NOT the usual cam advice...

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Professor Fate said:
Hey, I'm retired and it's winter in Wisconsin... I've got nothing else to do until the Packer game on Sunday... :)
Click to expand...
My wife is a packer fan, and I'm from Michigan.. since the Lions did nothing this year I've been on the 49er bandwagon... I like what they've done turning around from last year.. and every game after the first five or six the announcers kept saying this was going to be their challenge and that all the earlier games were fluke and this was going to be there challenge and they kept winning.. of course I will keep my mouth shut during the game... I'm not stupid...
 
j par said:
My wife is a packer fan, and I'm from Michigan.. since the Lions did nothing this year I've been on the 49er bandwagon... I like what they've done turning around from last year.. and every game after the first five or six the announcers kept saying this was going to be their challenge and that all the earlier games were fluke and this was going to be there challenge and they kept winning.. of course I will keep my mouth shut during the game... I'm not stupid...
Click to expand...
Smart move...!
 
I think I missed something
You don't have to run maximum pressure.
But if you don't every next size bigger, sdame type cam, with same advertised tappet spec, will drop your pressure even more. and this leads to ever decreasing low-rpm torque, which IMO, with 2.76s, is an insurmountable condition until the stall speed is increased so as not to make the engine run in that soft zone.
Lets look at your 5.9 can installed in three same engines each with a different Compression ratios; first 8.4 then the stock 9.4, then 10.4 And I'm gonna use 55* as the Ica in each, and same 800ft Elevation.
Static compression ratio of 8.4:1.
Effective stroke is 2.99 inches.
Your dynamic compression ratio is 7.18:1 .
Your dynamic cranking pressure is 137.68 PSI. ............................ 138
V/P (Volume to Pressure Index) is 124 ........................................ 124
next
Static compression ratio of 9.4:1.
Effective stroke is 2.99 inches.
Your dynamic compression ratio is 8.02:1 .
Your dynamic cranking pressure is 159.81 PSI. ........................... 160
V/P (Volume to Pressure Index) is 144 ....................................... 144
next
Static compression ratio of 10.4:1.
Effective stroke is 2.99 inches.
Your dynamic compression ratio is 8.85:1 .
Your dynamic cranking pressure is 182.15 PSI. ......................... 182
V/P (Volume to Pressure Index) is 164...................................... 164

Notice how the pressure changes 22 psi between each. Remember the only thing I changed was the Scr.
Also more importantly, the VP changes 20 points.
VP is a sortof low-rpm performance index. When it gets too low, you have a dog engine. When it gets too high, it's hard to take off without smoking the tires. And it matters not one little bit what cam is in it. Well it sorta does; big cams generally steel VP trading it for power somewhere up the rpm scale. And small cams generally make more VP, at the expense of high-rpm power. So it is entirely possible within a given engine size, from idle to ~3000/3500rpm, to have mega-torque with a small cam, or it be sucked out with the bigger cam.
Now what are good or bad VP numbers? Again, at 800ft elevation;
84VP is what an 8/1- 225slanty makes
104VP is a lo-C 273
110VP is a smogger-318LA
124VP is a stock 5.2 Magnum at 9.4Scr, like yours. 124 sux in a 4500 pound tank, but in a lightweight-A is reasonably good..... depending on the rear gears. This is why a truck would have 3.91 gears and an overdrive trans with a slightly higher stall. Cuz you, the operator, can't tell in first gear just how doggy this is gonna be, When the trans goes into second, the truck doesn't usually need to be speedy anymore, so again you are lulled into a false sense of power. Then comes direct gear, and if it wasn't for the 3.91s, tou would be screaming "what a pos lazy truck". But the revs are so high now, that the OD is practically a must-have.
I would never build that for myself.So that is 124VP.
134VP is about what a hi-compression 340 made;and nobody I ever met that owned or drove a 340 ever bragged on it's torque. They were revers from day one, having traded away ow-rpm torque, for a top-end charge.
144VP is starting to get to be fun. At 30 mph you can go hammer down and with 3.23/3.55s at least, expect tirespin.
154VP is getting smoking hot! You can kick down a gear at 50mph and expect tirespin with just about any street tire.
164VP is what a 68 magnum 440 maths out to. I have run it, in my 367,and it is ferocious. Once you have had it, it's hard to give it up.This is where my experience ends.

Final shot;
since this is a low-rpm performance indicator; if you install a 3500TC, then NONE of this will be important. At this point, you go look at the cylinder pressure alone. which will help you look at the power from that point on. The higher the pressure, the more power.... until it detonates itself into pieces. Again, pressure is not or may not be, the absolute quest, but IMO
125psi will forever suck
135 is what most old smoggerteens will measure, still very lo-po
145 is the low end of the scale for performance street.
155 is pushing the limit for 87 gas and iron heads
160 is about it for 89,
165 is pushing it for 91
170 IIRC is what YR is successfully running, but not with 2.76s oor a stock TC,lol.
when you get to aluminum, some guys on FABO have indicated that they are running 200 on pumpgas.
185 is the highest I have run... on 87E10 with ignition timing of 34*@3400 rpm.

OK, short post
 
I didn't get the ECU with the motor or any of the wiring. So my initial start up will be with proven carbs that I have. I had a bad experience with after market F.I. so I'll go with a carb for now. Thanks so much for the info in your post.
 
GREAT THREAD NAME OR THIS CHEVY TBI POST
have not fooled with TBI in 20 years but here's some links
Fuel Injected Engine Camshafts

from a comp cams sponsored chevy article
Keeping all this in mind, with a conventional, MAP-based, pure-TBI system, at least 15 to 16 inches of idle vacuum is needed. In terms of camshaft duration at 0.050, that comes out to only about 196 degrees on the intake side with an 8.5:1-compression-ratio engine, about 210 degrees on a 9 to 9.5:1 engine, and about 216 to 218 degrees at 10 to 10.5:1. The exhaust duration should be about 8 to 10 degrees more, with an overall intake/exhaust lobe-separation angle (LSA) of 113 to 114 degrees.
A typical cam for the pure-TBI combo would be Comp Cams' Xtreme Fuel Injection 252XFI HR113

edelbrock breaks out a 244 adv 194 @.050 Intake cam 400 lift 112 lca 107 icl for close to 200$
EDELBROCK PERFORMER-PLUS CAMSHAFT KIT FOR 305-350 V8 T.B.I. & LG-4 CHEVROLET - 3702
from a forum
-Edlebrock 3702 flat tappet uses 194/.398 intake and 214/.442 on the exhaust with an LSA of 112. It will carry about 16 inches of manifold vacuum versus 19 to 20 for the Vortec roller (just a data point.
The long exhaust duration seems built in for stock exhaust manifolds and single exhaust and stock converter and muffler. With headers and duals this long duration high lift exhaust is not so necessary.
This cam is a bit edgy with its long duration, higher lift exhaust combined with a shorter LSA so it can get you into a chip which Edlebrock will supply if necessary.


Be careful, the TBI setups use a speed-density injection type which isn't very toleant to changes such as cams, esp. cams that would "sound" differently. ECM tuning would be required with a lopey camshaft.

That being aid, I know that the 1996 LT4 Production camshaft with 203º/210º duration at 0.050" and 0.446"/0.450" on a 115ºLSA is a strong runner in a TBI truck. I know a guy that installed one in a 1989 truck with a 350 with Vortec heads and it has great street manners, but I wouldnt say its a "lopey" camshaft. But it is the most aggressive of the GEN 2 LT1/LT4/L99 roller camshafts.

For a roller block the GM cams that will work without reprogramming are:
Durations measured at .050 lift. Lift measured with 1.5 rocker add 7% for 1.6.
- 10241264 1996 Vortec 190/.414 intake; 195/.412 exhaust;LSA 116. (The Vortec cam will run with 1.6 rockers without problems)
111º. 0.412"/0.428" 191º?196º duration at 0.050" lift(you will also see 192º/197º duration as well.

This cam was used in the 1996-2003 Vortec 350 L31 (255hp/330lb/ft)
96 L31 Camshaft Profile
Intake:
Opening Closing Duration
.004 14 BTDC .004 61.5 ABDC 255 Degrees
.050 13 ATDC .050 22.5 ABDC 190 Degrees
Inlet Centerline 106.25 Degrees
Max Lift .275 X 1.5 = .412
max lift .275 x 1.6 = .440
Exhaust:
.004 62 BBDC .004 24 ATDC 266 Degrees
.050 31.5 .050 16 BTDC 195 Degrees
Exhaust Centerline 115.75 degrees
Max Lift .281 X 1.5 = .423
maz lift .281 x 1.6 = ..450
Lobe Separation 111 Degrees

- 14093643 350 TPI 97-94 roller 202/.403 intake; 206/.415 exhaust; LSA 115
- 12551705 350 LT1 93-95 roller 201/.447 intake; 208/.459 exhaust; LSA 117
(TBI loves this cam because of the 117 LSA it will also accept 1.6 rockers without issue)
- 12551142 350 LT4 95-97 LT4 203/.446 intake, 210/.450 exhaust; LSA 115 (with more duration and lift with less LSA this cam is a bit edgy with the stock programming, especially if mixed with a 1.6 rocker)
production LT4 cam p/n 12551142 is a very good piece for TBI or any engine that like TBI uses a Speed Density fuel management system. These like high manifold vacuum as seen at idle the 115 degree LSA provides that. Timing of this cam is 203/210 at .050 lift with a 1.5 rocker lift at the valve is .446/.450. .006 duration was 258/265
LT4 cam. It has 46º of overlap while the stock LT1 cam has overlap specs of 41º.
I knew a guy that ran this cam on a TBI/Vortec head combination.
He said it was a great cam and provided lots of vacuum for the TBI.
The LT1 cam is the better choice it times pretty close to the LT4 not HOT but it spreads the LSA out to 117 degrees which makes a very torquey engine and preserves a high idle vacuum that the factory TBI likes. You can run this with 1.6 rockers, actually using 1.6 on the intake and 1.5 on exhaust will offer the best torque and power.
Anybody's aftermarket cam that falls real close to these parameters will work just keep the LSA not less than 111 degrees.

Recommended 350 TBI modifications | TBI



The LT1 can p/n 12551705 trades a couple degrees off the LT4 cam at .050 lift but adds a little lift though still well under .5 inch and brings an even TBI friendlier LSA of 117 degrees.
 
tonysrt said:
I didn't get the ECU with the motor or any of the wiring. So my initial start up will be with proven carbs that I have. I had a bad experience with after market F.I. so I'll go with a carb for now......
Click to expand...

:thumbsup: Agree 150%! I can take a well sorted out carburettor / intake and distributor and make same (or more) power than EFI any day of the year...... And at 1/3 of the price of aftermarket EFI (4bbl TBI) changeover parts even if I must buy carb, intake and distributor new.

This is what we are doing with my son's engine. Its a 350 Chevy TBI truck engine and we are replacing it with a fresh 350 truck engine (warmed over slightly) with a carburettor and reworked distributor (breaker points distributor recurved and changed over to magnetic pickup) running early '80s vintage NOS MSD 6A ignition box and late '60s vintage Mallory oil filled Voltmaster II coil.

My youngest son is putting together what started out as a '96 - 2000 GM L31 (Vortec) crate engine for his '92 Camaro. He bought the engine back in '98 for his previous '88 Camaro whilst serving in the Navy. As he worked his way through college, began a family and career, the L31 engine has sat sealed and covered in my garage on the shipping pallet since '98. The '88 Camaro long ago gave up the ghost and he bought the '92 about 10 years ago. Youngest son is in his mid-40s and is a grandpa now and we are finally getting around to putting the top end of his engine together for the '92 Camaro.

Some years back, I sold the L31 Vortec heads to some circle track guys. He bought this engine from Sallee Chevrolet (no longer in business) and they installed ZZ4 timing gears and chain along with a mild CompCams RV type roller cam to boost low and mid-range power. A couple weeks ago, we bolted on a set of AFR 180 heads and when he can get down here next, we will finish installing the valve train and setting valve lash.

I might add that like the 5.9 litre / 360 Dodge truck engines of the late '90s, the L31 GM 350 truck engine suffers from low static compression. These engines are supposed to have 9.0:1 static compression (advertised), but due to having dished top pistons that sit down in the hole a bit at TDC...... If you pull one apart and actually measure them....... Most will fall short of that, coming in with only 7.5 to 7.75:1 static compression (actual).

This being a new engine and not wanting to disassemble the short block, bore it, install new flat top pistons and have the block decked so new pistons are at zero deck at TDC...... I got the cam specs from CompCams (intake closing angle in degrees is what I needed most), cc'd the dish top pistons and calculated DCR and thought about what we could do to optimize compression ratio without disassembling the short block. Ideally, we needed between 9.0:1 and 9.25:1 static compression ratio with this cam to optimize DCR.

What we did was this...... When we ordered his AFR heads, aside from a spring upgrade, we had AFR flat mill them to reduce chamber volume from 64cc to 60cc. Then we brought a piston up to TDC, laid a metal straight edge across it and used a feeler gauge to measure how far down in the hole (how short of zero deck) it was. The flat part around the circumference, not the dished portion.

The dished portion will have no quench anyway (too far below flat part of cylinder head). We only needed this measurement to maintain adequate piston to head clearance and calculate DCR.

Ideally, if pistons were at zero deck, we could have used a head gasket having 0.045" compressed thickness to set quench and distance to bottom of head (excluding combustion chamber). 0.040" to 0.050" will give good quench and its wise not to go closer than 0.040" to avoid piston coming in contact with head once engine reaches operating temps. So I like to set this at 0.045" when I can.

In this case though...... The flat part of his piston head was 0.024" below deck at TDC. Now GM and Fel-Pro both make head gaskets having 0.026" thickness and there are steel shim head gaskets 0.018" thick as well. I have used them all and they are good so long as you prep everything properly. Yes, I'm old enough to remember factory steel shim head gaskets. If both surfaces are absolutely flat and true and you torque them down just so, they seal well. Otherwise, a good quality composite gasket is better at sealing. First engine I ever built when I was a kid was a '53 DeSoto hemi. When I disassembled it, I saw that it had steel shim head gaskets and it looked as if the gaskets had been painted (both sides) with aluminum paint when installed at the factory. I always brushed KopperKoat on the steel shim type gaskets, though.

Anyway...... Last thing we want is to blow a head gasket on this engine, so I contacted Cometic. They can do one of their MLS (multi-layer steel) head gaskets as thin as 0.027" compressed thickness. These are viton coated and seal well. Also allow for movement as aluminum head and cast-iron block have differing rates of expansion and contraction whilst heating and cooling. I custom ordered a set and had Cometic make bore exactly 4.00" in order to pick up the small amount of static compression lost when gaskets having larger bore size than engine allow some compression to be lost in the crevice between head and block before reaching gasket bore size. Not the cheapest way to go, but by doing all of what is mentioned above, we were able to bump true static compression from 7.5:1 to 9.2:1. Piston to head clearance (and what little quench is present due to dished piston design) came out at 0.051". Close enough.

Only reason I mention this is the same can be done with MOPAR engines so long as pistons are not too far down in the hole at TDC. Otherwise, its necessary to disassemble engine, bore and deck block and buy new pistons, rings and gaskets. Or if not decking block...... Order custom pistons having compression height adjusted to reach zero deck.

Another way to go...... With a really low compression engine and short duration cam, you can get a noticeable power boost at lower RPMs by tightening up LSA and installed centerline as Hughes have done with their 'Whiplash' cams. If you are interested in boosting power from off idle through low to moderate engine speeds...... This will make a noticeable difference. Yes, tightening LSA will increase overlap a few degrees and cam may have a very slight lope at idle. But that is no reason to do it. Tighten LSA only if it will pick up power in the RPM range where you need it.

Tightening LSA with a short duration cam will also narrow your powerband and favour power at those lower engine speeds, but if you are cruising at seriously low engine speeds (2,000 RPMs or less) at highway speeds, you don't need max power at higher revs your engine will never see anyway. Your main concern at that point (heavy vehicle turning low RPMs with lock-up converter or manual transmission at highway speeds) is not lugging your engine under load and beating the main bearings out of it.

And then there are Rhoads lifters (think of them in terms of variable valve timing without the complication of computer controls and added moving parts as today's more modern engine designs have for the same purpose). They will broaden your power band whilst decreasing effective duration and valve lift at lower engine speeds. But they won't fully restore duration and lift until engine speed exceeds 3,000 to 4,000 RPMs depending on which of their lifters you use. And some guys dislike the 'solid lifter' sound they make at idle. So probably not what you need to boost off idle power when you will not be turning the engine fast enough to actually 'use' the duration and lift specs ground into your cam. In those instances, its better to begin with a cam specifically designed for what you are doing.

Hope this gives you some ideas,

Harry
 
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6gears.gif
Ya gotta have fun with this stuff, j par!

HB
 
I like it. Real-world experience, interspersed with opinion that is based on real world experience, interspersed with insight and the why of things. Give a man a fish to eat and you solve his hunger for a time, but teach him to fish, and maybe he feeds a community for all time.
 
Great post
plan your work-work your plan
the ice of Texas are upon you

OP if you do not have the TBi just skip it and go to the later MPFI
I have TQ on one chevy truck, ported heads, Jones FTH cam, rams horns
and Tuned port MPFI on another replacing earlier TB EFI Tuned port is much better- otherwise stock engine with duals HR cam but not original one 1.6 rocker on the intake
Jones camed motor is better but everything is perfect, compression, heads cam etc TQ has the altitude compensation on it which works ok but not as good as the EFI
but the FI works better in the winter
 
Wyrmrider said:
Great post
plan your work-work your plan
the ice of Texas are upon you

OP if you do not have the TBi just skip it and go to the later MPFI
I have TQ on one chevy truck, ported heads, Jones FTH cam, rams horns
and Tuned port MPFI on another replacing earlier TB EFI Tuned port is much better- otherwise stock engine with duals HR cam but not original one 1.6 rocker on the intake
Jones camed motor is better but everything is perfect, compression, heads cam etc TQ has the altitude compensation on it which works ok but not as good as the EFI
but the FI works better in the winter
Click to expand...
The TBI is in and running fine, original question was just to see if there was a *little* better cam (or cam advance) that still plays nice with the factory pcm; since I have to tear the top end off anyhow to replace a head, this would be the time to do it. It's just the wife's cruiser and family road tripper.
 
AJ/FormS said:
I like it. Real-world experience, interspersed with opinion that is based on real world experience, interspersed with insight and the why of things. Give a man a fish to eat and you solve his hunger for a time, but teach him to fish, and maybe he feeds a community for all time.
Click to expand...
Or, as I like to say: Give a man a fish, and he'll eat for a day. Teach a man to fish, and he'll sit in a boat and drink beer all day... :) JK
 
...... And then pick up some fish and chips and malt vinegar at Long John Silver's on the way home! Don't ask me how I know that...... :)

HB
 
proff
you have more than enough info to make a decision
stay stock
250 lunati
or a custom if you can get one ground for the price of the lunati
for roller tappets then regrinds come into play
high ratio rockers are not cost effective when you need a b3 kit plus rockers plus pushrods
cheers
 
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