[pmd400]

Now needless to say this cam was piss poor choice. Pinging starts at 2750rpm at half throttle. Vac advance disconnected and timing retarded so there’s only 30* max at 3000rpm. Still pings. So my question is do I put the crower 60919 cam with rhoads lifters in or a cam with single pattern due to the high exhaust flow ratio. I could put a cam with 235* intake and exhaust duration on a 112 LSA and have a similar overlap to a 231 intake and 240 exhaust on a 112 LSA.
Thanks

[Cliff R]

NOT good news at all and I take no pride in pointing out that I already put up some good information on why it wasn't going to make the grade, at least based on the testing I've done here.

I've stated on many occasions when these cam selection topics come up that the WORST camshaft you will ever put in a 455 pump gas street engine will be a relatively "small" cam on a tight LSA. Nearly 20 years ago now I had a customer we did a carb for bring his Super Duty T/A here for pinging issues. The engine was a fresh build, just a tad over 9 to 1 compression and Comp XR276HR cam in it. That engine pinged everyplace but at idle. We were unable to add an vacuum advance at all, and super slow timing curve with 28 degrees total still resulted in some audible detonation at heavy/full throttle. Had to go to less than 26 degrees to get it to stop pinging, and by then it wasn't making much more power than a couple of Briggs and Stratton push mower engines under the hood!

My post #44 pretty much covered this topic.

Designed by Straub, blessed by the Donut Guy, recommended by Comp, or custom ground by Bullet every single one I've been associated with has been a piss poor choice and nearly impossible to tune for pump fuel in a 455 build, even those with less than 9.5 to 1 compression.

Not a single 455 that leaves here at any compression ratio gets a cam with less than 230@.050", and very, very few will have LSA tighter than 112, unless we're doing an engine oriented more for the track than the street.....FWIW......Cliff

[pmd400]

I should definitely have listened to your advice the first time. Sometimes I just have to see it for myself I guess. Would I be better off with the 60919 cam or this lobe as an a take and exhaust on a 112 LSA with rhoads
.006 .050 .200 Lobe lift
292 235 143 0.3265

[Stan Weiss]

Have you done a cranking compression test? if so what is it?

Have you called and talked with Chris about this?

Before I changed / bought a new cam. I would try this in at 109 icl.

Stan

[Cliff R]

The cam is actually too good at cylinder filling too early in the rpm range. So on paper Straub actually did a very good job for you. Problem is that the 455 is a little different animal than a 454 BBC with much less stroke, bigger bore, shorter rods and HUGE port flow.

As I've put up on these threads many time, the 455 by design is going to try to make all it's power right off idle, it's undersqaure and fed by heads with no more cross section than an "average" set of SBC heads. So dynamic compression will be high and early in the rpms right to start with. When you bring in a small cam on a tight LSA, it just takes what the 455 does best and makes it better.

Problem is that your 9. something to 1 455 now acts like 11 to 1, so it will NOT want any timing from the vacuum advance, and very little total timing. When the timing is retarded enough to make it happy, power goes to shi@. Been there and done that enough times to know the cure is to put more cam in it.

Another thing that will help if you don't replace the cam is to put high ratio rockers on it for more effective duration. I did just that to the 455 SD mentioned in the my last response and although it didn't completely cure the issues, it allowed us to bring loosen up the timing curve a bit, and total timing to 28 degrees, plus 8 more degrees from the vacuum unit.

More of a "crutch" than a cure, but it sure pointed us in the right direction and told us why we were having issues in the first place.......cam too small and LSA too tight......FWIW.......Cliff

[tom s]

I would at least try to retard it some before pulling it all the way out.It made a diff on my SP cam in my 455.Pump it first as Stan asked and pump it after just for grins.Mine was put in at 106 and we moved it back to 109.Tom

[jonmachota78]

I did the same thing with my old faithful. Went from 106 to 109 and its much happier since then

[pastry_chef]

Originally Posted by Stan Weiss

Have you done a cranking compression test? if so what is it?

Have you called and talked with Chris about this?

Before I changed / bought a new cam. I would try this in at 109 icl.

Stan

X2
Get the cranking PSI..
Obviously part throttle VE is significantly less than max. Intake close would need to be WAY early to be the root of this.

[Cliff R]

No, the "root" cause is installing a cam better suited for a 350 build instead of the HUGE 455 engine. The big 455 is much less efficient as well with it's over-square design and small intake runner cross section. So by design it's going to be a very good air pump at low rpm's, but not all that great in the upper mid-range and top end. So IF and WHEN you put a small cam in one with tight LSA, you simply make it much better at what it's already very good at. Cylinder pressure is high at low rpm's, and it will take one with 9 to 1 compression and make it act more like 11 to 1. I've seen this MANY times because I tune for a living and have been asked to help folks out with 455 builds using Comp XE262, XE268, and XR276HR cams where the owner/builder or tuner was not able to get good results no matter what timing and fuel curves they tried. The little Straub cam used here would actually be WORST than the two larger cams mentioned here as far as octane requirements and fall somewhere close to the XE262 camshaft....which, IMHO wouldn't be worth two squirts of duck poop in a 455 build with large chamber 4X heads on it and 7.7 to 1 compression......FWIW......Cliff

[chiphead]

Check out GTOfreek's latest dyno posting of a Poncho 460 with the Lunati 231/239 on a 112LSA. Probably the closest "shelf" cam with real world dyno results. You might be able to run the next size up cam, but you don't quite have the compression. That Straub cam looks upside down and backwards...

[pmd400]

The straub cam has an intake closing point of 60* abdc. Dynamic compression is 7.88.

The 60919 intake duration at .006 is about 285* from memory. With an icl of 108 the ivc will be 70.5* abdc. Dynamic comp is 7.29.

Is takes 10.35 static compression with a 60919 cam to get the same 7.88 dynamic comp as the straub cam and 9.5 static comp.
that must be a significant diffence

[Cliff R]

I've used the 60919 PLENTY of times in 455 engine builds and have had literally scores of customers use it as well. It is nothing more than a RAIV camshaft no matter how much Crower "juggles" the specs on it.

The first cam cards they sent with them back in the 1990's actually posted the specs at 304/314, 231/240 on a 113LSA. Even back then the website said 112LSA. Putting a degree wheel on it shows that it is most like a CMC blueprinted copy of the Melling SPC-8 or original OEM 041 grind.

This is good and bad news. Having that much overlap and 308/320 duration at .002" tappet lift it's going to be very happy in a 455 build at 10 to 1. My first 455 was exactly that, and it only made about 10-11" vacuum at idle speed without adding Rhoads lifters to it.

I have done ONE 455 with that cam with 6X-8 heads and it works pretty good, but far from ideal due to the low static compression ratio (about 9.3 to 1). It has to have manifold vacuum to the advance at idle (which is almost never the case with my engines) and is just a tad "soggy" below about 2500rpm's even with Rhoads lifters in it.

Don't get me wrong here, it flat ars makes the grade at full throttle and does a very good job of pushing around the heavy vehicle it's in, but we put a low gear set in the TH400 and custom Continental converter to help optimize that deal.

Bottom line here, I would NOT use the 60919 cam in a 455 much less than 10 to 1 true static CR.

What I've done instead for our "low" compression 455 HO and Super Duty engines is to go to custom ground HR camshafts. Same thing for 455's with 7K3, 96, 6X-8 and other heads with pretty large chambers than only yield about 9 2-9.3 or so compression.

Below is a dyno chart from one of them and best news is that I had NOTHING to do with that engine besides helping out with the carburetor (supplied a custom HP rebuild kit with tuning parts).

The builder owns a machine/speed shop and very knowledgeable with this sort of thing, but when he was hired to build the 455 for his customer (first one he ever did) he just called Comp Cams and they sent him the XR276HR camshaft.

He ported and flowed #96 heads to 250cfm, tight squish, and put the engine on the dyno. It was a complete "turd" according to the owner of the machine shop, and EVERYONE involved with it was blaming the Quadra-Junk carburetor.

Since it was coming up WAY short on expected power and idled very poorly they cranked some timing into it and blew it up on the dyno, yes, detonated it and spun the rod bearings right out of it, and that was with premium pump fuel and only 9.3 to 1 compression using 36 degrees total timing!

So I get the call, and got the guy settled down and instead of discussing the Q-jet I asked about the engine specs. He told me what cam so I quickly had him install a larger cam with 289/236, 308/245 (.381" lobes) specs and have Comp grind it on a 114LSA and to put the ICL at 109-110. There was a moment of silence, but he agreed. Couple of weeks later got a call and EVERYONE involved in the project was amazed at the difference in power. They also couldn't believe that the new cam produced better idle quality as well, it made no sense to anyone involved except me.

My previous testing with small cams on tight LSA's in 455's not only showed problems with octane, they also idled like horribly. Instead of just having a little "lope" from the 110LSA, they "skipped" and missed and "chopped" horribly and showed noticeable "reversion" out to 1500rpms or so where they finally started to smooth out and be happy.

Anyhow, the dyno charts from both combinations are below and show us how much better a long stroke 455 with decent flowing heads LOVES a big cam on a wide LSA despite what the "experts" and "guru's" tell us we should be using in them

When looking at those dyno comparisons also keep in mind that the larger cam on the wide LSA idled very nice, smooth right off idle, no signs of "reversion", and made a BUTT LOAD more power (torque) over a much broader rpm range, and it did it with pretty "low" compression....Cliff

[BGus16]

I use the Crower 231/240 cam with Rhoads lifters and 1.65 rockers in my 462 with 6x-8 heads. the heads were milled .030" when I bought them from a member here years ago. I did smooth out the runners before I installed them but never CC'd them. I estimate my compression at 9.3 but it is only an estimate. I can tell you for sure that this cam in my 4 speed T/A with 3:42 gear will run 13:30 @ 107 mph in the 1/4 mile. The last chassis dyno years ago put 342 hp and 422 ft/lb to the wheels. I shift it at 5000 rpm. Engine will idle at 800 no problem with right at 13 inches of vacuum with some attitude. I think it sounds nice. Car is totally streetable and never overheats and starts right up. I run a stock 1969 cast intake and Q-jet. I do run headers and 2.5 dynomax exhaust. Simple and effective really. I think it runs great for the mild set up it is. I have run this for at least 15 years. I replaced a Crane HMV-278 (224/234) which did idle smoother, had more low end, but really fell off fast at 4000 rpm. Overall I like the Crower much better.

Just my experience, hope this helps.
Barry

[STEELCITYFIREBIRD]

With an icl of 108 the ivc will be 70.5* abdc.

IIRC.. the IVC is up in the 80's* (81* ~ 85*?) ABDC installed on a 109* ICL for the 60919.

[Formulajones]

Originally Posted by pmd400

The straub cam has an intake closing point of 60* abdc. Dynamic compression is 7.88.

The 60919 intake duration at .006 is about 285* from memory. With an icl of 108 the ivc will be 70.5* abdc. Dynamic comp is 7.29.

Is takes 10.35 static compression with a 60919 cam to get the same 7.88 dynamic comp as the straub cam and 9.5 static comp.
that must be a significant diffence

Wait a minute....you're finding your dynamic compression is only 7.88 and you're having serious detonation issues at 2700 rpm and beyond with only half throttle and no vacuum advance assist, and only 30 degrees total??

Something is amiss. Using many of the calculators online, I'm coming up with the same number......running 8.9 DCR with an iron head on mine, and it's running perfect on 91 octane and 34 degrees of timing.

If you truly have 7.88 with that cam, and the RA IV is only going to drop it to 7.29 using your math, that's not a huge change. Not enough in my opinion to completely cure the severe detonation you're describing of pinging starting at only 2700 rpm and half throttle with no vacuum advance and only 30 degrees of timing.

Not to mention many sources state that DCR in the 7.5 to 8.5 range is perfectly safe for 91 and up pump gas (discussing this in another thread) I find this statement to hold water since I'm pushing 8.9 DCR on 91 pump and it's perfectly happy.

[pmd400]

Formulajones, iv read the other thread about dcr. There's not a cam that closes the intake at 41 abdc on a Pontiac, even the xe 250 closes at 51abdc. You must be using .050 numbers instead of seat timing(.006)

[chiphead]

Most calculators want the advertised valve closing event to calculate DCR, not IVC at .050. I posted the formula in the other thread.

((ADV duration/2)+LSA)-ground in advance-180= Advertised intake closing point.

Use the calculated Advertised intake closing for most DCR calculations.

Even then It's only a rule of thumb, not the be-all end all.

[scott70]

Originally Posted by BGus16

I use the Crower 231/240 cam with Rhoads lifters and 1.65 rockers in my 462 with 6x-8 heads. the heads were milled .030" when I bought them from a member here years ago. I did smooth out the runners before I installed them but never CC'd them. I estimate my compression at 9.3 but it is only an estimate. I can tell you for sure that this cam in my 4 speed T/A with 3:42 gear will run 13:30 @ 107 mph in the 1/4 mile. The last chassis dyno years ago put 342 hp and 422 ft/lb to the wheels. I shift it at 5000 rpm. Engine will idle at 800 no problem with right at 13 inches of vacuum with some attitude. I think it sounds nice. Car is totally streetable and never overheats and starts right up. I run a stock 1969 cast intake and Q-jet. I do run headers and 2.5 dynomax exhaust. Simple and effective really. I think it runs great for the mild set up it is. I have run this for at least 15 years. I replaced a Crane HMV-278 (224/234) which did idle smoother, had more low end, but really fell off fast at 4000 rpm. Overall I like the Crower much better.

Just my experience, hope this helps.
Barry

what is your 1/8th mile 60ft,ET and MPH? Have any time slips with 1/8th mile info? I run a very similar drivetrain to yours.

[krisr]

Originally Posted by pmd400

The straub cam has an intake closing point of 60* abdc. Dynamic compression is 7.88.

The 60919 intake duration at .006 is about 285* from memory. With an icl of 108 the ivc will be 70.5* abdc. Dynamic comp is 7.29.

Is takes 10.35 static compression with a 60919 cam to get the same 7.88 dynamic comp as the straub cam and 9.5 static comp.
that must be a significant diffence

If you have an adjustable timing set, try retarding the cam 4* and see what it does first. It'll only cost you some silicon and time.

[pastry_chef]

On the OPs engine would be interesting to see the air/fuel ratio at part throttle.
Two 600's is a lot of venturi for a mild engine, Edelbrock's usually need to be dialed for the application. This could be very lean.