The Stovebolt Site Forums The Shop Area The HiPo Shop Holley Sniper install on a 235

When I said, "determine your shift points", I wasn't thinking of creating new internal transmission ratios. I should have said "see or visualize your shift points". The graph shows three slopes. The more vertical the slope the less time you have to do your shifting in the power band. At least this is how I see it. Hopefully someone will speak up if I'm in the ditch.

The graph can be used to help visualize, in a very rough way, the transmission you have now and the transmission you thinking about going to. Based on past conversations we have 3 speed, 3 speed O/D, 4 speed (SM420), 4 speed Hydramatic, conversions with 3 and 4 speed Saginaw transmissions, Tremec versions, T-5 and others. I've heard it said that you don't need a T5. A 4 speed Saginaw with a 3:11 first gear and a ?? rear axle ratio with ?? tire size will give you the same results.

To continue on, we figured out the cruising speed but what about launching this heavy metal truck to get it moving? As a general rule you want the launching gear ratio times the rear axle ratio to be around 9. A plain 3 speed with first gear of 2.85 times 2.70 (gas saving Camaro rear axle) = 7.7. You have to ride the clutch to get the truck to move. Ask me how I know. A 4 speed Saginaw with first gear of 3.50 times 4.11 (generic truck axle) = 14.4. Jack rabbit starts. A few dragstrip pulls then failure.

Looking back at 52Carl's setup. First gear is a granny so it is given that you launch in second gear of 2.37 (I am assuming this is the correct ratio for his transmission) times 4.64 = 11. That is on the stout side. He probably gives it light pedal to get it moving "pulling stumps down the road".

That stout first gear with that 4.64 rear end gears comes in handy when traffic is at a crawl. Leave it in first and snail along. It rolls right along without my foot on the gas. This setup would be perfect for teaching a newby how to drive a stick. It is hard to stall it out when upshifting. I will say again that going from 28" to 30.5 tires made 1st gear much more useful to start out in.

What is the ratio of 1st gear in your transmission? Taller tires could hurt you in first gear if your 1st gear ratio is not conducive to the 3.38 rear end you are running.

52Carl,

The Shop Manual lists first gear at 2.94 to 1.

The change in engine speed will of course vary with axle ratio and tire diameter, but a Muncie 2.20:1 and 2.52:1 (both available in most GM muscle cars) will have very different RPM recovery on the 3-4 shift with the same axle + tire (1-2, 2-3 shifts remain constant).

With that 1st gear ratio and a 3.38 axle ratio and 28 inch tires I am guessing that doing burnouts in the parking lot to impress the chicks isn't happening.
Those same chicks will be even less impressed if you change over to 30.5" tires when you burn your clutch up from milking it, trying to get the truck rolling without stalling.
It all boils down to the chicks. That's why we do all of these mods isn't it?

I’ve taken off from a dead stop, on flat ground in 2nd gear with the 338 gear set and my 27” tires. I didn’t do it intentionally, the chick I was trying to impress (my wife of 40 years) was critiquing my driving skills at the time and I got distracted. She wasn’t impressed but it worked out.

If I can do that, I’m pretty sure I should be able to go up an inch or two in tire diameter and still have adequate low gear performance. A 30” tire is probably a bit much.

D B Cooper,

What is the recommended fuel pump for this application? Sorry if i missed it. I went through their inst man on their site also and didnt see it.

Holley sells a whole line of pumps:
https://www.holley.com/products/fue...s_and_filters/fuel_pumps/efi_fuel_pumps/

That said, you can use any generic EFI pump and regulate it to the proper pressure. I ran an Aeromotive inline 255lph pump on my holley system and it worked great.

327amc,

Fibonachu is absolutely correct, Holley has a bunch of pumps to choose from. I went with the Holley 12-305, 255LPH, in tank pump. The TB has a regulator and regulates fuel pressure to 58.5 psi. The inline Earls fuel pressure gauge shows 60 psi at the TB inlet.

Are you thinking of installing an in tank pump or an inline pump?

So far so good with my system, no issues.

Looks super space age on that old stovebolt! I bet it runs good too, and removing the tank from right behind the driver is a big boost for safety in the event of accident or upset, heaven forbid.

This debate rages on in the Cadillac forums too-carbs vs EFI. I've owned and driven multiple '77-79 C body DeVilles, (and older ones too, back to the '60s) and the best running one I ever had was the one with the factory multiport EFI. Even that primitive analog ECU system was, in actual use, better all the time. More power, more snap off the line, better MPG especially in mixed driving.. just better all the time.

Regarding TBI and its rapid replacement of carburetors back in the '80s, well.. that's when I became a mechanic, and can I just take a moment to thank the Gods of Chevrolet for doing away with those frankly AWFUL computerized carburetors?! Look me in the eye and try to tell me those bastardized 2bbl half a Quadrajet things were in any way the equal of the throttle body injection systems which soon replaced them. And gave every engine they put it on, 40hp vs that slap in the face to a real QJ of a carb.

I did it the old way-from points, to advance weights and springs, to metering rods and color coded power valve springs and vacuum pulloffs. Got great service from those, but you know what? My next big engine project on my bus-the almost last carbureted vehicle in my fleet-will allow me to tune it all with my tablet. If they drop the bomb and the EMP takes out all the computers, I'll still know how to make a rig roll.. but until that day, I'm ready for the modern way. Even on a pre-CAD engine design.

Hi - D B , would you have any of the "iceing - up issues" , yet . Just asking, and I like the way you're 'Thinking' .. . . . . keep going, we're all in "learning Mode" .

Thanks , jim

I recently swapped rears in my 1951 and accidentally ended up with a 3.38. I was concerned that I’d be needing to slip the clutch from a takeoff. Can’t really say that there’s much difference there from the 3.90 it replaced. I have 215/85r16 tires. They are 30.5” tall.