The Chevvy 327 was an incredibly popular motor here. The bloke across the road from me had a beautiful HQ Monaro that he did up. The 327 got "ported". They were dirt bike boys and tried to treat it the same as their 2 strokes, they miscalculated and ended up having to rebore the ports in a slightly different position. This meant the ports ended up huge.
Dave reckoned what he'd done was called "tunnel ramming" because of the size of the ports, and the car ended getting named Joe Tunnel. Stainless steel extractors, Tarantula manifold and twin 650 double pumper carbies.
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Poor porting techniques are a surefire way to kill performance on the lower end.
As port velocities decrease, so does the fuel air mix flow.
Sometimes it will even have a detrimental effect on the top end too.
This is what we consider a tunnel ram intake manifold:
This was made by Weiand and will support either the Holley square bores or the Carter AFB units.
They are typically a track only item because of poor streetability at low port velocities.
They do however excel then the volume is increased on the higher reaches of RPM.
The larger box plenum volume reduces low flow signals to the venturies in a carb because of the lag that is present when you introduce a change in throttle plate angles.
Venturies require a fairly healthy negative pressure in order to properly atomize the fuel being introduced to the air.
A recip internal combustion engine operates like a air pump, and changes to the cam timing, the overlap of the openings of the valves that are conducive to higher RPM performance have a detrimental impact on low RPM performance.
Often that is manifested in the lumpy choppy idle you hear in a racing unit, or for that matter on a street based unit that has more camshaft that it actually needs for low to mid range RPM usage where driveability is most important.
Not often do you get to use the upper reaches of RPM on a streetmachine, so that in effect has a drastic effect on low RPM performance at the cost of your top end.
Yeah, but I know, they still sound cool as hell
One morning while taking my nice 283 powered car to work, I spun a rod bearing on her mill.
Easy enough, build a 327 sourced out of different options
At first, as a street based 327, the performance fun on the street, but was lackluster on the track.
The engine made sufficient power at the top end, but it's low end performance suffered. The next step was to install a set of Rhoads variable lift and duration valve lifters. They also served as anti-pump up lifters which would let me rev it higher without the typical valve float associated with a valvetrain that wasn't stout enough to close the valves as fast as the cam lobe moved away. It gave me back some bottom end torque while still providing the 100% lift at top end and without the issues related to higher seat pressure valve springs that are required for higher lift cams in some applications.
Those tend to wipe out cam lobes on flat tappet cams, so their durability on a street engine takes a back seat.
The real answer for that would have been roller lifters that can stand the higher spring pressures and more radical lobe ramps, but at the time, that wasn't where I went with it.
The next bottleneck was the stock stall speed torque converter coupled to the two speed Powerglide transmission.
That ain't going to fly, so we performance built a 3 speed Turbo 350 with full racing clutch plates, removed the dampening wave washers from the clutch packs, installed a full manual valve body and eliminated the vacuum modulator so each shift was at full line pressure.
That made it sturdy enough, but the next bottleneck was the torque converter, B&M provided a 3800 stall speed unit that was included in the upgrade.
The performance level was amazing, but the car was still gear bound thru the third member. After some calculations, I determined that a 4.10:1 final drive ratio would optimize the engine RPM thru the traps.
That put the strip times where I wanted them, but actually killed the fun part of the car on the street
What I ended up with instead of a pleasant Sunday driver, was a finicky, higher revving underpowered wannabe racecar that was uncomfortable to drive on the street.
The final straw that broke the camel's back was the morning it shredded the rear suspension upper crossmember out of the frame on a 1-2 shift.
That usually big block territory, not mouse motor stuff
Oops, frame off time kids.
As I dug into it deeper, I decided that instead of a street driver that did track time, I wanted a dedicated track machine powered by yet another of my favorite engines, the Mark IV 427 cubic inch big block Chevy.
It has a ten point monkey bar interior with plans to shoot two more point forward of her firewall.
Thus far, she weighs in at a svelte 3400 pounds down from her chunky original 4100 pound curb weight.
I might be able to shed a couple more hundred pounds by scrapping her bumpers in trade for carbon fiber ones.
Can you say 900 horsepower with a rear spool?
3200 pounds puts me in Fox body territory so you better leave your Rustangs at home kids, because all you will ever see is my tail lights
I was never really one that played by the rules, so I suppose that when finished, it will see some sketchy but fun street time
