Need a plan - component selection for restoring 68 340 that runs on 91 oct

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Hank’sFS

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There are a lot of threads on the subject of camshafts and compression ratios, but I haven't quite found one that shows comprehensive approaches to this question:
From a standard bore 1968 340 block, what are the cam, piston et-cetera selections to get an engine that runs great on California's 91 octane fuel and is as close to original 1968 4-speed as possible? This is for a 68 Barracuda 340 Formula S convertible. I'm trying to keep the restoration as close to original as possible. So, I'm starting with a 68 block and X heads, standard crank and connecting rods. I need pistons and camshaft. I'm interested in what your recommendations are, so please share.
 
Well, your fuel limitations do not deny you power.

With the stock engine, and all the stock components, the only thing that I can see to be changed is the compression ratio if that year engine has a high enough ratio not to work with 91 octane.

If the engine is all stock and running, then I would use a thicker head gasket to drop the ratio a tad. You’ll need to do some investigation and math to get to a pump gas friendly ratio. A 9.0-1 should do it.

You’ll need to measure how far down in the cylinder the piston is exactly. Then the valve reliefs must also be cc’d, I’d there is any. Bore width, cylinder head cc amount, and then head gasket width and thickness. (The one that is currently being used and the one you want to use. You can then go to “Wallace racing” (Google that name) and find the compression ratio calculator.

Cometic can custom size your head gaskets and they have many in the shelf in various thickness from a low (& may be lower) of .030 up to .100 (and maybe thicker!.)
 
If the goal is originality, then the SpeedPro H116CP pistons are about as close as you are going to get to the early 340 configuration. There are numerous cams that are close. Edit to add: OOOPS... big mistake on my part. H116CP is for a 360! Try L2316F.....my apologies.

The original engine's static CR was not really the advertised 10.5, but, in reality, around 9.5 to 9.75. If you use a head gasket like the Felpro 1008 and those pistons, then static CR will be a tad lower than original, right around 9.4 or 9.5.

That original-like combination should run fine on 91. Just tune it properly, in terms of ignition advance, etc.
 
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use the KB quench dome pistons, I'd suggest the lower compression ones with a short cam
or if you have gears etc the higher compression ones with a bigger cam
here is the standard 340 piston
KB Hyper Piston- Chry 340 Rod 6.123 Flat Top 6cc 2V [KB243KTM] - $448.62 : United Engine & Machine Co. Incorporated, Performance Pistons
but I'd stroke it with a 360 crank and use one of the top three pistons from this list otherwise with stock crank think custom pistons of similar design
Chrysler : United Engine & Machine Co. Incorporated, Performance Pistons
click on the piston picture to get cr info
cc your heads or get a real number not the advertised number which is smaller than reality
IF you go Flat top pistons you have to deal with detonation on the street with street gas
The other option is a 4" crank and similar desigh pistons to the three above
what you are doing is moving all of the combustion chamber under the spark plug, providing quench by putting the piston and head cold surfaces close to each other and providing squish when the gas is forced out of the intake side of the chamber
I (and others sharper than I) helped design these pistons with then KB Chief engineer John Erb specifically for what you are trying to do
you can make it run a lot better than you ever can with flat tops
what gears and where do you want your torque/ power band?
iron heads 9.5 is pushing it without having to screw with (retard) the timing which causes more heat- a vicious circle
stock cam has really long ramps so late intake close hides the higher compression
 
And there is a second witness to what nm9 said, in that the later Low-C engines weren't much, if any slower.
And then there's the math.
But since you say you need pistons, and a cam, really you have almost a clean slate. Now,if you could loosen your grip, just a little, on those X-heads........
But then it wouldn't be a "restoration" any more,lol.
But since you are asking about cams and compression and pistons........ it ain't a restoration anymore either.
So, then which is it?
You could run it as a purely stock restoration, with the addition of water/meth injection for those occasional WOT blasts. Or even just an Octane booster, either in the tank or also injected.

But as far as that goes; Wrymrider has some great ideas; I especially like more cubes,lol, 367 is a fantastic number! And I'd like to try those step-pistons in SOMETHING.
Why more cubes? Cuz you can run at least one size smaller a cam, without losing any street performance with the typical 3.55 gears. And pick up a ton of low-speed performance and even fuel-economy. And in your slightly heavier Heavy-A-vert, that could be, depending on your driving style (like with 4 passengers ALL the time), That could be a real boon. FormulaS Barracudas are NOT light. And the vert will easily put you into or close to B/E body territory. Mine is 3450 with aluminum; heads, intake,4-speed case,and wheels, plus lightweight RX-7 seats and NO rear seat at all; but with; a 23# GVOD added, TTIs and full-length 3" duals, P/S and P/B.
>The fold down rear seat weighed 70 pounds, same as the dual exhaust.
>The GVOD and Passon aluminum case, weighs same as the original 4 speed.
>The aluminum heads and intake allow me to keep the ps/pb for about a zero weight penalty over stock.
>The al. big wheel/fat tire combos, weigh similar to the factory Rallys and skinny E70-14s
 
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With the limits of the X heads I figured make them work at a broader rpm range with some more CU in
Depends on how OP wants to drive
If hes back roads and curves and mountains then a high winding build would be fun
around town or even urban freeway the more torque the better
just step down on the gas and go with less shifting down
his call- and it's an important one
what you are not going to get with today's gas is the sharp, crisp bark of a big cam high compression motor- It's never going to sound like a 327 vett (sob)
bye the way Stock Manifolds? Stock intake and Carb- which carb? Do you have the larger 68 340 4bbl stick only cam in it now?
would you consider a Solid cam?
for your stock rods the SPS (Mopar performance) bolts work just fine
here is the piston for a 4" stroke
KB Hyper Piston - Chry 408 Rod 6.123 Quench Head 23.5cc 2V [KB356KTM] - $518.30 : United Engine & Machine Co. Incorporated, Performance Pistons
even if you do not go away from stock stroke you can see the design required for an efficient combustion created with the stock heads
 
Good thinking. I would not want to go any higher than
AJ/FormS said:
But since you say you need pistons, and a cam, really you have almost a clean slate. If you could loosen your grip just a little on those X-heads........
Click to expand...
Why-O-why would he want to get rid of the X heads?

Wyrmrider said:
use the KB quench dome pistons, I'd suggest the lower compression ones with a short cam
or if you have gears etc the higher compression ones with a bigger cam
here is the standard 340 piston
KB Hyper Piston- Chry 340 Rod 6.123 Flat Top 6cc 2V [KB243KTM] - $448.62 : United Engine & Machine Co. Incorporated, Performance Pistons
but I'd stroke it with a 360 crank and use one of the top three pistons from this list otherwise with stock crank think custom pistons of similar design
Chrysler : United Engine & Machine Co. Incorporated, Performance Pistons
click on the piston picture to get cr info
cc your heads or get a real number not the advertised number which is smaller than reality
IF you go Flat top pistons you have to deal with detonation on the street with street gas
The other option is a 4" crank and similar desigh pistons to the three above
what you are doing is moving all of the combustion chamber under the spark plug, providing quench by putting the piston and head cold surfaces close to each other and providing squish when the gas is forced out of the intake side of the chamber
I (and others sharper than I) helped design these pistons with then KB Chief engineer John Erb specifically for what you are trying to do
you can make it run a lot better than you ever can with flat tops
what gears and where do you want your torque/ power band?
iron heads 9.5 is pushing it without having to screw with (retard) the timing which causes more heat- a vicious circle
stock cam has really long ramps so late intake close hides the higher compression
Click to expand...

Now, IMO, this is a FUK'd up post. Your so not helping him and suggesting spending ore money in a direction he is not asking for.
IF you go Flat top pistons you have to deal with detonation on the street with street gas
Click to expand...
:bs_flag:
The other option is a 4" crank and similar desigh pistons to the three above
Click to expand...
Would would yopu send him to spend more money? He plainly states;
and is as close to original 1968 4-speed as possible?
Click to expand...
I (and others sharper than I) helped design these pistons with then KB Chief engineer John Erb specifically for what you are trying to do
you can make it run a lot better than you ever can with flat tops
Click to expand...
:bs_flag:
:wtf: It's like you didnt even read the post in full.

Edit, And now you ask more questions?
 
Hey Rumble, I see you are no longer picking on just me.
From a standard bore 1968 340 block, what are the cam, piston et-cetera selections to get an engine that runs great on California's 91 octane fuel and is as close to original 1968 4-speed as possible? This is for a 68 Barracuda 340 Formula S convertible. I'm trying to keep the restoration as close to original as possible. So, I'm starting with a 68 block and X heads, standard crank and connecting rods.I need pistons and camshaft.


I'm interested in what your recommendations are, so please share.
Click to expand...

I recommend a low-deck 451 set up to run 87E10. OOps did I say that out loud?
Like said earlier;build it exactly to stock and inject an anti-detonant as required; there is your "as close to stock as possible" recommendation.
It's a 50 year old combo of a 54plus year old design. IMO, you could do a lot better,today. But, it all comes back to application.
 
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get some Sunoco 260 or Cheveron Custom Supreme and you can run as close to the 1968 4 speed as possible
I'm assuming he wants it to look as stock as possible

good idea AJ
just using a thicker head gasket means that you have to give it more throttle to get the same amount of go which just creates more heat and not more power
"
But, it all comes back to application.
"
Exactly
If standard crank is a must I'd pick the design of one of the KB quench dome pistons and get bids from the custom piston mfgs
I first used Arias but since then have used most of the majors (mostly for BBM but SBM should be similar)
been doing this since they dropped compression in the early 70's and the good gas went away
there is NO good/ cheap solution pick one
tried them all welded up the chambers, big mill jobs plenty of Dyno time on the Big Blocks but same problem
stock cam i optimized for high compression (and long warranty life (no lifter noise) with long ramps) would not think of using it today
and for low compression it leaves a lot of torque on the table (you have to use low gears and buzz it up to make it work and even then there are better choices)
 
FWIW.... Having run moderately higher compression 'back in the day' (10.3, iron heads, some quench/squish), the octane of fuel was not as consistent as it is now, yet that was all doable. So I personally would not worry much over a mid 9's SCR and today's fuel, especially with an older, slower ramp cam like the older 340 design.

DCR will end up the low to mid 7's with the H116CP pistons, 1008 head gasket, and 340 type cam... that about 100% detonation proof, even with the open chambers, unless you really mess up the tuning. You can mess any engine up enough to get detonation... I had a distributor move radically in a rally and advance things so much as to detonate in an engine with a DCR in the high 5's LOL.
 
I fully expected this would start a fun conversation. You have not disappointed. The one thing that I would love to have heard is what the original car sounded like. If that was known I would have added that criteria as well. Make it sound like it once did. But my main point is to make it street drivable and look original. Most of the suggestions have met this criteria. To answer a couple of questions. I have the stock exhaust and intake manifolds. And the stock AVS 68 manual carb. Oh and it has the original 323 rear end.
 
The sound was mostly in the rectangular tips, the small diameter pipes,and the overlap.
But you can't reproduce the sound unless you have the same tips and pipes, and that kindoff limits your power potential, cuz the pipes were skinny-azz pipes. And it is those skinny pipes which hustled the exhaust to the back, and put the power into the tips.
Another reason for a stock-rebuild.......... I guess,lol.
 
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Paul G wrote in another thread
"I have been fidling with my 72 Charger with an iron headed mild built 360 for 5 years trying to control engine overheating, detonating, hesitations, poor idle quality, lack of power, etc."
What we are trying to avoid
measure twice- cut once
Bottom line is that flat top pistons in open chamber heads leave torque on the table (not necessarily top end hp but that rpm range when the engine is working hardest)
so do long lazy cams of which the stock 440 HP and 340 are among the worst not nearly as much area under the curve as the penalty of long duration imposes
glad your octane is consistent nm out here in CA it varies all the time and especially "summer blend" vs winter blend"- gotta build for worst case for pump gas
 
AJ said;
Hey Rumble, I see you are no longer picking on just me.
Click to expand...
I actually don’t, but I can if you want me to....
I just can’t reach Manitoba from here. Wait, I think I see a big stick to poke you with, hold on, I gotta put my beer down... watch this ****...

LMAO!
:lol:
:realcrazy::realcrazy::realcrazy::realcrazy::realcrazy::realcrazy:
:lol:

I recommend a low-deck 451 set up to run 87E10. OOps did I say that out loud?
Click to expand...
Well shhhhhhh eeeet, if your boo a go big, you should have spent all of his Internet money and suggested a mountain motor at 600+ cubes and made it a blown Hemi!
 
Wyrmrider said:
glad your octane is consistent nm out here in CA it varies all the time and especially "summer blend" vs winter blend"- gotta build for worst case for pump gas
Click to expand...
Yeah, I had not thought of the summer blend crapola.... we live away from all that nonsense. 'Round hyar, the fuel usage has made old/bad gas at the pump pretty much a non-issue.... You gotta realize that I come from an area and time when I can remember my dad getting fuel from a station with the OOOOLD pumps, where the first attendant hand-pumped fuel up into the glass container up top..... LOL

Using a lazy cam in this case is actually an advantage.... it lowers the 'area under the curve' and thus lowers cylinder filling to some degree, and that in turn lowers 'effective DCR'....which jives with the matter of 'leaving torque on the table'. So my reasoning for the older style 340 cam in this case was to make the engine better for poorer octane fuel.
 
Stock build...Just duplicate the factory specs including the cam,the info is widely available.
Use a sealed power C28P, a stock replacement cast piston that sits a hair below the deck.
Classic Exhaust out of Ohio make a stock exhaust system (very economical). Make sure you use the the stock replacement mufflers they provide,not their hi performance muffler. It will be reasonably quiet until you step on it but sounds just like it did in 1968 and you will hear the moan of the unsilenced air cleaner.
In an A body with stock 14" tires and 3.23 gears it will pull hard to past highway speeds and probably get 20 plus rpm driven sensibly!.
 
If you lower the compression with pistons below the deck you are building a 73 340 not a 68
HP dam is a dog in those motors till you get it really wound up that's why the loosend up the converters
Remember when GM went to the "switch pitch" to get the rpm up on takeoff same problem
it will pull hard if you shift it down but just stepping on the gs it will be flat
not my kind of fun
why not just build it right for today's gas
 
ir3333 said:
Use a sealed power C28P, a stock replacement cast piston that sits a hair below the deck.
Click to expand...
428P..... but not a direct replacement for the original '68 piston. Not a bad choice but the L2316F would be closer.

Not at all sure if the OP wants this 'original' on the inside and out, or just the outside.....
 
yes and yes.
I have used the L2316 and the compression becomes an issue unless you increase the cam duration.The 428P works well with the smaller stock style cam and even then requires careful tuning.Very economical too!
 
re-arranging the deck chairs on the Titanic
BTW using stock heads I'm trying to build to get those heads flowing their max at as early a RPM as possible-
getting the valve open to best flow area quick and holding it open then shutting it as late as possible
They will not flow enough for a big cam so you do not get the top end you would expect and loose your low end
Running a 340 cam in a drag class is different as you rev the snot out of it and low low gears so the lack of low end gets offset by some extra HP up top
you are running a race gas or at least the best legal gas and the motor never runs down in the hard working area where the problems occour
this setup is miserable on the street
 
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Wyrmrider said:
re-arranging the deck chairs on the Titanic
BTW using stock heads I'm trying to build to get those heads flowing their max at as early a RPM as possible-
getting the valve open to best flow area quick and holding it open then shutting it as late as possible
They will not flow enough for a big cam so you do not get the top end you would expect and loose your low end
Running a 340 cam in a drag class is different as you rev the snot out of it and low low gears so the lack of low end gets offset by some extra HP up top
you are running a race gas or at least the best legal gas and the motor never runs down in the hard working area where the problems occour
this setup is miserable on the street
Click to expand...
I'm having an understanding problem without punctuation but I think I got enough of it to give you a like
lol.
 
2316 pistons stock 340 cam. Use .051 felpro head gasket that comes with most felpro gasket sets. Should be about 9.25 comp.
 
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