just got the speedblaster heads trouble is they are for flat tappet cam , i'm using 1.6 hughes roller rockers and lifters so have to change the springs and need a cam , . now this cam is not for all out speed more of a daily driver if i want to go fast i'll drop the 426 in it . i want it to get 20-22mpg like my last 340 .
looking for 425 hp at least just like the old 340 . and i don't care what it sounds like .
i want it to get 20-22mpg like my last 340 .
It's unclear to me if you are talking about BOTH roller rockers AND roller lifters; but assuming yes both;
Nat, I know you're a smart man.
but 425hp, hydraulic roller cam, 340 cubes, an automatic, and 20/22 mpg?
Good luck with that.
Next;
3.55 gears with a GV overdrive .
Ok now yur talking 65=2260 with 27s. Nat, I don't think this will ever make 20/22 at 425hp; at least not normally aspirated. This is messed up.
But to help you get close;
you will need to pump the pressure to the max with alloy heads. and
Run about 218@.050 on a 110LSA max!
Forget the 425hp.
With 3.55s and an auto you can't get to the powerpeak in first gear until about 40mph, and not to it in Second, until 70.
But you have a GVod. So to make your 340 feel like it has 425hp, in those two gears, all you gotta do is put some more gear in the back
Since you are gonna want to run a 2800TC (guessing), you might as well gear the car for 65=2800 or a hair less. And with 27s that would take 4.30s for 65=2740 at zero-slip, in overdrive.
But the 4.30s will make your car feel like it grew 4.30/3.55= plus 21% more torque.. At 2800 rpm, that Plus21% torque is the equivalent of about 30 hp, so more than one cam size.
And cruising at 2740, will allow you to run more cam without getting into efficiency problems
Couple that with 185 psi versus 160psi and yur looking at what feels like about another 10% more bottom end over the 218/110
Now that we know how to make the 340 feel like a 440 at below 65 mph, you can start whittling it down, to get the best mpg it can, whatever the number might be. And let the horsepower be what it will be.
> yur gonna need the high cylinder pressure, and that points to alloy heads. It seems like only YR can run 170psi with iron heads. I'm NOT dissing YR. He seems to know how to do it; I cannot. But I can run 185psi in a 3.58 stroker,with alloys all day long, and on 87E10, at that.
> yur gonna need to get the stall up some
> and you'll need more than 3.55s with a 2.45 lowgear trans.
> that picks the cam for you, in the range of 218 to 235, BUT, at the upper end (235), you are gonna need to adjust the LSA to compensate for the long ramps on the hydraulic roller cam, so you don't kill the pressure at cruising speed. To make the 425hp you will need to spin that 340 so that points to the 235, but honestly I think that is too far away from your goal of 20/22 mpg. So, in the middle is 226* , which will not get you to 425 no way. Maybe 360hp on a good day. But, a 226 cam will get you to 20/22mpg, just not with 4.30s x .78=3.35 final drive.
So lets back back up the bus a sec..
This combo is screaming for SOLID lifters. The ramps on a Solid-roller are about the fastest ramps out there, allowing you to run about 1.5 cam sizes bigger @.050, (Than a hydraulic roller), without the penalty of lost low-speed pressure.
Ok so 1.5 sizes from 226 is 235ish@ .050 and now yur in the ballpark,powerwise.
With say 39* ramps, you're looking at 274* to zero lash when the cam finally takes up the lash. That will get you an Ica of around 64* and, and with 11.2Scr a pressure of ~187. Now we're talking.
The V/P index is predicted to be 148 so extremely powerful down low. Now we can re-evaluate the stall and gears.
read about V/P here;
V/P Index Calculation
Ok so since the VP is so high, we can bring the stall down, say to 2400 about stock, for a stock 340. And you can even try the 3.55x2.45 starter gear=8.70
The 235* cam will powerpeak at near 5300, and on a 110LSA, you can rev that out to 6000 in first/5800 in second, so your speeds will be 48 in First, 81 in Second.
And 65=2260 at zero-slip/ say up to 2350 @4% slip. Good deal. The 235* cam will be out of reversion by 2200 or sooner, so 2350 is right on.
Now getting to 20/22mpg with a solid-lifter cam of this size is a bit of work. She's gonna want about 56* of spark-lead while cruising; plus or minus a couple either way. Once you got that done, you just lean out the primaries, until she won't hold a smooth steady speed any more. I think you'll need a spreadbore carb, or a small 4bbl, so you can get up on the mains.
Will it make 20/22mpg?
I think so.( see note-1)
Will it make 425hp?
Not even close.
Will it be fun to drive?
You better believe it! A V/P of 148 is in stock BB territory, maybe better than.
note-1
For a streeter, there are basically three things that kill hiway fuel economy;
A hi cruise Rpm,
an early opening exhaust valve,
and operating in a low efficiency rpm range.
Jus trying to help.
PS
If you run that GVod as a gear-splitter, the above is ALL wrong. Except the part about running a solid; I would still run a solid, but on a 106LSA, cuz the GearSplitter, has a very tight split of 78%
So then your gears would be;
2.45-1.91-1.45-1.13, then straight into third-over .78
with splits of .78-.76-.78-.69, instead of .59-.69-.78in the A727/904s
Since the splits are so tight, the engine will feel bigger than it actually is an ET better as well. So then, you can run the next size smaller cam
PS-2
If you need 425 hp to get a certain ET, well that's a whole different story, and NONE of what I talked about applies. But I fail to see the relevance of mentioning fuel-economy then,lol.
PS-3
If you are stuck with hydraulic roller lifters, budget-wise, and fuel economy takes precedence, forget a 235*@.050 cam; the exhaust valve will open WAY to early for economy.
