Short Track 340 Or 360??

[JMB]

340 OR 360 WHAT SHOULD I BUILD, Must run 500cfm holley (no modifications) with stock heads & stock block. Flat top pistons, solid lifter cam & stock 273 style rockers.

Here are the cyl head / deck height rules:

360: Piston deck height with min. 58cc head volume may NOT be less than .020 from the top of the block. Piston deck height with minimum 64cc head volume may NOT be less than .0 from top of block. Minimum head gskt thickness for any 360 application is .039.

340: Piston deck height with minimum 58cc head volume may not be any more than .020 ABOVE top of block. minimum head gasket thickness may not be less than .052 for this application.

This is the only rules distinguishing 340 / 360 in our Late Model class. We race on a 30 year old slick 1/3 mile, 10 degree banked paved oval.

Any thoughts on which engine to build?

Also would the Hughes 1.6 ratio rockers be worth my while?

[DYNO360]

No doubt about it the 340 is the legendary racing small block. I had a hard time finding any, and what I found was junk. They do make a new 340 block with the thick pan rails (TA block) but it is pricey. On the othe hand 360 block are easier to find. Since you are going to put in your own aftermarket rotating assembly, I think the answer comes down to finding a block. Does your local rules prohibite the "R" blocks. If not, they are the same price or less than a new 340! Good luck.

[JMB]

No "R" Blocks, we must use stock blocks. I have 2 340's & 3 360's
so that is not an issue. Just looking for opinions on which engine would be a better for the short track. I believe the 340 would make more compression based on the piston/deck height rules.

[340king]

With the info you have provided, I would go with a 340. There are several reasons why.

First, I like the shorter stroke of the 340 for restricted carb classes. This is because you have a flatter torque curve with the smaller displacement. I feel this leads to a more forgiving situation with gearing. With a 360, you must be spot on for gearing.

Second, I agree with the increased compression with the raised deck (stock) pistons. This should allow a slightly larger cam or at least more torque with the same cam (compared to a lower compression engine).

Finally, I like the way 340's react on slick tracks. They are easier to drive and have a better feel in my opinion.

Besides, the competition is scared of 340's!

[gotcha]

Gotta jump in here on this one. The 360 will outperform any 340 with the same parts combo. A zero deck 360 with the cc heads required by your rules is a better performing engine with a much flatter torque curve than a 3.31 stroke .020 above the deck 340. Broader powerband, long stroke, quicker off the corner with LESS gear, gets into the track rather than on top of the track. This is the primary reason Mopar ran the 3.46 stroke 355. At that time, the national displacement rules limited cubes to 358 and not 360. 1.6 rockers work very well on the exhaust side. With the 500 Holley you need to run a tight manifold....(keep the velocity in the ports up) and set up the final ratio depending on avg. tire size (height) to turn the motor about 6200 (no more is needed). Work in the torque range of the 360. Torque is what moves the car, not HP.

As an engine builder, I can tell you that you can run about one step stouter cam in the 360. The 360 is the small block that thinks it is a big block. This is not idle conversation. The dyno does not lie and on track results have proven themselves.

The cast crank is perfectly acceptable. Rods are the same (bushed or unbushed) and piston weight is slightly less on the 360.

The cost of the blocks are vastly different. Should you break it....finding a replacement 360 is much easier than the 340. There are now many, many, after market parts available for the 360.

Head gasket problems on above deck smallblocks are frequently encountered. Zero deck height is preferred on the flat top pistons. (Flame travel and valve shrouding) especially with the limits of the 500 Holley. Run alcohol if they will let you.

With your rules package, the net gain on the above deck 340 is only .007 when you look at the head gasket requirements. The average Fel Pro gasket is .040 which meets your requirements on the 360.

On your home "slick track" the torquey 360 with the right gear/cam will let you come off the corner with less rpm and more forward bite.

I am a devout fan of the 340. Own several, but race 360's. The 340 is a wonderful engine package but too valuable to risk for lesser performance.

[sanborn]

What can your competition run? Can the GM guys use aftermarket or Bowtie heads? Can the Ford guys use SVO parts? There's not many tracks around that still require "off the showroom floor" stock parts.

What chassis are you going to use? What tires? How well can the car "hook up" an engine. Most short track races are won/lost from the middle of the turn to 50 feet out of the turn. Everywhere else you are just along for the ride.

What is your budget? What are your abilities?

This 340 versus 360 discussion is an eternal one. It's hard to give a flat answer-it depends on a lot of other factors. The GM and Ford guys only have one basic engine to choose from-a 4.000" bore and a stroke of about 3.46 to 3.50" (unless there are some really slick racers that use short stroke cranks). They are stuck with that. There are advantages to BOTH a 340 and 360-but disadvantages as well with both.

Give us a little more information.

[RonsDirt]

My 2 cents worth,
A large bore short stroke is OK if there is LOTS of intake (2 Fours, Tunnel Ram, Big heads, Etc. AND Lots of RPM). With a SMALL intake flow (500 cfm 2 brl.) a longer stroke will fill the cly. bettor (pulls Longer on Intake cycle). Which means MORE power & torque at a LOWER RPM. Drag race a 340, Circle track a 360. D/C must think so, look at the new Hemi. 3.92 x 3.58. This is to pull a load in the Ram pickup.

[JMB]

We run 9" Goodyear eagle bias ply tires (used tires from the Cascar Superseries), 1 tire can be over 4/32 so 1 new tire per race meet (most guys run the new on the right rear). We must use a stock cast iron 2bbl intake manifold with a 500cfm holley carb bought thru the series office, no modifications. We run the 360 high swirl port heads (p4529269) The G.M. guys run vortec heads, however with the stock intake they are rather limited. Dodge is allowed 2.02 int/1.60ext valves & Chev 1.94/1.50. During the past week I have talked to the only guy in Canada to win a Championship in a Dodge with this rules package, he ran a 340 & says he'll kick any 360's ?#$. He maintains that he will get about 11.4 to 1 compression with the 340 rules package. and with the 360 the best you will get is about 10.2 to 1. He believes that the 340 gets into the corner better because of the higher comp. & running it at 7300 rpm as opposed to the 360 @ 6200 rpm. Better in, better off he says. I am working with a team right now that runs a Dodge and we run a 360. The engine makes great power but we can't seem to get it to hook up. Maybe the 340 will drive easier for a rookie driver in this class.

[340king]

This is what I have learned just this year. A junk, worn out stock 340+.040" with "J" heads and a 20 year old Reed cam will run right with anything brought to the track. This includes the $5,500 360 Magnum headed engine that is used as the primary power plant. These engines are required to run 500 cfm Holley carbs also.

Sure, a 360 will make more peak torque than a 340. But how about average torque throughout an rpm range? What gear ratio does a dyno run? The idea is to use the rpm capability of the 340 vs the 360, use the torque multiplication of the rear end gear and put more torque to the ground on average throughout the rpm range. You can't forget the torque multiplication that lower gearing gives you. We need to compare the actual torque at the ground and not brake flywheel torque.

Besides, the 360 will run out of air much faster than the 340. Plus, the increased stroke drastically increases the parasitic friction loss associated with the rotating/reciprocating assembly above 5,500 rpm.

I haven't looked at the cam size difference between the 360 with zero deck flat tops and open chamber heads versus the 340 with positive deck pistons with open chamber. (I use a computer program to find the limits on camshafts.) A 360 can use a slightly larger cam than a 340 if all things are equal, but in this case the static compression ratio is different. Cam size selection is limited by the dynamic cranking compression and intended rpm range. Cam selection is more involved than can be explained here, but basically, the dynamic compression limits the cam size and is related to static compression ratio.

Think about what happens in most auto racing. The guy that can rev the most runs the fastest. This is especially true in restricted CID classes. The boys in CART, IRL, F1 and NASCAR don't rev those things to the moon just to hear the sound. There is a competitive advantage to increased rpm.

Now don't get me wrong. This comes at a pretty high price. But hey, who hasn't spent a little more moola on racing just to try and get that plastic trophy! My preference remains 340. I am not saying anybody is wrong here, just that there is another way to look at it. The choice is yours, both combos can work.

[340duster1]

Here are some more ideas

1)In most short track situations the longer stroke bigger bore engine is a better way to go, but the CASCAR sportsman engine rules (which I am 99% sure they are the old superseries rules) allow a higher compression engine with the smaller displacment. The same was true for the chey, a 327 was allowed a higher compression than a 350. This is designed to equalize that.

2) I was a crew member on a superseries car quite a few years ago and at that time we raced under your engine rules (I was on a chevy pit crew....oh well at least it was racing). The fast dodges from eastern canada ran 360 engines they said due to the larger torque band the 340's could not keep up. (Actually both of our old cars went to saskatoon, one is still racing as I saw it at the draggins car show this spring, i think it was sponsored by CJWW. The other car which was old and heavy was driven by BJ somebody a few years ago.)

3) I have done a lot of comparisons using desktop dyno and the extra displacemnt and longer stroke is the way to go.

4) I now race a dirt track A-body and have two engines for it. First is a 340, 10.5:1, hemi grind cam, unported 2.02 heads. The second is a 360 magnum, 9.5:1 using a hughes cam, stock unported magnum heads. We use a holley 500cfm 2bbl. I know this isn't a direct comparison but the 360 has way more power out of the turns and improved my lap times. It put me from the middle of the pack to the front.

5) Having said all that, saskatoon is a slick track that is hard to hook up on. Handling seems to be the key to success there, not big power. We were on a limited budget when we were racing the superseries car so we did not have the motor that other guys did. But we had good success and had a fast car at saskatoon based on handling. Now if you are racing at Regina, that is a big power track - two drag strips and two harpins - I would use the 360 no question. Same with Calgary if you venture out there.

If you do go to other tracks, I still have all the track sheets and set-up records from the superseries car email me if you are interested, I travel to Stoon once in a while to visit family.

email rodw@albertanewsprint.com

[Goldigger]

How heavy is your car? Does the track have momentum corners or tight stop and go corners? What are some realistic rpm figures with the two barrel carbs? I honestly believe there is no substitute for cubes. If you can put it down on the track that is. Although when it comes down to engine internals and really high revs, I would prefer the 340 over the 360. If I had to, and I had access to a boring machine, I would sleave up a 318 before I would run the large bearing 360. The Honda rod journal might also interest me. If I were running less ludicrous rpm's like 6200 and below, the 360 would be my choice. I honestly believe the 360 should make more torque to pull you off the corners.

[sanborn]

Hey Golddigger, are you interested in a LA Billet crank(3.30") with Honda journals, fresh from LA? I got one on the shelf-need to get rid of. Sorry for the sales pitch!

[Goldigger]

No, oh great one. I am currently trying to sell - sell - sell. I have lots of Bowtie stuff for sale. Currently I am searching for the cheaper side of racing.

[340king]

Attached is a comparison between a 360-2bl and a 340-2bbl. I even left the 360 with 11:1 compression to give it a boost. Otherwise these engines use all the same components or values in the computer simulation. The current values are for the 340. This is a dyno simulation from Eangine Analyzer 2.51. I also ran one in Engine Pro. It came out to be within 4 hp. The 340 with slightly more compression can run up to 252° duration at .050" before losing both Hp and Tq. While the 360 falls off at 248° @ .050". Just more fuel for the fire