rx7speed

ok I was reading a mag from a LONG time ago where they made a 502 with 1.7 intake valves 1.4 exhuast valves (yes I know small and I'm not sure if those where the exact numbers but I know they where smaller then even the 305 valves) running 12.5:1 comp

can't remember the rest of the specs other htne about 650lbs/ft of torque and about 500+hp and all this was on 87 octane... and yes the 12.5 compression is correct...

my question now comes with how can I get high compression on a SBC using pump gas

I know using a larger cam would help being that it bleeds off pressure at low rpms.

any ideas here?

305sbc

iTrader: (3)

aluminum heads
thermal barrier on chambers, valves & pistons
high swirl chamber design
very tight deck clearance *necessitates tight piston/bore clearance.
longer connecting rods for increased dwell time
retard valve closing events on the camshaft. (may reduce power)
increase overlap of cam (tighter LSA's)
water/methanol injection (less power)
Lower intake air temperature significantly.
Run a very restrictive intake induction system (less power)
Gasoline with high ethanol content ( less power though)

not all of these things help power, but they just allow higher mechanical compression ratios without detonation.
I know there are other things but this is a pretty good list.

rx7speed

ok here are the specs for that 502


they ran 12.3 static compression with an a/f ratio of 13.2
an accel ECU
timing was set at 21 degrees total
an accell stealth intake manifold
a feuling cylinder head with 1.850inc intake and 1.435 exhuast
evans coolant
kieth black bypereutectic pistons.
cam specs are 216/220@.050 with 114* lob sep angle unkown lift

the BSFC was somewhere around the .35-.38 mark




what else could be done without getting rid of lots of power

305sbc

iTrader: (3)

Oh yes the Evans coolant is
proplyne glycol
it runs with no water and no pressure...
takes much more heat away from the metal around the chambers and eliminates all hot spots in the water jacket.
coolant hotspotting in the water jacket around the combustion chambers are responsible for most detonation.
The coolant is said to make a ton of difference.

rx7speed

only thing I don't like about the evans though is water has a better conductivity of heat

F-BIRD'88

Thats the key... Get Fueling to make ya a 1 off
Figure 8 combustion chamber head with central spark plug, supper swirl and tumble, Control the AFR , timing and cylinder head temps exactly.

Works good in the labratory but will it climb a steep hill in 100+ F
weather.

Feuling is a very smart cookie. has some beauti designs.

http://www.feuling.com/

black83z

There is an article in Hot Rod in which a person is running high compression on the street in a SB 400. April 99, how to run 10s on 8500 buucks. Took a 1973 400 bored .030 with a torque plate. Forged 14.5:1 pistions, plasma moly rings, forged steel stock length rods. Manly 2.08/1.6 valves, crane roller cam 283*/283* .630 inch lift. He used mildly ported cast iron chvy bow tie heads that flow 268 cfm@28 in. He uses an incredibly loose GER 8in converter, 4.56 gears, and an overkill cooling system. He uses 37* ignition timing and a very light throttle foot. This allows street driving on 92 octane, when its time to race, he puts in a few gallons of 108 octane race gas. This is good for 10.98's in his Nova. High compression on the street can be obtained. I think it has to do with minimizing load and heat within the motor, and the cam needs enough overlap to bleed of some compression at low speeds i THINK.
matt
ps: this is a carbed motor that makes 585hp @ 7000 RPM

ME Leigh

The reason they could run that high of compression is that they had a big cam and tiny valves. Meaning that there was nothing in the chamber to compress.

rx7speed

how did they manage to get over 6050lbs/ft of torque with that then?

Breadfan

If you are going to build a strictly or manely street engine , and if i was you i would stick close to the 10.5 mark . You can get away with more but you are just going to pull timing . Know with the hyper pistons you can run tighter piston to wall clearenace ( less piston rock ) enabling you to run a tighter quinch area . A head with a better swirl numbers will also reduce the chances of det. Plsu there are many other ways to increase power with out using alot of compression , though it does sound cool as hell.

305sbc

iTrader: (3)

FYI the new TRW forged pistons come teflon coated on the sides and with a recommended .002" side clearance vice the old & sloppy .004"

thermal barriar coatings & teflon on the sides will allow a tighter piston/bore.
If you're careful you don't have to cut spark advance with 11:1 on the street.

muchwhitesmoke

you can tryboyleworks this is a very good compression article.

there are some just plain and general good tech articles here they are pontiac articles, but thay are practical to most apps.

F-BIRD'88

But is it practical. Will it pass my formentioned test.

Not likely.... Anything more than light part throttle cruising
will need more octane.
Adding a water injection system is a possibility for full throttle/ full timing performance on street gas.
Been done before...

rx7speed

agreed


the motor I was posting about was able to be a daily driver

you could run it about at WOT and that is what I was curious about

F-BIRD'88

Yes the secret is in the Fueling figure 8 combustion chamber
and close control of the EFI and cooling system.
Forget the big cam timing and overlap stuff. It's not used here.

An inefficient overcamed motor is a gas hog. Not practical.

black83z

I have a feeling that gas mileage was not a large concern to this individual. But in driving it did well. The guy drove 45 miles in bumper to bumper traffic in Cali w/ 92 octane in the tank. I think that street driving isnt really that bad, but EFI will be necessary for good mileage. And you dont really need 14.5 compression either.
matt