97 454 L29 build plans

[Piratehunter]

I'm getting ready to rebuild this 454/7.4L L29 motor and want to run the mods past you guys for recommendations. I've been researching all the other build plans and results already to get me started.

1997 chevy K2500 7.4 vortec 3/4 ton long bed truck, NV4500 5spd manual trans, mainly used for errands and towing 7-9k# trailers

454/7.4 Vortec stock MPFI

5.13 gears, 32" tall tires

Live in Colorado at 7000 foot, most towing is between 7-10K feet, with long grades between

What I'm wanting to solve is the power drop above 3500 rpms. looking to have some power band above the stock cam.



Current gearing RPMs and Speedo:

4 gear 1:1

45 mph = 2500 rpms

55 mph = 3000 rpms



5th gear OD

62 mph = 2500 rpms

70 mph = 2800 rpms

74 mph = 3000 rpms



This truck seems to run out of torque after 3800 rpms, but I don't push it there often. Pulling a trailer in 5th gear on level ground seems to run out of power at 65 mph, downshift to 4th and it is still bogged down, would like more power at 65-70 mph and the higher side of the 2500-3500 rpms.


The plan for the rebuild is keeping the compression stock, might raise slightly with head/block resurface, and thin gasket

Rebuild the stock L29 heads for higher lift cam; valve springs, elimate rotators, valve seals, rocker studs for adjustment, 3/8 pushrods,

I'll install shorty headers, stock duals to a single magnaflow 50, remove the egr and cats.

upgrade to 30# injectors from 5 O

Blackbear tune on my ECM.

Cam selection is where I'd like some options. Comp tech suggested the XR264HR 212/218 @.050 on 113, saw that PowerNation used this in a peanut head upgrade and only gained 15# torque over stock and the power curve ramped fast and fell off at 3800.
saw the video of Richard putting the XR276HR in an L29 head motor and got to 515# torque @3600 with a wider torque band.

thanks

 

[Supercharged111]

I'm not sure that the cam is to blame for the way the power drops off. I stuck a 212/218 into mine. I think it sits on a 114 or so LSA, advanced 2 degrees. .518/.527 lift, pretty much drove line stock. I think the blower helps it to pull cleaner toward 4500. Those headers and tune are gonna make it pull harder everywhere. Stock is 208/208 .480"/.480" and I think 16 LSA/120 ICL or thereabouts. The longer legs are nice when you have a load hooked up and it forces a downshift.

 

[Schurkey]

You live at 7000 ft altitude. Why would you NOT jack-up the compression ratio?

The only valid reasons I can think of is that you pull trailers at low altitude sometimes; or you plan to supercharge in the future.

The L29 cylinder heads are inherently RPM limited; they're more related to the crappy swirl-port small block heads than the Vortec small-block heads. Bigass ski-jump cast into the intake port.

Removing EGR and cats in Lib_Tard Colorado is a risky move. I project increased scrutiny on emissions and emissions equipment as time goes on. "I" would want EGR; although it might be fairly moot when pulling a trailer at altitude.

 

[Piratehunter]

You live at 7000 ft altitude. Why would you NOT jack-up the compression ratio?

The only valid reasons I can think of is that you pull trailers at low altitude sometimes; or you plan to supercharge in the future.

The L29 cylinder heads are inherently RPM limited; they're more related to the crappy swirl-port small block heads than the Vortec small-block heads. Bigass ski-jump cast into the intake port.

Removing EGR and cats in Lib_Tard Colorado is a risky move. I project increased scrutiny on emissions and emissions equipment as time goes on. "I" would want EGR; although it might be fairly moot when pulling a trailer at altitude.

well I'm hoping to just re-ring it and polish the crank, it has low miles. keeping the existing rotating assembly. gaining a little compression with block and head milling, maybe .5, though that is not much. if I have replace the bottom end, it will be a stroker kit build and will have a differnet attitude and compression. by the time the libtards here get emissions passed again, i'll qualify for a collector plate.

 

[Papablunt]

I suspect there's more going on with the XR264 and XR274 comparison. Those cams are very similar, with the XR274 being only marginally more aggressive. I compared these two cams for months, and can say that the torque curve is shifted by ~250 RPMs at best, so you may want to look into something more aggressive than these.

I have the XR264 and have been happy, but I strictly wanted low end torque. I live in CO too and have no problems going up and down 70 with a load.

 

[yevgenievich]

I would go with most used rpm range for a cam choice. I have different heads ordered, but cam spec is just a very mild high lift cam. Uses stock stall and peaks around 5500rpm. Lift up to max usable flow for the heads

 

[L31MaxExpress]

Holdener used a dual plane intake and a carb to get to his power numbers. The stock long runner and restrictive truck intake will fall off much earlier.

 

[yevgenievich]

Holdener used a dual plane intake and a carb to get to his power numbers. The stock long runner and restrictive truck intake will fall off much earlier.

I had some other plans for the intake. Either get the edelbrock piece or heavily modify existing. Still trying to find enough relevant information on stock modified intake once boost is applied

 

[SS Performance]

Which intake are you thinking about. I was thinking about a 4 barrel dual plain. I wasn't sure what to do about the AC lines.

 

[Carlaisle]

Everything about that engine is designed for low RPM torque. A supercharger or turbo would be the easiest and probably most cost effective way to increase your power and then you wouldn't need to bother about the RPM. Rather than investing much money into refreshing or improving the existing heads I would be more inclined to replace them. I think the 1997 engine already has 3/8" pushrods. A different intake will definitely free up higher RPMs, but you'll have to change a lot of other things if you go that route.