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 1.5 rocker arms vs 1.65 rocker arms
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Steve C.
Crazy Horse

1121 Posts

Posted - 23 Jun 2012 :  11:53:49 AM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
After coffee this morning I had a "Google urge".

Reading material on the subject if interested....

Higher Ratio Rocker Arms by Jim Hand, July 1999
http://www.pontiacstreetperformance.com/psp/RockerArms.html

Comment made by another on another website:

The reason you need to possibly do the grinding is that 1.65's are closer to the rocker stud, and there could be interference on the head when the pushrod is moved slightly closer. The part being removed is 1/8" or less on the stud side, and usually is just at the top portion of the pushrod hole. This makes removal of the heads mandatory because of all the grindings flying around. The 1.65's have exactly 10% more lift (1.50+.150=1.65). Therefore, the lift added is exactly 10% more (old lift of .475+.0475=.5225 new lift), and duration comes out around 4 degrees more (228+4=232). If you bought the correct cam to begin with, then there is no reason to use the 1.65's. Some racers would run the 1.65's on the exhaust side only on a single duration cam to add a little extra to the weak side of the exhaust. But with the dual pattern cams, this isn't necessary. When you get in to really nasty stuff, the 1.65's offer an advantage when you have pushed the opening and closing ramps to their design limits. Then you can squeeze a bit more. In reality, even strongly reworked Pontiac heads have flow limits well within the 1.5's range. Also, there's going to be a small percentage of heads with after-market cams that will get by with the lesser ratio but be so close to coil bind on opening, that the larger ratio will cause problems.

Interesting discussion on the topic in Archived Topic: 9706 http://www.classicalpontiac.com/

High-Ratio Rocker Arms - Off Your Rocker
We install high-ratio rocker arms onto a Pontiac V-8 and measure the results
From the October, 2011 issue of High Performance Pontiac
By Rocky Rotella
Photography by Rocky Rotella
Read more: http://www.highperformancepontiac.com/tech/hppp_1110_high_ratio_rocker_arms_install/viewall.html#ixzz1ydFDep70

Steve C.
Crazy Horse

1121 Posts

Posted - 23 Jun 2012 :  12:11:38 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
Related, searching will also point out information that one might not need or want additional valve lift on the exhaust rocker arms.

Personaly on a previous "700 hp" 450cid motor with 2-inch headers I had 1.65 ratio on the intake and 1.6 ratio on the exhaust. Heads had a average 75.4 percent exhaust-to-intake flow ratio. On the cam both intake & exhaust had the same .4267" lobe lift. Today those same cylinder heads with the 1.65 / 1.6 ratio are installed on my pump gas 505cid combo, and the cam has the same lobe lift on both intake & exhaust.

Of interest...

"The proper combination of exhaust heat, speed and pulsing is required to maximize the speed of the initially slow-moving intake charge. If the sizes of the exhaust tubes are too large, exhaust temperature and speed is lowered, greatly reducing the overlap supercharging effect and even aggravating reversion. In some cases, too much cam lift on the exhaust can also have the same effect, cooling off and slowing down the exhaust gases. For this reason, a change to higher-ratio exhaust rockers is sometimes counterproductive."
(from "Overlapping Experiences", Pete McCarthy, 7/8 '02 PE)

Further discussion here:
http://forums.performanceyears.com/forums/showthread.php?t=408088&highlight=exhaust-to-intake

Edited by - Steve C. on 23 Jun 2012 12:12:57 PM
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Christ
Howling Wind

USA
1804 Posts

Posted - 23 Jun 2012 :  4:20:34 PM  Show Profile  Visit Christ's Homepage  Reply with Quote
Always good reading.

I wonder how much the cam has to play into this effect. I goofed around with a mild 400 motor and decided at the track to put 165 on the intake side only leavening the 1.5 on the exhaust. I saw no difference in 1/4 miles times.


I would be curious to see test done on differant special grinds of cams?


Steve you run a any of these test in your years of racing?
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Steve C.
Crazy Horse

1121 Posts

Posted - 23 Jun 2012 :  5:07:15 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
I've personaly never been involved in any back-to-back cam or rocker arm ratio testing on a engine dyno or at the track. For me too costly as a hobby. And with my car for the most part we have never done any equipment back-to-back testing other than intakes and carbs.
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Lee
Buffalo

70 Posts

Posted - 27 Jun 2012 :  07:59:29 AM  Show Profile  Reply with Quote
I find it interesting that the new LS motors - even the little 4.8 liter truck motor - come with 1.7:1 rockers (and some with 1.8). I've seen motors putting over 1,000hp to the wheels with the stock rocker arms! The factory L92 truck heads also flow over 300cfm as delivered, and even the older truck heads will flow about 250cfm.

Dealing with these motors has made me re-evaluate many of my thoughts on airflow, rocker ratios, reliability, etc.

Lee

67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP http://www.highperformancepontiac.com/shootout/0502pon_lone_star_pavement_shootout_2/drag_racing.html
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR http://www.popularhotrodding.com/features/1002phr_1969_ford_falcon/index.html
72 Cutlass Convertible, first car, owned since '82
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Phil
The Great White Buffalo

USA
6281 Posts

Posted - 27 Jun 2012 :  08:18:36 AM  Show Profile  Reply with Quote
The SFI system has alot to do with the LS "approach".

"Chevy": even the name sounds cheap.

Edited by - Phil on 16 Jul 2012 6:49:24 PM
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 27 Jun 2012 :  11:49:32 PM  Show Profile  Reply with Quote
quote:
Originally posted by Steve C.

Related, searching will also point out information that one might not need or want additional valve lift on the exhaust rocker arms.

Personaly on a previous "700 hp" 450cid motor with 2-inch headers I had 1.65 ratio on the intake and 1.6 ratio on the exhaust. Heads had a average 75.4 percent exhaust-to-intake flow ratio. On the cam both intake & exhaust had the same .4267" lobe lift. Today those same cylinder heads with the 1.65 / 1.6 ratio are installed on my pump gas 505cid combo, and the cam has the same lobe lift on both intake & exhaust.

Of interest...

"The proper combination of exhaust heat, speed and pulsing is required to maximize the speed of the initially slow-moving intake charge. If the sizes of the exhaust tubes are too large, exhaust temperature and speed is lowered, greatly reducing the overlap supercharging effect and even aggravating reversion. In some cases, too much cam lift on the exhaust can also have the same effect, cooling off and slowing down the exhaust gases. For this reason, a change to higher-ratio exhaust rockers is sometimes counterproductive."
(from "Overlapping Experiences", Pete McCarthy, 7/8 '02 PE)

Further discussion here:
http://forums.performanceyears.com/forums/showthread.php?t=408088&highlight=exhaust-to-intake



Steve,why do you have the "bigger" ratio on the intake?

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Steve C.
Crazy Horse

1121 Posts

Posted - 28 Jun 2012 :  12:57:43 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
Bill, When my Edelbrock heads were built and flow bench tested the intake air flow continued to increase well above 0.700" valve lift. Knowing that a typical engine responds to high valve lift the extra 1.65 rocker arm ratio provided the extra lift we desired.

(Side note, in contrast today some advocate building in the extra lift thru a bigger cam lobe lift and use less rocker ratio)

At the time Jerry Goodale was building the heads he also set up the T&D shaft mounted rocker system that was going on them and he had a lower 1.6 rocker ratio installed on the exhaust side. As I understod it when the exhaust valve opens early the velocity in the exhaust port can begin to exit and thus the piston on the next upward stroke will not have to fight to get the exhaust gases past the valve and into the port. The gases nearest the valve, and spark plug, are the first to leave the chamber, under hundreds or even thousands of pounds per square inch pressure. It is my thinking this mass exit of exhaust gasses was accomplished soon after the exhaust valve opened and the majority of exhaust gasses are gone and thus in some circumstances more exhaust lift may not be a benifit. I just presume this was the reason for less ratio on the exhaust side, if I'm not correct in this thinking help me out. When it came time to re-use the heads on my 505 I just left them alone.

Plus I'm not sure if this was the situation at the time but the upward movement of the piston is "chasing" the exahust valve as it closes so potential exhaust valve clearance might be necessary with less lift in some circumstances.

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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 28 Jun 2012 :  1:20:47 PM  Show Profile  Reply with Quote
quote:
Originally posted by Steve C.

Bill, When my Edelbrock heads were built and flow bench tested the intake air flow continued to increase well above 0.700" valve lift. Knowing that a typical engine responds to high valve lift the extra 1.65 rocker arm ratio provided the extra lift we desired.


O.K.so why the 1.6(smaller)on the exhaust which hurts exhaust flow.And exhaust flow is where Pontiac heads suck the most.


Edited by - Cobrabill on 28 Jun 2012 1:21:31 PM
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BearGFR
Bear

USA
567 Posts

Posted - 28 Jun 2012 :  1:25:41 PM  Show Profile  Visit BearGFR's Homepage  Reply with Quote
Interesting thinking, Steve. I recently read David Vizard's book on head porting and flow testing. He asserts that the overlap period is much more important to intake flow and cylinder filling than is the pumping action of the piston on the down stroke. He refers to the overlap period as the 5th cycle and thinks it's that important. If he's right then I can see where building maximum exhaust flow velocity as quickly as possible and also maintaining it throughout the overlap period would be very important because that would maximize the effectiveness of the exiting exhaust helping to pull in the next intake charge. Seems like you'd want that exhaust valve open "early enough and wide enough" to really get things moving, but not "so long or so wide" that the gasses would lose "too much" velocity.

Bear
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 28 Jun 2012 :  2:39:22 PM  Show Profile  Reply with Quote
quote:
Originally posted by BearGFR

Seems like you'd want that exhaust valve open "early enough and wide enough" to really get things moving, but not "so long or so wide" that the gasses would lose "too much" velocity.Bear

Simpler put,the exhaust rocker ratio should never be smaller/shorter than the intake.

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Steve C.
Crazy Horse

1121 Posts

Posted - 28 Jun 2012 :  6:34:41 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
"And exhaust flow is where Pontiac heads suck the most."

Bill, The Edelbrock heads have a excellent exhaust port as cast. In my situation the ports were further modified to flow 248 cfm at higher valve lift, I was under the impression additional exhaust lift may not always be necessary. The exhaust port didn't need the higher lift to get the job done. That and this was in conjunction with 2-inch headers coupled with a high flowing exhaust system including larger diameter tubing, X-crossover, Dynomax Ultraflow mufflers, etc.

BearGFR- Overlap can have it's pros and cons. And much involves around the RPM involved. Too much and it's not always good from what I've read on the subject.

"Simpler put,the exhaust rocker ratio should never be smaller/shorter than the intake."

Bill is this statement FACT regarding all situations or simply your personal opinion ! Again, note Pete McCarthy's comment I previously posted.

Plus another opinion....
"The higher ratio on the exhaust side never works ( maybe once in a hundred times)== Dont waste your money on the exhaust side.I have been disappointed several times when the customer buys a higher ratio ( even just for the intake ) and the car runs exactly the same== There is NO guaranty that it will do anything.The amount of money to get the higher ratio does NOT justify the cost in many cases"
http://speedtalk.com/forum/viewtopic.php?f=1&t=28661



Edited by - Steve C. on 28 Jun 2012 6:47:21 PM
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 01 Jul 2012 :  10:03:28 PM  Show Profile  Reply with Quote
Steve,you seem to continually forget that there are significant differences in building/operating engines such as 99% of the board readers have, or would like to have - an engine that is suitable to drive on the street but will run decent at a track, as compared to a real high RPM race engine that will never see a load of any kind below 5500-6000 RPM, such as the 1000-1200 (or more) HP race engines that as Joe Sherman builds,


Another thing, if you have way overkill on intake flow, duration, and lift such that the engine can't use it all, cetainly added exhaust capability is not needed. A moderate exhaust system is adequate in that case. And that is why some guys claim great performance with single pattern cams - they go way to big on the intake and there just is not enough flow to tax the exhaust.


Finally, that it is the increase in rate of exhaust flow that really tweaks an engine's performance. Buy the time the exhaust intake system reaches peak flow, you better hope a large part of the exhaust has already left the chamber - otherwise you will not get the big kick of high velocity exhaust flow that may help the intakes begin to fill on the other cylinders. That is why low lift exhaust flow is extremely important - it starts the exhaust flow rapidly and allows very quick exhausting such that the piston does not waste power having to purge the exhaust from the cylinder.

Obviously, more exhaust then needed is not going to make a car run better, but the real key is not just airflow, lift, ratio, or other physical features. Rather, it is adequate exhaust performance for the amount of exhaust the engine actually generates, how quickly it starts exhaust flow after the valve begins to open, correct time for it to open, and the rate of flow through the primaries for best intake tuning for that specific engine.

And in most cases higher ratio rockers on the exhaust accomplishes, or at least assists, in all of the above.


Pontiac put 1.65s on the RAIV-but what do they know-right?As far as Pete McCarthy goes,i used to have him on speed dial 20+ years ago.Although i haven't seen him in years.
I also first put a wrench to a Pontiac in 1966 when i was 7.Any other non-sequiturs?


Edited by - Cobrabill on 01 Jul 2012 10:06:31 PM
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Steve C.
Crazy Horse

1121 Posts

Posted - 02 Jul 2012 :  10:14:36 AM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
Simply put Bill my purpose was to post general information about increasing the rocker arm ratio from 1.5 to 1.65 for interest only, nothing more. As an afterthought I added that not in ALL circumstaces may it be necessssary or desired to do so, whether it be a higher RPM engine or milder combo. That fact can be proven. I'm leaving it at that.

Edited by - Steve C. on 02 Jul 2012 1:00:03 PM
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Bill Boyle
Horse Feathers (Charter Member)

USA
3992 Posts

Posted - 16 Jul 2012 :  09:24:53 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
High Performance Pontiac's current magazine (Oct 2012) explores rocker arm ratio and cam phasing on their mule 455 (467 cid) Pontiac V8. Ray Bohacz wrote the article and took photos.

I found it to be an interesting article. However, nothing explored and revealed in the article changed my belief and understanding of rocker ratios and cam phasing and how they worked or didn't work in our street engines.

One of the things confirmed by the article is that the cam manufacturer's recommendation for installing a specific cam, at what degree, is usually the right place to install it.

Secondly, the article reiterated the fact that going up in degree retards timing while dropping in degree advances timing. This is often misapplied when people degree in their camshafts. So, if the cam manufacturer specifies 106 degree intake center line, changing the phasing to 110 retards timing, while dropping it to 102 advances timing. Advancing (102) puts more grunt into the low end and retarding (110) the phasing makes less low end torque but gains on the top rpm range. The best performance is usually in the middle as specified by the manufacturer. In this instance, 106 degrees intake center line. The middle, so to speak, provides the best overall torque and hp average.

What also was confirmed is that there is a slight difference between 1.5 and 1.65 ratios. The latter does make a little more torque and hp. There is a gain. Therefore, one can detune a 1.65 ratio engine by installing 1.5 rockers in their place. Mixing ratios proved to be nothing more than an attempt to see if there is a midway point--a point of acceptance for the practice. The reasons for doing such a thing, at least on this mule engine, showed no performance advantage. And, I think that's generally the case. There may be exceptions. All and all, I wouldn't mix ratios unless engine dyno testing with a particular head design and flow supported it on a specific engine.

Bill


"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Steve C.
Crazy Horse

1121 Posts

Posted - 16 Jul 2012 :  09:40:12 AM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
Also noted in this article was the FACT that using a lower ratio on the exhaust side can be considered. Although in this specific article testing it did not fair well, they surmised that it may be possible for the engine to like less valve lift on the exhaust side due to the high ratio of exhaust flow when compared to intake flow. Called the intake-to-exhaust ratio. Many believe that you need a value of around 80 percent, while others feel that an engine can be more effecient with a ratio much less than that.


Edited by - Steve C. on 16 Jul 2012 4:50:14 PM
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 16 Jul 2012 :  7:03:44 PM  Show Profile  Reply with Quote
Steve...why did Pontiac put 1.65's on the RAIV?

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Lee
Buffalo

70 Posts

Posted - 18 Jul 2012 :  11:19:46 PM  Show Profile  Reply with Quote
Here is my take. The heads NEED to be flowed. There will be a certain lift where the flow levels off, or possibly goes into turbulence. If the head's max flow is at 0.xyz lift, then you WILL get maximum performance by getting the valve very close to that lift value, and keeping it there as long as possible - that seems pretty self evident to me. Applies to intake and exhaust, with piston to valve being the other consideration.

If the cam needs a relatively small duration lobe for best performance, then you may need a higher ratio rocker to get the optimum lift. Likewise, if you need a really big duration, you may need a lower ratio.

Now, the companies I use to supply cams have HUGE catalogs of lobe designs. I can typically find lobes to give me the lift AND durations I need with any given rocker ratio. I've had 30-something cams ground for me over the last several months, and have never had to use different rocker ratios between the intake and exhaust.

Maybe in the old days, when a cam company only had a few dozen lobes to choose from, the rocker ratio bingo was needed. Maybe on some really extreme cases it is still needed (I did a cam for a turbo LS that needed an exhaust lobe bigger than anything Comp Cams offered!) but for anything street-driven you should be able to spec the cam to match whatever ratio you want.

Lee
p.s. DatsunBill, I'll be in Tuscon in August for a few days :-)

67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP http://www.highperformancepontiac.com/shootout/0502pon_lone_star_pavement_shootout_2/drag_racing.html
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR http://www.popularhotrodding.com/features/1002phr_1969_ford_falcon/index.html
72 Cutlass Convertible, first car, owned since '82
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 20 Jul 2012 :  11:48:52 AM  Show Profile  Reply with Quote
quote:
Originally posted by Lee

p.s. DatsunBill, I'll be in Tuscon in August for a few days :-)



You know what to do...dontcha'?

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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 21 Jul 2012 :  3:28:37 PM  Show Profile  Reply with Quote
How come no-one wants to second guess the factory engineers?Maybe 'cause they knew what the bleep they were doing?

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Blued and Painted
Chief PONTIAC

USA
2415 Posts

Posted - 21 Jul 2012 :  4:42:27 PM  Show Profile  Reply with Quote

Bull Nose Formula, 461, R44TS, DEX/MERC
69 GTO-400/670/373/4Spd
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 28 Jul 2012 :  1:00:39 PM  Show Profile  Reply with Quote
Still no reply as to why the factory put 1.65s on the RAIV?Shock,surprise,dismay.

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Steve C.
Crazy Horse

1121 Posts

Posted - 28 Jul 2012 :  9:43:58 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
The RAIV are the only round-port heads to come from the factory equipped with 1.65:1 ratio rockers. The RAIV head has a .150" taller intake port as compared to the d-port heads. Plus the RAIV intake port entrance dimension is wider. Not only is there a difference in port entrance size, the RAIV intake port has added volume and is shaped to flow at higher valve lifts. This is why the factory used the 1.65 ratio for additional valve lift on the intake side. Dispite the fact that a higher rocker ratio on the exhaust can produce slightly less power below approxmatly 4000 rpm the factory used the higher 1.65 ratio on the exhaust port to improve higher rpm potential to help overcome limitations of the factory exhaust systems, especially with the transverse muffler system on the Firebird. The factory intended the RAIV applications to involve higher rpm performance.

Today with extensive modifications to factory exhaust ports or the use of aftermarket cylinder heads providing improved exhaust-to-intake flow ratios, modified exhaust systems in place, higher rpm applications, higher lift camshafts, the use of single-plane intakes, valve to piston clearance, etc, etc. ..... one might CONSIDER less valve lift on the exhaust rocker arms. This was not a recommendation on my part at the start of this thread nor one now, I only mentione it for conversation. Proper testing will determine the outcome and each total combination will be differant.



Edited by - Steve C. on 28 Jul 2012 9:53:42 PM
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 28 Jul 2012 :  11:01:24 PM  Show Profile  Reply with Quote
quote:
Originally posted by Steve C.

Today with extensive modifications to factory exhaust ports or the use of aftermarket cylinder heads providing improved exhaust-to-intake flow ratios, modified exhaust systems in place, higher rpm applications, higher lift camshafts, the use of single-plane intakes, valve to piston clearance, etc, etc. ..... one might CONSIDER less valve lift on the exhaust rocker arms. This was not a recommendation on my part at the start of this thread nor one now, I only mentione it for conversation. Proper testing will determine the outcome and each total combination will be differant.

You are describing engines that 99 out of 100 people here DON'T HAVE.They don't twist their engines to the "moon" and they don't run single plane intakes."Modified exhaust"?Now that is funny.




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Cliff R
Cochise

USA
439 Posts

Posted - 30 Jul 2012 :  08:01:24 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
We just had a customer dyno a RAIV engine that he had rebuilt for his Judge. Not a single part was touched with a grinder or sanding roll. It made 420hp. That is quite a bit higher than the factory rated them, and it was using the Melling 041 camshaft, iron intake, and original factory Q-jet.

Rick Mahoney went 11.19 last Fall with his 68 RAII Firebird in the stock street tire class, not FAST.

Jim Mino has always been very competitive with the RAII set-up.

Maybe Pontiac knew what they were doing with those engines?.......Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 30 Jul 2012 :  09:30:29 AM  Show Profile  Reply with Quote
I won't mention that Jim Hand runs 1.7 rockers.

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Steve C.
Crazy Horse

1121 Posts

Posted - 30 Jul 2012 :  1:49:57 PM  Show Profile  Visit Steve C.'s Homepage  Reply with Quote
Actually I believe Jim has stated his 1.65 Harland Sharp rockers check out more towards 1.72 ratio.
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Cobrabill
Talking Dog

Aruba
2807 Posts

Posted - 30 Jul 2012 :  8:21:39 PM  Show Profile  Reply with Quote
O.K.

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