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Friends don't let friends run XE flat tappet cams. Roller cam lobe with flat tappet riding on it.
Adam
I have built over 200 engines....half of those have flat tappers in them....not counting the 100 camshaft jobs I have done for people when I lived in Detroit..over a 25 year period......I have had exactly three cams round off lobes....all three were XE Comp sticks.....
I really like this cam for the 383. It's designed specifically for the SBC stroker and a dual plane manifold (4 pattern). I bought one for my 383 that I'm building for my 81, haven't got it running yet though.
This cam is a bit bigger than the one you posted but that one should be fine too. You'll probably need a stall if you go with this 4 pattern cam:
Last edited by htown81vette; 03-14-2019 at 05:23 PM.
I have built over 200 engines....half of those have flat tappers in them....not counting the 100 camshaft jobs I have done for people when I lived in Detroit..over a 25 year period......I have had exactly three cams round off lobes....all three were XE Comp sticks.....
Jebby
I agree with your sentiment. I prefer roller cams but flat tappet cams do have their place too, mainly for the budget minded. Such as the kid in high school who wants to mod his car but only earning minimum age. I'm not laughing because I WAS that kid 35 years ago! Gotta start somewhere! My first pair of headers cost me 60 bucks I think....back in the day...was a great mod too!
The camshaft you described at the beginning of this thread has the same specs as the camshaft in the BluePrint 383ci 420hp/450lb engine.
I was looking for the cam you referenced since most of the cams mentioned early in the thread were low lift cams. The blue print 383 425 Gross HP/450 Gross Tq requires a fairly high lift roller cam with at least 10:1 compression. This is the blue print cam needed for the 383:
The camshaft you described at the beginning of this thread has the same specs as the camshaft in the BluePrint 383ci 420hp/450lb engine.
I was looking for the cam you referenced since most of the cams mentioned early in the thread were low lift cams. The blue print 383 425 Gross HP/450 Gross Tq requires a fairly high lift roller cam with at least 10:1 compression engine. This is the blue print cam needed for the 383 or any 355 making that type of Gross power:
That is the engine in my ‘72 when I purchased it 6 months ago. I found the ID tag on the side of the block and called BluePrint to verify what it was. Part # BP3834CT1
Last edited by Batty Mantis; 03-14-2019 at 06:54 PM.
EBlueprint has that cam made for them and they don’t disclose the other relevant specs (advertised duration and lsa ).
having said that, BluePrint provides the warantee and are trying to keep costs down so its probably got a nice longevity focused lobe. It’s the perfect cam for an SBC flat tappet build with a 5,800 rpm HP peak, like their spec says.
383s have higher piston speeds at every rpm than a 350 and with hyperpistons and an externally balanced engine you don’t want to go crazy with RPM or things go boom.
I saw the cfm chart for thre blueprint heads before and from memory I’m pretty sure they’d appreciate more lift. A nice set of 1.6 roller rockers on the intake and exhaust sides (only 1 deg duration split on cam) would be an easy power upgrade and the extra 2ish degree of duration you’d gain @ 0.050” might move the rpm peak right to 6,000 in the process). Note: I have NOT modeled this; guesstimate only.
Adam
Last edited by NewbVetteGuy; 03-15-2019 at 09:07 AM.
That’s a valid point Adam. I have used Comp Cams 1.6 roller tip rockers on other SBC builds and noticed a slightly gain. Nothing dramatic, but they do increase the lift of the cam. Just make sure your piston to valve clearance is ok.
That’s a valid point Adam. I have used Comp Cams 1.6 roller tip rockers on other SBC builds and noticed a slightly gain. Nothing dramatic, but they do increase the lift of the cam. Just make sure your piston to valve clearance is ok.
Higher ratio rockers make the valve action move more like you have a more aggressively lobed cam; you get a TINY increase in duration at lift (which is why peak rpm normally goes up with higher ratio rockers) and you spend more time at higher lifts; both of which always increase power a little bit. The power increase is more significant when the increased lift gets you into more CFM from your heads, which I’m pretty sure will be the case here (195cc heads And a low valve lift). -In this case you’re putting more airflow through the same port crosssectional area so it means improved average airspeed without changing the valve open or close points (more VE/ more trapped air)== torque improvement AND hp improvement.
I’d try to model the improvement but I’m missing the cams advertised durations and LSA...
CFM Port Flow Average @ 28"
.100" - 83
.200" - 130
.300" - 166
.400" - 193
.500" - 207
.600" - 213
The Intake stops flowing more CFM somewhere between 0.500" and 0.600"... so not ideal to see max benefit from a rocker ratio switch.If you look at some of the top tier SBC heads in this size the flow keeps increasing to 0.550" or 0.600" so the extra ratio would be a no-brainer. BUT moving from a 1.5 ratio rocker to a 1.6 would only bump up the max valve lift to .512 so maybe not to the point at which flow starts DECREASING.The BP 38313CT1 crate motor which is exactly the same as yours but with a roller cam has a max intake lift of .528 and .536 (with a 221 / 226 duration @ 0.050" and a 110LSA) (makes 10 HP more with 8 degrees less duration because of the more aggressive lobe possible from the hydraulic roller cam) -I'd say BluePrint spent a lot of time figuring out the "ideal" cam for perf and longevity with those heads. A 1.6 ratio roller rocker would probably still be a good thing, IMHO.(David Vizard's testing says +5-7 HP for moving from a 1.6 to a 1.65 ratio on a 383 with good heads and the jump from 1.5 to 1.6 is more significant.) -Maybe get that 10 HP difference vs. the roller motor back, but at a higher RPM because of the extra duration on the FT motor. (I can't model it without advertised durations and LSA and BluePrint doesn't seem to share that info.) So is 10 HP worth $300? (rough ball park of the question at hand anyway.) Adam
Last edited by NewbVetteGuy; 03-15-2019 at 12:55 PM.
I really like this cam for the 383. It's designed specifically for the SBC stroker and a dual plane manifold (4 pattern). I bought one for my 383 that I'm building for my 81, haven't got it running yet though.
This cam is a bit bigger than the one you posted but that one should be fine too. You'll probably need a stall if you go with this 4 pattern cam:
I find the concept of a 4 lobe cam pretty interesting and the goal a worthy one (equalizing the amount of trapped air between cylinders even with a dual plane intake); but I'm just not clear how much it actually gains you in terms of performance; what it COSTS you in terms of $$$ is pretty obvious. I'm a little skeptical that the cost diff will be overcome.
-I wish you could have your intake stuck on a flowbench and submit the per-cylinder flow data to comp and have a custom multi-lobed cam built to do this for any intake. (My strange long-runner intake has some weird variations cylinder to cylinder AND pretty intense airflow competition between two of the cyliders with the SBC firing order. It would be a "Best case" to see a custom multi profile cam like this tested (with the LS swap firing order) back-to-back. -The flow variance in my intake makes NOS and forced induction iffy as the AFR differences between cylinder just get worse; a "16 lobe" cam profile could even out airflow on even crazy intakes like mine. (I'm sure the cost would be unaffordable, though...)
Most intakes will vary runner to runner, even EFI wih the TB up front, dual & single planes etc.
Just an opinion but I think its almost a benefit when some runners are longer than others on a street car
03-14-2019, 04:46 PM
