383SB or 400SB retro into a L31 1998 Suburban

[1998_K1500_Sub]

There is a new Dart block on one of the FB groups I follow not far from you.

5hrs away from my home

No sales tax

I have friends in Indy, maybe I could talk one of them into driving to Cincy, it's only about an hour away

Hmm...

(edit) I've learned the block for sale uses the two-piece rear seal, so I didn't pursue.

 

[cj8scrambld]

I'm with the others....400sbc in this application. Nothing to add differing from other comments. I am a fan of 400's and never had issues running them. Sure, crappy R/S ratio but perfectly fine for low rpm.

 

[1998_K1500_Sub]

Let's turn to a related topic: The OE L31 intake / injectors.

I would like to re-use my current intake (stock L31) / injectors (Delphi MPFI) on the bigger engine, but should I consider some modifications?

I would like to keep the L31 log exhaust manifolds but plan to improve the exhaust everywhere else. I haven't picked a cam yet.

Regarding the injectors, I believe either @L31MaxExpress or @Supercharged111 has commented that the unmodified MPFI is suitable for something like 400HP... I'm not looking to achieve 400HP necessarily, and I'm guessing the bigger engine would be south of 400HP, and it would be nice to reuse the MPFI system I already own.

Regarding the L31 intake, can I leave it as-is or should the flow be improved, and if so by whom? I'm not considering the marine version BTW.

 

[Blue Max]

I just completed close to the same upgrade. Went with the Dart SHP 4.125 bore and 4.0" stroke aka 7.0L. long story short it was a 3 year engine build with Covid and parts availability issues every turn. Dyno completed with [email protected] and 530Tq at 4K on 87E10 pump gas . AFR Vortec heads, OEM style CISF 46lb/h injection for ASUS. Blk Bear Perf did the starting LS1B PCM custom tune. Now to get it fine tuned for pulling the grades in Colorado with my camper. Highly advise you get a AFR gauge on it to ensure proper fueling. I also have a dual band EGT to ensure it doesnt get to hot of EGT. Better safe knowing than burning valves. Good luck its a long journey.

 

[Moofus02]

I just completed close to the same upgrade. Went with the Dart SHP 4.125 bore and 4.0" stroke aka 7.0L. long story short it was a 3 year engine build with Covid and parts availability issues every turn. Dyno completed with [email protected] and 530Tq at 4K on 87E10 pump gas . AFR Vortec heads, OEM style CISF 46lb/h injection for ASUS. Blk Bear Perf did the starting LS1B PCM custom tune. Now to get it fine tuned for pulling the grades in Colorado with my camper. Highly advise you get a AFR gauge on it to ensure proper fueling. I also have a dual band EGT to ensure it doesnt get to hot of EGT. Better safe knowing than burning valves. Good luck its a long journey.

What are you using for a cam and exhaust?

 

[L31MaxExpress]

Let's turn to a related topic: The OE L31 intake / injectors.

I would like to re-use my current intake (stock L31) / injectors (Delphi MPFI) on the bigger engine, but should I consider some modifications?

I would like to keep the L31 log exhaust manifolds but plan to improve the exhaust everywhere else. I haven't picked a cam yet.

Regarding the injectors, I believe either @L31MaxExpress or @Supercharged111 has commented that the unmodified MPFI is suitable for something like 400HP... I'm not looking to achieve 400HP necessarily, and I'm guessing the bigger engine would be south of 400HP, and it would be nice to reuse the MPFI system I already own.

Regarding the L31 intake, can I leave it as-is or should the flow be improved, and if so by whom? I'm not considering the marine version BTW.

I ported mine, but while I was at Lloyd Elliots place when he was porting a couple of pairs of heads, he had a L31 manifold there he was porting. He is atleast familiar with what they need done to them.

Stock EFI system is good for ~425 hp without pushing too crazy on the Injector Duty Cycle. I found the limit at about 465 hp or so at about 4,600-4,800 rpm on my 383. At that rpm the IDC hit 100%. It held the air/fuel ratio consistently in the mid 12s to 5,200 rpm with IDC rising close to 115%. What I found odd is that it did not lean out going above 100%. I think there is something wrong with the IDC conversion math in HP Tuners TBH. It was reporting 100% and I was still able to add fuel up to a reported ~125%.

 

[L31MaxExpress]

One thing I will throw out as well. IDC is also relative to RPM. The less RPM the engine is turning the more time the injector has to flow the required fuel.

 

[Blue Max]

What are you using for a cam and exhaust?

Long tube chassis headers, Custom Thermal Barrier coating on interior tubes and a custom anti- corrosion coating on the outer tubes. Have to save them for the long haul, CARB legislature has killed availability of long tube headers for Colorado street use. Cam is a custom grind by builder from COMP Cams, billet core while running hydraulic rollers and stinger 1.6 rockers so .560"/560" lift, 211/217 dur. LS113

 

[Blue Max]

Long tube chassis headers, Custom Thermal Barrier coating on interior tubes and a custom anti- corrosion coating on the outer tubes. Have to save them for the long haul, CARB legislature has killed availability of long tube headers for Colorado street use. Cam is a custom grind by builder from COMP Cams, billet core while running hydraulic rollers and stinger 1.6 rockers so .560"/560" lift, 211/217 dur. LS113

Still idles pretty nice at 850RPM.

 

[Pauly1119]

I have a 383 Stroker. Brand new block. Great power. All forged internals. Has a total of 3k miles now on the build. I love this motor in my 1996 Silverado, truck looks stock until I start it up.