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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Wondering if anyone has ever seen anything like this. Came out of a junkyard '87 'vette motor I just bought. Engine is no virgin, has .030 pistons. These are the only markings on this thing. A few different angles, lighting in case anyone with better eye than me might catch something.
With the cam on centers in a lathe with a dial indicator, this is what I measure:
Int/Exh Dur. = 190/200
Int/Exh Lift = 436/462 ( varies a little between cyl)
lsa 112 or 113
I tried to reply an hour ago, no errors, but no post either. Same thing happened with my original topic, hours later I re-posted, it worked, then eventually my original (and duplicated) topic showed up on the forum. Oh well, lets try it again:
It's a roller cam, the block casting# is 14093638 (4-bolt, so definitely NOT the original block from the '87 vette this was in at the junkyard, with 128 aluminum heads I assume might be original.
If this post shows up, I'll incrementally add more info.
I tried to reply an hour ago, no errors, but no post either. Same thing happened with my original topic, hours later I re-posted, it worked, then eventually my original (and duplicated) topic showed up on the forum. Oh well, lets try it again:
It's a roller cam, the block casting# is 14093638 (4-bolt, so definitely NOT the original block from the '87 vette this was in at the junkyard, with 128 aluminum heads I assume might be original.
If this post shows up, I'll incrementally add more info.
I have pulled partial vin stamped blocks out of TPI Vettes that were 4-bolt, roller cam. Fact of the matter every TPI Vette engine I have had apart was 4 bolt main. Cam seems like a down grade from the factory L98 cam. 638 casting is a pretty generic casting from 87-95. Came in everything from cars to trucks to boats to fork lifts , generators and irrigation pumps. I pulled apart a very undisturbed 92 van 638 engine that was roller cam years ago. Was VIN stamped to that van. Nobody in their right mind changes a cam in a Van.
If my other post ever shows up, this will be duplicated, so I apologize in advance. Anyhoooo...
Long story: I have an '86 T/A, I'm the original owner. Doing a partial restoration (started out as a 5-speed conversion, became a third mortgage like everything does...)
My 305 was in fantastic condition for its age, but NO WAY am I putting it back together with the 'peanut cam'. It's a flat tappet engine, and I just can't justify dumping money into a flat tappet 305. So I bought what I THOUGHT was a stock '87 vette junkyard motor, mostly for the cam, the bigger injectors (gonna reuse my TPI setup, since it's minty ( I know, I know, it's a HUGE performance bottleneck), the roller block, and the aluminum heads. I know they ain't great heads, but they're light, and I have to assume a step up from 1986 305 heads.
So the plan was: stock '87 vette l98, hedman shorties, 3" catback, in my T/A. Everything else (other than perhaps some chip tuning) BONE STOCK.
I've researched this to death. Here's what I THINK I know. Please feel free to correct any misassumptions:
Stock, long-tube TPI works because of 'resonances' (kinda like an expansion chamber on an old two-stroke dirt bike?) which rely on the velocity of the air (as opposed to volume) to greatly enhance induction at LOW to MIDRANGE rpm. And it pretty much poops it's 'jammies at 5 grand give or take.
I'm cool with that. I'm not gonna abuse/race this thing. I'm just looking seat-of -the-pants fun, and gobs of torque, right off idle.
I've read over and over that with this setup, TOO MUCH exhaust flow is a bad thing, hence my choice of 1 5/8" tubes on the headers.
I've also repeatedly heard that too much cam is a REALLY bad thing for a stock TPI setup.
Specifically: lsa should be 112 or more. Lift should be high (within limits of heads/springs/etc) duration should be not much more than 200, exhaust a little more is OK. If I understand this all, the goal is to open the valves as high and as fast as possible, which,(I think) increases dynamic compression/torque.
But here's what I can't find a definitive answer on: in a stock (except exhaust/chip mods) l98, is it possible to increase torque/hp across the ENTIRE power band (i.e. giving up NOTHING at low rpm) with a 'better' cam than the stock l98 (Part# 14093643) cam?
If so which cam(s)????? Most of what I've seen in the forums involves cams with higher duration/lower lsa, and I have to assume that's shifting the power band upward??
Don't want that.
P.S. I'd love a lopey, filthy idle, but I KNOW that will trash my low end performance(with stock, long-runner tpi), so I've resigned myself to live with a boring idle...
RE: 4-bolt '87 l98's, the 'internet' says it isn't so. Just parroting the 'consensus'.
Thanks so much for reading this far, and grateful for any informed direction from anyone who's been down this path.
If my other post ever shows up, this will be duplicated, so I apologize in advance. Anyhoooo...
Long story: I have an '86 T/A, I'm the original owner. Doing a partial restoration (started out as a 5-speed conversion, became a third mortgage like everything does...)
My 305 was in fantastic condition for its age, but NO WAY am I putting it back together with the 'peanut cam'. It's a flat tappet engine, and I just can't justify dumping money into a flat tappet 305. So I bought what I THOUGHT was a stock '87 vette junkyard motor, mostly for the cam, the bigger injectors (gonna reuse my TPI setup, since it's minty ( I know, I know, it's a HUGE performance bottleneck), the roller block, and the aluminum heads. I know they ain't great heads, but they're light, and I have to assume a step up from 1986 305 heads.
So the plan was: stock '87 vette l98, hedman shorties, 3" catback, in my T/A. Everything else (other than perhaps some chip tuning) BONE STOCK.
I've researched this to death. Here's what I THINK I know. Please feel free to correct any misassumptions:
Stock, long-tube TPI works because of 'resonances' (kinda like an expansion chamber on an old two-stroke dirt bike?) which rely on the velocity of the air (as opposed to volume) to greatly enhance induction at LOW to MIDRANGE rpm. And it pretty much poops it's 'jammies at 5 grand give or take.
I'm cool with that. I'm not gonna abuse/race this thing. I'm just looking seat-of -the-pants fun, and gobs of torque, right off idle.
I've read over and over that with this setup, TOO MUCH exhaust flow is a bad thing, hence my choice of 1 5/8" tubes on the headers.
I've also repeatedly heard that too much cam is a REALLY bad thing for a stock TPI setup.
Specifically: lsa should be 112 or more. Lift should be high (within limits of heads/springs/etc) duration should be not much more than 200, exhaust a little more is OK. If I understand this all, the goal is to open the valves as high and as fast as possible, which,(I think) increases dynamic compression/torque.
But here's what I can't find a definitive answer on: in a stock (except exhaust/chip mods) l98, is it possible to increase torque/hp across the ENTIRE power band (i.e. giving up NOTHING at low rpm) with a 'better' cam than the stock l98 (Part# 14093643) cam?
If so which cam(s)????? Most of what I've seen in the forums involves cams with higher duration/lower lsa, and I have to assume that's shifting the power band upward??
Don't want that.
P.S. I'd love a lopey, filthy idle, but I KNOW that will trash my low end performance(with stock, long-runner tpi), so I've resigned myself to live with a boring idle...
RE: 4-bolt '87 l98's, the 'internet' says it isn't so. Just parroting the 'consensus'.
Thanks so much for reading this far, and grateful for any informed direction from anyone who's been down this path.
Cam in the 218/228 range can run really well with the correct tuning. That being said for purely stock type stuff stick with something around 206-210. I would honestly use the Comp Xtreme 4x4 roller. 206/210on a 111 lsa and ground 4* advanced. It has 0.458/0.458 lift. Either that cam or the Elgin E1136. The Elgin cam is 210/215 @ on a 110 LSA and ground 4* advance. Both run really well in EFI applications. The MAF TPI setup is much more forgiving than the MAP to cam specs. I have messed with a MAF car that was running a LT4 Hotcam on the stock tuning and it actually ran suprisingly well. Neither of the cams I mentioned above will signifigantly raise the power band but will add a good chunk of torque. They tighter LSA closes the intake valve sooner and the tighter LSA also helps get the cylinder scavenged and helps promote the resonance of the tuned runners. That also being said the TPi engines actually like larger primary headers than say a carb 350 would. The TPI makes the 350 have airflow and VE numbers of a larger engine where the runners are doing their thing. I had 1 5/8" primary tri-y headers and a production LT4 cam in a 305 in my G20 van. It would spin the tires with 3.08 gears and the stock 1,600 stall converter in the 700r4. Factory LT4 cam is 203/210 on a 115 LSA retarded 1* with .476/.479 lift with the 1.6 rockers. The factory 305 TBI/TPI peanut cam is 109 LSA. It less of a function of LSA than it is overlap. With a small cam you can run a tighter LSA and still have relatively short overlap. GM makes a small cam that makes very strong low end torque in a 305 or 350 as well. Its the 395' Marine cam aka Ramjet/HT383 cam. It is 196/206, .431/.451 lift, 109 LSA and +3 advance. Works very well up to 5,000 rpm. It works with new stock valve springs and factory stamped steel rockers as well.
I have actually run that little Comp 4x4 cam I mentioned. It does need a stiffer spring and I would run 1.5 full rollers to help reduce frition in the valvetrain. I had it in a 350 Vortec in a 6,000 lbs Express van. It had BBK shorties, the factory exhaust, 2010 Tahoe Electric fans and a homebrew cold air intake. It actually ran fairly well on the factory rune but ran better once it was really dialed in. I never felt it lagged anywhere compared to the stock cam. That was also pulling against the stupid tall 1st gear of a 4L85E with only a 3.42 gear in the rear. It would run well up to about 5,200 rpm.
Thanks for all the good info. I'll add those cams to the list of the ones I'm considering. Not gonna reuse the "mystery cam". Motor is at the shop. A couple of cyl out of spec, so going .040. Somebody did a hack job trying to balance the crank, and the journals were not looking that terrific, so not reusing it. Looks like the heads are OK, just a grind needed. We'll see where it all takes me, besides to the bank (to withdraw, lol).
09-12-2019, 08:46 PM
