ok, ive been trying to tune my car to run off 87 octane (due to gas prices). it runs pretty good exept when i test it on this one huge hill. if i gun it all the way up its fine, but if i step on it, then slow down, then step on it lightly i get detonation. i have an adjustable vacume advance canister installed by "crane cams". right now i have one medium spring and one heavy spring on the distributor weights. ive tryed adjusting the canister many times and i thought i had it, but it started doing it again. it says to turn it counter clockwise 2 times each run untill it stops. ive done that and it doesnt seem to be gettiing better. i think i also have an unusualy high compression because i have my old tpi heads on my carbed engine. i was thinking about trying two heavy springs on the distributor but it says thats usualy recomended for trucks that are towing heavy loads. heavyer springs would give me more of a vacume advance curve to play around with because the total timeing ends at 3800 rpm (i think). where as my current set up's total timeing happens at around 2800 rpm (not really sure on these numbers, but you get the idea). my base timeing is set to 8 degrees. basicaly my question is, should i change the distributor weight springs to 2 heavy's? if not, what should i do to stop the detonation?

 

Hook up the EGR. Slow the advance curve a little.

 

my manifold doesnt have a port for an EGR valve, ive removed basicaly all of the emission system exept for the pcv valve if that counts. ive changed the advance curve every way possible that the adjustable vacume canister will let me. the only thing i can think of is either go back to 89 octane or change the springs in the distributor. any input on the tpi heads causeing higher compression?

 

Too bad you eliminated the EGR. Thats it's main purpose.

Do a net search for "Water Injection" and "detonation"

Works good.

 

i thought the EGR valves main purpose was to recirculate exhaust gas back to the intake manifold. i cant see how this would benifit me at all exept help out the environment. i was told by several people that EGR valves reduce performance and encourage carbon build up

 

Forget everthing you've been told about EGR.
Unless I told ya ...LOL

The recurculated EGR Being that it does not burn ( twice)
Is relitively cool and inert in the combustion process.
It reduces peak combustion temps during the fuel/air burn.
This not ony reduces NOX emissions but also reduces detonation
under cruise and moderate load. Like going up a hill.
or rolling into the throttle.
This allows you to run more compression, timing and less octane than without it.
It is a plus overall and because you can run more compression and timing. Power is actually improved overall.

Water injection esentually does the same thing.
Think of it as a cooling buffer in the chamber. Keeps things from getting too hot.

They do not cause carbon build up but sometimes
the EGR valve get gummed up with carbon and sticks upen when its not supposed to. Thats about all that ever goes wrong with them.
Egr is not used at idle or WOT. Just part throttle.
Thats why the EGR vacuum line hooks up to Ported vacuum on the carb.

 

i did a quick search on water injection. every reference i can find points to turbo chargers and hi-performance engines. this seems like a pretty expensive alternative to an EGR valve. tell me one thing though, what will happen if i put 2 heavy springs on the distributor weights, and then start adjusting the vacume canister again from the start? power is not a huge issue here, i just want a reliable daily driver with a fair bit of *****

 

Water injection is used on turbo and supercharger motor. True enough. But is quite effective on motors just like yours.
A expensive elaborate system is not nessessary on a N/A motor like yours. A simple windshield washer pump/ check valve and squirter, spraying a little water from your windshield washer resivoir down the carb during hill climbs is about all that needed.
Has been used for years on Motorhomes etc.
Read up on it some more. You won't find many N/A kits cause its too easy to build your own. There are lots of projects plans on the net. You can buy all the nesssessary parts from a auto parts store like CTC. In fact you can get most of the stuff from any auto wreckers.

The cheap Blue windshield washer fluid is essentually water and methanol mixed and makes excellent "Anti detonation Fluid"
It's something your already using now in your car.
You're half way there.

Play with the timing if you want , but when it doesn't work
for ya look into a Home Build Water Injection system.
It will do what you want.

You'll be the Envy of all your friends.....

 

well.... does anyone else have any other suggestions in the timeing department? building a water injection system just isnt gona happen for me due to lack of time/money.

 

are you sure it's detonation and not preignition? if it's PI you can try running a colder heat range plug. if it's detonation i'd suggest using 89 gas, it's only like a dollar extra per fill up

 

i think im going to try 89 gas. yes i do think its pre-ignition, because after i go over the big *** hill any time i step on the gas fairly hard it starts makeing "spark knock" sounds. first off i have to burn a whole tank of 87 so im going to try setting the base timeing to 4 degrees. its weird though..... any time i drive the car its fine untill i hit that one big *** hill...... also, forgive my ignorence, but what are heat range plugs? are you talking about spark plugs? if so im useing bosch platinum +4's. alot of people dont seem to like these for some reason. a friend also told me to try unplugging the vacume advance and then try the hill to see if its the springs.

 

a plug with a colder heat range will have more ceramic towards the tip of the spark plug to make a bigger path for heat to travel from the cylinder and dissipate to the head. you can tell by the plug number what heat range it is, like an AC delco r43ts is one range colder than an r44ts. bosch +4s are terrible, they're just a gimic. also, 4° btdc is not enough base timing. the factory setting is 6 degrees btdc. if you've built the engine up at all then you need to advance your timing, not retard it.

 

the engine is basicaly rebuilt to a stock GM engine. the pistons and cam are probly not GM though. the base timeing was 8 degrees but i ended up setting it to 6 anyway just to test it out. i havent had any detonation on my whole drive to work and back today, and i was driveing like a maniac. my engine is basicaly a tpi engine with a carb slapped on top(roller set up, tpi heads....) they gave me back the exact equivelent of what i gave them. the only mods i have done are external (headers, 600cfm edelbrock carb, performer intake manifold.) this isnt gona be a race car, its just my daily driver/weekend warrior. i have a stupid question... why does the timeing indicator even display retarded timeing if 6 is the minimum its suppost to be at?

 

probably just as a reference so you know how far it's off when you're adjusting it.

 

1 more thing, you said 4 degrees base timeing isnt enough.... what exactly determines that? i ran my timeing at 0 for a week and it ran fine. i only changed it because a mechanic guy i know told me to. i never asked why though.

 

it's just physics. when the fuel/air mixture ignites it burns and does not instantly explode so you have to ignite it before the piston is all the way at the top so that the flame has time to spread before putting all its pressure on the piston