I have hot rodding questions about a Pontiac 455 and 400.
- Thread starter SteveSS
- Start date
snakeyes
Well-Known Member
rumblefish360
Well-Known Member
SteveSS, the Poncho 400 is a 4.121 bore X 3.75 stroke & a 3.00 main.
Valve sizes are IIRC, 2.11 / 1.66.
Since there is a rebuild going on, an increase in compression is the first thing to do and @ 7500feet, I myself would look at a min. Of a 10-1 ratio.
Then add a cam of choice. The larger the cam, the lower the dynamic compression ratio. That equals lower power.
The same basic principles apply to this engine as any other. Re-use of the factory 4bbl. intake and carb can yield good results. Headers are of course a excellent plus.
Valve sizes are IIRC, 2.11 / 1.66.
Since there is a rebuild going on, an increase in compression is the first thing to do and @ 7500feet, I myself would look at a min. Of a 10-1 ratio.
Then add a cam of choice. The larger the cam, the lower the dynamic compression ratio. That equals lower power.
The same basic principles apply to this engine as any other. Re-use of the factory 4bbl. intake and carb can yield good results. Headers are of course a excellent plus.
lewtot184
Well-Known Member
see if you can find the car craft magazine Pontiac build article, probably done in 2001. basic torque monster.
YY1
Well-Known Member
I always thought poncho motors were pretty torquey.
At least the ones in my family, and the ones I was exposed to in the 70 were.
My grandpa had a 67 400 bonneville, and my uncle and then my mom had a 59 389 bonneville. One of my friends had a 77 400 trans am and another had a 69 grand prix with a 65 421 in it.
At least the ones in my family, and the ones I was exposed to in the 70 were.
My grandpa had a 67 400 bonneville, and my uncle and then my mom had a 59 389 bonneville. One of my friends had a 77 400 trans am and another had a 69 grand prix with a 65 421 in it.
Sweet5ltr
Well-Known Member
He's losing 80-90 HP simply due to elevation over a car at sea level. Any engine that has poor flowing heads, small-duration cam, with big cubes is going to be a torque monster. My father had a 74' 455 SD trans-am BTW! Just looked at the value on those cars this morning, I had no idea 
.
It's difficult to say, the only difference he may feel would be with a gear and converter change. Maybe an FTI/Dynamic/Coan/(reputable branded) 3,000-3,500 10-11" converter and 3.73-4.10 gearing; when the converter flashes he'll be right at the peak and have even more torque multiplication with gearing. To make any serious suggestions, to simply upgrade just the 400 engine enough to 'feel a drastic difference' would probably be a 461-stroker kit and good heads. That will cost a bundle over an LS based swap, but it will still be a 'poncho motor' if that makes a difference.
To me, I would LS swap anything that was remotely GM (or even FORD) related; that's hotrodding' at its core.
.It's difficult to say, the only difference he may feel would be with a gear and converter change. Maybe an FTI/Dynamic/Coan/(reputable branded) 3,000-3,500 10-11" converter and 3.73-4.10 gearing; when the converter flashes he'll be right at the peak and have even more torque multiplication with gearing. To make any serious suggestions, to simply upgrade just the 400 engine enough to 'feel a drastic difference' would probably be a 461-stroker kit and good heads. That will cost a bundle over an LS based swap, but it will still be a 'poncho motor' if that makes a difference.
To me, I would LS swap anything that was remotely GM (or even FORD) related; that's hotrodding' at its core.
Last edited:
kowalski
Well-Known Member
http://forums.maxperformanceinc.com/forums/
is also a good source.
Kinda dead, but worth searching the archives is: Classical Pontiac
is also a good source.
Kinda dead, but worth searching the archives is: Classical Pontiac
64 Post
Well-Known Member
Building a N/A engine will likely get very expensive. At that altitude, you'll have to shoot for a static CR of 13.0:1, subtract 30% for alt. loss, then fine tune cam specs for around 175/180 cylinder pressure. And it still won't run like it should. Plus, you've locked yourself into a combo that will kill you if you take it to sea level.
Do the ls swap and put a blower on it later. It'll be cheaper in the long run.
Do the ls swap and put a blower on it later. It'll be cheaper in the long run.
YY1
Well-Known Member
...or you could put a blower or turbo on it now to make up for the compression, and then take it off (or leave it on) later if you move.
I vote for keeping a pontiac with it's pontiac power.
I vote for keeping a pontiac with it's pontiac power.
Sweet5ltr
Well-Known Member
"what's the easiest dirt cheap way to make lots of torque?"
"In college.. Squeezing every dime"
"Hello chain auto store, do you have the budget-minded roots blower kits in stock for a mid-70's Pontiac 400?"
wyrmrider
Well-Known Member
My two cents
don't forget the hidden oil galley plug
Build for Torque
use the 1.65 rockers in the intakes (only) no need for roller rockers
use the stock 4bbl carb and manifold unless you go the blown route - which is the obvious answer to the altitude problem- you don't note even have to change the lower end KISS all the number Pontiac cams are way obsolete for what you are doing the heads make no difference unless you are using to change compression without doing the rotating assembly
If doing the rotating assembly GO BIG (but do not bore any more than absolutely necessary) stock rods with ARP bolts are fine for what your are doing
Buicks, Olds and Cads are not cheap to build either
I have a 6.0 in my motorhome- way to go unblown- sweet motor I would not trade it for a 500 Pontiac, maybe for a late FI BBC but actually it has plenty of power for my 24 ' I also have a 32' Winnebago with a carb 454- what a dog and what to do...
don't forget the hidden oil galley plug
Build for Torque
use the 1.65 rockers in the intakes (only) no need for roller rockers
use the stock 4bbl carb and manifold unless you go the blown route - which is the obvious answer to the altitude problem- you don't note even have to change the lower end KISS all the number Pontiac cams are way obsolete for what you are doing the heads make no difference unless you are using to change compression without doing the rotating assembly
If doing the rotating assembly GO BIG (but do not bore any more than absolutely necessary) stock rods with ARP bolts are fine for what your are doing
Buicks, Olds and Cads are not cheap to build either
I have a 6.0 in my motorhome- way to go unblown- sweet motor I would not trade it for a 500 Pontiac, maybe for a late FI BBC but actually it has plenty of power for my 24 ' I also have a 32' Winnebago with a carb 454- what a dog and what to do...
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