crossfire mods.

retired guy with time on his hands. a lot of this is theoretical. I know there's much smarter people out there then me, but this is what I've learned and encourage others to correct or add to this.
want to write this stuff down before I move on to next project. maybe someone else wouldn't have to spend as much time researching all this stuff. I do enjoy learning.

first thing is a narrow band O2 sensor are always trying for 14.7 to 1.
this is where the benefits of a wide band O2 sensor and programable ECM come into play to tune in more HP.
there must be a way to trick the stock ecm to run richer. I'm guessing crossfire is not reaching hp potencial because of lean afr.

numbers aren't necessarily actual, because they vary. stock ecm is for best fuel efficiency and not most HP.
numbers are for comparison. using these numbers, because of lean condition from stock narrow band o2 senser and non-programable ecm.
exhaust acts like 100cfm per tube(it's more like 128cfm). maybe the tubes could be cut back at the inside of collector and rewelded where GM squished them. never tried. I got headers.
intake runners 140cfm per runner (more like 148-160). I believe the lean condition is a cause of lost HP. Using lower numbers to compensate for lean condition.
100/140=.71 140x.26x8=291hp 291x.71=206hp.
in theory, with a programable ecm and high flow cat and mufflers, 265hp could be possible.128/150=.85 150x.26x8=312 312x.85=265hp
with stock camshaft and heads the max cfm is 135cfm exhaust and 182cfm for intake
header and free flowing exhaust, programable ecm. 135/150=.90 150x.26x8=312 312x.90=280
mildly ported intake 192cfm, stock heads and cam flows 182cfm.
135/182=.74 182x.26x8=378 378x.74=279. so, no gain. of course, a cam change with more exhaust duration would produce more HP.
At this point the best mods are free flowing exhaust and tunable ecm 280hp. also 14psi fuel pressure. will need 3 wire O2 sensor. don't know if 14 psi needs external fuel regulator.

to go further, need to port heads or get aftermarket. Porting exhaust port on stock head would help. maybe get 150-160cfm exhaust. could get around 300hp. IMO aftermarket are the way to go.
can easily get heads that flow at least 240/180 at .500.
with mildly ported stock intake manifold that flows 192cfm. 180/192=.93 192x.26x8=399 399x.93=371hp. this is theory and depends on cam used. if renegaded intake manifold comes back and the use of bigger heads. hp will go up imo.

this is going to need more fuel. Dynamic EFI has formula to calculate this. stock injectors 67#/68# @11/12 psi. the other choice is 81#@ 13psi. will also need external fuel regulator with vacuum outlet. example, with vacuum to regulator, at idle, psi would be 10psi and at wot be 20psi.also will most likely need to parallel plumb fuel lines.
most likely need larger TB's also.

for me the easiest HP gain is programable ecm, followed by headers and free flowing exhaust.

Mike

 

20 years ago I put A LOT of time and money into building a Crossfire 383 for my 84. The biggest improvement by far was swapping in a 7747 ECU. This allowed me to change the tune. But in today's day in age that would be a mistake. There are so many options now for aftermarket ECU's that would work much better.

I tried several things to get more power with a CFI. I had an X-Ram intake with bored out throttle bodies. I had installed larger GM "police" Caprice injectors. Ported the stock heads with 2.02/1.60 valves and then swapped those out for Edelbrock Performer heads. I also had a Comp Cams hydraulic roller kit. I had a D.U.I. distributor and an MSD box. This was all on a short block with a Summit 383 crank kit with forged flat top pistons with 10:1 compression. In the end I was never happy with the power. I even put a 125 shot of nitrous on it. It just never ran how I wanted it to. No matter what I did the CFI just didn't meet my requirements. So after a failed carb swap, I swapped in an LS and am now very happy.

 

My advice would be to swap out the whole engine for a low mileage vortec 350 and adapt that to a truck style tbi unit, bypassing the cross ram intake and the twin tbi units.

 

LS engines are nice, for sure.

 

4bolt block would be nice.

 

I always viewed it as how much do I want to financially hurt myself for this... So far I'm having fun but I agree... gets to a point where a whole aftermarket EFI system is very attractive.

 

I like this idea. I would like to add a twist to it.

So if you were to go to your local U Pick It or U Pull & Pay or LKQ whatever your local self service salvage yard is. And look for a 1999-2002 Chevy Express 3/4 or 1 ton cargo van. Look at the VIN number and find one of these that has an "R" as the 8th digit. (This won't be hard). This is a 4 bolt 350 with Vortec heads. If a guy were to pull the engine and the transmission. The trans is the later style 4L80e with the dual bell housing bolt pattern. These routinely sell on ebay and Facebook marketplace for around $1000+shipping with the converter. If you needed to ship it you can do that through your local Fastenal store for around $200. So that extra cash would go a long way in paying for a Holley Sniper EFI system for Vortec heads. Or at least pay for the engine. This block will already have a roller lifter cam so you don't have to use the very expensive conversion lifters. But a guy could build a very reliable 400 hp 350 that would cost very little.

The nice thing about pulling parts like this from vans is they are almost always in the salvage yard because the frame is rotten. Every time I pull an engine or a trans from one I see fist sized holes in the frame. So I know it ran and drove all the way to the shop that failed its last inspection.

 

aftermarket was the first thing I looked at. would have been easier. Edelbrock sequential injection, with adapted crossfire air cleaner and housing. can still do that. I enjoy experimenting, learning and researching.
didn't your crossfire make around 400hp at the crank. that's a success in my book. mines not going to do that. smaller heads and cam on mine. I'm going to buy a standalone afr gauge , so I can see what's going on while I'm driving.

 

Yeah like 350 to the tires or so on a 350. It is plenty fun and does power wise, what that build should do but if the renegade flowed better it should really have made more like 400 tire. It is good but should be better but that is what is holding it back.

 

Yeah, too bad about the core shift.