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

[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.

[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 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...

[cooters]

im not going to get into a long drawn battle but here it is. V advance comes in where mechanical advance doesnt have enough prm to push the weights out. Here is the test, do a timing test on your truck or car at 3000rpm then disconnect the v advance and tell me if the number is the same. If your car will even run at 50 degrees nevermind while pinging like crazy, consider it a bonus. Just try it. Maximum advance is max advance, the rotor can only advance as much as mechanicaly alowed due to design. take the cap off and turn the rotor, thats max advance.

[cooters]

without getting into a major discusion on timing, a motor will not run at 50 degrees advance, keep in mind 50 degrees of crank rotation means on a 350 spark would happen when the piston is .966 inches from the top of the cylinder. 34 total degrees timing is with mech and v advance

[Billla]

Originally Posted by cooters

without getting into a major discusion on timing, a motor will not run at 50 degrees advance, keep in mind 50 degrees of crank rotation means on a 350 spark would happen when the piston is .966 inches from the top of the cylinder. 34 total degrees timing is with mech and v advance

We'll have to agree to disagree. If an engine is > 3000 RPM steady-state with full mechanical advance in for a total of 36 degrees, is there manifold vacuum? If so, what is the vacuum advance doing at that point?

In any case, this is all well-documented in the notes I attached.

[WorkinLonghorn]

OK,thanks for the replies. I may need a new damper because all the timing marks are WAY off.This is the way it came back from the shop.
Also that original 4MV Q-jet seems to rum real lean because when i start off under partial throttle it kinda sea-saws between power and lower power until I'm well under way.It's very pronounced. I checked and double checked float level and put in a kit but it still happens so I'm thinking it needs re-calibrating.
I just went out to get a casting # but it is blank.And I notice the pad is the short style from later engines.Probably not even a 4-bolt.
>>To give you some idea of how professional this guy was he just cut my AC lines to facilitate engine removal.
I am now drooling over the idea of getting some new Vortec heads with the settlement money. Would add some good HP right?

[Billla]

I would double, double check the damper before assuming the marks are way off. I wouldn't say it can't happen - it does - but I see other issues way more commonly when these don't line up.

I would definitely sort out the timing before getting into the carburation - this is a broad generalization but the timing is way easier to get baselined and by doing this first it ensures you're not chasing timing demons by adjusting the carb.

A blank casting number?

Vortec heads are great heads for the money and flow as well as some of the aftermarket iron heads. I wouldn't expect a significant HP gain without a cam in the .450+ range; stock Vortecs are lift-limited to .475 but there are a couple of ways around that.

[stsalvage]

HELLO ALL i WAS READING ALL OF YOUR POST AND i THINK A FEW OF YOU HAVE CHIMED IN AND HELPED ME SO I'M TRYING NOT TO HAVE ANY ONE THROW A BRICK AT ME BUT I HAVE A 1965 3/4 TON LONG BED AND I'VE USED THIS TRUCK FOR THE BETTER PART OF 17 YEARS HAD 2 ENGS IN THIS BABY THE ONE I STARTED WITH WAS A WORE OUT 327 7 YEARS AGO I GOT A REBUILT FROM A ENG SHOP 350 2OO HP MABEY 220 I RAN A 4V COVETT RODCHESTOR CARB IT DID FINE WHEN I CHANED ENGS I UPDATED TO HEI BIGG DIFFRENCE MADE THE TRUCK PULL HARDER AND JUST MADE LIFE EASYER ON ME I WENT TO A 600 ELDALBROCK CARB AND INTAKE MAN IT COOL THE TRUCK DOWN 5-10 DEGREES AT 110 DEGREES DAYS HERE IN CALIF OUT HERE IN THE DESORT HEAT IS A ROBBER OF HORSE POWER


NOW I GOT A 1971 3/4 TON THAT A FRIEND OF MINE HAS AND HE WAS HAVING THE SAME PROBLEM AS YOU WHEN HE GOR HIS NEW ENGINE IT HAD NO BALLS SO HIS FATHER HAD A 1986 CAMARO 305 ENG THAT WASTED THE CRANK BUT THE HEADS WHERE NEW SO HE THOUGHT THE TRUCK HEADS WHERE JUST NOT UP TO PARE SO HE DROPED THE 305 HEADS ON THE 350 IT HAD A VERY MILD RVCAM IN IT AND MAN LETS PUT IT THIS WAY HE RUNS THAT 87 OCTANG IT PINGS AT 89 IT DOSE BETTER 91 GRATE SO THE CHEEP WAY MIGHT BE THE 305 HEADS THERE GOT A BIGGER CC CHAMBER LIKE 194 I THINK BUT HIS TRUCK PULLS LOADS AND RUNS FINE IT RUNS A LITTLE HOTTER BUT NEVER BLOWN A HEAD GASKET AND YES GET THE POINTS OUT OF THERE ONCE YOU GO TO HEI YOU WILL NEVER GO BACK

[WorkinLonghorn]

Thanks STSalvage. I've been sitting on the fence for a year now about whether to get an HEI,and now I think I will,only from a junk yard I think.Hopefully find one with good bushings etc.
I may look at re-jetting and other performance optiond for the Q-jet when it comes time to pull that trailer.
As to distributor timing advance,I believe the centrifical advance advances the actual lobes,whereas the vac advance pulls the plate with the points around,so you actually do get centrifical plus vacuum advance simultaneously at certain RPMs and part throttle.-cougar

[cooters]

305 heads do not have 194 valves, they have 184 or smaller valves. as for chamber a 601 head is a small chamber while a 416 head has a large chamber i agree that v advance can add to mech advance if you have a diaphragm with low vacuum operation. when total timing is set, you need the v advance connected.

[Green Machine]

Billa is right about mechanical and vacumn advance. You could weld the mechanical advance weight and the vacumn advance will still work. Yes mechnical advance moves the rotor and the pole piece clockwise causing advance. The vacumn advance moves the pickup coil counterclockwise causing advance. One is not tied into the other, but related of course.

[cooters]

if you weld the mech advance you will have no advance at wide open throttle so this only works in circle track racing. Every setup is based on a specific application but the main principles apply

[Blue85]

sorry to hijack, but how is total timing determined? I have never used a timing light on a vehicle, always powertimed, don't most timing tabs only go to like 6 or 8 degrees. Can't believe i'm asking this question lol.

[Billla]

Originally Posted by Blue85

sorry to hijack, but how is total timing determined? I have never used a timing light on a vehicle, always powertimed, don't most timing tabs only go to like 6 or 8 degrees. Can't believe i'm asking this question lol.

I posted a thread on this with attachments; worth a search.

To set total timing, you need either an advance timing light or a degreed balancer - along with accurate TDC indexing.

http://store.summitracing.com/egnsea...115+4294853094

http://store.summitracing.com/egnsea...115+4294840140

[WorkinLonghorn]

Vortec heads are great heads for the money and flow as well as some of the aftermarket iron heads. I wouldn't expect a significant HP gain without a cam in the .450+ range; stock Vortecs are lift-limited to .475 but there are a couple of ways around that.

Thanks Billa. I called the local Chevy Dealer and the guy in parts says the vortec is ONLY for f.i. engines so forget it.(!) So I called a "performance" GMC place and they said $650 a pair assembled or $1250 for aluminum but those have an even smaller comb. chamber.
>>Let's say I'm 8.0-1 now with 76 cc heads,the vortec cast iron heads are 64cc so I will be going up,which is good.
The cam i'm looking at is Comp Cams High energy 260H that has 4.40"lift.