Building a 420CI motor to run on my HSR. What rpm and power level do you think the HSR will support on this size motor?

 

Well I Have a 415cui with a well ported HSR and it goes to 6000+rpm without falling off.

A victor jr would also be good.

 

ALmost cant put too big of an intake or head on a small block that size
what are you wanting the engine to do?

 

Limited to a 1206 gasket likely which would be a 200-220's cc head. Bigger head, ported hsr to match port area, i dont see why it couldnt support 6500 rpm range. Got to have a big cam, 250-ish at .050 for a hyd roller, .600"+. I'd be happy with 600-650 hp on that. Manifold does need alot of work for that. But i dont think that was your intention with that build

Small head like a 195cc then 6000 and no more. Maybe even 5800 before starts to choke

 

Well Orr you've been following my other posts regarding this build. I am asking about the HSR's rpm range, typically head/cam/intake mfg ratings are based on a 350 so I wanted input on a 420CI build. Not wanting a high rpm engine but still target peak in the 58-6000 range. You feel the head port affects the intakes usable range. Interesting, I hadn't thought of it that way. I have been leaning toward AFR's 195cc ports but it seems a 210 wouldn't be too large for this size motor. Regardless, I'm planning to cam it to 58=6000. Looks like the XFI280 may be too small. The intake I am "stuck" with as well as the OEM computer (maf) and 3rd gen exhaust. Got to keep the combination right all things considered.

 

Intake flows into head and head into cylinder. Its a package deal. An intake could hurt a good flowing head, sometimes it can help a bad flowin head.

I would go 210's on that motor. Pipemax recommends a head with a csa between 1.96-2.22 for 6000 rpm and afr 210 is about a 2.0-2.05 i believe. 195's fit up to 383's well. 210's are the 195's for 400's.

Cam you can do a 280xfi but it is alittle small imo. Custom spec from xfi lobe catalog would be something like their 288/236 lobe for intake and 292/242 for exhaust or something like that. That should get you into the 6000 rpm range.

Look up 88blackz51's build. Miniram, afr 195 comp port, 236 deg xe high lift cam, i think it was 415". It peaked 5800 ish but did hold power beyond. Head was choked at that point. Cam was about getting maxed as well. Thats kinda what you are building. Still hear some cam sound but it will drive great. Should have no issue making 380-400+ whp without breaking a sweat.

I run around in a 245cc head 246/252 deg cam on a smaller 400" motor and its surprisingly docile. As said earlier its hard to over head and over cam a 400. That big bore really requires alot larger cams and heads than most are used to with 355-383's

 

That's what I am thinking. I will sacrifice some power for drivability but don't want this laying down at 5000 either. That seemed to be one of the problems I had with the 350, there was no reason to rev much past 5200 or so. Really dropped off quick after that point. I'd like to shift closer to 6k but as long as the drivability and cruise torque is still good may as well let her rev. It just seems going much past 6-6500 starts to add costs or wear issues. Plus I feel somewhat limited by the MAF and exhaust constraints.

So, for a 420CI small block using HSR manifold, a ~236/242 cam with decent lift and a set of AFR210's should all work together to peak at ~58-6000 and still be something I can tune and live with all around? Generally speaking, I know you don't know whether I can tune a fish but that combo shouldn't be a nightmare to tune due to the duration etc. I just want to make sure it idles and cruises ok and has enough vacuum for power brakes. This is a fun car not a race car.

 

Yeah it shouldnt be a problem. Maf will make it easy. You'll have to add alot of fuel via the pe mode enrichment vs rpm table. Very easy to work with however. With a wideband o2, you just roll into throttle gradually workin towards wot and making a full rpm sweep in whatever gear, watching wideband o2 data. When its goin lean let off and note that rpm area. Go into the table and add %. Typically i find 15% or so is about 1 full point air fuel ratio. To go from 14:0 to 13:0 would be adding 15 to the table. Sometimes it maybe 10-12 and respond well sometimes its closer to 20. But 15 is a good rule of thumb. Example with using aujl bin on my 383, by mid 4000-5000 rpms i had increased the pe vs rpm value from 0 to 87 lol. The base bin was set to 40 and it was showin 17:1 air fuel. But with arap bin on the 360 motor i tuned, i actually had to pull 12 at peak rpm

I've done the 280xfi on a 360" and my bigger 230/245 on a 109 lsa in a 383 with 6e maf and it worked well. Didnt take all that much to get it running well. Just alot of fuel work to pe vs rpm.

236 cam in a 420 would be milder than a 280xfi in a 360 or 383 for that matter. It should be a great combination. My old 233/233 in a 400" afr 195 head was a good low rpm 5800 ish shift combo. Your combo may peak 5700-5800 and hold to 6000-6200. Depending in lsa and valvelift. I like more lift for big inch motors and short duration cams. Xfi may be abit harsh. I like the magnum high lift series. Easily get near .600" with good manners

 

Thanks for the input Orr. So you think the AFR210's with a 236 and ~.600 lift would be a streetable combo with decent life? I don't expect 100k but will give up some power to keep it from eating itself alive.

And I will get advice from Comp on the whole cam/lifter combo but if you were to spec a cam I take it you wouldn't go XFI. I am not familiar with Magnum high lift but I suppose it is just what it sounds like. Magnum series with more lift- lol. Are they a "kinder, gentler" profile than the xfi grinds? It sounds like we're thinking the same here. I don't want a dyno-bullet that sacrifices life for 15-20 more ponies. I want a solid motor that drives well, makes a lot of usable torque and pulls up high in the 5k range. I also want long life, by that I mean 30k+, 50-60k would be better. Not just the lifters but valve guides and related components. I need it to at least match the life expectancy of the pistons/RA. I am a little worried about the short compression height of the pistons with the 3.875 stroke/6 rod combo. If I can expect the bottom end to last say 50k then I want the top end to match if possible.

In regard to the MAF system, I was refering to the stock MAF sensor's size being a limiting factor as well as the exhaust system. I don't plan on changing the headers/exhaust location so I'm stuck with the factory routing/single pipe senario. No need to plan on a power/rpm level higher than these two factors will allow.

 

My 383 worked well enough at 400 whp with stock gutted screen maf. When i went 3.5" housing maf i expected more hp but track times didnt show gains.

I think you will be fine. If you want talk to tequilaboy and or visit blowerworks.net. They make upgrades to maf that will read 600+ hp and work with ecm.

As far as cam, xfi will kill the springs in 15k miles likely. Maybe 20k. If you want long life you will need a less aggressive lobe. More seat duration and less ramp so little less .050 and .200 duration.
I'd possibly look at something like a 290/304 236/242 .608/.587 on a 112, magnum hi lift 3122/3113 lobes. Used for more longevity and make decent power. My 383 and turbo car seem to like them. Or do xe exhaust lobe for abit less duration at advertised. Afr heads like less duration splits but my 383 cam was opposite of that and was awesome, and it liked spray

 

Ok, whew- we're covering a lot of ground here. I do appreciate it tho.

Now as it relates to the stock MAF/computer/exhaust, I just want to keep the air filter to tailpipe systems in mind when specing the build. I don't intend to get exotic and will have to tune it so I don't want to throw some crazy vairable in here.

When I am discussing reliability/longevity I am more concerned with oil consumption, loss of compression and valve guides. I wouldn't mind changing springs at 15k on the way to 50k. Just don't want to build a motor that will need to be tore down to deal with valve guides or rings. I'd rather give up 20HP. I'm sure you get the idea.

I was planning to use the AFR 195 street heads but am now leaning more toward the 210's. If I'm not mistaken the 210's already have better springs and 2.08 valves. But I will run whatever spring required. I do like the "idea" of the beehives.

The cam. Always seems to be one of "the" questions. Important decision for many reasons. I wish I could try half a dozen but time and budget makes it impractical. So I am relying on good advice and appreciate all of the shared experiance.

I understand good flowing heads (exhaust/intake ratio) don't need a split duration cam (or not much) so I only plan to use a split cam if it helps somehow. Something in the 236 range with as much lift as practical maybe ~.600 appears to fit my goals. I also have heard the wide lobe separation may not be helpfull on a large CI motor. Some sources recommend as tight as 104. And I'm not married to CompCams but I have had success using them in the past and have a pretty decent connection via my machine shop. Which, by the way, is an engine builder for a lot of racers locally and around the country and the reason it's taken almost 3 months just to get going on the build. They are swamped building race motors but have less experiance with "street" builds. I rely on my 3rd gen brothers & sisters because the EFI in the equation affects cam selection so much.

 

You should consider the afr 8019 springs in either head. You can run 195's with a 230's type cam and will still cover your goals. Its totally up to you. 195's are a solid head but given the big cubes i recommend bigger heads to help that 5800-6200 rpm range.

Spring life and guidelife will depend on valvetrain rigidity and geometry. Wrong pushrod length will wreck things in a hurry. Valve float will wreck things but you shouldnt float with 8019 springs and those milder lobes. Get bigger 7/16 studs and thickest pushrods that you can clear. Maybe even a stud girdle. Ultimate setup is shaft rocker system but they run 700-1000$. I find them so nice i dont think i'll ever use conventional again.

The idea here is to use the cubes to make up for power lost by picking milder cams for longevity imo. And you wont see a huge difference in an xfi lobe vs milder ones in a typical 6000 rpm street motor. If its 15 hp i'd be surprised as long as the valve events are right to begin with.

Engine bottom end life depends on how clean the oil is kept, how well balanced everything is, and ring seal depends on cylinder finish and how motor was broken in. Once done properly, you shouldnt need to touch bottom end again for long time.

Alot of sbc stuff love tighter lsa. 108-110. Better the head sometimes dont need tight lsa but wider tends to push trq curve up in higher rpms while narrow brings it down and sacrifices rpm range after peak. Very general idea. I just recommend alittle wider for better idle and tuning ease. Tight lsa just makes it abit harder to get idle closed loop to work well. O2 sensors get fooled. You can disable it tho like i did and it will be fine. Or play with o2 swing points to compensate. Once its over idle speed it doesnt matter what lsa is.

Theres little reason this motor shouldnt make 400 whp a drive almost stockish once tuned. Mild cam lope sound but good muffler no one will know its 420" and makes that much steam