454 tbi mods?

[Xenon]

I'm sure this has been covered but I can't seem to turn up anything in a search.

Just got a 1995 GMC suburban 2500 with the 454 a while back. Just got it cleaned up and started driving it some the other day. Nice smooth running truck. But the reports are true... I am somewhat underwhelmed by the power. It's certainly quicker than a 350 but it's not on par with some of the Vortec 454s I've ridden in at all.

Seems ms there's not much in the way of mods aside from a rebuild with cam/higher compression/etc.

just wondered if the gurus here had any tips.

Thanks guys

[stegey]

i'm No guru , keep it simple bigger throttle plates , k&n filter , throttle body spacer helped my small block tbi's a lot with power and mpg, open up the exaust ? let it suck and blow better . going to be pretty hard for it to keep up with the vortecs but , i'm sure it can be improved.

[dave w]

There are programming options for the PROM chip. I usually adjust both Power Enrichment, Power Enrichment delay along with Acceleration Enrichment in the PROM chip programming, to help throttle response. A few degrees of advance in the correct places in PROM chip timing tables will help also. A good flowing exhaust with a cold air intake (depending on where you live) will help performance also.

dave w

[billygraves]

In tuning a Big Block, there is extra fuel to cool the cat converter in the calibration. If no cats, I'd lean it out but only if I was using an Air Fuel Ratio set up.

Allowing the engine to breath is best. In N.D. you may want to keep the hot air tube in the cold weather. If it's aboe 45, plug the vac line to the Thermac door to keep the hot air OFF. Headers with dual exhaust helps. If ya can't do the headers, at least try dual 2.5". The Air inlet if it's in the fender, route to the front core support. Snow does get in though.

The Heads and intake are small or a peanut port. A bit larger ovals would help, but at slow engine speeds, the intake runners will get wet and rain. (The larger port at lo RPM tend to run wetter because the fuel falls out of suspension.)

[1project2many]

If it's aboe 45, plug the vac line to the Thermac door to keep the hot air OFF.

I seem to remember that TBI trucks used only thermostatic control for Thermac but maybe some years did, some didn't? ND will be similar to MT in that icing will be a problem, esp. driving on highway and keeping warm air is critical to prevent this. Switching to non-heated intake can make more power but driveability can suffer without tuning to make up for the wider range of typical operating variabes. I've found nice gains for stock or mild trucks using low end towing type cams. Overall power may not increase but you'll have more power and torque in the portion of the power band used most often. '95 block might be provisioned for factory roller cam. For the power hungry it's worth knowing that Whipple once offered (and may still offer) a supercharger kit for TBI 7.4 engines.

[Fast355]

The 454 SS trucks ran dual exhaust setups and a little different spark map and were up 20 HP and 20 TQ over any other 454. Add a small cam, a decent exhaust, and a set of headers and the power will come up noticeably, along with efficiency. SMALL is the key word for the cam here. If you go too big you will bleed off most of the cylinder pressure you get from the 7.9:1 compression ratio and the cam will have too much duration to work with the beyond tiny peanut ports.

[1BadAction]

There is no vacuum line on a later TBI hot air tube. They are fully controlled by heat. Every time I have fooled with disconnecting the hot air from the air cleaner, the truck runs less predictably and gains nothing in power. This may be different with an air temp sensor but I wouldn't fool with it, the evaporation of fuel in the intake pulls a ton of heat out of the air.

There are always freaks toward the end of a production run, but generally, there are no roller provisions in a gen V (1995) BBC.

Without going into the engine you're limited. The best seat of the pants mod will be a good tune followed up by exhaust. DO NOT just go buy a set of used big block heads. The GenV is an oddball and you need to be careful bolting earlier heads on it, some of them will leak coolant, no matter if you use the "conversion" gasket or not. I wouldn't risk it, myself, but mine is a daily driver...

[Fast355]

There is no vacuum line on a later TBI hot air tube. They are fully controlled by heat. Every time I have fooled with disconnecting the hot air from the air cleaner, the truck runs less predictably and gains nothing in power. This may be different with an air temp sensor but I wouldn't fool with it, the evaporation of fuel in the intake pulls a ton of heat out of the air.


Thats what I thought as well. I knew my later model 454 van air cleaner I had on my 350 did not have a vacuum line, all thermal. The OEM setup works very well after your remove the baffle blocking the entrance. W

[Xenon]

Good info guys. Thanks

[kevinvinv]

I am just finishing up a Gen V BBC project. Replaced the 350 in my 94 Blazer with the BB. I kept the stock peanut heads b/c they seemed to be what the doctor ordered if you want torque. I toyed around with putting vortec heads on it but too many complications. My block was not ready for roller cam and to retrofit it was way too much dough.

I did put roller rockers on it but hated the extra noise... so took them back off.

I used a crane RV type cam (133902) and SpeedPro domed hyper's (H693CP) to get the CR close to 9.5:1. Other than that, things are mostly stock on the motor. (BTW- I first built it using KB Pistons...which was a horrible experience... I would never use them again myself- but I do have some lightly used ones for sale now! :) ).

What I've been told is that the stock 454 injection system won't support much more than 300HP - so what one guy is advising is for me to go back to 350 injectors to get more flow... why would smaller injectors give more flow? B/C 94 (and 95?) BBC TBI rigs up the fuel pressure quite a bit from what the 350 was- I think the 94/95's were at like 35 PSI FP. Anyway- Going to a lower pressure injector with higher line pressure will yield more lbs/hr overall and supposedly I'll get more WOT HP.... but really all I wanted was pulling power anyway... so not sure if all that is worth it.

If you want to ever adjust your FP up a bit- there are still available factory GM adjustable TBI regulators which are cheap and pretty cool. They come off of marine applications.

One last thing as far as the cold air intake is concerned. There were a couple years where GM used a larger snout air cleaner on the BBC's and a correspondingly larger diameter flexible duct and "resonator". If your's is a 95- you most likely have the smaller setup... I think the snout is probably 6" across. To find the better setup you have to look for a 88-91 BBC air cleaner. If you want more info on this... I think I have some info and P/N's etc.

[Randy 79]

I did a 92 454 TBI into my 79 GMC with a few of the mods listed and it pulls pretty good, better than I thought a TBI engine would. Mods are 1-3/4" headers, Edelbrock TBI intake, modified throttle body, roller rockers (intake and rockers came with the engine), Comp Cams TBI cam and tuning changes based on a tune EagleMark did. Definitely has good torque with decent hp. Pulls my 28ft enclosed trailer with no problems, getting a little over 8 mpg doing it. Not bad considering I don't have overdrive, turning 2800-3000 rpms on the highway.

[1BadAction]

^ Every time I hear someone quote their highway RPM in a turbo 400 truck I am SOOO thankful for my 80E. My cruise speed at 2800rpm is 95mph LOL! Lockup and OD rule! :rockon:

[Fast355]

^ Every time I hear someone quote their highway RPM in a turbo 400 truck I am SOOO thankful for my 80E. My cruise speed at 2800rpm is 95mph LOL! Lockup and OD rule! :rockon:

^^^^

Same here my cruise speed at 3,400 rpm is 110 MPH.

[Randy 79]

^ Every time I hear someone quote their highway RPM in a turbo 400 truck I am SOOO thankful for my 80E. My cruise speed at 2800rpm is 95mph LOL! Lockup and OD rule! :rockon:

It could be worse, my truck came with 4.56 gears from the factory, it now has 3.73s.