XE is so old now; Flat tappets are that aggressive now. I agree the 406 with 210cc heads, 1.055” intake valve and 5500 rpm peak might like more lift. -I just hate XE lobes; valve train destroyers in flat tappet form; pointless in hyd roller form. (Why spend $1,000 extra to run a hyd roller conversion on a lobe you could run with a flat tappet?) IMO, if you’re going to go Roller and <6,500 peak rpm, get a more aggressive lobe than you can buy as a flat tappet or don’t bother. -Long runner builds should run with nasty, aggressive lobes, IMHO. You want max avg torque under 6,000 so throw those valves open!

If people spend more $$ to go with a modern valvetrain they can get more lift and more longevity; just steal the LS “recipe”: good short travel low bleed down lifters (ls7 if you have a roller block), beehive or conical springs, stout pushrods (none of those floppy noodle 60s pushrods) ESPECIALLY if you want to be done making HP at or below 6,500.


Adam

 

If Chad Speier is still lurking on here I’m interested in his thoughts on whether the 1.055” intake valve on a 400 bore like this with an obviously low rpm, max torque build makes sense here vs a 1.080” valve. I’m liking it. I’m guessing you get less shrouding and a higher discharge coefficient given that you’ll get more flow on the bore side. I particularly like the idea of getting to the bigger curtain areas faster with the aggressive lobes here.

Chad, I know you’re a fan of your fancy 45 deg valve jobs, but if you’ve got more CSA than your cubic inches+ max hp rpm calls for and you’re willing to pay for the valve train to support an aggressive ramp isn’t this the situation where a 50 degree seat could provide a benefit? Get that valve open fast and far and into the good curtain areas and get that port speed up?

Adam

 

I am looking to do retro-roller lifters... So yes with that investment, I would certainly want to take advantage of that modern roller tech.

Thoughts on a good current cam that should match the long runner / RPM range?

 

I've modeled the wave tuning of the FIRST for a 350 and a 383 with 5.7" and 6" rods with the stock 1.75" diameter runners, but I actually haven't done it for a 400 SBC. I think the RANGE of seat-to-seat and 0.050" durations on good long-runner engines with dyno results you find online and FIRST builds on here isn't super huge so it's a good guideline, but, IMHO, you should get a few recommendations from a few professionals. I don't think I have a single SBC 400 build in my list and your 11:1 static CR is probably the highest I've seen on a FIRST build, too. I'm not sure what vacuum / overlap you can get away with if you're going with a stock computer.


A modern aggressive lobe is what's called for IMO, like previously mentioned, XFI but maybe tighter LSA, Mike Jones EHR lobe, QXI if you want max perf and don't care about valve train longevity. -Mike claims that one major factor limiting the acceleration off of the seat of a hyd roller lifter is that it requires a tighter negative radius on the flanks of the lobe profile and that lots of cam companies aren't equipped with grinding wheels of a large enough radius to make them as aggressive as they can be off the seat. -My guess is that if a company is advertising having an inverse radius / concave flank roller cam that they have that ability but heck if I know.

-Compare the advertised vs. 0.050" and 0.200" duration numbers and max lift between multiple cams to tell how aggressive the lobes open side is. The greater the difference between the adv, 50 and 200 durations, the more aggressive the lobe is. ---> You'll want your heads' spring and valve stats and you'll want to ask the cam company whether those springs are going to work or not. -Your other option is to limit the aggressiveness of your cam lobe based upon what your current springs can support.

I'd also ask whether "normal" retro roller lifters are going to be ok give those lobes and your RPM goals or if you should go with a short travel / low bleed-down hyd roller tappet to prevent bleed down at your shift RPM.

-Call at least CompCams to see what they'll recommend for you, and fill out Mike Jones cam request form and see what he recommends.

Adam

 

Badss / Orr89RocZ:

I'm resurrecting this, to ask about a good ROUGH estimate of the peak MAP Intake pressure on a TPI motor like this. I'm assuming it gets reached at the torque peak RPM.

Background: I'm looking at the dwell times I should use with my LS2 514a ignition coils and the estimated spark durations and max voltage outputs and I'm trying to put that into Paschen's Law to estimate the max spark plug gap that I could run in this motor.

I bought regular boring NGK spark plugs, but I think I'm going to pickup a set of Laser Iridium IZFR6K11 #6994 because they last basically forever, are extended projection and are made for running a big gap and with my LS coils I should be able to run a big spark gap, which will help me with my MPG goals as a bigger spark gap can set off a leaner mixture at my low load cruise RPM and I can tune to have a lower ignition advance to take advantage of the larger cap; heck, my holley HP can do per cylinder ignition advance.

I'm trying to enter my info into the Paschen's Law calculator at the bottom of this page in the MegaSquirt manual but I don't really have any idea of a reasonable intake pressure in kPa to go off of.

I'm pretty sure that calculator is built assuming a typical spark plug and not a super small iridium tip, but I l'd rather go off a good margin of safety.

http://www.megamanual.com/seq/coils.htm


Adam