Vortec stroker quench build
12-23-2016, 05:31 AM
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Vortec stroker quench build
Greetings all--first time poster but I've been searching, reading and learning a lot here while planning a re-power of my boat this winter. She's a 31' Marinette express cruiser--all aluminum with a loaded weight in the neighborhood of 7500 lbs. Single sbc. Obviously--I need a lot of torque--so I'm looking to build a stroker. This boat will rarely see WOT--in fact, I'd like to have the engine all-in well before 4500 rpm. And...it needs to run well on the crappy gas we often see at marinas around here, plus pretty restrictive exhaust manifolds--so I'm shooting for static cr in the low 9's. I'm hoping y'all will weigh in with your thoughts/suggestions/criticisms of the choices I've made so far:
Heads: Enginequest hybrid Vortecs, stainless valves-1.94 intake/1.50 exhaust- set up for max lift .520 cam, 64cc chambers Since they're hybrids, I can use my existing intake(Performer), carb(Holley 600) and valve covers
Crank: Scat 9000 cast steel 3.750
Rods: Scat 4340 forged, 5.700
Pistons: Speed Pro Hyper, D-dish to mirror head, +23cc's 1.425 compression height
Head gasket: Felpro stainless, .039 compressed thickness
Cam: Comp XM262 flat tappet 218/224 duration 112 lsa
Exhaust: standard cast iron marine logs, through hull
Assuming zero deck, I get a static cr of 9.23 and a dynamic cr of 7.58 with quench at .039. I understand vortecs will be more forgiving of lower octane if the quench is right--and .039 seems to be about spot-on. I thought I might be leaving something on the table with the 262--but when I plugged in the 270 specs, dynamic cr actually dropped a lot. This seems(to me) to be a pretty detonation proof set up--especially if I keep total timing to 32 degrees or less. Am I on the right track here? Am I being too conservative? Any and all thoughts gratefully accepted!
Heads: Enginequest hybrid Vortecs, stainless valves-1.94 intake/1.50 exhaust- set up for max lift .520 cam, 64cc chambers Since they're hybrids, I can use my existing intake(Performer), carb(Holley 600) and valve covers
Crank: Scat 9000 cast steel 3.750
Rods: Scat 4340 forged, 5.700
Pistons: Speed Pro Hyper, D-dish to mirror head, +23cc's 1.425 compression height
Head gasket: Felpro stainless, .039 compressed thickness
Cam: Comp XM262 flat tappet 218/224 duration 112 lsa
Exhaust: standard cast iron marine logs, through hull
Assuming zero deck, I get a static cr of 9.23 and a dynamic cr of 7.58 with quench at .039. I understand vortecs will be more forgiving of lower octane if the quench is right--and .039 seems to be about spot-on. I thought I might be leaving something on the table with the 262--but when I plugged in the 270 specs, dynamic cr actually dropped a lot. This seems(to me) to be a pretty detonation proof set up--especially if I keep total timing to 32 degrees or less. Am I on the right track here? Am I being too conservative? Any and all thoughts gratefully accepted!
12-23-2016, 09:58 AM
#2
Comp cams specs the intake closing at .006 not .05 so I think your dynamic compression is quite a bit higher, probably 8.3 or so.
Are you zero decking it? They are usually .02 or so in the hole so you should account for that.
Seems like a good combo, but I would go with a roller cam especially if the block is a roller block. I have used the lt4 hot cam as have many others.
Are you zero decking it? They are usually .02 or so in the hole so you should account for that.
Seems like a good combo, but I would go with a roller cam especially if the block is a roller block. I have used the lt4 hot cam as have many others.
12-23-2016, 02:35 PM
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Thanks Mr Maine and CIG3. Just did more reading on rollers vs flat tappets--really does seem the way to go for good smooth power delivery. Plus no worries about zinc. I'm sold!
Any point in going with 1.6:1 rockers with the LT4 Hot cam given the low rpm nature of my cruising or would 1.5:1 be sufficient? And yes, I was planning to have the block zero decked
Any point in going with 1.6:1 rockers with the LT4 Hot cam given the low rpm nature of my cruising or would 1.5:1 be sufficient? And yes, I was planning to have the block zero decked
12-23-2016, 03:16 PM
#5
I don't think going with less lift will improve your low end, I would go with the 1.6s but only with full roller rockers. A 383 will take more cam than a 350 and will probably top out around 5k with that cam. Remember, a smaller cam will increase your dynamic compression and be more prone to detonation and spark knock at high load lower rpms.
12-23-2016, 03:49 PM
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Very good points! When you say top out around 5k--are you referring to the LT4 hot cam or the Comp 262 I was considering?
Last edited by 31 Express; 12-23-2016 at 04:29 PM.
12-23-2016, 04:31 PM
#7
Yeah, although maybe a bit less with stock exhaust and the performer. Should try to step up to the rpm performer for that many cubes.
To have it all in before 4500 would require a much smaller cam and you would lose horsepower and torque everywhere. Except maybe below a 1000rpms where a camper or tow truck might need it right off idle.
To have it all in before 4500 would require a much smaller cam and you would lose horsepower and torque everywhere. Except maybe below a 1000rpms where a camper or tow truck might need it right off idle.
12-23-2016, 09:13 PM
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Comp cams specs the intake closing at .006 not .05 so I think your dynamic compression is quite a bit higher, probably 8.3 or so.
Are you zero decking it? They are usually .02 or so in the hole so you should account for that.
Seems like a good combo, but I would go with a roller cam especially if the block is a roller block. I have used the lt4 hot cam as have many others.
Are you zero decking it? They are usually .02 or so in the hole so you should account for that.
Seems like a good combo, but I would go with a roller cam especially if the block is a roller block. I have used the lt4 hot cam as have many others.
12-23-2016, 10:22 PM
#9
Looks to be a good combo. Quench is right on and that cam will build plenty of low end with the longer stroke crank. I have run that cam in a 355 and will say that it is plenty tame, which is a good thing. It wont revert with stock exhaust and will build peak torque nice and low. 4100-4300 if had to guess. Should make 370hp/400tq on 87octane easily.
For your Application I would drop the CR to 8.5 static, get a performer RPM intake and a 750 carb. and not worry about a roller cam. There are benfits to a roller, but to me on a mild 383 its money that could be better spent elsewere.
For your Application I would drop the CR to 8.5 static, get a performer RPM intake and a 750 carb. and not worry about a roller cam. There are benfits to a roller, but to me on a mild 383 its money that could be better spent elsewere.
12-23-2016, 11:15 PM
#10
I've used it with glm aluminums which I believe are the same as stock regarding reversion and later stainless marines. Motor has ran 8 years without issue.
I agree about the cam, but if it's a roller block why put a flat tapped in it?
I agree about the cam, but if it's a roller block why put a flat tapped in it?
