JakeFusion

iTrader: (7)

Are the AFR 205s enough for a fairly large hydraulic cam that will peak around 6700-6800 in a 383? I had decided to go fairly mild on a 383 build up for a project Vette, but now I've decided to go with a 3.90 rearend and a PT4000 stall with a Comp XER 244/248 114+1 cam for about the same price. So, I want as much top end as I can get on a hydraulic setup.

I like the 205s because of the possibility of a 60 or 59cc combustion chamber vs 65 or 66cc of the 225, so I can run more compression without going to a dome. Although, I am not against running a dome if I knew I wouldn't have P-t-V clearance problems with the 225s.

Any thoughts? Will the 300cfm 205cc runner support air at 7200 rpm in a 383? What about the small port 225? I know it's supposed to include a different port for a smaller bore, but will it also include a 2.05 valve or other 3.9" bore friendly changes? Is it worth waiting for?

Thanks!

Ryan02SS

iTrader: (3)

I believe Tony Mamo @ AFR did some 205 & 225 testing on his 383 with results from both combos. I believe it was posted not too long ago in the Dyno forum. HTH

TXCAMSS

iTrader: (60)

Here is the thread he's talking about. Very impresssive testing IMO.

Your set sounds great, but I doubt you'll peak that high with that cam, but I could be wrong. Then again you will make good power anyway.

I have an HPE 383 with ET Performance heads and the Comp 244/612 114. I am running 3.73 gears w/PT4200 and it peaks a good bit earlier than that. I hope to have a good accurate dyno graph to show soon.

I'll keep you posted!

TXCAMSS

iTrader: (60)

Oh, were you looking for this? LOL. I forgot.

https://ls1tech.com/forums/showthrea...+Mamo+225+dyno

JakeFusion

iTrader: (7)

Yeah, I saw that thread; it is a great reference, but the testing was done with a 225 on the bigger cams. He did the 205 on the 224 and 234 cams. Anyway, the 6700 peak comes from the 242/248 testing that Tony did, and it came in around there. I know the IVC is identical with a 244/248 114+1 as a 242/248 114+0.

242/248 244/248
Intake Valve opens - IVO 7 9
Intake Valve closes - IVC 55 55
Exhaust Valve Opens - EVO 58 59
Exhaust Valve Closes - EVC 10 9
Exhaust Centerline - ECL 114 115
Overlap 17 18

That's at .050"; the Comp solid roller lobes are more aggressive than the XER or LSK, so that might have something to do with it.

But, back to my orginal question, I'm wondering if the 205s will run out of air? If it was a 346, I wouldn't worry, because the 205s have plenty for 7k, but adding 30cid might change that.

Also, I'm going with LG Pro 1-3/4" 32" primaries headers, and I'm curious if it wouldn't be better to go with the Kooks 1-7/8" 24" primaries. Any thoughts on that?

TXCAMSS

iTrader: (60)

Yeah I was comparing the peak hp to actual RWHP rather that an engine dyno and FWHP.

Do yourself a favor and go with the Kooks 1 7/8 headers. You will thank me later. I went from FLP 1 3/4 to the Kooks 1 7/8 and added a 12 bolt rearend at the same time and still went from 436 rwhp to 459 rwhp one day apart on the same HPE dyno with no other changes. There IS a difference trust me on this one.

Good luck to ya!

JakeFusion

iTrader: (7)

Yeah, there's only so much math you can do before it doesn't seem to hold true in the real world anymore. I know the 32" primaries on paper make the 1-3/4" headers look good, but I've always wondered on a high RPM 383+ cid engine what it would do vs the Kooks 1-7/8". The FLP are basically 24" 1-3/4" so of course the Kooks were going to crush them, but the differing primary lengths make this one a toss up. Hmm, the Kooks are cheaper, though...

Thanks for your experience. I think I'll go with the Kooks.

Ryan02SS

iTrader: (3)

This is the response that LG posted as to why their 1 3/4's were better than the Kooks 1 7/8's for the LS7 427 engine...........

Our headers have flanges that are cut to 1 7/8", then the 1 3/4" primary tubes are swedged out to meet the flange. This was done to allow the tubes to be welded while keeping the opening larger than the port.

Our 1 3/4" pipes meet the head with larger than 1 3/4 opening. And it is round rather than "D" shaped like the old Z06.

Next you will have to please take into consideration all the premium features that we included in our LG Pro Long Tube Headers when we built them. These premium features include a 3" "Merge" collector which is the standard in the racing industry and broadens the entire power curve. goto www.burnsstainless.com and check out the section on Merge Collectors and you will understand. You will also learn how every angle, length and shape of a collector will affect the power output and power curve.

We also have a unique X pipe which is more like a "Siamese" pipe that allows the exhaust pulses to cross over but when the exhaust pulses are "In phase" they pass easily by each other rather than fight each other.

Normally a shorter header will make more high rpm hp over a longer header. But when the header is built with other premium features, like the Merge collector the power is lifted up through out the whole rpm range which expalins the big gains of our system.

Even thoug one company coppied our primary design on the face of it, they did not copy the whole system which causes the difference in power output compared to our system.

As for the power numbers that you state being within 5hp of each other, that is only the peak number. the power number at say 3500 rpms is always in favor of the LG headers. This is power that is useable. And the more an engine is modified, the better the LG Pro Long Tube headers perform. So a totally stock car will not be able to use All of the potential of the LG headers. But make the engine put out more hp with some mods and you will then see the LG Pro Long tube Headers show their stuff.

It is all about air flow and the LG headers are designed to not only flow but the Merge collector helps pull the next exhause pulse out of the cylinder head which also helps to pull "Intake Charge" into the cylinder also.

I personally would still go for the LG's.

Tony Mamo @ AFR

iTrader: (13)

I would bolt the 205's on without any hesitation. They will be very effective on a small bore 383 CID application. Also, the higher airspeed of the smaller port will allow slightly more duration and have similar bottom end of the 225 head and a slightly smaller cam. The larger cam will obviously increase the top end charge of the smaller headed 205 combo. Bottom line, all things equal, I bet there isn't 10 HP between them and the right camshaft could narrow that even further. Assuming your running a FAST or LS6 style intake, most of the peak flow the 225's show on the bench doesn't make it to the cylinder head anyway, and the additional shrouding of the larger valve also reduces the 225's effectiveness in that particular application (although it will still flow 5-10 CFM's better than a 205 on a bench with the 3.900 bore).

After seeing all the results, if I had to do it over again I might have opted for the 205's and the same solid roller cam in an effort to build a small stroker with big stroker low RPM TQ figures (and still screams upstairs)....much more fun on the street that way, and probably less than a tenth of a second slower at the track.

I think you will be surprised how well the 205's will work....keep us posted as to the results and feel free to call me if you need any other assistance, etc.

Regards,
Tony
(818)890-0616 Ext. 109

TXCAMSS

iTrader: (60)

Wow that's service!! Good answer Tony...and quick too.

JakeFusion

iTrader: (7)

Thanks, Tony. It will have the FAST90 on board (port matched of course). I figure with a mill of 60cc and with .040" Cometics, a 383 with a .000" deck height will come in around 12.25:1 SCR and 8.57:1 DCR with the XER 244/248 114+1. That should keep torque up.

As for the LGs, they just seem like the perfect match to the 205s as far as velocity and scavenging go, and 383 isn't too big, so I'm swinging back toward them again.

Tony Mamo @ AFR

iTrader: (13)

Personally, I would definately keep the smaller header as well. The LG is an excellent system and will compliment this package well.
Let me know if you need some help with the intake mods.

Looking foward to the results....

Tony

383ss

iTrader: (14)

just a little added info. I swapped from Dynatech 1 3/4 headers to TR 1 7/8th WITH high velocity merge collectors and only picked up 5rwhp PEAK. it did draw my powerband out about another 400rpm up top though gaining about 25rwhp at 6800rpm.. I LOST about 20rwtq.

Tony Mamo @ AFR

iTrader: (13)

Good info....

The "overlays" between the two would tell the story even better I'm sure. Also, I would think a "merge design" 1.75 might have showed even a larger disparity in TQ and might have narrowed the high RPM HP deficit. But the bottom line is that a bigger tube will always want to do that....does the average HP of the usable power band actually improve enough to warrant the obvious loss of low and midrange power the smaller header obviously improves. For a "dual purpose car" IMO , the smaller choice is probably best....an all out high RPM drag car on the other hand would probably benefit from the larger tube design.

BTW, I'm installing my stout solid roller 383 (610 HP flywheel #'s) with the same 1.75 LG system I ran my 346 in front of. While I'm sure it's costing me some bragging rights for peak power numbers, I think it will help the little stroker generate big TQ numbers everywhere and peak TQ figures that are more associated with 400+ CID combinations. Should be interesting....

JakeFusion

iTrader: (7)

You know, I'm not so sure you are giving up a whole lot when you talk about the LG Pros vs Kooks 1-7/8. The 8" primary length difference is much bigger than the 1.75 vs 1.875 difference. Remember, primary length has as much to do if not more than primary diameter for a given CID and RPM.

Optimal header for a 383 that makes peak HP at 6700 is a 32.07" primary length header with a 1.88" diameter using the formulas from A. Graham Bell’s Performance Tuning in Theory and Practice. I figured that 88.2 in^3 is what the volume of air the "optimum header" can move before the collector when I multiply the primary length by the area of the tube. The Kooks comes to 66.26 in^3, and the LG comes in at 76.97 in^3. Both are simply not enough, but the LG is closer. Note, I do not know the inner diameter of the headers, so I will not include it as a variable in the calculations. With the LG's superior collector, the gains may be even more pronounced.

Thoughts? (Note: This applies to the Corvette. The F-Body has a different header design. A 1-7/8" on the F-Body will do better than a 1-3/4" because the only change is the header diameter; the primaries are unchanged.)

JakeFusion

iTrader: (7)

ttt

Even though it's a little off topic, it still has to do with engine breathing at high RPMs...

Kraest

iTrader: (3)

The longer LG Header will make more low-end and peak torque because the header is simply longer than the Kooks.

I probably lost 20rwtq peak and even more than that from 3000-4500rpm by going with the Kooks 1-7/8" instead of the LGs (LGs were on a 2 month backorder when I wanted to order them)


Mike

JakeFusion

iTrader: (7)

I wonder how much you gained above say 5500 RPM, though? With a 4000 stall and a cam designed for high end, I will be around 5500+ a lot, and I wonder if the shorter, bigger tubed (even though it seems to hold less air prior to the collector) header would get the air out of the engine faster at say 6500rpm?

AINT SKEERED

iTrader: (2)

Damn with all this header talk , makes me not like my little old macs as much. So far they work fine but just how much would my car gain going to the qtp merge headers?

JakeFusion

iTrader: (7)

You'd gain HP and either lose a little torque or stay about the same. Those QTP HVM headers are similar to the LGs.