Getting a smallblock to rev

-
Daz570

Daz570

Thread Inturpreter
Joined
Jul 27, 2008
Messages
148
Reaction score
2
Location
Australia
Have been looking into a historic circuit race class down here in aus, considering running a 1967 Valiant, the class is limited to standard components with the exception of consumables (pistons, rings bearings etc..) cams, intake and exhaust are free as long as it was available before 1972.

The catch is here, the only small block mopar that raced here and is therefore ellidgeable in the class, was a 273 and auto.

Now I'm wondering, if we can make up for cubes, with rpm?

What have you all found to be a reliable combination that could suit our aim?

Thanks in advance,
 
Seems to me you are thinking wrongly. What is RPM going to gain you, besides, broken parts?

If you are stuck with stock heads, breathing might be a problem. I say build the best engine you can with what you "got" and then change what you need with gearing and tires.

I'll trade high RPM, short life for torque anyday.

I'm thinking a regrind of a 68 340 stick cam? Better heads if legal? Certainly mill heads/ deck and change pistons as necessary for more compression. Run a mechanical cam if you can, stock 273 rocker gear.
 
Well, if he is limited by rules of the class racing, you really didn't help him out now did ya?

First up, read the sticky thread on oiling mods needed for the small block. Second, what RPM are you thinking to spin at?

Thrid, what are the limitations of the class? Will they tear you down to. He k bore and stroke? Cam type? Cylinder head casting numbers?

A wise man once told me that the rules tell you what you can do and if you read I between the lines, what you can get away with legally.

Can you stroke the engine, run a roller cam and rockers, etc…
Does it say you MUST run the intake
For that year car, must the heads be iron, etc…
 
RPM can make up for lack of CI

The engine is just an air pump, the more air the more fuel that can be burn. A 7,500 SBM would wake a few BB owners up

Solid cam is a must, I shoot for 11 to 1 compression, maybe 12 to 1 depending on how much racing fuel you want to buy. Built right 8,000 rpm is possible with the short stroke crank. Pistons might be expensive..sure you can't use a 318 block
 
Buy the strongest, lightest crank you can run (will they let you trim it down?), ditto the rods, and you might think about aluminum flywheel and a four speed. With that high, narrow powerband you're going to want to keep in the powerband as much as possible and that spells four-speed.

If aluminum is not legal, run the smallest flywheel you can get away with. Good valve springs, light valves, and light pistons.
 
rumblefish360 said:
Well, if he is limited by rules of the class racing, you really didn't help him out now did ya?
Click to expand...

I really don't know how you figure that?

If he can't change heads, improve breathing, he's not going to get more power at higher RPM, now is he?

What I'm saying is, increasing the ability to wind the snot out of the engine is not necessarily going to make more power, make it more competitive, nor make it last longer.
 
Some good replies here chaps, thanks for the effort.

To try and clarify the rules a bit;

I have to use factory cast heads (but in my interpretation, j or x heads are still factory with a trim around the top of the bore??) larger valves can be incorporated.

Their wording, 'performance can be improved by the removal of metal'
Stroke must remain the same
Bore can be a maximum of 1.5mm over
Induction, exhaust and manifolds are free as long as they were available before 1972,
Roller cam is allowed
decking heads, block or higher compression height pistons is allowed,

Long story short, as long as the component can be described to run in the same manner as it does factory, eg oil pump uses similar internals and runs off the same part of driveline, there are certain freedoms to upgrade it.

the main circuit in consideratin for the class, as you can see it's overall a pretty fast circuit, lots of top end, most cars in the class are doing this 2.4 km stretch in around 1:04 so 8,000 rpm down the back straight would be a great advantage

round-2-photo.png



The other circuit down here requires more mid range




800px-Baskerville_Raceway_%28Australia%29_track_map.svg.png





it's not the best example as it's a step up on the class i'm playing with (more freedoms) but gives an idea of the track / class in question
[ame="http://www.youtube.com/watch?v=ri2wD7PqepY"]Symmons Plains Touring Car Masters.Raw no commentary., - YouTube[/ame]
Hope this helps
 
My opinion is to build for a power range. With 273 cubes and the ability to use a roller cam and some 1.88ish intake "J" heads, i would think a 4000-7000 rpm range could make decent enough torque and a good top end. Then you could just gear for the size track and speeds you'll be running. Good luck, sounds like alot of fun:thumblef:.
 
Sorry my man, I should have stated a big LOL, because your trying to help in earnest and I just laughed at the reply because I did think it funny. I ment no harm. Sorry.

67Dart273 said:
I really don't know how you figure that?
Click to expand...
Cause he said this, "The catch is here, the only small block mopar that raced here and is therefore ellidgeable in the class, was a 273 and auto." which makes bigger displacements illegal to a high degree.



If he can't change heads, improve breathing, he's not going to get more power at higher RPM, now is he?
Click to expand...

There are tricks as well as give and takes.

What I'm saying is, increasing the ability to wind the snot out of the engine is not necessarily going to make more power, make it more competitive, nor make it last longer.
Click to expand...

Think Trans Am racing. De'stroked 340's down to 300/305 area that would spin 7500 all race long.

Edit, OH SNAP! Knightly posted what I was thinking.
 
knighty said:
Some good replies here chaps, thanks for the effort.

To try and clarify the rules a bit;

I have to use factory cast heads (but in my interpretation, j or x heads are still factory with a trim around the top of the bore??) larger valves can be incorporated.
Click to expand...

Be clear here since there NOT 273 heads and they may be illegal to use. Just be sure about this. A 1.88 valve will require a notch in the cylinder bore.

Their wording, 'performance can be improved by the removal of metal'
Click to expand...

Porting, heads, intake!

Stroke must remain the same
Bore can be a maximum of 1.5mm over
Click to expand...
Who has the mm to inch conversion for this?

Induction, exhaust and manifolds are free as long as they were available before 1972,
Click to expand...

Could you clarify this for me/us? "Free?" Free to change and up grade? Then that is sweet!


Roller cam is allowed
decking heads, block or higher compression height pistons is allowed,
Click to expand...
OH! MY blood pressure just went up with excitement!

Long story short, as long as the component can be described to run in the same manner as it does factory, eg oil pump uses similar internals and runs off the same part of driveline, there are certain freedoms to upgrade it.

the main circuit in consideratin for the class, as you can see it's overall a pretty fast circuit, lots of top end, most cars in the class are doing this 2.4 km stretch in around 1:04 so 8,000 rpm down the back straight would be a great advantage
Click to expand...

Did I mention the oiling mod sticky you need to read and follow?
 
yes, have read and saved the oiling mod thread, a great read.

by free, you are allowed to manufacture manifolds, and can run anything that was available in the period, it's not uncommon to see vehicles running tripple and quad weber intake setups like the one below, (belongs to the barracuda that was imported and elidgable to compete due to it being pre 1965) the only 273 car i have ever seen competing in the historics, around 400hp

Carbs.jpg

64-Barracuda.jpg



edit,

1.5mm is close enough to .060"
 
Y'know....Magnum heads with better valvesprings would be great on this, IMO.
 
also light reciprocating parts and very good valve springs
 
To help keep it alive, I'd suggest floating piston pins and balanced crank. Were commando(4bbl) 273's available there? If so you'd be ahead to start with those parts aside from the single plane intake. The 2bbl heads actually work pretty good if they're ported to 4bbl gaskets
 
There is no, excuse me, NO difference in 2 or 4 bbl heads because there was NEVER such a thing. The closest it did come to this was later year (mid/late 70's) 318's that used 360 heads for the 4 bbl option.

Port matching is OK'd by his rules as well as porting.

Balancing a engine is 101 type of work on any engine.
 
Quit worryin about what anyone that has not done this has to say and start doin it within the rules,build the car and the engine and just do it, what cant be made in horsepower can be made up for in handeling and driver, pm me if you would like to talk more......I'll give you my phone number but git some seat time as soon as you can....handeling and driver are more than 50% of a racecar, if you have to start last in the race you can surely rely on other drivers performance and other mechanics performance to get you to the front of the pack. Ive ran a pro figure eight car for abougt fifteen years and done good with less power, handleing is it and you just cant buy a better driver than you......search for driving technique's and on the car focus on its reliability, check every nut and bolt every race, when you get to the racetrack already know the car is good so you can put that out of your mind and focus on the one thing you can add to the mix to make your car better......Driver Performance, coast into the corners and the race starts coming off of them...hard to write the driver feel inside a racecar but ther is a lot of advantage to coasting as opposed to heavy braking entering a corner......I'll look for your pm and do the best I can to help out but please be serious about this, I have much to share
 
he's not lookin for cheats he's lookin to work within the rules.....really a commando 273 will wind 7500 rpm's all day long if properly built he could look for a gear that will keep him at 7000 rpm's down the longest straigt and keep reliability

jos51700 said:
Y'know....Magnum heads with better valvesprings would be great on this, IMO.
Click to expand...
 
I like the way you guys go road racing down under.

Back in the early days of TransAm, Mopar teams ran the 273. Group 44 was the most successful finishing second in the 67 season. IIRC, Bob Tullius said their 273 made around 400 bhp with a single 4 bbl carb.

The engine Mopar teams used for the 70 season was a de-stroked 340 making about 440 bhp. This engine, as run in the 71 Daytona 500, car owner Mario Rossi quotes the output as being 450 hp. I pass this along not to tease you with a 5 liter Mopar, but to give you an idea of what to expect from your efforts with the LA motor.

I'd like to be more helpful, but am concerned I'd land you in hot water with the tech inspector. As for some bargains on various Mopar competition parts, suggest you contact Penske Racing, Inc., 200 Penske Way, Mooresville, North Carolina 28115. I understand they may be clearing out some inventory in the near future.
 
Great feedback guys! And waggin, I will defiantly get back to you soon.

Am picking up another 273 and driveline on the weekend to get a slow start on the project, until them I have a 273 car we can run in a lesser event to set sort geometry while we set up the actual body (would hate to ruin an original one)

Thanks for the feedback guys, I'll keep you posted
 
knighty said:
Now I'm wondering, if we can make up for cubes, with rpm ,
Click to expand...
Yes you can, but your main limit is gonna be cylinder heads 273/318 aren't
the dog heads everyone makes them out to be but if you can't port them with 9:1-10:1 CR and a high lift 268-274 cam your gonna get 300-325hp @ 6000 but with 11:1+ CR and 284+ cam 325-350hp @ 6600, without porting 350hp will be your max power, if you can fully port add 100hp and a 1000 rpm to those numbers. If you can swap 340 heads on CR will be your biggest problem.
 
Iam no expert but i would think you would want to shoot for something will make the most wide powerband that you can get as you will only hit your peak hp rpm for only a couple seconds per lap. A 450HP car with a wider powerband will be faster then a car with 550 hp with a super narrow powerband exspecially on a road coarse where you wont always be at the top of each gear like you would in a drag race.

IF you can run magnum heads amd solid roller cam that would be my choice we took a 360 out of a 95 van stock super low compression 8.7:1 copied the 380HP crate engine to a "T" "mopar cam and intake" and made a dyno of 280HP at the wheels roughly 335-350HP at the crank not bad for $1000 worth the parts and that was when everything just came out and cost alot more.
 
Looking at the rules, I don't think you can use anything newer than 72 for heads, block, intake, manifolds etc... For heads I'd run fully ported closed chamber 273 heads with custom domes to get 12:1+ CR, ported 340 intake and exhaust manifolds with a full roller valvetrain and the lightest valvetrain you can afford if done right you should be able to make 450hp around 7000-7500 with an 8500 redline. Good thing about the small displacement engines the powerband has a gentle slope after peak power that's one I'm building one for my 65 Cuda that's gonna used on road courses.
 
11.5-12.5 comp, port the heads if u can, look into old MOPAR roundy round cams , probably in the 320* duration depot, u can rev 8 grand or so with a few oiling mods and good well preped stock 340 rods and good bolts. The 273 has a small piston that weighs a lot less if u go with custom forged pistons..so ablot less rotating mass.anything u can rev with the rout cam, but it will only last if the oilsystem is up to par.
 
You must log in or register to reply here.
-

Back
Top