Topic: Question about my setup

[Vgm]

I was unsure where to put this so if it is in the wrong category I apologize. I have a 78 trans am with a 70 455 yh code with a Borg warner SuperT 1-10 with what I was told is 4.11 gears. I don't really know much about the engine, I tried looking online but kept getting the same answers that its has 360hp, I can't even find if this is one of those HO engines etc. Anyone have any other info on that engine? I believe it has a cam but I am unsure of the specs, it I also have 6x heads. Can anyone give me a general idea for hp or torque or is anyone else running a similar setup. I'm really just looking for any information on anything so everything would be greatly appreciated. Thank you.

[Rick]

If you truly have 6X heads, it's not an HO engine.  To approximate the base HP for an engine like that you would need to check the factory ratings for a 75-76 455 4 barrel engine.  The original engine code doesn't mean much as that's only the short block -- the power is determined by the top side stuff and the displacement, and a 455 is a 455 if you know what I mean.

If perchance it has 6X-4 heads then it will be running a potentially higher compression ratio.  That might or might not make more HP depending on the fuel you feed it.  The 93 octane pump gas readily available today doesn't like CRs higher than 9.5:1 or so with heads like yours.  What is the secondary stamping on your heads?

Are you sure about the 4.11:1 rear gear?  How many RPMs are you turning when you are going 60 MPH and what is the tire size you have on the back?

[Vgm]

The engine casting code is 9799140, which I pulled off the back of the engine block passenger side, which correlated to the 1970 455 but I get what you mean a 455 being a 455.

The heads code stamped on the side is 6x where can I find the secondary stamping? (I'll check tomorrow and get back to you)

And no I'm not sure on the gear ratio thats what the guy told me but it wouldn't be the first thing that he had the wrong information on. The tires on the back are 450mm wide and 15 in diameter. At 60 mph at approximately 3000 possibly a bit more.

[Vgm]

The secondary stamping is an 8 it looks like.

[Rick]

Sounds like you got the secondary head stamping, but here's a pic just to be sure:



What are the numbers on the tires on the rear (like P255/60/R15, etc.)?  I appreciate the width and the diameter of the wheel, but knowing the tire size tells how many revolutions per mile it makes -- the width doesn't tell you that.  Once we know how many revs per mile it make it will be easy to get a close approximation of the actual gear set.  From the sounds of things, though, I doubt you have a 4.11:1 back there.

[Vgm]

Okay I gotta recheck the secondary stamping the 8 i found was on in the place the GM 4 is in the picture so I'll recheck that tomorrow.

My rear tires are P450/60/R15.

Thanks you very much for helping me this is my first manual, carburetor, etc so I'm learning it piece by piece.   

[hada76]

not sure ive heard that size before...some kind of slick?

[Vgm]

Wow holy crap that was a bad typo, guess thats what I get for not reading over what I typed, Thanks for picking that  out for me.

My rears are P245/60R15

[Rick]

According to BF Goodrich, a P245/60R15 tire makes 782 revolutions in 1 mile.  At 60 MPH you will cover 1 mile in 1 minute, so that means that your axles are turning at 782 RPM.  If your tach and speedometer are close to accurate and you are turning 3000 RPM at the engine at 60 MPH, then your axle ratio is 3.83:1 (ratio of 3000/782).  That's a direct ratio because unless you have an OD unit the transmission top gear is 1:1.  If you had a 4.11:1 rear gear you'd be making 3214 RPM.  A 3.73:1 rear gear would give you 2954 RPM at the engine.

Since the speedometer is driven off the transmission, and that obviously runs the rear gear, it's kind of important to this calcuation that you know the actual speed of the car.  You can double-check that with a GPS unit or timing the car through a know-distance mile.

[Vgm]

Okay thank you very much, I'll make sure the speedo is correct like you said and see.

As per my heads it took a picture of where the second marking is and got this

so I guess I have 6x-4 heads even though it says GM8 where in your picture that has a secondary stamping of 4 it says GM 4?

I've been running 93 pump gas should I be running something else or is my compression less than 9.5:1 like you said?