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73-87 Chevy _ GMC Trucks => Performance => Topic started by: 305chevy c-10 on May 13, 2014, 08:30:35 PM
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got my motor running but it has no real power .it picks up speed fast but this thing wont even break tires loose .vortec heads ,373 gears ,th350 trans , roller cam,1.5 roller rockers,air gap intake ,1" spacer and 750 holley carb .i bought a trans that supposed to have 25-2800 stal in it .the only thing i can come up with for why it make no power is that the trans may have a stock coverter in stead 25-2800.i thought with a stall it takes a while for truck to move once it put in gear and rpm reaches stall point .my truck does not hesitate when its put in gear its ready to move .my cam has a range of 24-5600 rpm .would a stock stall cause me to not have no power until rpm reaches above recomended stall piont .CAM SPECS BELOW
HOWARDS 180305-08
NA
282
282
229
229
.480
.480
108
104
Hyd.
Hyd.
1
2400-5600
Choppy idle, strong low & mid range performance. 2500+ stall
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This thing should be a screamer with or without the stall converter. All of your combination seems to be well chosen for the total package. No crazy cam stuff or non streetable parts. A stall converter basically just has looser tolerances on the vanes inside it so that it locks up at a higher rpm than a stock one with tighter tolerances. They will still grab and drive somewhat easily on the low end, especially a mild one like yours as opposed to a wild 3500rpm+ one. The converter is essentially just a cetrufugal pump. If you brake stand it, and i dont mean sit and burn the tires, but just allow the stall to slip up to its rated lock up and then let it fly it should show you what you want to know. Timing and carb tuning should be looked at closely also. Thats a pretty sizeable holley and maybe the lack of vacuum on the bottom is causing it to hesitate.
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Well i was expecting a screamer when i first drove ,but nothing . :'(
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would a stock stall cause me to not have no power until rpm reaches above recomended stall piont
No, the cam spec says you will have no power until rpm reaches the recommended stall converter rpm. That's what "recommended stall converter rpm" means. That "2500+" stall speed torque converter recommendation says it all.
I had the same problem with the GM 350/290 hp engine. It was a two-lane terror. The 50-90 times were incredible. Getting off the line? Not so much. All the hot rod guys will tell you, horsepower gets the headlines, but torque is what you drive. And those cam specs you have are close to the cam specs in the GM 350/290 engine. Yes, vortec heads help a lot, but still.
As one example. The 1970 Hemi Cuda was a very fast car. 426 hemi, 425 horsepower. Mopar guys drool when you talk about that engine. The 1970 Chevelle LS-6 was a very fast car, rated by GM at 450 horsepower. They both completed the quarter-mile in the low 13s, in darned near a dead tie. In contrast, the 1970 Buick GS 455 Stage 1 was only 360 hp, but it had 510 lbft of torque at a low 2500 rpm. It was a quarter-second slower than the Chevelle and the Hemi Cuda in the quarter-mile, but it would positively smoke both of them in the 1/8th mile. Gonna race in circles? Hard to beat that hemi. Drive on the street? I'll take the Buick.
What I did was swap out the cam in my 350/290 (yeah, the cam I paid $500 extra for over the 350/260 hp base crate engine) and put in a torquer cam. I gave up a little horsepower, and there's no "choppy idle", but I am getting over 420 lbft of torque at 2500 rpm. So my cam is in the middle of its torque curve at the same rpm that your cam specs say is where your torque curve starts. When you think about it, it makes sense. Unless you are a circle-track racer, you are almost always in the 1500-3500 rpm range in normal driving; that is, in the lower half of the working rpm range. And "choppy idle" means the engine doesn't like to run at low rpms.
I just ran a dyno simulation on your setup and ran through some choices on a cam selector. Put a Comp Cams 12-408-8 cam in there. 350 hp at 4500 rpm is cool, but 494 lbft of torque at 2500 rpm will make it a serious launch vehicle. Note: Recommended rpm range: 1000-5000 rpm.
The 12-408-8 has a .480/,487 lift; if you can't go that high you could use the 12-409-8 cam at .458/.458 lift. You come down to 345 hp at 4000 rpm, but you keep 491 lbft of torque at 2500 rpm. Same recommended rpm range.
Even with the cam you have, however, you should be getting a bit over 400 lbft of torque (probably at around 3500 rpm) and maybe 380 hp or so. It won't be as quick as a more torque-oriented cam with a lower peak-torque rpm, but it shouldn't be a slug. So here are some other things to think about.
The air-gap manifold will keep the carb from overheating, but it will also keep it from getting to operating temperature very quickly without warm-air induction. The original air cleaner had warm-air induction off the manifold until the carb was up to temp. I have the air-gap manifold, and in cold weather the engine always ran like it couldn't warm up. I put the stock warm-air induction back on, with a cold-air induction tube to the radiator bulkhead, and that helped a lot -- the carb got to temp quicker, and then it stayed at optimum temp as the thermostatic air cleaner dialed in the induction temperature. Then I put an electric fan on it that is temp-controlled to maintain engine temps at operating temp and that helped as well.
Another issue to look at is ignition timing. You should be able to run 16*-18* of base timing on a SBC, with 20* of vacuum advance. Just keep advancing the timing 2 degrees at a time until you start to get pinging under low rpm heavy load, then back it off a couple degrees.
Plugs and wires and coil matter a lot too. What plugs are you running? The AC Delco R45TS is probably the right plug, or even better the Autolite 26. I am running Taylor stainless steel conductor wires instead of the crappy resistor wires, and an Accel high-voltage (tan color) distributor cap and rotor with the Accel 48000 volt coil. I can give you part numbers if you want.
Finally, where do you have your vacuum advance connected? It should be to manifold vacuum (the lower port, under the throttle plate), not "ported" vacuum (the higher port, above the throttle plate). Connecting the vacuum advance to ported vacuum will give you off-idle hesitation and boggy starts.
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my vac advance in connected to top timed spark port.My brake booster goes to port on intake.my trans vac goes to full manifold vac on lower front of carb .pvc goes to port on back of carb .
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Move the vac advance to manifold vacuum. That's one of your problems.
http://www.corvetteactioncenter.com/forums/c3-technical-performance/60830-ported-vs-manifold-source-vacuum-advance.html
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Check timing, initial and total. Make sure mechanical advance in distributer is working all the way. I agree with previous post's, this should break the tires loose with ease.
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Motor was built a year ago . Guy dont remember where cam was set .(degrees).another guy installed the motor and set timing without knowing how cam was degreed. I have 9 keyway dbl roller timing set (+-8 degrees) .lsa is 108 i think Howard's cam told me to set it on 104 .i really feeling this is why i have no power .i will get to the bottom of this .
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With that said I'd pull the cover and figure out where your cam is degree'd in at. Unless this thing lives on the strip I dont see any reason to move it from standard, and until you know what its at for sure then you cant time it correctly.
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Can this be done with motor in truck or will it have to come out
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Yeah it can and thats a matter of preference. You'll need to pull the water pump, balancer and drop the oil pan to get the timing cover off. Might be alot easier out of the truck but it doesnt have to happen that way. With the cover off you can just check the keyways and timing marks to see where you are and go from there.
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Great im getting some one to look at at it to give me an estimate on what he will charge to do this .hope its not to expensive.just ready to feel 450 ft lb. of torqe .atleast thats where i hope its at with my setup.$300-400 should handle this fix i hope .
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That should be a very nice working engine...something is wrong with the basics. Cam timing, ignition timing, engine sealing. Does the engine operate "normal"...as in, idles fine (not all rough & the engine shaking around), goes through the RPM range smoothly, ect.?
The ideal converter would optimize the components, however there should be plenty of torque there to put a smile on your face with even a stock converter...It's 383 inches, good flowing heads & a nice sized cam for the combo & 3.73 gears...it should make a very nice running/driving truck.
Before you take anything apart, I would suggest you do a compression test...it will/could help you down the right path. A leakdown test or simply an air tank plumbed into the sparkplug hole will tell you if you have a valve or ring sealing problem. A dial-back timing light so you can check timing at 2000, 3000, ect. will be next. Keep us posted, Lorne
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Yes operates fine just no power .dont know how true it is but i always heard as young boy that when water drips from tailpipe that s a sign of good compression .i know people have different labor rates but whats a reasonable price to degree a cam ?if thats the problem.i read that being +/-1 degree would not make alot of diff except maybe track time, but performance wise no .for instance mine should be 104 ICL which is +4 advanced .a 103or105 would be ok .anything beyond that performance will suffer greatly.
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My setup is similar but smaller in inches,358, with dart SHP heads a smaller 600 holley with vac secondaries, and an M21 trans backed up by a 4.11 posi. When I step into this thing with no assistance from the clutch or brakes she flat out boils the tires through 1st and 2nd and then slips em for a good 20ft before they grab in 3rd. There is no reason why that 383 shouldnt do it just as well on any converter really. As for the cam degree, I dont know your level of comfort so dont let this be an insult at all, but if you're comfortable tearing it down that far it really isnt difficult to do for a street engine. You just line up the marks on the crank gear with the corresponding marks on the cam gear and set it for 0 not + or - anything. Guys correct me if I'm wrong on this next part, but the distributor makes one revolution per trip through the firing order. So when setting the timing there as you will have to do either way, you can get way beyond a few degrees of adjustment out of it. If you arent comfortable, the going rate in any shop in my area is every bit of $40/hr and theres several hours involved here, especially if they're going by what the book estimates it to be and not actual time.
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Cam timing and ignition timing are two different animals. One times spark against the pistons, the other times valve events against the pistons. That being said, for street use the cam should be timed at zero degrees by the marks unless the instructions with it specifically call out differently. The best timing for the cam should be handled in the grind right out of the box.
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ok heres what a machinist told me today over the phone . i explained to him the problem im having and he said even if cam is wrong it would either make power on top or on bottom .he asked me how does it crank ? fine i said .then he asked was it balanced . it said yes , but i had 350 pistons .i replaced them with 383 pistons .(guy who assembled motor took them to machine shop and had them switched out .) he told me thats the problem and it got to come apart to see whats damaged and rebalanced an line hone block if needed .this makes sense to anybody . my first motor im learning alot from my mistakes and trust in peole >:(
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So wait a minute the engine was balanced with the 400 crank rods and stock,bore pistons
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When I 1st fired up a new bbc 396 in my Chevelle, it didn’t fire right up. Played with timing and got it running good, but BY EAR ONLY. Couldn’t get the timing-light to make any sense. My headers also started glowing and baked off some ceramic coating on my new headers (grrr). So I ended up leaving it timed by ear/feel, and ran it for a while. Started fine and GREAT, with NO power at all. Struggled to even get a chirp out of the tires, but did run smooth.
Ended up finally taking off the front timing cover…to discovered the cam was 3 teeth off from the dot-to-dot alignment. I watched the guy install the cam using a fancy degree wheel, but I didn’t watch him in detail and assumed he knew what he was doing. WRONG. So I put it dot-to-dot….WOW…. have trouble keeping the tires from NOT spinning now.
I'm about to swap in a nice sb400 in a couple weeks, so I'm nervous about this start up also. I'm watching this post to learn from. Good luck.
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No ,they were .030 dished 350 pistons ,i did not know there was a diff in height between 350and 383 pistons . When i found out they came out block about .100 .then realized after talking to summit tech guy .shop that clearanced motor never fliped block over to check because ,he thought i bought a complete rotating assembly .@74k20 ,thats exacly what mine is doing ,but machine guy thinks or more like gaurantee this is whats wrong its out of balance with the new pistons
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Cam timing and ignition timing are two different animals. One times spark against the pistons, the other times valve events against the pistons. That being said, for street use the cam should be timed at zero degrees by the marks unless the instructions with it specifically call out differently. The best timing for the cam should be handled in the grind right out of the box.
Rich that makes a lot of sense now that you said it that way. Thanks
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Any luck with your 383 ??
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Just took it to shop today ,guy gonna run compression test on it .before looking at cam index.i read that a 383 compression should be about 185-190 .howard 's cam told me that it should be installed " straight up ".the +4 degrees in the cams 104 ICL with 108 LSA already, no need for additional advance .soon as i find out i will update you all .
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Little test i done ,put truck on lift and held brakes and floored it .engine stalls down a little .put in park and floored it ,it didnot stall any .guy told me he thinks converter is bad thats why it stalls down in gear if u give it alot of gas .he said he will do compression test tonight .if it fine he said it the converter .We will see. Anyone ever had any bad converters that made ur motor a dog .
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Here's a dumb question for ya, was the converter full of fluid when it was first installed?
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Yes ,
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UPDATE ..one problem was i had wrong spark plugs in .regular tbi heads use a short reach plug s(thats what i had ) vortec and aftermaket vortec use long reach plugs .i had short ones .the correct ones are APP606 autolites .about $4.49
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Still needs a stall though ,but runs alot better ,did get it to turn those 22's loose .loving my shortbed right now ;D
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update .one day out the shop and white smoke everywhere .i did a mean power brake BURN OUT with my new 22-2800 boss hog converter and when i got home white smoke comes out both tail pipes like a train .i think i blew a head gasket . CRAP :o :'(
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BOTH tail pipes? If you have full duals with no crossover pipe, you blew both head gaskets.
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Full duals with xpipe,is this a simple fix ,get some new gaskets and im. Done
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puzzled do know whats wrong? checked modulator on trans and no fluid come out .there is no water in oil .but still smokes like a train if u mash gas .
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You can have a leak from the water jacket into a combustion chamber without getting a lot of water into the oil.
Let me ask you this. If you sit and idle, like at a light, for a couple minutes, then you give it gas, do you get a lot of white smoke right away, then it sort of dies down as you are driving?
And, does it miss first starting out from that sit and idle, then even out as the smoke dies down?
Does the exhaust smell "sweet"?
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yes if u give it gas its a lot of white smoke.if i let it idle theres a little but hardly noticable . only have water in on antifreeze .the more gas the more white smoke .i used stock rebuild head gaskets not high performance gaskets .may drain oil tom to see whats in there
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Sure sounds like you dynamited a gasket. What about the smell of the exhaust? You can usually smell it if it's antifreeze.
Ask me how I know....
Another thing you can do is pull the plugs and inspect them. Let it idle for about five minutes, then shut it off. When it cools down, pull the plugs and check them. Why at idle for five minutes? Highest vacuum is at idle, so it'll pull the most water, and won't blow it all out. Check the plugs for wet. Should be obvious. You can also stick a long (12") pipe cleaner down each plug hole to the bottom edge of the piston and see if it pulls up wet and smells of antifreeze. (Of course, if you have a bore scope laying around, that's the way to go.) Might want to pull the center four plugs first (3, 4, 5, 6), they run at the highest temperature, then the end four (1, 2, 7, 8).
Another question: This didn't begin right after you filled up with gas, did it?
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No ,it begin shortly after driving it hard ,trying to do burnouts .
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Checked all fluid ,oil has no water in it ,radiator has no oil in it .changed vac modulator it had a little trans fluid in it .still smokes like a train .when u cut it off one tailpipe still smokes for a while .i'm thinking rings did not seat or went bad .this motor may have 50 miles on it .when i first drove it ,it never smoked even when it had no power because of wrong plugs .i was told u can drive it in 2nd gear 30-45mph @25-3000 rpm and take foot off gas and let it coast about 5-6 times and this will sometimes seat the rings .my thing is with all that smoke i dont want to blow it .other option is take apart and re ring it .
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Did you happen to use chrome moly rings? Takes quite a bit more heat to seat them..
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Hastling rings .i may have spelled it wrong
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Do a compression test. If the water is getting into the combustion chamber (to blow out the tailpipe) it will have to show up as a LOW reading. A leakdown or simply air plumbed into the sparkplug hole will likely tell the story also. Bubbles in rad cap, head gasket, crack, ect. Lorne
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UPDATE***compression test 105 it was 180 but after my big foot gaskets let go.* blown head gaskets (both sides )i used stock head gaskets instead of some good performance one .* busted a rocker arm (stamper steel roller tip ).*destroyed roller lifter (hydraulic plunger part on top of lifter).* bent a valve .*and block was not decked piston .025 from top (gonna be decked to zero this time). guy told me i must have over rev it because one cylinder had glazed walls .he said i can get more hp by going with flat tops because it will raise compression (10.5.1 from about 9.1). machinist told me unless i put forged pistons in stay with dish because higher compression increases detonation chances and it may not be pump gas friendly .he said mixing gas everytime u want to take a cruise gets old fast .
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Update ....motor being put back togather(machine shop was way behind with dirt track motors ) .totally redone , decked to .005 , new rings , reused my speedpro dished pistons, new stainless valve , replaced roller lifter , correct cam timming (index wrong is why it made no power ).polished crank , reseated valves , beehive springs (z28 springs did not have enough seat pressure and was binding at full lift ),trashed my steel procomp roller tips rockers for a set of full 1.5 aluminum roller rockers .Vortec heads milled flat for a good seal with copper gaskets .hopefully this is the last time building this motor .
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would a stock stall cause me to not have no power until rpm reaches above recomended stall piont
No, the cam spec says you will have no power until rpm reaches the recommended stall converter rpm. That's what "recommended stall converter rpm" means. That "2500+" stall speed torque converter recommendation says it all.
I had the same problem with the GM 350/290 hp engine. It was a two-lane terror. The 50-90 times were incredible. Getting off the line? Not so much. All the hot rod guys will tell you, horsepower gets the headlines, but torque is what you drive. And those cam specs you have are close to the cam specs in the GM 350/290 engine. Yes, vortec heads help a lot, but still.
...... They both completed the quarter-mile in the low 13s, in darned near a dead tie. In contrast, the 1970 Buick GS 455 Stage 1 was only 360 hp, but it had 510 lbft of torque at a low 2500 rpm. It was a quarter-second slower than the Chevelle and the Hemi Cuda in the quarter-mile, but it would positively smoke both of them in the 1/8th mile. Gonna race in circles? Hard to beat that hemi. Drive on the street? I'll take the Buick.
What I did was swap out the cam in my 350/290 (yeah, the cam I paid $500 extra for over the 350/260 hp base crate engine) and put in a torquer cam. I gave up a little horsepower, and there's no "choppy idle", but I am getting over 420 lbft of torque at 2500 rpm. So my cam is in the middle of its torque curve at the same rpm that your cam specs say is where your torque curve starts. When you think about it, it makes sense. Unless you are a circle-track racer, you are almost always in the 1500-3500 rpm range in normal driving; that is, in the lower half of the working rpm range. And "choppy idle" means the engine doesn't like to run at low rpms.
I just ran a dyno simulation on your setup and ran through some choices on a cam ............
i realize this thread is a few months old----but i just saw it now. Could you give us the cam brand/model/specs that you used?
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Assuming you're talking to me, I used the Comp 12-300-4. This is a torquer cam, with 420+ lbft at 2500 rpm, and 275 hp at 4500 or thereabouts. Then it runs out of steam. The Comp 12-235-2 has also got a lot of torque, 410+ lbft, but winds up more, for 290 hp at 500, I think.
Google my last name and those cam numbers and you will get a lot of discussion, dyno curves, etc. from various forums.