Engine vs Torque converter question

[jimszx]

Will this combination require higher than stock stall torque converter?

 

79 280zx

Engine

283 block stock bore

9.25 compression ratio

Crane Camshaft Specifications

Part Number: 113802

Grind Number: H-278-2 (REPLACES HMV-278-2)

Engine Ident: CHEVY 57-87 V8 262-400 ALSO 87-95 TRUCK

GOOD IDLE, DAILY PERFORMANCE USAGE

(ALSO 1987-95 NON-ROLLER TRUCKS)

 

VALVE SETTING: INTAKE .000 EXHAUST .000 ----> HOT

 

LIFT:

INTAKE @CAM 3114 @VALVE 467 ROCKER ARM RATIO

EXHAUST @CAM 3294 @VALVE 494 1.50

ALL LIFTS ARE BASED ON ZERO LASH

 

CAM TIMING OPENS CLOSES ADV DURATION

@ .004 INTAKE 26 BTDC 72 ABDC 278 °

TAPPET LIFT EXHAUST 80 BBDC 30 ATDC 290 °

 

SPRINGS

PART NUMBER 99848

 

LOADS:

CLOSED 105 LBS @ 1.700 OR 1 45/64

OPEN 280 LBS @ 1.240

RECOMMENDED RPM

RANGE WITH MATCHING COMPONENTS

MINIMUM RPM 2500

MAXIMUM RPM 5500

VALVE FLOAT 6500

 

CAM TIMING OPENS CLOSES MAX LIFT DURATION

@ .050 INTAKE 2 BTDC 40 ABDC 109 °ATDC 222 °

TAPPET LIFT EXHAUST 56 BBDC (2) BTDC 119 °BTDC 234 °

 

1.5 ratio rockers

Ported Iron heads

Weiand Stealth intake

670cfm Holley street avenger carb

Hei with MSD 6AL

2 1/2 Flowmaster exhaust

700R4

3.90 R200

 

Looking forward to your feedback.

 

Thanks Jim

[spdsk8r]

I am, by far, no expert. All I can tell you is my similar setup and how it works. My 79 has a 350 +.030, 9.5 comp., a little more cam, Performer intake with a 1" spacer, Holley double pump, 700R4, R200 w/ 390:1. I have a Bowtie Overdrive 2200 rpm stall converter. I wish I had a higher stall (@2600 to 2800) converter as it still has quite a load when it's in gear. I hope this helps.

[jimszx]

What problems are you having with the 2200 stall converter? Does the car stumble on acceleration?

[spdsk8r]

When I put it in gear, I better have my foot on the brakes. as the car wants to jump forward. I've been told, with a lighter car, the stall will be lower than advertised.

[jimszx]

Thanks I wasn't anticipating that.

[Guest zfan]

My 385 sbc/700r4 combo really liked a 26-2800 rpm converter. That said I now run a 3500 rpm Edge 9" converter that is just ok on the street but when you hammer it, well you damn sure better have good tires and a tight grip on the wheel.

 

Mike

[jakeshoe]

That's a pretty healthy cam for a 283...

So you may need more converter.

 

Also check your initial timing. More cam means more initial timing to get quality idle. If your timing is slow, it will require more idle speed adjustment to attain proper idle and cause issues with the idle transfer slots at idle and off idle throttle positions.

 

Set timing for fastest smooth idle with the least amount of idle screw. Record timing. This may cause your total timing to be too fast. You will have to limit the distributor to compensate.

[jimszx]

I was concerned about getting too large of a Cam for the engine so I wrote to Crane with the car specs, (Weight, tire size, rear axle ratio, transmission) and the Cam I was looking at. I was trying to recreate the performance level of one of the 270hp 283s from the early 60's Corvettes. To my suprise this was the Cam recomendation they gave me. (It was larger than my original selection) Looking back maybe I should have gone with my instincts. Oh well it should be a lot of fun to drive, I still need to mount my radiator and finish the exhaust before I can start it.

[jakeshoe]

It's not a huge cam by any means, but in a 283 it is the equivalent of about 10 more degrees of duration in a 350...

So you will have to do some tuning to get it to have good driveability.

Main thing is plenty of initial timing, it will probably like ~20-25* of initial, maybe even more. Some motors like the timing locked out, but this can be rough on starters without a retard box.

 

Just remember once you get it running, that you need to get a good clean smooth idle, so advance the timing until you get the best idle, then maybe back it off 2*,

 

You will need to go over the timing, idle mixture and speed a few times until you have the least idle speed screw setting, proper timing, and proper mixture.

Then rev the motor to 3000 rpm and check timing with a dialback light. You will want ~36* usually with old style SBC heads. If you are running Vortecs, they seem to like no more than 32*. If you have plenty of initial timing, you will find the total timing at 3000 rpm is usually too much.

 

There are a coujple of tricks to fix this...

One is to simply limit the distributor advance, but this can be involved if you don't have a distributor machine.

You can also set you're total timing at 3000 rpm to 36*, because you know this will be close, then use lightweight advance springs to bring in more timing at idle.

A Crane adjustable vacuum canister allows you to use manifold vacuum on the distributor.

I've done this often.

You set the total timing first, then set the idle timing using the adjustable vacuum to bring timing up from base.

What this does is it allows the engine to crank against slow timing like say 8*, then when the engine starts, it builds vacuum, bringing the timing to the desired specs set with the Crane part, and total is where it needs to be.

[Corzette]

I would go at least 500 above your CAMS starting specs...2500 plus 500 = 3000 stall. If you looking for more strip Id go 1000 above as did ZFan and myself. I cut .5 off the quarter just by changing my convertor. Street only is a different story...however your torque ban is pretty short so that confuses me....maybe better with less convertor to get a longer torque ban....my 2 cents.

 

Terry

[jakeshoe]

I would go at least 500 above your CAMS starting specs...2500 plus 500 = 3000 stall. If you looking for more strip Id go 1000 above as did ZFan and myself. I cut .5 off the quarter just by changing my convertor. Street only is a different story...however your torque ban is pretty short so that confuses me....maybe better with less convertor to get a longer torque ban....my 2 cents.

 

Terry

 

Without dyno'ing the motor, you don't have a good idea when the "torque ban" starts..

If you want to get really technical converter selection should be based off peak torque, not the beginning of the power curve.

With a 3 or 4 speed auto, for drag racing a couple hundred rpm before peak torque rpm.

If you have a Powerglide, peak torque or a couple of hundred rpm after.

 

However,

for a street car it is more personal preference. He's obviously not after a max effort deal or he would have more cubes..

I would run a generic ~2500 rpm converter. Hughes, TSI, TCI, B&M, whatever.

[Corzette]

I was concerned about getting too large of a Cam for the engine so I wrote to Crane with the car specs, (Weight, tire size, rear axle ratio, transmission) and the Cam I was looking at. I was trying to recreate the performance level of one of the 270hp 283s from the early 60's Corvettes. To my suprise this was the Cam recomendation they gave me. (It was larger than my original selection) Looking back maybe I should have gone with my instincts. Oh well it should be a lot of fun to drive, I still need to mount my radiator and finish the exhaust before I can start it.

 

Parts matching is a must for best perfornance. We all know that story. What does the spec sheet say for your cam exactly? MIne is 2500-6000. Peak torque is 4500. Dyno showed 4500-6129 respectfully. Comp Cams are usually pretty close. A convertor rated at 3500 will usually brake stall about 1000 below or so and flash there after. You also have to remember we are not launching 3300 pound sleds so the stall doesnt have to compensate for vehicle weight as much. Your rear gears will also have alot to do with cam selection etc. I would tend to agree with Jake in the fact that a 2500 stall would be better for street/strip but it would be nice to know what your numbers are real world before choosing.

 

By the way, large cams will only hurt your power if you dont have the right heads to accomodate...been there done that!

 

Terry

[jakeshoe]

Parts matching is a must for best perfornance. We all know that story. What does the spec sheet say for your cam exactly? MIne is 2500-6000. Peak torque is 4500. Dyno showed 4500-6129 respectfully. Comp Cams are usually pretty close. Terry

 

What you have to remember is, the advertised rpm range of most cams is based on a 355 cube motor. If you take the cam in question in a 355, it is a decently, fairly mild cam, in a 283 it will be a different animal, you are looking at almost 1000 rpm difference in the peak power, so any advertised ratings are out the window.

 

You are correct, the lighter car will require less converter, and it will also make the flash stall of a converter less.

[dr_hunt]

You'll need a 3000 stall, since that is torque sensitive also, your little 283 won't stall a 3000 converter anywhere near that. probably about 2600 or 2700 max. That is alot of cam for a 283. I've run 3500 stall converters on the street, you'll be happier with too much stall rather than not enough IMO.

[desert dog]

You didn't state what kind of heads you have. Even the fuelie heads of that era do not flow well compared to modern selections, like 493's, or 882's that are plentiful in junkyards and will wake up a small bore SB...

[dr_hunt]

yeah, but he'll loose compression with those flat tops in the 283 and that'll hurt him more than a few cfm on flow. The 283 power pack heads had like 62 cc combustion chambers as measured with a burette and still only garnered 9:1, so if he drops to 76 cc heads, he'll be at about 8:1 from his 9.25:1 he's at now. The camel irons work very well with the small displacement since the airflow requirements are likewise smaller.

[jakeshoe]

I disagree that he would be happier with too much stall than too little. I would always go with a lesser stall for a street car than too much.

Too much stall makes a street car feel slower and mushy.

In this scenario a 2500 converter would be fine, even with the ligthweight car and relatively low torque of the motor, it will be enough to loosen up stall to allow decent idle.

You COULD spend bucks and get a 9.5" or 10" converter built to a ~2800 so that it would be efficient yet still flash.

 

I would call PTC and see what they recommend.

[jimszx]

I am using ported stock heads, desktop dyno shows this combination is worth 286HP @ 6000 and 280TQ @ 4500. The idea was to have a peppy vehicle with driving characteristics simular to the L6. My cruise RPM at 70 MPH will be around 2600 and at the low end of my torque band. I didnt follow the standard 350-383 mindset because I wanted to do more than just smoke the tires, I will be in the area of 10 lbs per horsepower which is plenty.

[dr_hunt]

sounds nice

[Kevin Shasteen]

Jim,

 

I love camshaft discussions. I dont have too much experience w/lock up conveters so I cant respond on that issue other than an old Cutlass w/455 V8 and it had a 3600rpm stall converter on it - that was a fun car and a very heavy car at that.

 

I think you going the route of a nice road handling car is a cool one, but I too believe like you, the cam they chose for you is slightly too large for the smaller displacement 283. I would like to know if you want a choppy and wavy idle in the 1000rpm range or would you prefer a smooth idle in the 700rpm range.

 

My .02c's worth would be to get a cam whose Intake Valve closes about 10* sooner and then bump up the Static Compression Ratio to 9.5:1.

 

Keep in mind what you want and what the tech line thinks/believes you want are not always one in the same: every little parameter has to be qualified. Remember that in the 60's the big 3, Ford, GM, and Mopar all utilized cams whose profiles bled extreme amounts of cylinder pressure to obtain that choppy idle. They could get away with it because of the characteristics of how the pump gas ignited and burned in those days. Now days the ignition and burn is just the opposite.

 

My .02c's worth comes from the angle that the Static Compression Ratio to Dynamic Compression Ratio must match the desired output at a specific rpm and do so with minimal losses at lower rpms and at the same time maximize the gains at the upper rpms. I believe this relationship is the foundation which an Engine/Car Combo should be built upon.

 

I believe with the cam you have been offered your Volumetric Efficiency will suffer so much so at lower rpms that your gains at upper rpms may be compromised more than you'ld prefer: so much so that the cylinder head's smaller ports may reach their potential way before your engine is capable of coming on the cam.

 

This is why I think this. Ever since I first read David Vizard, Elgin of Elgin Cams, and a few other major engine builders talking about how important the Dynamic Compression Ratio is, I created a few performance calculators to help me understand and diagnose this thing they called Dynamic Compression Ratio. BTW, Vizard claims for a street engine the best DCR for an engine would be in the 8.25:1 DCR range - so you could go a little less and you could also go a little higher but not to exceed the 8.5:1 value for pump gas.

 

Here are some numbers created by your cam's spec's and I used a 283, 350, 383 as examples. I included these larger displacements to show that everything is a ratio. As displacement increases - so too does the Dynamic Compression Ratio, yet the Static Compression Ratio stays the same: once you've looked at this you'll say "Duh" but many people dont look at it because they dont know how the Dynamic Compression Ratio aids the regulating of pressure in an engine. The purpose of a Static Compression Ratio is to correct the negative affect brought on by the Dynamic Compression Ratio. The Dynamic Compression Ratio takes into account the Cam, Bore x Stroke after IVC (Intake Valve Closing) and must match the level of performance, at a specific peak rpm you desire. We're merely talking about how we are going to regulate port pressure and cylinder pressure.

 

Keep in mind of all the engine build ups I've looked at, over 100, I've only found 1 that fell in the 7.1:1 range and it was an all out blown engine for the street, all other engine build ups indicated a 7.27:1 DCR or higher (for street engines.., not full race engines) as low end torque begins to be traded for high end horsepower when your DCR falls in the 7.70:1 range. These numbers are only for Small Blocks as there isnt really that much info out there on big blocks.

 

I'm sure this doesnt mean you cant build an engine that wont run on a lesser DCR - it is merely a pattern that appears everyone (all pro engine builders), are following.

 

Anyway, here are the numbers:

 

283 SBC V8

9.25:1 Static Compression Ratio

IVC @ 72* = 6.90:1 DCR

IVC @ 70* = 7.04:1 DCR

IVC @ 65* = 7.32:1 DCR

IVC @ 60* = 7.60:1 DCR

 

350 SBC V8

9.25:1 SCR

IVC @ 72* = 6.98:1 DCR

IVC @ 70* = 7.29:1 DCR

IVC @ 65* = 7.59:1 DCR

IVC @ 60* = 7.60:1 DCR

 

383 SBC V8

9.25:1 SCR

IVC @ 72* = 7.05:1 DCR

IVC @ 70* = 7.11:1 DCR

IVC @ 65* = 7.45:1 DCR

IVC @ 60* = 7:72:1 DCR

 

The small block engines I've looked at that had a 7.30:1 DCR were pretty radical street engines and had a very wavy idle in the 900rpm range and Vacuum at idle was like 8lbs - not very fun at stop and go rush hour traffic nor if you are running power brakes and A/C, and they were larger displacement SBC's. What this tells me is that your 283, with the 6.9:1 DCR, will idle in the 1000+ rpm range.

 

Now if you were to utilize that very sam cam and merely bump up the Static Compression Ratio to 9.5:1 things would be a little better - but not that much better, here are their numbers.

 

283 SBC

9.50:1 SCR

IVC @ 72* = 7.06:1 DCR

IVC @ 70* = 7.22:1 DCR

IVC @ 65* = 7.50:1 DCR

IVC @ 60* = 7.80:1 DCR

 

350 SBC

9.50:1 SCR

IVC @ 72* = 7.16:1 DCR

IVC @ 70* = 7.29:1 DCR

IVC @ 65* = 7.59:1 DCR

IVC @ 60* = 7.87:1 DCR

 

383 SBC

9.5:1 SCR

IVC @ 72* = 7.23:1 DCR

IVC @ 70* = 7.29:1 DCR

IVC @ 65* = 7.65:1 DCR

IVC @ 60* = 7.93:1 DCR

 

If you want a 60's like performance out of your 283 - you can get that w/out bleeding off excessive cylinder pressures. I dont know how old you are but I remember the late 60's and early 70's in the Dallas/Ft.Worth area - their engines were running so rich that it would give me a headache at times. This is why I wish all engine articles would give their Volumetric Efficiency numbers when they give their Hp/Tq numbers - as then we'ld all see exactly how efficient said engine was performing.

 

After all,it was the fact that the old cam profiles were so outdated for the newer unleaded fuels that the many numerous aftermarket cam companies sprang up like they did.

 

I think you could run that cam w/the rear gearing you have chosen - I personally think that you would like that cam a lot better if you bumped up your Static Compression Ratio to 9.5:1 and went with an IVC @ 65*.

 

Kevin,

(Yea,Still an Inliner)