Ragtop 99

iTrader: (7)

So it is time to change my set-up. The plan is to go to a bit more streetable set-up with a focus on top end power. Non-WOT tuning in closed loop is a requirement. The plan is to put on some first rate heads (e.g. MTI, TEA, AFR), with a CR of ~ 11.2:1, plus a 90mm LSX intake and TB. I have an existing exhaust optimized for top end (1 7/8" headers, 3" into 3.5" Y-Pipe and 3.5" cut-out) and a motor than can spin to 6800 - 7000 with no problems.

My current cam is a 228/228 114 +4. It idles fine at 875, but surge has been a problem (Yes, I've experimented with various VE's and timing strategies). So I want to keep (or improve) the idle quality and reduce surge a bit.

I've read the big long cam threads and besides knowing that I don't know jack; I think that I've learned:
* increasing overlap can have a negative effect on idle quality.
* closing the intake valve a little later can help with surge.
* Using ghetto math, a 228 cam should be enough with good heads and a low restriction intake to flow enough CFM to hit 6800 rpm.
* Using our nifty valve events calculator spreadsheet, the intake close should be 1 to 4 units higher then the exhaust valve opens (i'm talking about absolute values as Excel calculates them)
* A low LSA can be very beneficial for low compression motors, higher compression allows you to cheat with a higher LSA.
* If you truly know what you are doing, you can get a low LSA cam to perform and drive very well. However, since I previously stated that I don't know jack and cam swaps get to be expensive, I decided to apply the above to a higher LSA cam.

I looked at a couple cams for my baseline: MTI's Stealth II and TR's 230/224. The MTI cam is a little too weak for what I want to do and the TR may be a hair more radical. So I came up with 2 options: 228/224 114 +0 and 230/224 113 +0. The table below (if it works) compares my current cam with them:

Intake Duration - ID 228 228 230
Exhaust Duration - ED 228 224 224
Lobe Center Angle - LCA (LSA) 114 114 113
Intake Centerline - ICL 110 114 113
Intake Valve opens - IVO 4 0 2
Intake Valve closes - IVC 44 48 48
Exhaust Valve Opens - EVO 52 46 45
Exhaust Valve Closes - EVC -4 -2 -1
Exhaust Centerline - ECL 118 114 113
Overlap 0 -2 1

The 228/224 cam has a little less overlap then my current cam and has valve events similar to (probably not identical to) the MTI Stealth II at .05. The 230 cam is slightly more intake biased than the TR 230 cam (hopefully will reduce surge)and has a little less overlap for a better idle (assuming TR's lobes are similar to an XE-R lobe). The 230 cam would also meet the above criteria with 1 degree advance ground in as IVC / EVO become 47/46.

So what do you think:
Can I reduce the surge and keep the power of my current cam?
Will the combo perform?

CHRISPY

I would not go reverse split but that is my preference (Unless you are running open headers full time)

You have a bit of an interesting situation. You want to maintain idle/reduce surge but increase top end.

To do this you'll need to reduce overlap with low duration on the intake side, use a VERY aggressive intake lobe and crutch the exhaust very slightly if you happen to run cats or even full exhaust.

What are the flow numbers of your heads? What rpm are you looking to peak at? How do you want power to drop off after RWHP peak?

Is your current cam on XER lobes?

Something in the 229/233 115LSA (229 XER intake lobe and softer 233 XE exhaust lobe) would work pretty well and carry power well after RWHP peak through a full exhaust combination (or cutout).

Driveability would be good as well.

You wont need too radical a departure from what you are running now. EVERYTHING will depend on the head flow numbers and intake/exhaust choice

GrannySShifting

iTrader: (10)

Wide lobes suck with good bit of duration. 226/.590 228/.588. Or the exhaust 232/.575 ( a slower lobe)

Ragtop 99

iTrader: (7)

Chris:

I'm not running open headers, but my exhaust flows very well. Regular split patterns tend to make the absolute highest numbers, but the drivability issues associated with the extra exhaust duration don't return enough power to warrant them in my case. I think reducing exhaust duration, rather than intake duration, results in less power lost for a given overlap. The difference in a 228/224 114 and your 228/232 115 is a fair amount more overlap for probably a few HP gain. If I went that route, I would consider a single pattern 228/228 115. A little less overlap than what I have and I could use an intake centerline more biased to intake.

In the end, I think I can get make good power w/o having to go over 230* of duration. I'll leave the last few HP on the table in exchange for something I can tune in closed loop and make easy to drive.


I don't have flow numbers since I haven't selected the heads yet, but all the top heads flow in the same general ballpark.

Colonel

Hmmm....should I tell him the specs of the new Stealth III cam or not?

We can theorize and toss specs out here all day long...and many will do basically what you're wanting to do but with slightly different results. A point here or there. Reverse, standard, or straight splits, so long as they're small, aren't going to make it a big winner or a big loser.

From a power v/s drivability standpoint, I don't see the point of going with a less aggressive lobe on one side than the other. With a less agressive lobe we will obviously have a higher seat to seat duration for a given .050 lift, therefore, we have more overlap. You can move the same air with less seat to seat duration with a more aggressive lobe. That's the beauty of a solid lift cam, afterall.

We KNOW you'll want a wide LSA if you're looking to make great RPMs with a nice smooth idle and great drivability. How wide? Depends on how much duration we use v/s how high we want to spin this thing. If you go throwing too much duration at it AND a very wide LSA you'll be shifting higher than you want...or you'll have to bandaid the situation by advancing the cam a bunch which is no good and is defeating some of our other goals here, IMO. Also, keep in mind that the higher the LSA, the lower the midrange punch. This matters not if we use enough stall.

So...how high are you willing to spin this thing?

FASTONE

Hey Ragtop,I noticed a few thinks in your post,not trying to slam you just maybe help.First you stated closing the intake later woul help idle when closing the intake sooner helps idle and lowend, hence advancing the cam usually helps here.Second you said a lower compression works best with a lower LDA this is not really proven,has more to do with the powerband then your cr.Wider LDA will always make less overlap and smoother idle.Why don"t you go with around 224 duration,.600 lift and a 113LDA installed about+3 advanced or 110 ICL.with better flowing heads you can get equal or better performance then big cam and stock heads.What about the TR224 seems like a good cam,or if you get AFR heads go with their cam,I think its about the same size.Seems like the cam you got should idle OK ??Hope this may clear up a few things for you and help you to pick that new cam.Good luck!!!

Ragtop 99

iTrader: (7)

Closing the intake later seems to help with surge. I meant cam surge off idle, not idle surging. It will not help low end power, but the car never sees above 40% TPS at low rpms because of my tranny programming. Therefore, I don't need gobs of low end torque. I just don't want any surge when stuck in traffic.

I saw several posts suggesting the use of a tighter LSA on low CR motors to build cylinder pressure. My understanding is that is also effects powerband, but that is also a function of duration and valve timing (e.g. advance / retard from the LSA)

I had the TR 224 112 and liked it; it was a great cam. I'm just trying tweak things a bit.


Colonel:

I'd like a 6800 shift point; 7000 max.