Maybe we're looking at this all wrong
Maybe we should ask why do you want to run those little tires with so much engine?
Or;if 200hp annihilates those skinny rollers, why are you building potentially a 400 hp engine?
You said;
So let me get this right;
Street cruiser, skinny tires, traction device,sporty engine that won't constantly break the tires loose,hi-compression,no headers,hi-rpm heads,full range intake, No cam yet, no rearend specified, no stall specified.
IMHO
This is all messed up.
But maybe I/we can help you.
I once slapped an entire teener top end onto a 340 with the teener cam,and the teener 2bbl,
and headers. Stock 1700TC and probably 2.76s. I called it my big-bore teener experience. All this in a 65 V100 wagon.
This turned out to be one of the funnest combos I ever had.
You have the potential there to have the same. But, but, there is no way to harness the torque of something like that, but by pure willpower. I had none and it never crossed my mind to not spin the tires every chance I got.
So you have the wrong size engine for your application. But you have already spent money on it, and it's too late to bail. So we are gonna have to make the best of it.
What we are gonna need to do is to reduce the torque at the starting line.
To do this, you will need a tiny rear gear, a tiny stall TC, a tiny cam, and low compression.
Typically we go the other way. I for instance have a clutch, so any stall I want. and I have a 3.09 low gear, and not so long ago, I had 4.30s. Doing the math,for first gear, I mighta been able to put something like 425ftlbs x 3.09 x 4.30=5600 plus ftlbs into the rear axles. And this will spin 325/50-15DRs like nothing.
Currently I have 3.09 x 3.55s and the same engine. The math says this can now put down 4600 plus ftlbs. It still spins those DRs like nothing. On the street I run 295/50-15s and they spin at 2000rpm or less. Lets say at 2000rpm my engine can put down 125 ftlbs on the 2 bbl not even fully open.That would math out to 1371 ftlbs into the rear axles, and it still spins those 295s,allbeit very slowly. Now if I had 205s, what do you suppose it would take to not break those loose. I'm gonna guess a 2.66 low gear and a 2.76 rear gear and less rpm. This might math out to 800ftlbs into the axles.
So that will be your target at the starting line.
How to get it.
Well number one, we need to limit the engines torque by manipulating the cam, the compression and the carb size. So we are gonna soften the hit with compression. No 10.5Scr here. No 9.5 either. We are gonna shoot for a Dcr of 7.5.
Since this is a streeter,and you want sporty, you really want a two gear charge to 65 mph. This is very sporty. So lets pick a cam and gear to work together to do this, while using the smallest TC you can find. We can't pick too small a cam, cuz it will pump up the Dcr, and that will get us tirespin right away. We don't want tirespin. On the otherhand, you are gonna probably run Caltracs, so we don't have to sacrifice everything. The Comp268 is known to be soft with low compression, but with a 904, it wants to be shifted at 6500 to 6800. So that is too much for sporty and street. We need to go down 2 or 3 sizes, but not too much more cuz then the Dcr starts to rocket up.So lets start with a 360 2bbl cam which is 252*. This cam will power peak at maybe 4800 to 5000, and will want to be shifted around 6000. Ok that's better. This cam will make a Dcr of 7.3 @ 8.5Scr,perfect; a little soft off the line.
>Now to be a two gear car and hit 65 @ 6000 will require 4.56s, OOps, maybe a bit too sporty. How about if we hit 32 mph at peak torque say 3700. This will require 3.55s in first gear; pure magic. So now we are getting somewhere. Oh but peak torque at 3700, is gonna be around 360ftlbs and with the 8.70 starter gear, this makes 3130 ftlbs into the rear axles, and that is almost guaranteed to blow the tires away. Those Caltracks are gonna be busy. So lets play it safe and go with 3.23s.This will drop the Rs at 32mph, to 3500.
Lets recap; we have a 8.5 engine with a 252/112 cam that gets us 7.3Dcr@142# cranking psi. This is a soft start,it has 3.23s to blast off at 32 mph with.
Now we have a few problems to solve. First is the 2.45x3.23starter gear of 7.91. Remember our 800ftlb target. Well it turns out that this combo will not peg there unless we severely limit the TC...800/7.91=101 ftlbs. This engine will make that right around a typical 2bbl stall of 1600. So,Yeah I think that's gonna work.
Next is the AG. I'm afraid that is too much manifold. To be sporty with that 7.3 Dcr, we are gonna need to keep the airspeed up at low rpms. To that end we are gonna pick a carb first. And I choose a small spreadbore. And then slide a proper spreadbore dual plane manifold under it. Pick one anyone.The spreadbore has smaller primaries to soften the bottom a little more , yet the big back dumps will let her breath at 6000. I know; how about the stock 1970 340 AVS and its manifold. Or the 71 TQ, and its manifold.If we do that, then we can put a bit more TC into her. Now maybe an 1800 TC will work.
Another recap; Now we have the TC of 1800, the 3.23s,SG of course, and the induction figured out.
Now what about those heads? Well first,they are way more head than you need. But you already got them so lets use them. They will allow us to put a half a point more compression into the program, giving us a 7.7 Dcr@ 9.0Scr and 152 psi cranking pressure. This will make it easier to achieve the proper Scr. They are a really good head, even for this combo. These heads and this combo will now want a custom cam. The heads will accept I think 550lift and we want an advertised of 252/112. You ill need 1.6 arm to get there, but you and the grinder can work that out. This will put the Sport back into the midrange, and extend the operating range at the top. To get the most of the custom cam, you should consider some specialty port work.
Another recap; now we have the heads and custom cam figured out.
>Now what about this 9.0 engine, how to do that? Well assuming a 4.08 bore and a 3.31 stroke, this requires a total chamber volume of 88.78cc. I think the heads are 65cc, the gasket is 8.9, the eyebrows are 5, and that leaves the deck clearance to be 9.88. This would require the flat-top pistons to be .046 down in the hole. That would get you a Q of .085. That's a lot. So perhaps some stepD-cup pistons. I don't see them in the KB catalog for 340s so you will have to shop around. This type of piston has to be custom fit.So this is gonna be the tricky part. They do have a #243 piston which appears to have a step on top. if you machine that off just right, You might be able to achieve a tight Q AND drop the cr to where it needs to be.
Final recap;
What I have outlined here is basically as powerful as a warmed up teener, and it's gonna cost you a lot of money. It's a low compression 340 with a highlift 360 2bblcam, a good breathing top end,saddled with log manifolds. It has a 340TC and 3.23 gears
I wouldn't spend my money like this.
You can get almost the same thing by going to the junkyard and grabbing a 5.2 Magnum. For like,under $1000.And converting it to your EFi.
And if you blow it up, you can get another for less than $1000.lol
You can do that 3 or perhaps 4 more times and still not have spent as much as on this 340.
And that Magnum will still smoke those 205s
Well maybe not with caltracs. I heard those work pretty good.
It would be far more reasonable to get 275s under there, and build an easy 325 to 350hp 340
