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1.6 rockers on exhaust = more torque?

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tommyg

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Discussion starter · #1 ·
my build:
355
edelbrock 750 carb
RPM air gap
AFr 195cc heads, 10.325 compression
1.5 roller rcockers
1 3/4 headers
2.25 exhaust
comp cam XE 274
4 spd
4:10s

What benefit would I get out of putting 1.6 rockers on the exhaust side - would I gain torque????


[This message has been edited by tommyg (edited 12-02-2002).]
 
#2 ·
I don't think you will gain anything at all. The reason I say this is because you have great heads already and on your 355 they are flowing plenty. If you had stock GM heads I would say you would gain some power, because the exhaust ports are not the greatest. The only way to truely know would be to try it. I think if anything I would run 1.6's all the way around, if you are going to gain anything in your combo I think that would be a better option. This is only my opinion, I didn't do any research on your cam or combo, so take it for what it's worth.

Royce
 
#3 ·
If anything you would probably extend the RPM band just a little on the top end.

The 1.6 rockers MIGHT make your cam ACT just a hair bigger.
 
#5 ·
I think it really depends on the combo (heads cam, intake and exhaust). If you have a cam that is slightly to small the 1.6's should help. I run them all the way around on my car, but I was trying to get every little bit I could out of the combo. I wanted the extra lift. Really to many variables to know for sure. I think the only real way would be to try. I still don't think it will make much difference at all in his case. Just an opinion. I guess it would also depend on the flow numbers on his heads. In my case the flow with the added lift made sense to me (meaning the head flowed better at the higher lift numbers).

Royce
 
#6 ·
i'm with camaroman, the exhaust on the afr's is very good, and i would say that probably with your combo 1.6 all the way around would be the way to go. although you probably won't really feel the diff, it likely would improve things, making your cam think it's a scoche bigger. just buy a set and swap them from intake to exhaust and so on, if you really want to know, it would probably be more noticable at the track, so you had e.t and mph to compare, but who knows? imo, just do it if you are considering it, its not going to hurt anything, imho, unless your valvesprings are already close to bind (which i highly doubt) or are a touch weak . just check things out, and good luck.
 
#7 ·
Tommy,
I use them all the way around. A couple things to remember if you change to them. One make sure you have enough clearance in the pushrod openings where they pass through the heads, I suspect the AFR's already are opened up for this, the stock Chevy heads need to be clearanced. Two make sure you're using screw in studs. Three make sure you recheck you valvetrain geometry through out it's entire travel, the tip of the roller should travel equally off center of the valve stem in both directions, never getting too close to the edge of the valve stem, many manufacturers like Comp Cams makes various length pushrods to help correct yur geometry. Most importantly remember the more agressive ratio will stress the exhaust much quicker than the intake, this is where you'll see failures first. Make sure your springs are up to the task.

Dave
 
#8 ·
You already have a dual pattern cam (which in my opinion isn't needed with those good heads). If you do anything do both in & ex or step up in the cam itself. You don't have to compensate for poor head flow by using a dual pattern cam, you might want to consider the Magnum series (280 to 292 range) You have the 4 speed and gears with good bite big headers you can cheat a bit and oversize your cam and get away with it. Just my opinion - good luck
 
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#9 ·
Sneaky Pete is on to something. The XE274 cam over-exhausts the AFR195 heads. The AFR's really appreciate more duration on the intake than exhaust in a high performance application, and about equal in a medium performance applicaton (like with the 274 cam). A cam like: Intake XE274-5445 at 107ILCA(274,230,143,0.488"), exhaust XE280-5216 at 117ELCA (280,230,138,0.459") beats the off-the-shelf XE274 across the entire RPM range (with the AFR's). It works great with 1.6's on the intakes, and 1.5's on the exhaust.

As far as your engine goes, don't put any more energy into that 2.25" exhaust system because it is already too small. My simulation shows no gain anywhere from using 1.6's on the exhaust, even with 1.6's on the intakes. On the other hand, using 1.6's just on the intakes is worth about 15HP with no real performance losses anywhere. Hope this helps.

------------------
Rodney Davis www.HeaderDesign.com

[This message has been edited by Need a Camaro (edited 12-03-2002).]
 
#11 ·
I didn't take the time to get the intake conditions modelled exactly, but my calcs show 480HP with the 1.5's, and 495HP with 1.6's on the intake only. That was with open headers and perfect tune. The headers were 1 3/4" x 34" primaries, and 2 3/4" x 13.5" collectors.

------------------
Rodney Davis www.HeaderDesign.com

[This message has been edited by Need a Camaro (edited 12-03-2002).]
 
#13 ·
I got 480HP with A/F at 12.5:1. At 11:1 I get 440HP, and 14:1 I get 445HP. All are at 6000RPM. Timing is set for peak pressure at 15degrees ATDC.

Have you tried to run your car at the track with open headers? Your 2.25" exhaust might seriously be reducing your HP. That cam has alot of overlap, so backpressure is a bad thing. I can calculate that your primary header pipes should have an ID of about 1.6" for 480HP. Your tailpipes in a street/strip setup should have an area of about 60% of the total area of primary header pipes that feed it. So (4pipes*60%*1.60ID"*1.6"ID)^0.5 (square root) gives 2 tailpipes of 2.48"ID each. So 2.5" tailpipes are borderline.

------------------
Rodney Davis www.HeaderDesign.com

[This message has been edited by Need a Camaro (edited 12-03-2002).]
 
#15 ·
The 1 5/8" headers would be good for about 440HP on down. But the AFR195's will do alot better than that. How long are your headers right now, what does the collector look like, and where is your crossover?

The 2 1/2" pipes will enhance the midrange torque your engine should be making. The 2 1/4" pipes would be best for part-throttle, low-RPM performance (like (4*45%*1.6"*1.6")^.5=2.15"ID).

------------------
Rodney Davis www.HeaderDesign.com

[This message has been edited by Need a Camaro (edited 12-03-2002).]
 
#16 ·
I think you would stand to gain a whole lot of power across the entire RPM band with a better exhaust system. 2-1/4" is way too small IMO, especially if it is not a mandrel bent system.

In my opinion the perfect exhaust system for your car would be 3" in 2-1/2" out X-pipe into Dynomax Ultraflows and 2-1/2" tail pipes out the back. Dr Gas makes the X-pipe - it is 3" from the headers into the X-pipe, then 2-1/2" out of the X-pipe to the mufflers.
 
Discussion starter · #17 ·
I have hooker super comps 1 3/4" to 2 1/4 exhaust (no crossover) to flowmasters to 2 1/2 tail pipes. Should I change my configuration? It is a weekend street cruiser and I woiuld like to maintain torque.

Whats your opinion?
 
#18 ·
A crossover will help smooth the engine out alot, and help the upper midrange torque and top end power. I suggest (without considering the 2 3/4" collector detail) that you use 2 1/2 pipes off the header flange to the mufflers and beyond. The Super Comps are either 30" or 32" I think, since you didn't give the model, so you need to add about 3" to the collector length I gave before. That means install the 2 1/2" crossover pipe about 17" from the ends of the primary header pipes.

Hopefully this will allow you to loop the crossover pipe under the rear of the transmission. Keep the crossover as short as possible by putting a slight s-bend in each 2 1/2" collector between the ends of the primary header pipes and the crossover pipe.

It's also nice to make provision for a 2 3/4" or 3" bolt-on collector for the strip (open header). You would need to be able to tie the exhaust system out of the way to do this, so plan ahead.

------------------
Rodney Davis www.HeaderDesign.com

[This message has been edited by Need a Camaro (edited 12-03-2002).]
 
#19 ·
<BLOCKQUOTE>quote:</font><HR>Originally posted by tommyg:
I have hooker super comps 1 3/4" to 2 1/4 exhaust (no crossover) to flowmasters to 2 1/2 tail pipes. Should I change my configuration?

YES!!! Your money is much better spent on a new exhaust than on 1.6 rockers!

It is a weekend street cruiser and I woiuld like to maintain torque.

Whats your opinion?<HR></BLOCKQUOTE>

ONE LAST TIME, put in the Dr Gas X-pipe with 3" inlet and 2-1/2" outlet. Use 2-1/2" Dynomax Ultraflows and 2-1/2" tail pipes.

If you don't want to lay out the cash for the Dr Gas stuff, just use a 2-1/2" in x 2-1/2" out X-pipe. Or Summit sells the entire Flowmaster 2-1/2" American Thunder system for about $275 - it includes mandrel bent 2-1/2" pipe, H-pipe, Deltaflow 40 mufflers, tailpipes, and all the hangers/clamps.
 
Discussion starter · #20 ·
Sounds like I may go with an x pipe. I understand I will gain upper midrange and on top but will I loose torque down low?

Need a Camaro, you say an x pipe will smooth it out a lot, what exactly do you mean, will it be more quiet?

Eric, What doe s the Dr Gas X pipe go for?
 
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