Hotrodder

Today I have a 210 hp factory roller Block L05 first gen Chevy small Block 350 V8 from a '93 Buick Roadmaster.
Stock engine, but rebuilt from TBI to a Holley 670 cfm double pumper carb.

Mileage is app 24 miles pr gallon, probalby mainly because of a 6 speed manual trans with 0,5 overdrive on 6th gear and a very helpful wide band A/F gauge to optimize the carb adjustment.

The plan is this:
-Change to Vortec heads rebuilt for higher lift.

- GM LT4 cam:
Intake Duration at 050 inch Lift:218
Exhaust Duration at 050 inch Lift:228
Advertised Intake Duration:279
Advertised Exhaust Duration:287
Intake Valve Lift:0.492 in.
Exhaust Valve Lift:0.492 in.
Lobe Separation (degrees):112

1.6 ratio full roller rocker arms.


What will happen to the gas mileage after a modification like this?

86LG4Bird

iTrader: (1)

You'll lose very little. less than 2 mpg, probably only 1.
Help yourself by doing this: degree the cam at 106 ICL rather than the "drop-in" position of 109 ICL. You'll help the mileage AND prevent it from being a dog at the low rpm's. Very important if you want to utilize 6th gear with the Hotcam installed.

Get the compression to at least 10:1 via .015" shim gasket and milling the heads.

What's your rearend gearing?

Hotrodder

Rear end gearing is 4.09:1

Fast355

iTrader: (2)

I recently tuned a Lunati Hotcam in a coworkers 1998 Tahoe. I talked him into camming the engine while he was rebuilding it and it has a Lunati BareBones 218/228 cam I bought a while back new from Lunati for $70. The Lunati cam is slightly bigger and drops in on a 108°ICL. The engine was a stock rebuild other than a .030" overbore, LS6 springs and Comp 787 retainers. We made sure the machine shop that built the shortblock kept 1.56" compression height pistons in it although he did use a Felpro 0.38" compressed head gasket. The truck has a set of shorty headers, 2.5" catless midpipe, and a Volant CAI. The truck also has 5.13 gears and a 2,200 stall. It also has a 6" suspension lift, 3" body lift and 35" tall mud terrain tires. I have never noticed a big drop-off in low-end torque with a Hotcam even in a stock Vortec. Once you get rid of the obnoxious tiny stock cam the Vortec emgines like running much higher timing values which keeps the low-end power and adds to throttle response. This truck absolutely JUMPS with a touch of the throttle and can easily break those 35s loose. With the stock truck intake manifold it pulls to 5,500 rpm shift points with the MAF reading still rising at the shift point. Overall with the fresh engine and added power in normal driving his fuel economy stayed about the same. Use the go pedal much however and he said the added power makes the gas gauge drop like crazy. I adjusted his speedo for the tire size and gearing and completely remapped the shift points and converter lockup at part-throttle and WOT. At 40% throttle it holds the upshifts out to about 3,500 rpm so it is an aggressive shifting setup but gets great power and performance out of the new cam. I also set the shift points and lockup to keep the engine at or above 1,600 rpm at all points with the throttle cracked open. The only time it is under 1,600 rpm you are off the throttle and coasting. The lightest throttle upshifts happen about 2,200-2,500 rpm and with the looser converter the transmission feels alot like a CVT at light part throttle. The RPMs just kind of sit in the 2,200-2,500 rpm range and the truck accelerates with ease at minimal throttle. Above about 25% and below 75% throttle I have the converter setup to lock around 2,500 rpm in 2nd-4th gear during acceleration. It eliminates the converter slippage, reduces the parasitic losses, gives a few more MPH out of the gear for a given RPM, helps the MPG, and helps keep the 4L60E running cool.

Fast355

iTrader: (2)

I will also say with the 35s/5.13s the shift tables are close to what my brothers 1999 Suburban was with P275/60R15s and 3.73s. The overall gear ratios are very close. The Tahoe turns 2,400 pm @ 70 and the Suburban turned 2,200 rpm. The Suburban had a stock LT1 F-car cam with 1.6:1 rockers, Volant CAI, long tube headers and 2.25" dual exhaust with a H-pipe. The Tahoe makes more HP but being a lifted 4x4 on heavy wheels and tires is heavier and catches more wind. The Suburban had a S10 converter that stalled 2,800 rpm but was still very daily driving friendly. In a drag race type of run the Suburban was noticeably quicker but the Tahoe rolls out nicely for what it is and sounds great. I have not heard what the MPG on the Tahoe is but the Suburban would pull 22 mpg on a long road trip with the cruise set at 75 mph. I am sure the 2008 Tahoe electric fans helped the MPG on it some on the open road.