Can we talk about 350 ci power

[WorkinLonghorn]

Hi. I recently got a "rebuilt" 350 for my '69 GMC 2500 and,to make a long story short,I ended up getting a much lower compression ratio than intended.( I'm guessing 7.5-8.0-1). I recovered my money (plus some) but I am not too happy with the "power" produced by this dog.
Let me say that I am a pretty cheap SOB and so I will not be installing a blown 454.I'm just looking for some tips for getting more power.
A) Will switching to HEI actually make a difference? I realize that the entire timing curve will have to be re-adjusted due to the lowered CR.I put an adjustable vac advance on but it seems that there is not enough centrifial advance.
B)Would it be advisable to have the heads and Intake mani milled to increase CR or is it better to just change the pistons?
C)What about jets? It is a bone stock quadrajet. Any suggestions on upgrades for carb?
This is a heavy truck (about 5100 lbs.with tools) and it will do alright as a work truck,but there's more to life than work. -thanks-cougar
'69 GMC Custom Camper Longhorn 435CR 4spd,350 4brl,373 Dana (open),stock wheels,stock distrib.

[PanelDeland]

More info on the combo would help.The CR may be helped thru a head swap depending on what cc's your heads have for combustion chambers.Also though CR does affect power there are lots of other variables that will cause lower performance.A different cam may help.HEI will not help performance but it will provide a hotter spark and more consistent firing if all else is equal.
It will be really hard to give you many ideas with out knowing the existing combo.It's like asking directions to Toledo,first we gotta know where you're coming from.

[Billla]

When you note you're unhappy with the power, what exactly is the concern? Factory 350s had 8:1 CR...so if you pulled a stock engine and replaced it with another basically stock engine then you shouldn't see a major difference. It's possible there are other factors here.

It's possible you could gain a power increase with bolt-ons, but IMHO the only way to significantly increase the power is to get the CR up a bit. As PanelDeland noted, the key question is the head casting number - if it's a 76cc head there may be an easy solution to the problem. If you've got a build sheet, that would sure help with options.

I wouldn't bolt anything on until you've sorted through the options.

[WorkinLonghorn]

The origional '69 motor was a 9.0-1 CR (255 HP,355 torque) and I ran it on 89 octane. The difference I notice is that coming down a hill that I used to use 4th gear on I now have to go to 3d gear to maintain a steady dissent.So I know there's a lot less compression.
The truck is absolutely stock,except that the guy SAID he put in a mild RV grind cam,(which I did notice the lower power band).
OK,so I won't bother with the HEI because I keep the points in perfect shape and it is very smooth.
I may enlongate the slot that permits centrifical advance and try some lighter springs.
I can put 5000 lbs. wet sand in the back (8 1/2 ft bed) and is quite capable of keeping up with traffic,etc.It's just that my last '69 had some sort of reworked engine and would "light 'em up" (OK, light one up) in 2nd gear and scare the hell out of any fool trying to jump in front of me in traffic.Of course that truck was over 1000 lbs lighter so maybe I shouldn't complain.

[Billla]

I don't know how a SOTP difference like that demonstrates lower compression; I would be careful making changes based on that assumption.

Adding more advance won't help the situation; you should time for ~36 degrees total advance that should be all in before 3000 RPM (changing spings as required) - then set the initial wherever req'd to maintain that 36 degrees total advance. I have a "whitepaper" on how to set that timing if you're interested.

[jeffspower]

Sometimes more isn't better- especially when you need low rpm torque in a daily driver. I had a pickup years ago with a dish-piston 350, big chamber/ small valve 307 heads & a small 60's 2bbl. rochester carb & a conservative size Clay Smith cam. After it bored itself .030 over with wear and was using a qt. of oil every 50 miles, I rebuilt it. I went .040 over with the same type of pistons, a similar grind Crane cam, but swapped to 300hp/ 327 heads and AFB 4bbl. I gained nothing. Maybe a little more rpm, but nothing where it's needed.

[WorkinLonghorn]

I'll take a look at that timing sheet Bill,Thanks a lot.I know the basic procedure but I've never actually done it.-cougar

[WorkinLonghorn]

Jeffspower,that sounds like a real drag. I am going to look around here and see what guys are saying about the 383 stroker.I read that that can be a good tow/haul motor with the right heads and cam.-cougar

[cooters]

I Have Built Countless 350 And 383 Combinations. Intake Manifolds Carb Setup And Timing Play The Most In Pulling Power. Forget Timing Lights, Set The Timing By Powertiming And You Will Always Get The Most Power Your Motor Will Produce. Outside Of That All Power Is From Heads. Vortec Heads Are The Best Bang For Your Buck And Will Also Raise Your Compression

[WorkinLonghorn]

Thanks,I may just be dreaming here,but if I was to go with vortec heads,what is the first year for vortec on a 350 and will they adapt to an old style block? thx-cougar

[Billla]

Originally Posted by cooters

Forget Timing Lights, Set The Timing By Powertiming And You Will Always Get The Most Power Your Motor Will Produce. Outside Of That All Power Is From Heads. Vortec Heads Are The Best Bang For Your Buck And Will Also Raise Your Compression

Respectfully but completely disagree on every point other than Vortec heads are the best deal on the planet. Vortec heads will not raise your compression unless your current heads are > 64cc.

[Billla]

Originally Posted by cougar

Thanks,I may just be dreaming here,but if I was to go with vortec heads,what is the first year for vortec on a 350 and will they adapt to an old style block? thx-cougar

Vortecs only fit GEN I ("old style") blocks. The LT1/LT4 heads are basically Vortec heads revised for reverse-flow cooling (not quite true, but close enough and then the entire series died for production use with the introduction of the LS-series engines.

You can go junking for used Vortec heads, but BRAND NEW Vortecs are available for ~$525 pair assembled! Figure on $300+ for a head overhaul, with the potential for more if there are problems and the new Vortecs are the best deal on the planet. The only real limitation of the Vortecs are .475 lift - which if you're looking for low-end torque shouldn't be a significant issue. I posted options in the Engines section where either CompCams "beehive" springs will bolt in, or you can have the spring seat and valve boss machined for other springs. SDCP and others sell already upgraded Vortecs for around $700 pair/assembled...still a screamin' deal.

L-31 Vortecs were installed in 1996 - 00 trucks and vans, and "aftermarket" Vortecs If you're going junking for used heads, be careful of the donor vehicle - some of the heavy-duty trucks came with Vortecs that have single-angle Iconel valve seats for durability...but these seats kill flow.

[Billla]

Originally Posted by cougar

I'll take a look at that timing sheet Bill,Thanks a lot.I know the basic procedure but I've never actually done it.-cougar

Here you go. Lars is an incredibly well-respected Corvette tuner and I've learned a ton from him on another board and put his teachings to use.

[cooters]

With The Majority Of Heads Kicking Around These Days On Carbed 350's Being Either 624, 882 Casting They Have 76cc Chamber Were Vortec 1996 To 98 Heads Are 64cc So The Compression Goes Up And The Heads Also Are Heart Shaped Chambers

[cooters]

The Main Reason I Dont Like Timing Lights Is The Balancer Marks Are Usually Out A Few Degrees. As Well Motor Temp, Operating Conditions , Fuel Type, Air Intake Temp Are All Related To The Timing. Giving A 350 1 Timing Spec Is Like Saying All 350's Are The Same. I Find That On The Dyno Most Motors Can Tolerate More Timing And The Horsepower Numbers Show It, But To Much Timing And The Torque Will Suffer

[WorkinLonghorn]

Also the compreesion ratio is different between motors and the LOWER the compression the more advance you need for optimal permormance. My engine was originally 9-1 CR and the advance spec in the GM shop manual is 32 total degrees. However the 366 at 8-1 gets 40 degrees per the book.
Now some moron "rebuilder" put a very low compression motor in and I have to set the initial timing WAY advanced to get any power.(spec WAS TDC originally)-cougar

[cooters]

Weather the motor is 9:1 or 10:1 will however not make a huge difference in a truck. if you have real pulling problems i would check stuff like how tight the valves are set, what kind of cam the motor has, what carb are you running? This rebuild may have a crappy no lift cam in it. What are your plug gaps set at. I personaly hate points cause the HEI or pertronix setup has way higher coil voltage allowing for 45 thousands gap instead of 30. These are all factors in HP. I dought your comp is at 7.5:1 as flattops are generally the rebuilders choice or something close to it ( lower comp pistons in a 350 usually cost more due to supply and demand)

[Billla]

Originally Posted by cougar

Also the compreesion ratio is different between motors and the LOWER the compression the more advance you need for optimal permormance. My engine was originally 9-1 CR and the advance spec in the GM shop manual is 32 total degrees. However the 366 at 8-1 gets 40 degrees per the book.
Now some moron "rebuilder" put a very low compression motor in and I have to set the initial timing WAY advanced to get any power.(spec WAS TDC originally)-cougar

This doesn't make a lot of sense to me; I may be misreading this. Generally we're looking for 36 degrees total advance (initial + mechanical) and up to 52 degrees of advance with vacuum advance added in. Still looking for the exact specs on the engine to see exactly how low the compression is. If you're running more than 12-14 degrees initial timing I would look for other problems IMHO.

[cooters]

your vacuum advance will not add more timing than the mech advance will. Vacuum adv is only thier to fill in untill centrifical advance from the weights take over when the rpms pickup. You will not likely get more than 36 degrees before it starts to ping. Base timing is also checked with the vacuum advance disconnected. Powertiming saves time and gets it right every time unless you are running a race engine.

[chevybill]

I fully second Billa's reference to Lars. He is almost a "god of timing" on one
of the corvette boards, that I frequent.

Originally Posted by Billla

Here you go. Lars is an incredibly well-respected Corvette tuner and I've learned a ton from him on another board and put his teachings to use.

[WorkinLonghorn]

If you're running more than 12-14 degrees initial timing I would look for other problems IMHO.

Yeah,there's something fishy here because with original motor I ran it at TDC as specified.Now it's so far advanced it's off the scale.I'd need timing tape just to see where it is,It's about on the top of the damper at idle.I can't remember if I had that damper re-worked,I think they just put a sleeve on it or something.(for the oil-seal surface).
But really it's not running badly,I'm just looking for a bit more power in case I finally get another trailer.It's more than adequate for work.
Thanks for the replies and info.-cougar

[Green Machine]

Can you get a compression gauge on there ? I know that won't tell the compression ratio, but I'd like to see about 150-160 psi.

PS - I'll let some else type up the long explanation why looking for a specific number is wrong - SCR, DCR, cams, octane, altitude, etc.

[WorkinLonghorn]

This is SUPPOSED to be a re-built 350 but it burns a quart of oil every 600 miles,leaked like a sieve,and is pretty gutless.I did slap a gauge on there last year and it was right at 150. I think they probably honed and re-ringed a used motor,maybe new rod and main bearings. For me,on my budget,this was a major major expense,and I got hosed.However I did get all my $ back plus some after their guard dog bit me in the ass on my 7th return to the shop.(Insurance took care of me in a big way).-cougar
Needless to say I might not have them do any more work on my truck.

[Billla]

Originally Posted by cooters

your vacuum advance will not add more timing than the mech advance will. Vacuum adv is only thier to fill in untill centrifical advance from the weights take over when the rpms pickup. You will not likely get more than 36 degrees before it starts to ping. Base timing is also checked with the vacuum advance disconnected. Powertiming saves time and gets it right every time unless you are running a race engine.

Apologies in advance, but this is incorrect. Vacuum advance absolutely adds advance in addition to mechanical advance. Vacuum advance adds additional advance at part-throttle cruise when the engine can tolerate signicantly more advance - as noted previously up to 52-54 degrees.

IMHO, "powertiming" always ends up adding far too much advance.

[Billla]

Originally Posted by cougar

This is SUPPOSED to be a re-built 350 but it burns a quart of oil every 600 miles,leaked like a sieve,and is pretty gutless.I did slap a gauge on there last year and it was right at 150. I think they probably honed and re-ringed a used motor,maybe new rod and main bearings. For me,on my budget,this was a major major expense,and I got hosed.However I did get all my $ back plus some after their guard dog bit me in the ass on my 7th return to the shop.(Insurance took care of me in a big way).-cougar
Needless to say I might not have them do any more work on my truck.

Not sure what to say other than yeah, it sounds like you got screwed I think we could probably troubleshoot from the outside and make things a bit better, but ultimately it probably needs to be pulled apart just to see what the heck they did

I would try to sort out the timing problems; it's an afternoon's work and would definitely show improvements. I have to wonder if you don't just have a HUGE vacuum leak...