Currently building my 383 HSR AFR combo. Looking for ~400 WHP but keeping it street/power brakes friendly. Right now the 280XFI looks good but I can't get over the ultra wide 113 LSA. It does keep the overlap down to 58 where the 110 version is around 65 overlap. Which brings me to my question how much duration is too much for tuning with the OEM computer and MAF system? There are important things to consider such as idle vacuum for brakes, O2 sensor signal at idle and cruise. Brian at Comp cams says the 292 or 280XFI's are the "only" choice for my setup. But he also said I wouldn't be able to tune it with the OEM computer and the 292 would be marginal with power brakes.

Respectable sources such as David Vizzard say keep the LSA way tighter than most cams are ground. He suggests closer to 106 LSA for a 383. With a duration in the 50-65 range that works out to about 278-282 seat duration. Right where the XFI cam falls. But that is a serious difference in LSA's 113 vs 106. Obviously his work is mostly with carbs and that may be the difference.

I have read a lot on LSA's and the reasons to alter them. But none of it really is for our applications with OEM controlled aftermarket EFI's such as HSR. What experiences have you had with tuning HSR via OEM computer with different duration cams on different LSA's?

Every cam is a compromise in one way or the other. I am hoping to get more input for experienced HSR tuners to at least narrow down the duration range and then the LSA range. From there it is pretty much get as much lift as I can...

 

I tuned a 286/306 230/245 109 lsa cam and it was fine on a 383 with maf. Lopey idle but brakes worked fine.

Leave the cam companys to can suggestions alone and disregard them on tuning advice. That is ignorance that you cant tune the oem computer. Many guys here do it all the time

Xfi292 will work ok and have decent brakes but it will want to rev to 7k plus for best use of the lobe. Its a big cam. It be better for 210 heads imo

You could go 280xfi on a 110-111 lsa and it would work great. Make alittle more midrange and not be quite as broad power curve upstairs. They are aggressive lobes and alittle harder on valvetrain than some others but makes good power

 

I have a 383 with the 280XFI and AFR 195 heads. It is not hard to tune, but for street driving I'm finding it would be better with at least a 3.73 rear gear. Matter of fact the idle is not even that lumpy.

 

As far as tuning with OEM that's what I thought. In the same conversation he mentioned I'd need something like the EzEFI setup, which they also sell.

Tibo In what way do you feel the 280XFI would be better with the lower gears? I still have a 3.70 R&P in my shop but don't really like them for daily driving.

I wonder if the XFI line's aggressive profile would be a good place to use AFR's hydra-rev kit. It seems it would take some stress off the valve train and possibly use a lower rate spring or beehive.

If I were to order the 280XFI on 110 it would be very similar to the XE282 using 1.6's. Less lift maybe easier on the valvetrain too. Obviously the XFI line is aggressive but I wonder if there would really be much different under the curve comparing the two.

I suppose I am willing to give up a little on the top end to ensure drivability and have decent component life. In the XFI line that means dropping down to the 268XFI which seems a little too conservative. The XE276 seems to be an attractive alternate as well.

I am leaning toward using the 280XFI or XE282 if I end up building the 396 and possibly the 280XFI or XE276 for a 383. Both would have AFR 195's & HSR. Always a compromise somewhere but I feel erring on the conservative side may be my best bet day to day.

 

With a stickshift it may be abit different driving around but 280 with hsr makes trq around 4000-4500 rpm. Its a flat curve but really doesnt come on til mid higher 3000's rpm just like an ls1 motor. So more gear is needed. Any cam could use it
I wouldnt go 268. If you want abit less cam go custom xfi, say 226-232. That be a great compromise

Xe282 on a 110 with 1.6's shouldnt be too far behind, and should be abit better on valvetrain. Either shouldnt need a rev kit but i guess it wouldnt hurt. Just think its better to spend on good springs and titanium retainers

 

I have a 3.42 rear gear and it works well enough for that cam. It's mostly what Orr said. It makes good power all over and isn't a dog below 3K rpm but with a five speed and 3.42 rear first gear at 3K rpm is 20 mph. Creeping along in a parking lot or in bumper to bumper traffic I really need to feather the clutch or else it will start to surge/buck on me. I am thinking that raising the RPM just a little bit (10%) should help at crawling speeds. If you have a six speed or you won't be driving it on the highway much I would say just skip the 3.73 and go straight to at least a 4.__ gear. Why don't you like yours for daily driving?

 

Dont skimp on spring pressures with those types of cams in fact I always add another 10 or so just cause. They work not a big fan of crazy ramps myself

Keep us posted

 

Thanks guys, all input appreciated.

3.70's and daily driving? I suppose it's mostly letting it rev. When I do "drive" the car it's usually to work. A fair amount of it is at ~45 mph. 4th gear felt like it was revving higher than necessary and 5th gear was a lug. The way the TKO trans is geared just "liked" the 3.27's better in the in-between speeds. Also, with 3.70's, 1st gear was pretty much worthless and 5th gear left the engine revving ~2600rpm on the highway. At the strip, there was only about .2 difference in 1/8mi times. Granted, the setup shown in my sig was not optimized for either.

I understand what you are saying about creeping speeds. I have had some of the same experience even with the small cam & 350ci.

It somewhat depends on the quote from my machine shop. We are comparing cost between 383 & 396. If I do end up building the 383 I will probably stay a bit more conservative. But my intention is to build the 396.

But either way the really wide lobe spacing of the XFI cams troubles me. It seems to have the valves somewhat out of phase with the piston and doesn't make sense to me. I am no expert here but my way of thinking is LCA phases the valves to the piston and determines the torque curve shape- duration moves the curve up and down the rpm range- lift determines the amplitude of the torque curve. 400 HP is 400 HP whether it occurs at 4500 or 6500. So, for my application, it would seem to make sense to have the intake valve close at a modest point in the up stroke to keep DCR up, duration in the modest range with as much lift as possible in keeping with reliability and component life, and LCA in the <112 range. All this also keeps from revving to the moon which should also be kind to the valve train.

It's not about Dyno bragging rights for me. The only reason I have a target HP is to have a starting point. And that is 10lbs/HP at the wheels from shift point down ~1500 rpm. It isn't set in stone and I would prefer to get there with lots of mid range torque than high rpm. This is one of the reasons I'm building the largest CI I can afford. "Manors" is a high priority for me. Any thoughts on these points is appreciated and I certainly will keep everyone posted. Following the build and some tuning time will be a trip to the local dyno and probably a 1/8mi test and tune event.

 

In regard to the rev kit. I don't look at it as a way to "skimp" on spring pressure or that it is necessary. It seems to me as a better way to apply the required force at the appropriate location. Why do hydraulic rollers need more spring pressure? Somewhat because of the fast ramps but mostly because of heavy lifters. The high ramps just make it worse. If we can keep the lifter inertia out of the equation then all we have to do is return the spring, rocker and push rod to the rest position. Less, not less than necessary, spring pressure here just takes stress off the rocker. Plus it look like from what I read the beehives do quite a good job of this. Isn't spring resonance what allows the valve to "bounce" on the seat? Isn't this the primary reason for lifter pump up rather than lofting? Again, I am no expert. If I were I wouldn't be seeking advice. Just posing the questions and offering an opinion. And no, I am not getting a commish for hydra-rev sales lol.

 

Weight on the lifter/pushrods side isnt as much of a concern. The ramp rates and valveside determine spring pressures. Most cams are fine with 150 lbs seat and 400 open. Stuff like my heavy valve with boost needs 180/450

If you like the gearing you have leave it. 383-396 will pull it fine. Just wont be optimal for drag racing. We pulled 3.73's with a 28" tire on stock trq converter with a 280xfi 360" low comp L98 hsr. Drove fine just left line like a slug cuz no converter and not enough gear.

Motor will like those cams with 108-110 lsa just will have abit more lope and skew closed loop idle alittle unless you change the o2 constants.

I dont see a 396 being too much more of an advantage over a 383 but either will make loads of trq with those cams. If you are abit nervous of the 280, just spec your own 226/232 with the xfi lobes and 110 lsa or so. Will work great in a 383 for a mild mannered car with good power.
Wishmaster87iroc ran a similar bullet racing cams 226/232 112 on his 383 hsr. It ran 11's i think and drove fine but these were auto cars

 

I would have guessed 3.73 would be fine with that cam, you think it needed more? Well 3.73 would be the bottom of gears that would work.