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After a lot of research based around the intentions of the vette such as street and some 1/4 mile with really nothing else for it after those two things. We have the peak tq right where we want it. Winding it out to 7 grand is great, but hp/rpm necessarily isn’t what is going get us what we are after.
As of right now, our power range is 3500-6000 rpm with max tq at 3900rpm. Running a stall of 3700(give or take 200-300 rpm for slip percentage) we are going to be launch closer to peak tq. Most guys are dead set on hp,hp,hp, and rpm, rpm, rpm. Which is is all find and dandy, but if we built the engine around higher rpm. That means our entire power curve will shift to the right. It would go against the entire goal of the build. Not to mention, the main reason why we are comfortable with the current numbers is we are at the threshold of what our posi tuned 3.73 rear end and block can handle. Which I didn’t know before establishing what our power goals would be.
its a proven fact that hp doesn’t dominate until past 5300-5400 rrpm. We would also have to spin the engine higher at launch to achieve the exact same results that we will get currently.
My question is this to you guys, if we were to step up the head size. Knowing that adds more volume but will kill or negatively impact velocity. What will that do to our power curve overall?
Seeing how the head CC in your case is so small.....it would do absolutely nothing. You are undersized at the moment....a 421 wants a 220-230cc head on it....
The swept volume of the 421 is such that it would still maintain velocity with a larger port....it fact your VE would actually improve as you would have the same air speed but more volume of it....that is the point of the larger port.....CFM numbers do not and cannot reflect this as it is vacuum that creates the draw
I run a 200cc Dart on my 406....I did this on purpose to boost torque in the midrange.....this engine will nose over at about 5800 rpm.....kinda what you are achieving......I have never dyno’d It but I can tell you it makes torque EVRYWHERE
Another reason we are perfectly fine with how the 421 is its turning out to be a show down with another one of our cars. We have a built 390 lt1 in our (C9)96’ callaways impala ss. The numbers are almost identical but flip flopped. The 390 run 535hp 497 ft/lbs of tq max rpm range at 6900 rpm. As most, I’m guilty my entire life dead focused on hp and higher revving engines.
However, comparing the two engines solely. The 421 will always win or put down a better 1/4 mile time of both engines were put into the exact same car.
Sure, a mile or even 1/2 mile race and it’s a different story.
Straight from the guy that built our e85 carb and specializes directly in e85 carburetors. Which isn’t being posted to degrade anyone or say I can’t be convinced otherwise. Merely to continue the open door discussion.
Last edited by 61grandsport; Jan 5, 2019 at 06:50 PM.
Also, I did mis label in my description. They are not 180cc but 195cc 62cc combustion chamber. dart aluminum heads. Our 180cc were on our 400 build prior to this build.
Last edited by 61grandsport; Jan 5, 2019 at 08:38 PM.
George is 100% correct about your heads being too small also your Cam doesn’t have enough lift.. there’s no way in the world you’re gonna make that power with thoes heads and cam
Finally after all this time picked up the engine. We were able to store it st the machine shop until we were ready for it. Now that all our chassis work is done, headers are built, and transmission is built.
You guys were right, we fell well short of our goal. After switching to a better suited intake mani. The numbers came up just a touch, final numbers are 510cHP @ 6000rpm & 542ft/lbs TQ @ 3900rpm. Went with a TCI 3600 stall converter. Still happy with the end result and what we have planned for the car. It’s plenty of power.... for now��.
Last edited by 61grandsport; Apr 11, 2019 at 12:22 PM.
Finally after all this time picked up the engine. We were able to store it st the machine shop until we were ready for it. Now that all our chassis work is done, headers are built, and transmission is built.
You guys were right, we fell well short of our goal. After switching to a better suited intake mani. The numbers came up just a touch, final numbers are 510cHP @ 6000rpm & 542ft/lbs TQ @ 3900rpm. Went with a TCI 3600 stall converter. Still happy with the end result and what we have planned for the car. It’s plenty of power.... for now��.
Dyno please... would like to see where she went flat///
Im guessing 5000 RPM
Last edited by pauldana; Apr 11, 2019 at 01:09 PM.
The RPM manifold peters out at about 500hp as you found out......your heads are too small.....a 215 should have been spec'd here or even larger.
The 421 3.875 stroke stuff wants a big manifold and a big head......the stroke "works" the port......although it runs very well for a small head setup and will have a pile of mid range...your torque is as flat as Kansas....and that makes for a bad *** street engine.
Your builder is on track with a CNC intake.......I spec the Brodix HV1 for these large small blocks.......the Victor Jr. is a surprisingly great manifold for being a 35 year old design but is just too low to make real power upstairs......but on a Vette that clearance is needed.
Keep us posted with the intake results.....
Jebby
x2 you (almost)cant have enough head wiht that CI....op once again showed where dual planes can hurt you on larger stuff, theres simply no need to crutch it with a giant cam or small intakes to make torque
CI and heads mean you can run a little less cam to get there. Should do burnouts a block long
I get a lot of crap cause I run a "too big" cam/heads on a little 383 but for usage, weight and gearing its pretty close to being what i need it to.
My question is this to you guys, if we were to step up the head size. Knowing that adds more volume but will kill or negatively impact velocity. What will that do to our power curve overall?
Its like what George is saying, your still kinda gunshy to the sbc/heads, its a 421, thats not a small cube engine anymore, it NEEDS more head, treat it like a big block
Last edited by naramlee; Apr 12, 2019 at 12:19 PM.
. As most, I’m guilty my entire life dead focused on hp and higher revving engines.
However, comparing the two engines solely. The 421 will always win or put down a better 1/4 mile time of both engines were put into the exact same car.
Sure, a mile or even 1/2 mile race and it’s a different story.
Same here.....fun but it comes w/a price. rpm gets expensive & makes the valvetrain a liability
edit-540 lbs tq at that rpm is damn stout, who would guess by a quick glance atyour engine. no need for a bunch of gear, that will be a hoot on the st.
