[oldblue1968chevy]

Hi guys. I have a 68 chevy pickup truck with a 4 bolt main 350 I rebuilt myself a year or so ago (I was 17).

I put some vortec style heads (summit/dart), performer rpm intake, 1406 edelbrock carb, ram horns, comp thumpr 279 camshaft, flat top pistons, balanced stock bottom end.

Im trying to get the curve igntionman (on other forums) talks about. 375-41 weight combo so far Ive got the 375 center weight,still looking for the pair marked 41, he also recommends limitng the vacumn adv to about 8-10*.

I bought some NGK TR5 sparkplugs awhile back, Should I gap them out of the box, if yes what do I gap them to???!!??!!

Thanks again guys

Ps I was using the mr gasket curve kit but the GM weights are so much better quality I decided to swap em.

My total timing (vac hooked to manifold vac but right now its plugged up) is 36 degrees but I have a bit of hot start -issue so i'll drop it to 35-34, then adress the 20* that the vac can puts out.

Thanks

[BEC]

TR5 is a .035 gap,

[Frisco]

Originally Posted by oldblue1968chevy

Hi guys. I have a 68 chevy pickup truck with a 4 bolt main 350 I rebuilt myself a year or so ago (I was 17).

I put some vortec style heads (summit/dart), performer rpm intake, 1406 edelbrock carb, ram horns, comp thumpr 279 camshaft, flat top pistons, balanced stock bottom end.

Welcome and glad to see the younger set interested in Hot Rodding.

Originally Posted by oldblue1968chevy

Im trying to get the curve igntionman (on other forums) talks about. 375-41 weight combo so far Ive got the 375 center weight,still looking for the pair marked 41, he also recommends limitng the vacumn adv to about 8-10*.

Ps I was using the mr gasket curve kit but the GM weights are so much better quality I decided to swap em.

My total timing (vac hooked to manifold vac but right now its plugged up) is 36 degrees but I have a bit of hot start -issue so i'll drop it to 35-34, then adress the 20* that the vac can puts out.

Thanks

The GM weights are much better than any of the weights that come in the aftermarket timing curve kits and your choice to use the GM units is a good one. What I do suggest though is to use one light spring and one medium spring from the aftermarket timing curve kit on the stock GM advance weights. This should get the 'all-in' advance in the correct range for street use. 2500-3000 RPM.

Do use the manifold vacuum for the source. Use an adjustable canister to limit the amount of vacuum advance to around 10 degrees. There are stock GM canisters available that will yield the correct vacuum but I don't have the part numbers on hand. Do a search on this site as I have posted them in the past. OK, I just did the search and have posted it at the bottom of this.

The 36 degree Total Mechanical Timing (with the vacuum advance hose dis-connected and plugged) should be OK. Your hot start problem can be addressed with a heat shield between the exhaust manifold and the starter solenoid or by using a remote solenoid (Ford Motors type). Most mini-reduction gear starters will also work without the heat shield or remote solenoid.

RickWI posted on 03-02-2005 the following info:

The following listing (HEI) is as follows: The first four part number listings are the 4 numbers that are most commonly used in a Chevrolet performance application. The “AR12” can is the most versatile and user-friendly unit for a good performance street engine. The AR 15 and AR23 are almost identical, with only slight variations in their “start-stop” specs. The “AR31” can is the HEI equivalent to the “B28” Hi-Perf can used on the early engines: The advance comes in very quick on this unit – too quick for many performance engines. Do not use this very quick unit unless you have a cam/engine combination that really needs an advance like this. It can be used as a tuning aid for problem engines that do not respond well to other timing combinations, and can be successfully used in applications where direct manifold vacuum is applied to the can (see paragraph and discussion on this above)

After this, the listing is by Echlin part number. All GM HEI vacuum advance units are interchangeable, so you can use a Cadillac or GMC Truck unit on your Vette, if that’s what you want to do.

*****************

In order to comly with copy/pasting guidelines, the rest of this post can be seen here.

[Frisco]

Originally Posted by oldblue1968chevy

I put some vortec style heads

My total timing (vac hooked to manifold vac but right now its plugged up) is 36 degrees but I have a bit of hot start -issue so i'll drop it to 35-34Thanks

On reading your original post again I noticed that you are running Vortec heads.

This limits the suggested Total Mechanical Timing to be in the 32-34 degree range. Skip what I originally said in my previous post about the 36 degrees being OK. That number is not for Vortec heads.

[sbchevfreak]

Frisco, you should add the vac can info to a wiki article. It is good stuff. I would, but credit where it is due is my motto....

[Frisco]

Originally Posted by sbchevfreak

Frisco, you should add the vac can info to a wiki article. It is good stuff. I would, but credit where it is due is my motto....

It is very good info.

Another member on this site, Rick WI, did the research and posted that list in addition to a list with the vacuum canister part # for non-HEI GM distributors.

A search on this site will find them.

Like you, I give credit where credit is due. In this case Rick WI is the original poster of the info and I am merely the messenger. I posted credit for him in my previous post above.

CONCERNING POSTING ON WIKI:

I don't post to WIKI because anyone can change the info there. This enables false or mis-leading info to be entered which could cause a reader to become mis-informed. I realize that is not what WIKI is intended for, but the possibility exists, so I don't post on it. I do occasionally read segments that have been posted on WIKI and then attempt to weed out fact from fiction.

[sbchevfreak]

Thank you for the clarification, Frisco. I can understand the wiki thing, I had never actually thought about it before (almost never been on wiki, actually...)

Kudo's to RickWI for the vac can info!

[Custom10]

That is good info, very detailed and allot of research went into that no doubt.

blue68 couple things, you have a thumper cam with 227/241 duration @ 50 intake exhaust, that is allot I would think it is going to need about 20-22 BTDC base timing without considering vacuum advance or mechanical advance. Hopefully your static compression ratio is at least 10:1, with flat tops and vortec heads (assuming 64cc chambers) you should be there.

An option for an easy solution to your ignition setup (assuming you have fire wall clearance) would be to purchase an HEI with adjustable vacuum advance like this one:

http://www.skipwhiteperformance.com/...px?Item=6500-R

Then get yourself one of these,,,http://www.summitracing.com/parts/CRN-99619-1/ to limit the vacuum advance to 10-12 deg.

On these HEI's you can then add a simple mechanical advance limiter screw to the HEI rotor base plate to limit the mechanical advance to get a initial + mech advance @ 34 Deg BTDC. Use a combination of springs to set in the mechanical advance rate vs rpm.

Also run a swicthed 12 volt 12 gage wire to the HEI power connection to eliminate hot start issue, locate the switch on/under the dash, turn the engine over then hit the switch, presto.

For about 60 bucks and some time you would have it all cased. Try running full manifold vacuum so that at idle you are giving it 30-32 BTDC timing. Assuming that cam is making any vacuum?

If using an HEI try .43-45 gap on the plugs

[oldblue1968chevy]

Using 375/41 GM weight combo, vac can gives roughly 10* welded a washer on it to limit it and cut the sides of washer off.

QUESTION-My bottom end is 'balanced' the machinest drilled a small hole in the balancer, he said i needed a new one cause my old one the rubber was rotten. Right now im getting about 33* intial (no vac adv) timing theres no WAY this can be right, the truck runs better than ever but the numbers throw me off.

My balancer/timing cover is factory style, timing tab is at 2:00 position. Balancer should be correct I would think, its new. Im calling my builder tomorow (been about a year and a half since i built it back in HS).

WHY is my timing @ 33* btdc and running good.

Ps i checked it with a dialback and standard timing light to verify my timing light wasnt on crack.

Thanks

[oldblue1968chevy]

Should I return my plugs for a tr55 (.45 gap right?) or can I just open the gap up to .45 (alot simpler cause autozone is about 25 minutes away).

thanks

[oldblue1968chevy]

8 inch diameter balancer btw[IMG][/IMG]

[oldblue1968chevy]

[IMG][/IMG]

gives roughly 10 degrees hooked to full manifold vac

[oldblue1968chevy]

heads are actually 67cc and accept up to .520 lift summit puts there name on em but they came with dart paperwork and those valvecovers are just sitting on there to keep from painting the inside of the head LOL

[oldblue1968chevy]

TTT

I opened up my TR5 sparkplugs from .35 to .45

this sound about right for stock hei/plugs

[oldblue1968chevy]

installed new plugs/wires gapped to 45 on the plugs

running the GM springs on the GM weights, will try the light/medium combo sometime soon.

Still dunno why I get33* base/initial timing (idle with vac adv plugged).

Also, have a oil leak from the nylon fitting behind the intake going to a mechanical sunpro guage, how can i fix it? i read on the interenet the copper line is better i bought it but havent intsalled it yet, will it fix the leak?