[bygddy]

Hey everyone, im have a couple of quick questions with a long lead up....first the car stuff, 1970 pontiac strato chief coupe, 350 (sbc) flat tops, patriot 195 heads (64cc), air gap intake with 1" spacer, bg 750 mighty demon, harland sharp rollers, comp xe284h, msd e-curve dist, msd 6a box, plugs gapped at 40, 1"5/8 long tubes with 3" all the way to thrush fully welded two chambers with turndowns. Th400 with tci 2600 stall, b&m stage 2 kit, auburn pro series diff, 411 richmond gear. 4200pnd whale.
Now the first is timing, right now i have it locked out at 38* total, all the time, No detonation using 94octane gas, last week got stuck running 91 and still not bad noises. Can i get away with more timing? As it is it seems like i have lot's but wondering if more is ok and what drawbacks i may have. It should be around 10:3:1 compresiion now and it runs fantastic. After going from a 3:55 to the 4:11 its' like a completely different animal, much much stronger and lot's more fun to drive. Runs perfect, no stumble, no bogs, idles at 800 in gear, 1000 in park, pulls clean until 6000rpm (rev limiter). So my two questions are the timing issue, can and shoudl i run more? Or am i reading it right? Confirmed tdc, have it marked at balancer confirmed tdc is at the right mark on my pointer., timing light set for 38*, car running warm and line is steady at the zero mark on my timing pointer with gun at 38*.? And seeing as im hoping tech inspector will chime in here and shed some light maybe you could ball park my hp with this combo? Assuming good traction and all things being equal any et estimate? Thanks In advance for any help.....
Dave

[cobalt327]

With traction, you have the potential to run 13’s.

From what I’ve heard about the heads you’re using, around 34º seems to be their ‘sweet spot’, and I doubt if there will be any real gains from going higher, w/only the risk of detonation as the reward.

That cam is not so radical that you couldn’t set the ignition up w/a timing curve, but by the way you explain it- there may not be much if anything to be gained. You sound a little like a (recently banned) member who has a similar set-up (his is a 383, IIRC)- he also says his performance is great w/o a curve and locked at max.

I’ve said it before- if it works for YOU, then go for it. But a back-to-back comparison on a track is the best way to evaluate just what IS happening, IMO. Also IMO the cam specs aren't so 'big' that locked timing is required. It does make setting up the distributor easy, though! lol

I see only 185 and 190, and bigger, but not 195cc runners.

[bygddy]

Originally Posted by cobalt327

With traction, you have the potential to run 13’s.

From what I’ve heard about the heads you’re using, around 34º seems to be their ‘sweet spot’, and I doubt if there will be any real gains from going higher, w/only the risk of detonation as the reward.

That cam is not so radical that you couldn’t set the ignition up w/a timing curve, but by the way you explain it- there may not be much if anything to be gained. You sound a little like a (recently banned) member who has a similar set-up (his is a 383, IIRC)- he also says his performance is great w/o a curve and locked at max.

I’ve said it before- if it works for YOU, then go for it. But a back-to-back comparison on a track is the best way to evaluate just what IS happening, IMO. Also IMO the cam specs aren't so 'big' that locked timing is required. It does make setting up the distributor easy, though! lol

Good luck.

Not me, not banned...promise....With only 350 ci the cam seems fairly aggresive, i love it, other then valvetrain noise which im told is common with teh xe series...I had it set up with 18* initial, and 36 total all in by 2500 and it seemed a little lazy down low, and idle quality wasn't as good, with teh e-curve setting timing is a joke, couple of dip switches and voila.....and the start retard makes it easy to start all the time....

[cobalt327]

Originally Posted by bygddy

Not me, not banned...promise....

I didn't think so, there are just a few similarities there.

Check out the posts HERE, there is some more good info on timing in general and vacuum advance in particular that you may find interesting. You just never know where good info might come from, even in the middle of a p-ing match, something interesting will sometimes come out. Not often, but sometimes....

With only 350 ci the cam seems fairly aggresive, i love it, other then valvetrain noise which im told is common with teh xe series...I had it set up with 18* initial, and 36 total all in by 2500 and it seemed a little lazy down low, and idle quality wasn't as good, with teh e-curve setting timing is a joke, couple of dip switches and voila.....and the start retard makes it easy to start all the time....

I found a shot of the chambers. They seem like a hybrid "fast burn" chamber, having a better quench pad on one side, but not so much the other side.

[bygddy]

Originally Posted by cobalt327

I didn't think so, there are just a few similarities there. But because of all the posts generated during that (and other) threads, there is some more good info. You just never know where good info might come from, even in the middle of a p-ing match, something interesting will sometimes come out. Not often, but sometimes....

I found a shot of the chambers. They seem like a hybrid "fast burn" chamber.

Dumb question here but ........"I found a shot of the chambers. They seem like a hybrid "fast burn" chamber"......???? meaning???

[cobalt327]

Originally Posted by bygddy

Dumb question here but ........"I found a shot of the chambers. They seem like a hybrid "fast burn" chamber"......???? meaning???

Good question, I edited my post above with:

They seem like a hybrid "fast burn" chamber, having a better quench pad on one side, but not so much the other side.

A "fast burn" chamber has a sort of 'dual quench pad' or kidney bean shaped chamber- which I suppose yours could also be said to have. In that just the quench pad(s) isn't all there is to a fast burn chamber, I might have been accurate to have just said "fast burn", period!


GMPP FAST BURN CHAMBER

[bygddy]

Originally Posted by cobalt327

Good question, I edited my post above with:

They seem like a hybrid "fast burn" chamber, having a better quench pad on one side, but not so much the other side.

A "fast burn" chamber has a sort of 'dual quench pad' or kidney bean shaped chamber- which I suppose yours could also be said to have. In that just the quench pad(s) isn't all there is to a fast burn chamber, I might have been accurate to have just said "fast burn", period!


GMPP FAST BURN CHAMBER

So does this equate to more timing? less timing? hmm.....I hate timing questions, tell me im reading this right....
I have the balancer marked, i have an aftermarket timing pointer, when the motor is at confirmed tdc, the line at my balancer lines up with the hole at tdc on my pointer. So, engine off, using a piston stop confirmed tdc, and everything lines up, start car, i have a snap on timing light, i set it at 38*, point at the tdc hole in my pointer and voila, clearly the line on my balancer is visable through tHE pointer at the tdc mark. Thus indicating 38* correct? Did i mention i hate timing? Oh and no vacuum advance, just 38, all the time...

[F-BIRD'88]

The motor will want 34 to 38deg timing at WOT to make max power.
More than what the motor wants will not make more power.

The converter stall is very low. 3600-4000 is what you need.
The XE284 in a 350 wants to rev. Take the wimp chip out of it. set the rev limiter at 6700rpm. Get some ET streets and some rear "Air Lift" air bags so you can use it.

Then go to the track and try different amounts of timing and watch the Q mile MPH. The timing that gives the best MPH is the amount hat makes the most power.

This big car could use easily 4.56's but definatly needs the high stall. A 9" is not too much for this car. "2600" is not even getting in the program. 3600++ with the xe284
You want to be able to launch the car high on the torque curve at or near peak torque rpm.

[bygddy]

Originally Posted by F-BIRD'88

The motor will want 34 to 38deg timing at WOT to make max power.
More than what the motor wants will not make more power.

The converter stall is very low. 3600-4000 is what you need.
The XE284 in a 350 wants to rev. Take the wimp chip out of it. set the rev limiter at 6700rpm. Get some ET streets and some rear "Air Lift" air bags so you can use it.

Then go to the track and try different amounts of timing and watch the Q mile MPH. The timing that gives the best MPH is the amount hat makes the most power.

This big car could use easily 4.56's but definatly needs the high stall. A 9" is not too much for this car. "2600" is not even getting in the program. 3600++ with the xe284
You want to be able to launch the car high on the torque curve at or near peak torque rpm.

Stone stock 40yr old bottom end, 50000 miles, need it to live for thsi summer until i can afford a 383, so wimp chip is in until i don't care if it breaks....I agree with the convertor, unfortunatly the car will get either a tremec or a 200r4 next spring, so i don't want to buy another convertor till then....and yes, with an od and 28" tire it could use a 4:56.....next year when the od is in maybe....you are sure are bang on on every suggestion tho.....lol....any hp guesses? I keep hoping techinspector will jump in here with a guestimate.....

[cobalt327]

Originally Posted by bygddy

So does this equate to more timing? less timing?

Less timing.

[bygddy]

HP or et guesses anyone? And less as in leave the damn thing alone it runs fine or less as in dial it back a bit and see how it goes?

[cobalt327]

Originally Posted by bygddy

HP or et guesses anyone? And less as in leave the damn thing alone it runs fine or less as in dial it back a bit and see how it goes?

If you were testing at the track, you'd advance the total until it slowed or detonated, then you'd back it up a couple for safety's sake.

There is no advantage in using more total timing than what's needed- even w/o detonation, the earlier the ignition, the more loss of power can occur from the pressure rising as the piston's still rising. It's finding that "sweet spot", where the pressure of combustion doesn't overcome the advantage in lighting off the mixture earlier.

It's MY opinion that I'd rather leave a couple HP on the table for the added insurance against detonation. Running on the ragged edge of detonation will bite you when you least expect it- even a 'bad' tank of gas can cause it, and detonation isn't always heard, either.

If you choose to use as much total as possible, be sure to keep an eye on the plugs for signs of "peppering" on the porcelain. This is an indication of detonation and if you DO notice it, back the timing down right then and there. That's not the only indication, but a bad one- that pepper is aluminum from the piston. The plugs may look overheated, the ground strap can get damaged and in real bad cases the porcelain will break.

[bygddy]

Originally Posted by cobalt327

If you were testing at the track, you'd advance the total until it slowed or detonated, then you'd back it up a couple for safety's sake.

There is no advantage in using more total timing than what's needed- even w/o detonation, the earlier the ignition, the more loss of power can occur from the pressure rising as the piston's still rising. It's finding that "sweet spot", where the pressure of combustion doesn't overcome the advantage in lighting off the mixture earlier.

It's MY opinion that I'd rather leave a couple HP on the table for the added insurance against detonation. Running on the ragged edge of detonation will bite you when you least expect it- even a 'bad' tank of gas can cause it, and detonation isn't always heard, either.

If you choose to use as much total as possible, be sure to keep an eye on the plugs for signs of "peppering" on the porcelain. This is an indication of detonation and if you DO notice it, back the timing down right then and there. That's not the only indication, but a bad one- that pepper is aluminum from the piston. The plugs may look overheated, the ground strap can get damaged and in real bad cases the porcelain will break.

Well i have a 450km roadtrip this thurs with a 4:11 gear and no od, so me thinks i will move it down to 36ish and go from there, maybe when i get back i will play with it some more and see what it likes better.....

[techinspector1]

For those of you who don't understand why I don't just jump right on every combo where the OP asks for hp figures for their combo, here is one of the reasons. I need cylinder head flow like the figures I'm showing here, using the manufacturer's published flow, but factored down by 5% in an attempt to circumvent the BS and get down to brass tacks. This takes time. Lots of time. I have to go to the manufacturer's site, pick out the head you have, write down the flow numbers, put them into the calculator and multiply by .95, then enter all the data into the software. If you'll do it for me and publish the figures like I have done here, it makes running a DynoSim much easier for me.

Factored Patriot flow figures by 0.95, new figures are here....
0.100 66 55
0.200 133 99
0.300 183 136
0.400 218 167
0.500 246 180
0.550 253 185
0.600 256 190
0.650 258 195
0.700 259 200

12-250-3 (XE284H), 423 hp @6000, 421 ft/lbs @4000&4500, 350 ft/lbs @2000, 178.8 BMEP @4000

12-246-3 (XE274H), 417 hp @6000, 435 ft/lbs @4000, 380 ft/lbs @2000, 184.4 BMEP @4000

12-242-2 (XE268H), 409 hp @5500, 440 ft/lbs @4000, 394 ft/lbs @2000, 186.2 BMEP @4000

12-212-2 (280H), 410 hp @5500, 430 ft/lbs @4000, 373 ft/lbs @2000, 182.3 BMEP @4000

Based on the results, for a street motor, I personally would choose the XE274H and give up 6 hp to pick up 30 ft/lbs of torque @2000.

On this particular motor, a XE274H combined with a high-rise intake such as a RPM or Stealth would result in these figures...
460 hp @6000, 465 ft/lbs @4500, 371 ft/lbs @2000, 196.7 BMEP @4500. Notice the dramatic jump in Brake Mean Effective Pressure. The motor is working much harder now with the correct cam and manifold. Good, tight squish will be critical.

[bygddy]

Originally Posted by techinspector1

For those of you who don't understand why I don't just jump right on every combo where the OP asks for hp figures for their combo, here is one of the reasons. I need cylinder head flow like the figures I'm showing here, using the manufacturer's published flow, but factored down by 5% in an attempt to circumvent the BS and get down to brass tacks. This takes time. Lots of time. I have to go to the manufacturer's site, pick out the head you have, write down the flow numbers, put them into the calculator and multiply by .95, then enter all the data into the software. If you'll do it for me and publish the figures like I have done here, it makes running a DynoSim much easier for me.

Factored Patriot flow figures by 0.95, new figures are here....
0.100 66 55
0.200 133 99
0.300 183 136
0.400 218 167
0.500 246 180
0.550 253 185
0.600 256 190
0.650 258 195
0.700 259 200

12-250-3 (XE284H), 423 hp @6000, 421 ft/lbs @4000&4500, 350 ft/lbs @2000, 178.8 BMEP @4000

12-246-3 (XE274H), 417 hp @6000, 435 ft/lbs @4000, 380 ft/lbs @2000, 184.4 BMEP @4000

12-242-2 (XE268H), 409 hp @5500, 440 ft/lbs @4000, 394 ft/lbs @2000, 186.2 BMEP @4000

12-212-2 (280H), 410 hp @5500, 430 ft/lbs @4000, 373 ft/lbs @2000, 182.3 BMEP @4000

Based on the results, for a street motor, I personally would choose the XE274H and give up 6 hp to pick up 30 ft/lbs of torque @2000.

On this particular motor, a XE274H combined with a high-rise intake such as a RPM or Stealth would result in these figures...
460 hp @6000, 465 ft/lbs @4500, 371 ft/lbs @2000, 196.7 BMEP @4500. Notice the dramatic jump in Brake Mean Effective Pressure. The motor is working much harder now with the correct cam and manifold. Good, tight squish will be critical.

Thank you soooo much, i didn't realize what all was involved, that was a lot of looking crap up for someone who contributes zip so far...so thanks. I really appreciate that. That and the numbers seem solid and pretty near what i was hoping for so that made my night....