sbc 400 in a 97 suburban

[DRAGGIN95]

you'll need to use a 400 balancer and flexplate/flywheel as has already been stated. for using the vortec PCM control (for the fuel injection/etc), you'll need the crank sensor as you know, but you'll also need to use a vortec distributor to get the correct CMP signal, and with using the vortec distributor, it doesn't have any built in ignition module like some SBC's did, so you'll need to use a vortec ignition module too, but it sounds like you're just planning on swapping most things from your L31 to the 400, so all the external sensors and stuff will be the same.

really the only sensors that are specifically block related will be the CKP (crank) sensor, CMP (cam) sensor (which is part of the vortec distributor), and knock sensor. at least thats all I can think of off hand right now.

EDIT- oh I forgot, the oil pressure sender lives on the block too.

Word, and the knock sensor will screw in to one of the block drain plugs on ther 400.

 

[MOBS]

tune out the knock sensor? since he already will need a tune, might as well tune out all the PITA crap right?

 

[Aloicious]

tune out the knock sensor? why?

 

[Tempted]

Maybe not tune it out but tune out the timing retardation associated with it.

 

[SixSpeedSS]

There are balance plates available to use a 350 flywheel on a 400. I used one many years ago on a 400 with a T5 5speed setup I ran in my Grand Prix. Oddly enough I still have the balance plate. It mounts behind the flexplate or flywheel and uses a longer bolt. It worked great on a motor that I didn't want to invest in balancing.

If I were building a serious effort motor, I would do it properly. Machine shops can add/remove weight on a flywheel if needed. My aluminum flywheel on my 454 has a hunk of mallory metal bolted onto it (welded onto a balance plate that was originally supplied with the aluminum flywheel) to match the balance of my 454 (same internal balance as a 400 SBC). The 454 components were all balanced at the machine shop. I originally had an automatic flexplate and a steel manual trans flywheel balanced with the motor. When I went to the aluminum flywheel, they just matched it to the steel flywheel's balance.

That all said...If you want to put a basically stock 400 with a flat tappet cam and use the Vortec heads & F.I., my guess is it will run worse than a stock Vortec. They hydraulic roller is what really makes the power with the Vortec heads. To retrofit a 400 block with a hydraulic roller cam can be somewhat expensive (~$700-900). You will be further ahead to stroke the 350 Vortec motor. I believe you can go up to 396 cubes on the Vortec shortblock (Lingenfelter and other companies used to sell 396 setups for GMT400 Tahoes and Suburbans back when they were new. 383 is simple, though. Plus you get the benefits of the one piece rear main seal, plastic timing cover with crank sensor, block ready for the hyd roller, etc, etc. SBC's are so plentiful and relatively cheap to build that there are so many options. It really comes down to how much you want to spend.

 

[Aloicious]

Maybe not tune it out but tune out the timing retardation associated with it.

What? that WOULD be tuning it out, that is what it is there for, and it only retards timing when knock is detected. the knock sensor is an VERY useful and important piece for running a modern motor with computer spark control, especially one that is a built for performance, or towing, or any engine that will be used more aggressively. its also a very useful tool for correcting and altering the tuning of the vehicle and to monitor while logging for potential issues. Tuning it out will result in ABSOLUTELY ZERO benefit, a properly running (and properly tuned) vehicle should not be getting ANY spark retard from the knock sensor, and tuning it out on a vehicle that IS getting knock retard from it will result in reduced performance, and may result in damage. if you're getting KR then the problem that is causing the KR needs to be addressed, whether it be something mechanincal, or something in the tune, or otherwise. but just tuning the knock sensor out is NOT what you'd want to do.

 

[MOBS]

Maybe not tune it out but tune out the timing retardation associated with it.

Yeah, that's what I was referring to....not the actual sensing itself, but tune out the automatic timing adjustment....this way you'd still get the alert to the scanner of a potential knock. If you run gears or anything that could throw the fault, then the scanner shows that it's pinging, you could adjust the spark and if it still detects it, then you'll know it's not the spark that's causing it.

 

[Tempted]

What? that WOULD be tuning it out, that is what it is there for, and it only retards timing when knock is detected. the knock sensor is an VERY useful and important piece for running a modern motor with computer spark control, especially one that is a built for performance, or towing, or any engine that will be used more aggressively. its also a very useful tool for correcting and altering the tuning of the vehicle and to monitor while logging for potential issues. Tuning it out will result in ABSOLUTELY ZERO benefit, a properly running (and properly tuned) vehicle should not be getting ANY spark retard from the knock sensor, and tuning it out on a vehicle that IS getting knock retard from it will result in reduced performance, and may result in damage. if you're getting KR then the problem that is causing the KR needs to be addressed, whether it be something mechanincal, or something in the tune, or otherwise. but just tuning the knock sensor out is NOT what you'd want to do.

Yeah but in motors running big cams and heavy springs with solid lifters they pick up too much. Knock sensor is useful, and is a good thing to have but they will get intrusive on occasion. Turning one down will reduce the amount retard and allow the engine to run on the edge of detonation. All it is is an electrical safety nanny, not required for an engine to run properly.

 

[Aloicious]

Yeah but in motors running big cams and heavy springs with solid lifters they pick up too much. Knock sensor is useful, and is a good thing to have but they will get intrusive on occasion. Turning one down will reduce the amount retard and allow the engine to run on the edge of detonation. All it is is an electrical safety nanny, not required for an engine to run properly.

yes, I'm well aware of what a knock sensor is and how it functions. It is an extremely useful safety device, sure it's not required to run an engine properly, but to recommend turning it off to someone who is building an engine for a towing vehicle is crazy. there is a time and place for desensitizing it, but that time and place is VERY rare, and it really isn't for daily drivers, street performance, and ESPECIALLY towing. if you're getting knock to the point that you can hear and feel it, then its way too late, and the damage is done. the knock sensor will typically detect the knock and prevent it before it becomes an issue. the need to run RIGHT at the point of knock is not necessary except for in racing where fractions of a ft/lb will count. in fact most of the time when tuning the spark maps for a DD, the spark is advanced JUST to the point that KR is detected, then backed off a few degrees for safety, then the knock sensor is left on to detect issues that may arrise from a non-controlled environment, like running lower quality fuel, fluctuating IAT temps, fluctuating ECT temps, etc, etc...I'd much rather have the knock sensor there as a failsafe than eliminate it just to squeeze a couple extra hp out.

as far as false KR, it is not as much of an issue with the more modern PCMs, with the primitive blackbox it was more of an issue, that is why they had things like the LT4 knock module which was very slightly desensitized. PCMs like the 411 are much more sophistcated and able to filter out most of the false KR noise, but chronic KR really its not as common as you'd think. the knock sensor picks up only specific frequencies, so just having general 'loudness' from a big cam will not set it off, false knock usually stems from the use of things like the noisy timing gears (vs chains), and other things which may fall into the very narrow and specific frequency that the knock sensor will actually pick up.

if the OP was building a dragster, then yeah, there may be use of desensitizing the knock sensor, but not for the situation he is describing.

 

[Tempted]

I normally leave spark tables alone, just advance the total timing a little. Factory table can't be improved on a stock or mild bolt on motor. It isn't until you get into radical setups that need completely reworked tables. Again, knock sensor is a great thing to have working but when they step in they can get intrusive. I believe the OBD2 systems generally retard timing and increase injector PW to counter it. OBD1 stuff just takes a little timing away. You're 100% right on everything. I was just replying to MOBS question about removing the function. Don't remove it, but it can be tuned for less aggressive step in if one wanted. And detonation doesn't kill motors. Doesn't hurt them much at all, it is the heat that is generally acquainted with detonation that hurts. Now if it the detonation causes the entire charge to erupt then you have problems.