Re: Syty vs blazer 4.3

Here's my issue. I currently have a 4.3 stock rebuild with less than 2k ready to put in the truck when the time comes so I'm using this motor more for testing and tuning to get everything sorted out for the new motor. I'm having issues finding out the specs for a syty stock engine though. From what I've read the stock boost is 13.8psi and the compression ratio is 9.0:1 is this accurate? I'm not looking to run a lot of boost but I want a bit more than it has currently. Just trying to figure out what all changes GM made to be able to add boost to the 4.3 safely. I'm guessing most if it was the fueling system and tuning which I've got covered but wanted to verify the stock boost/ compression before attempting more lol.
Thanks in advance for any help!

Stock 1997 4.3 rebuild?

The SyTy motor was based off the TBI motor, yours is a fairly different animal. You have a balance shaft block, vortec heads, and a fair bit of other minor differences. I can't remember but I think the 97's are a higher compression as well. I don't think there was any substantial crankshaft changes.

So, if you want to make a SyTy motor, pull everything off and out of the 97, put the rods and crank back with all the other syty bits and there you go! LOL. You have a better engine (except the balance shaft), lower the compression some and boost the crap out of it.

 

[s106banger]

Re: Syty vs blazer 4.3

9.4:1 here. ran 14* this year on about 18lbs spraying meth with the 61mm.

 

[ghettogmc91]

Re: Syty vs blazer 4.3

Thanks guys lot of info!
As for the rebuild it's actually from my 91 jimmy. I rebuilt it then swapped to a built LT1 so it's a fresh 91 rebuild with the exception of .040 bore, edelbrock cam, and a ported vortec conversion. I'm hoping when this one fails it doesn't hurt anything so I can pull it, freshen it up, and put some forged internals with maybe a bit lower compression in it. I rebuilt the other one right out of high school so I was afraid to mix and match parts which is why it's a stock rebuild lol.
I like the fact that the motors are fairly similar, the compression was my main concern. The boost I knew must not be an issue since most seem to raise it on stock setups.

I guess I could rephrase my main question to be rather than what the difference is to what the stock limits are? I'd like to raise the boost a bit just for the fact that I love the sound and feel more than the speed, but what is the limit before 93 octane won't be enough? What's the limit before the ring lands get weak from the pressure? I know its a lot of variables to consider in the equation and I know most if it comes down to avoiding knock but I figured that at some point it has to just be too much for parts to handle.

Also captain you mention different head gaskets? Are they designed different or just a different thickness?

 

[ghettogmc91]

Re: Syty vs blazer 4.3

My Syclone uses a later higher compression motor. I am in the 9.2:1 range. I was able to run 13 psi with Vortec heads on pump gas and low timing and no knock. I didn't push that tuning combo and have since added alky.

Is that motor stock? This sounds about like what I was looking for. How much boost would you feel safe running without the alky kit? Just out of curiosity.

 

[dgoodhue]

Re: Syty vs blazer 4.3

Is that motor stock? This sounds about like what I was looking for. How much boost would you feel safe running without the alky kit? Just out of curiosity.

Yes, my bottom end is a stock junkyard motor out of 2003. As for how much boost, I would feel safe running; I don't think it would be much more than 13psi, maybe 14psi. My turbo actuator was set to what I would consider to minimum setting (actuator is set one turn of preload past when the wastegate is shut) I wasn't quite expecting for it to make 13psi, but that is what it made; I slowly worked on the tune (part throttle boost and then WOT boost). It didn't knock for me on 14* of timing and 93 octane.

 

[dgoodhue]

Re: Syty vs blazer 4.3

I guess I could rephrase my main question to be rather than what the difference is to what the stock limits are? I'd like to raise the boost a bit just for the fact that I love the sound and feel more than the speed, but what is the limit before 93 octane won't be enough? What's the limit before the ring lands get weak from the pressure?

The killer of the pistons/ringlands is usually detonation. Keep the detonation to zero and it make a lot hp. One guy ran high 10's on stock Syclone short block, other have run well into the 11's. The stock short block is nothing special. On the other hand, owners blow the stock motor running 13 & 14's because the motor has detonation.

 

[ghettogmc91]

Re: Syty vs blazer 4.3

Good to know!
Guess ill just keep the tune in check and run it up maybe 10 or so. Definitely feel a lot safer with it now that I've gotten some first hand input on the setup!