Ahh, didn't realize the chambers were so big. Yes, my understanding is that the motor, as it sits, is 7.9:1.
1983 Big Block Monte Slow Build
- Thread starter Supercharged111
- Start date
Possibly worse than that. When I had the 7.4 rebuilt for my dually (GEN IV w/Peanut Port heads), I opted for flat-tops strictly as an attempt to get the compression over 8.0:1. The PP heads flow decent on the low end but run out of breath past 4k. 781's are better but @ the cost of compression w/o building to their size. My super mild 460ci/PP heads/flat-tappet RV cam/TBI/Th400/4.10's/5500lb truck will light off those 4 rear tires w/o issue so I imagine in a lighter car it would still be plenty of stoplight to stoplight fun. Would need a better parts combo for track type desires.
I'm watching for Vortec heads as a stopgap measure as well. They're less bad and should be able to produce 400+ crank. How big of a cam did you run for 500/500? And yes, this blew the tires off nicely last I checked. Well, at least the one did through 2nd gear.
It was around 300adv/256 @.050 & I recall under .600 lift solid/flat. Its an old school cam. I'm trying to remember the name but struggling @ the moment. I'll see if I can find the card/info.
When we built this particular motor (different motor vs my later dually motor), it was w/the intent of swapping to smaller chamber Alum heads as a future revision. As built, I recall the compression was between 9.0-9.3 & the aluminum head swap would have put me around 9.75:1. My plan was to lose weight/gain power when my checking account allowed but the project moth balled.
Oh wow, that's more cam than I was expecting to still have hp and torque be about equal. These motors really do swallow cams.
To be fair..... I wanted to punch holes in the parking lot of our local gathering spot in the interim 😎.
We tested 3 different cams. This one hit hard & didn't give up torque so it's the one that remained in place. This was a loooooooooooooow budget junkyard special. I'm sure technology updates has something much better now.
I imagine it sounded good and rowdy.
I came out to the car today to get the trans fluid at the appropriate level to see if it would shift out of 1st. Fluid was touching the stick so I dumped a quart in and went for a drive. No change, still no shift and still fluid barely touching the stick. Dumped another quart in and went down the street. Still no shift but now fluid slightly overfull hot and the trans damn sure wasn't hot. I drove it around the block back in MI July 2018 and it was fine. The car did this July 2019 in MI as well and has been that way since. The kicker is if I lay into it good and hard it'll rap out grab a gear and go. Does this sound like a vacuum modulator? I figured that just controlled line pressure based on load? It seems to hit pretty good just dropping the car into gear at an idle too which got me thinking maybe the trans is in WOT mode and, to my knowledge, the vacuum modulator is the TH400's only input for that. No kickdown rod like on the old C6 I had.
I came out to the car today to get the trans fluid at the appropriate level to see if it would shift out of 1st. Fluid was touching the stick so I dumped a quart in and went for a drive. No change, still no shift and still fluid barely touching the stick. Dumped another quart in and went down the street. Still no shift but now fluid slightly overfull hot and the trans damn sure wasn't hot. I drove it around the block back in MI July 2018 and it was fine. The car did this July 2019 in MI as well and has been that way since. The kicker is if I lay into it good and hard it'll rap out grab a gear and go. Does this sound like a vacuum modulator? I figured that just controlled line pressure based on load? It seems to hit pretty good just dropping the car into gear at an idle too which got me thinking maybe the trans is in WOT mode and, to my knowledge, the vacuum modulator is the TH400's only input for that. No kickdown rod like on the old C6 I had.
The solution is a retro roller. Not cheap, but a money saver. The only time I’ve torn down a BBC was because the cam was flat and spread its filings through the motor. It’s such a disappointment. I realize a roller is expensive, but I can’t recommend anyone to put a dime into a hydro FT build.
The proper roller will pickup whatever HP a set of 781’s will gain.
My two cents - Jim
Roller is my intent, they tolerate more lift and more aggressive lobes to get more lift under the curve. Plus the block being a GenVI has the bosses for the lifter spider.
I have a 3 speed again!
I brought a new modulator with me but this one looked a bit too new to be the culprit. The rubber line going to it was cracked on both ends and the screw was buried way deeper in this one than the new one. I backed it out 2 full turns to start with and had to steal a scrap from the line going to the vacuum accumulator to make it whole again. FINALLY I was greeted with a 1-2 and 2-3 shift at putt putt speeds. Good damn deal, now once I'm walking again I can deghettofy this thing enough on my friend's lift to make it safe(ish) to rip on to get the carb tuned and see what it's got. I'm inclined to shove a 150 shot down its throat and head to the strip.
I brought a new modulator with me but this one looked a bit too new to be the culprit. The rubber line going to it was cracked on both ends and the screw was buried way deeper in this one than the new one. I backed it out 2 full turns to start with and had to steal a scrap from the line going to the vacuum accumulator to make it whole again. FINALLY I was greeted with a 1-2 and 2-3 shift at putt putt speeds. Good damn deal, now once I'm walking again I can deghettofy this thing enough on my friend's lift to make it safe(ish) to rip on to get the carb tuned and see what it's got. I'm inclined to shove a 150 shot down its throat and head to the strip.
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