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Old 06-28-2010, 03:17 PM
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need help with timing

i have a 90s blocks with 193 heads shorty heads 270 magnum cam edelbrock intake and carb 3.73 gears stock hei dist. ok i tried 32 total and its a dog so i turned it to 40 total and its waking up so i was wonder should i keep going advancing timing or is something else wrong

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Old 06-28-2010, 03:54 PM
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I don't know what type of heads you got and I am assuming its a 350 sbc. With that cam somewhere between 12-18 degrees initial timing with vacuum advance unhooked and 34 to 36 mechanical all in by 2500-3000 rpm would be ideal but all motors are different depending on other factors but that would be the ball park numbers anyways.

Also make sure you hook your vacuum advance up to full manifold vacuum and make sure its an adjustable one and limit it to around 12 degrees total. You might want to check out your distributor and make sure the weights are not sticking and its working good. Also check your coil and make sure its firing good.

Also if you got old factory gm smog type heads and if you got only around 8 to 8:5 to 1 compression that does not help. With that cam you need some good flowing cylinder heads and your carburetor will need to be tuned as well. Give some more info as what carburetor you got and is your intake a edelbrock performer or the performer rpm?

I am certain others will help you out too. The more ideas posted on what to check will help.
Eric
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Old 06-28-2010, 04:54 PM
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i have tbi heads 65cc and just reg performer and 600 edelbrock carb

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Old 06-28-2010, 06:16 PM
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Well from reading on other threads on here the TPI heads are one of the worst flowing heads from GM. That is part of your problem not much power. It takes a decent amount of torque and some decent horsepower to make a car take off really fast and have excellent response.

My brother has a 88 chevy caprice with a stock 305 and it makes only about 175 horse power and somewhere around 250 ftlbs of torque or a little more and it does not run fast at all compared to something with more power. With that bigger cam it's more then what your cylinder heads can really handle.

You have basically over camed your motor. Why do I know this? Because I like many first timers have done this sort of thing. I once had a bone stock 350 with poor flowing 882 cylinder heads and a comp cam 292 magnum for a cam. That thing sound good but that was about it. It had poor throttle response and nothing on top end.

All parts have to match within a certain area for it all to work good. What you need is a cylinder head upgrade and keep your current carb nothing wrong with it. If you got a set of after market heads with 180cc intake runners and maybe switched out the performer for the rpm performer it would really wake up your ride.

I know if you don't got the funds that is not an option. At least get your heads ported and the exhaust ports opened up that would help some.
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Old 06-30-2010, 04:30 PM
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i think i found my problems i thought i had -12cc pistons but found out that the motor is HD and its 4 bolt main -18cc and 64 cc heads so compression is 8.75:1 so i was wonder can i mill the vortecs to 58cc
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Old 07-01-2010, 06:34 AM
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6 cc's is a lot to try and shave off flat mill, but it depends on the amount of material on your heads. Best bet would be to take to your maching shop and discuss options.

Another idea for getting compression up would be to angle mill the heads. I just had this done on my main car. You will also have to get the intake done(would anyway with the amount of flat milling you were looking at) and do a little work possibly to get the headers to fit right, but well worth it. They rolled my heads 2s from factory 23 and my combustion chambers went from 58 to 46.5cc.I opened them back up after that but you get the idea. Angle milling will get you there, just takes more work. Plus rolling the valves more center over the cylinder is not a bad thing either.

Josh
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Old 07-01-2010, 07:16 AM
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Quote:
Originally Posted by prettyboyced
i have a 90s blocks with 193 heads shorty heads 270 magnum cam edelbrock intake and carb 3.73 gears stock hei dist. ok i tried 32 total and its a dog so i turned it to 40 total and its waking up so i was wonder should i keep going advancing timing or is something else wrong
Those swirl port heads won't rev, but down low in the RPM range they will pull.

The reason turning the timing to 40 helped, isn't the 40 total, it's the increase in the initial timing that's helping.

So, what you need to do is run more initial, w/o going over about 36 total. This might mean modifying the distributor to limit the mechanical advance.

This is a rough guideline of how you can set up your distributor, tune it from this baseline for the best performance:

About 34-36 BTDC total, all in by about 2500 RPM (this is adjusted by the springs), with about 10-12 of vacuum advance. See where this leaves you as far as initial timing. You'd like there to be at least 14 BTDC at idle speed, more will likely be needed, but start lower and add timing, not vice versa. Be sure as you add initial timing that you do not exceed the 34-36 total timing. Connect the vacuum advance to a manifold vacuum source.

Be sure you readjust the carb idle mixture screws as you change the timing. If you were not using manifold vacuum for the vacuum advance, you will get an increase in idle speed when you hook up to manifold vacuum. Use the curb idle screw to lower the idle speed.

If needed, there are adjustable vacuum cans like the ACCEL #31035. It's an adjustable vacuum advance can for the GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

If you find the can is OK but has too much advance, you will need to physically limit the vac can's travel w/a VACUUM ADVANCE LIMITER PLATE- Crane #99619-1; #99619-1 INSTRUCTIONS.

If you're unsure, or just want to check the accuracy of the tab/mark for TDC, DETERMINE TDC will help you to see for yourself.

You can use MAKE A TIMING TAPE for instructions on making a temporary timing tape to use to check/set the total advance if you don't have a dial back timing light. Before removing the tape, permanently mark the damper w/the total advance position and any other positions you want.

Good luck.
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Old 07-01-2010, 07:39 AM
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Center Bolt heads

The 193 heads are mid-80s center bolt smogger heads. Those are among the most restrictive of the SB Chevy heads and are not any good for performance use. Maybe the trick milling and rolling as suggested would improve those heads. However, before I would go to all that trouble, it seems to me it would be better to find some better heads to start with.

I have not been searching for rebuildable SB V8 iron heads lately so I don't know how difficult it is to find the good ones. They are like all GM high performance heads and the good iron heads have been rebuilt to death. It may be time for you to purchase some new aftermarket aluminum heads rather than tie up a wad of cash in the 193 heads.
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Old 07-01-2010, 01:47 PM
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today in class one of my teachers brought up that back in the day he use to use 305 heads on his 350 and would boost his compression and torque but run out of power around 5K and i have a set of 601 heads on my other motor i was wondering since both heads run out of power about the same and the 601 will give me better compression would it be worth it
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Old 07-01-2010, 03:46 PM
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Quote:
Originally Posted by prettyboyced
today in class one of my teachers brought up that back in the day he use to use 305 heads on his 350 and would boost his compression and torque but run out of power around 5K and i have a set of 601 heads on my other motor i was wondering since both heads run out of power about the same and the 601 will give me better compression would it be worth it
Casting number 14022601 were used on 267ci and 305ci engines from about '79-'86. They had either 1.72" or 1.84" x 1.50" valves and the chambers were about 58cc. So the compression ratio would be higher. But if they have the 1.72" intakes, no way. Even the 1.84" valves are down in size for what you need to let the cam work at higher RPM's.

Overall, it's probably a wash between the two heads, the TBI heads better down low, the 601 maybe a little better higher up, w/no guarantees that will hold true, given the intake valve and port size.

Either head will be down a considerable amount of power from Vortec heads.
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Old 07-01-2010, 08:46 PM
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I am 4-5 hrs north of you, but I have a set of none tbi heads you can have. They would need quite a bit of work as they are "Hecho en Mexico" with 76cc chambers and all. But for $60 in gas, might be worth it. I don't know if your school (SAM?) has a maching class (If SAM I know they do), but the shop I use only charges me $45 per head and $45 for the intake to angle mill them. These heads have a lot of deck surface so milling should be no problem. Plus the valves are 1.94/1.50.

You would still have $200 plus valves and springs in them with gas money. I agree with cobalt in the vortec heads are a good choice. Valves can be had on ebay brand new for $80, springs depending on cam needs, $55-$150. So atleast $350 for "free" heads to do what you need of them. Might not be too far off from those vortec heads.

but the offer is on the table if you want them.

Josh
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Old 07-02-2010, 12:03 PM
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i can probably get some vortec heads in a couple of months so should i keep the tbi heads on or put the 601 heads on there till i get the money for the vortec heads and intake
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Old 07-03-2010, 12:24 PM
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i found some heads L98 corvetter heads ready to bolt on for 150
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Old 07-04-2010, 01:16 AM
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Use a pistons stop to verify true tdc on the balancer and timing tab and correct as nessessary.
If you have the wrong/mismatched timing tab for the three different possible balancers, the timing will be way off. If the balancer outer ring is slipped the timing will be way off. The 270 magnum cam works best after recurveing the distributor. More initial at idle is want you want.. 18 to 24deg base at idle.. 34-36deg max mechanical at 3000 rpm. (a 10 to 14 deg mech advance curve) {limit the mech adv travel}

Then, 10-12deg of vacuum advance. (Also usually needs to be limited.)

"stock" or "out of the box" distributors tend to be set up for stock applications
and need to be modified for perf applications with bigger cams and compression , no egr etc.

The 270 magnum cam does not like a tight "stock" low stall torque converter.
A 2200 stall is just ok not really enough .... a 3000-3200 stall converter is just right. (if you like going fast)
A low stall 1600 stall "stock converter" is not going to work.
The #193 TBI "swirl port" heads and a 270H magnum cam are a bit of a mismatch.
The swirl vane in the intake port that creates a strong low/mid rpm part throttle swirl effect with "stock" low loft cams . becomes a air flow restriction at higher rpms/valve lifts where the 270H magnum cam works.

Last edited by F-BIRD'88; 07-04-2010 at 01:38 AM.
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Old 07-04-2010, 01:25 AM
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The 305 head on a 350 deal only works well if the 305 heads are fully ported and larger "350" sized valves are installed. (1.94 x 1.60 best)
The 601 heads have very small 52cc chambers but once they are deshrouded for the larger (1.94x 1.60) valves the chamber will end up larger than stock.
61cc typical when done.
If you just bolt on a stock 305 head without the porting don't expect much other than the compression increase as the ports are modest just like any other stock smogger head.
After generous porting and larger valves they work pretty good on 350's.
+400hp when done right.
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