[Shiny]

It seems the CR is missing from a lot of these posts and it would be useful to "bound" expectations. I have to think there is a wide range what is described as "low compression" across all the 350 versions.

This prior thread was a disappointment for me, learning the 11 heads were approaching 90cc, but contains a lot of useful head comparisons.

Link to Thread About Head cc

On the other hand, the 70 350 had higher HP ratings than later years even with a low CR... So what's the relationship between the CR and HP across these engines?

I'd be interested in seeing a "cam vs CR" discussion targeting the 350. Is it even possible to increase average torque in a 350 if the CR is less than 8.0 as it seems for most 1970+ variants?

[Formulas]

Shiny, the examples of powerhouse 350's with 240 230 250 degrees duration I guarantee they did not have low 8.1 compression and highway smog gears

A 068 cam isnt big for a 350 BUT in a 8.1 compression 2 something gear stock automatic off idle response IS dismal while it's taking 3 seconds to get in its powerband your trying to figure out a personalized license plate

the advertised seat to seat duration is the detrimental player in a low compression 350 at low RPM low port velocity

350 / 068 / 10.1 compression 2500 / 3000 converter 3.55 plus gear ? Whole different animal

[SD455DJ]

Some 10-12 years ago Mark Weymouth built and dyno’d a ’68 350HO for an auto (TH400) ’68 Firebird (convert?) and my brother, Dan, built and dyno’d a ’69 version for an auto (TH400) Tempest. I recall the Firebird ran solid high 13’s with 3.90/4.10 gears. The ’69 Tempest was sold before it made any passes, so we’ll never know. Both of these builds were purpose built for the Pure Stock Drags.

The ’68 350HO (0.030” over, so 359.3 CID) with #18 heads dyno’d at 330 hp/395 lbft with 10.6 static compression and a 200/212/110 @ .403”/.418” cam (between the 066/067 and 2800 cams specs). This was with the factory Firebird log exhaust manifolds (unmodified), mandrel bent 2½” headpipes, and factory single snorkel air cleaner with paper filter with lid flipped (made a couple more hp/tq in the upper rpm ranges). The pulls ended at 5200 rpm.

The ’69 350HO (0.030” over, so 359.3 CID) with #48 heads dyno’d at 346 hp/402 lbft with same 10.6 static compression, slightly bigger cam at 201/217/110 @ .403”/.418” through factory Firebird logs and 2½” mandrel headpipes and same single snorkle air cleaner. The 350HO was also dyno’d with A-body logs did 348 hp/403 lbft and A-body ram air manifolds did 355 hp/411 lbft. The 7029262 Qjet ran best with 41 pmr/70 jets, ‘L’ hanger and DG smr (0.0337” tip). The pulls ended at 5200 rpm as well.

I’ll find out what rpms the max hp/tq numbers were made at and what the max timing was. Maybe Dan has the dyno sheets as well to make copies of and post later. Dan said the Desktop Dyno program got the best power with the cams retarded 4 degrees. Advancing to 0 degrees (straight up) lost a few hp and gained a little tq. I’ll find out where the cams were actually installed at too.

I guess the point of this is to say the 350’s are good runners and a low compression 350 with an 066/067/2800 cam is going to run fine. Certainly the 068 cam will push the power to a higher rpm level where I would be a little concerned about the push-in rocker studs, but would work. I would be so temped to install a factory 4-bbl intake and Qjet on top of any early 75-80 cc head with one of these cams along with a nice 2½” mandrel bent exhaust system with RA manifolds.

Dennis

[AIR RAM]

I always love to see a good P350 build! I'm a firm believer that the P350 gets a bad rap by people who really never gave it a shot to begin with. Sure I get it, you can do more with its bigger brothers for nearly the same exact price... and that is very sound advice. BUT that does not mean the P350 cant do very well with some love tossed its direction.

With that said, I built my P350 back in 1997 and shoehorned on a set of EDL PERF RPM Round Ports with 2.11/1.66 valves... The cam was a single pattern 222@.050 with .309 lobe with 110 lobe sep. I ran 1.5 roller rockers. I did have 10.5:1cr and it ran well on 93 octane. It actually had a favorite gas station (Mobil) and I could tell a slight decline in its performance using anything else... I always thought that was funny.

I dont have any DYNO numbers... and the only track times I had showed promise. The 69 Firebird Cov ran a 13.5 @ 108MPH... With a peg-leg, one wheel wonder open diff. So it was tough to launch off the line... It also spun the tire on the 1-2 shift... I'm willing to bet this set up had an easy mid to high 12 second pass in it with the Auburn and 4:10 gear ratio.

So although the cam I used was NOT the 068, it did have a bit more lift and I'm fairly sure significantly larger valves which has a roll in the performance.

The car ran great on the street and was actually my daily driver for about 6 years with this engine. I absolutely loved the way it ran. By the time I did get the 4:10's and Auburn diff installed, I only put about 2000 miles on the car before taking it off the road. It never did make it back the track with the new rear however, It held its own quite well on the street and was anything but slow. I know it was much quicker than the 2001 Ford Mustang SVT (NON-Supercharged) at the time as my neighbor had one and we would race each other all the time. His car ran 13.5 at the track and I could easily put 2-3 cars on him with those 4:10s and posi where as prior to that (at the track) he would always beat me by a nose. My MPH was always higher than his though...

I am fairly sure I could have gotten more out of that 350 today with a slightly bigger roller cam

All that to say, I should have given that 068 cam a closer look back in the day...

SPEED SAFE, NICK

[steve25]

I am not saying in the least bit that our 350 can’t be made to perform very well on the street and yet have a good top end blast to it, but once again Air Ram as so many have strayed in this string of post I will bet that the OP has no intentions of ever coming close to running 4.10 gears that you ran in your combo unless he’s open to a swap of a 5 or 6 speed.

In the OPs own words he stated that he “just wants to wake it up a bit “ and yet so many of you have taken things beyond what he wants , and it seem’s for no other reason many times but to pound your Chest!

[tom s]

I my opinion and 4 bbl change would have woke it up enough for the seat dyno.Tom

[MarkS57]

Originally Posted by tom s

I my opinion and 4 bbl change would have woke it up enough for the seat dyno.Tom

Yup, agree, kind of got me thinking. The 350 I posted about was a 68 LeMans. I also had a 73 Firebird 350, don't recall the heads. I suspect the OP already has done this but assume he's made the switch to dual exhaust? My 73 had single. I made the switch to duals and a stock Q jet and it was a different car. I never got the chance to mess with it any further; one of the cars a regret selling.

[Shiny]

Originally Posted by pastry_chef

.....Over nearly 7000 variations of valve events in Dynomation 6, all the best 5 had 61 ABDC intake close (7.5 compression 350 Pontiac).

You clearly have run a lot of simulations and have good experience with 350s. Do any of the cams mentioned in this thread come close to your predicted "optimum" 61 degree intake close event?

If OP's 46 heads are 96 cc, is his static CR even 7.5?

I'm curious what your simulator shows (ie hp/tq vs rpm curves or even peaks) for your "best 5" vs the stock cam at these low CRs. This may come close to answering the OP's question about the potential for "waking up" his 74 350 without changing the heads.

What does your simulator predict for the 068 cam at such a low CR? If there is higher tq and/or hp than OP's stock engine, does the simulator suggest it is still driveable or is it obviously a bad match to a high rear ratio?

[pastry_chef]

Originally Posted by Shiny

Do any of the cams mentioned in this thread come close to your predicted "optimum" 61 degree intake close event?

See my post 18 suggestion and post 42 similar cam used / track result video.

068 would not be the way I'd go personally.
Less valve area and looks like more seat duration than other options. Exhaust valve events are not where I'd want them.

[Dragncar]

Summit 2800 is a fine cam in a 350. Whitmore called it a '214 High Lift and recommended it for me. 350 with 48 heads sounded sweet. Came on strong at 3500 RPM.

[AIR RAM]

Originally Posted by steve25

I am not saying in the least bit that our 350 can’t be made to perform very well on the street and yet have a good top end blast to it, but once again Air Ram as so many have strayed in this string of post I will bet that the OP has no intentions of ever coming close to running 4.10 gears that you ran in your combo unless he’s open to a swap of a 5 or 6 speed.

In the OPs own words he stated that he “just wants to wake it up a bit “ and yet so many of you have taken things beyond what he wants , and it seem’s for no other reason many times but to pound your Chest!

I apologize for not making a post that pleases you. Ill try harder next time...LMAO

Did you forget pointing out the gear recommendation in your first post? So you can recommend gears with the 068 cam but I cant mention running gears with a less aggressive cam? I dont feel my post was anymore off track than your own. I didn't discredit your post for going off track with advice.

Personally I tend to want to give full context into my line of thinking so Its not misrepresented, this is why my post was so long, ill try to add pictures for you next time... perhaps that's why you became bored with it or got lost in the reading. I did included a picture of an Auburn Diff for your viewing...

You may find my post irrelevant, however there is plenty relevance to it... Just as yours was.

My advice was from my own first hand experience with a REAL WORLD P350 build. Not a copy and paste of someone else's.

The intention was to show that I had actually gone with a less aggressive cam than the 068 and had great results. I did share engine build details as well as what mods I had on the car and the 4.10 gears really where NOT the success of that combination. Because I didnt have DYNO info, I shared track results to validate performance. With all said and done, it was a Mid to high 12 second combination.

Why you got stuck on gears is beyond me... The gears where not added until later on closer to the the time it was taken off the road... you would have caught that if you took the time to read and comprehend. It was the POSI carrier that allowed me to put the power the car was making to the ground... although I dont feel the 4:10s hurt. With that said, I would agree with your first post that he would want to put gears on his list of things to do if he chooses the 068 cam for his P350...

So lets stay on topic and not attempt to start a flaming tread because you want to beat your chest and show everyone what your really about. Not everyone wants to be like you.

SPEED SAFE, NICK

[Stan Weiss]

Originally Posted by pastry_chef

See my post 18 suggestion and post 42 similar cam used / track result video.

068 would not be the way I'd go personally.
Less valve area and looks like more seat duration than other options. Exhaust valve events are not where I'd want them.

Mike,
For the cams you show. What does Dynomation show for estimated idle vacuum?

Stan

[Stan Weiss]

Originally Posted by Dragncar

Summit 2800 is a fine cam in a 350. Whitmore called it a '214 High Lift and recommended it for me. 350 with 48 heads sounded sweet. Came on strong at 3500 RPM.

The Summit 2801 is the one that has 214 @ 0.050" on the intake.

Stan

[Jay S]

Originally Posted by Shiny

You clearly have run a lot of simulations and have good experience with 350s. Do any of the cams mentioned in this thread come close to your predicted "optimum" 61 degree intake close event?

If OP's 46 heads are 96 cc, is his static CR even 7.5?

I'm curious what your simulator shows (ie hp/tq vs rpm curves or even peaks) for your "best 5" vs the stock cam at these low CRs. This may come close to answering the OP's question about the potential for "waking up" his 74 350 without changing the heads.

What does your simulator predict for the 068 cam at such a low CR? If there is higher tq and/or hp than OP's stock engine, does the simulator suggest it is still driveable or is it obviously a bad match to a high rear ratio?

The various year 2 bbl 350 engines are closer to the same compression than most realize. Starting out from 68 to 72 the 350s had valve bore scallops on both the intake and exhaust and had about 3 cc valve reliefs. Then later engines the valve reliefs disappeared, and I think the bore scallops may have been discontinued as well. Both bore scallops together add about 3 cc’s. The earlier engines had smaller cc heads, but lost quite a bit of compression from the bore scallops and valve releifs.

The OP’s engine might have the very small valve reliefs 1.5cc. I don’t think it has bore scallops, it may have one side. Swapping a 11 heads on a 74 350 will be higher compression than a earlier 350 because of the difference in the short block. It is still likely slightly under 8:1 with the 46 heads.


The ICL number for the intake closing is IRC 58.5*, but I add 2* for timing chain slack which is getting close to that 61* numbers Pastry posted. Pontiac heads flow enough at low lifts you can get by pretty well with fairly late intake closings. The 068 ICL number, using it’s actual .006” tappet duration and install dot to dot as it is ground the ICL is close to 70*. Plus the exhaust opens really early too, nearly 80* if I remember correctly. It would work very well with 9.5+ compression 350 but for a low sub 9.0 compression engine it is really a poor choice.

I have used that 2800 cam in a number of engines. If the engine has a 4bbl, the 2800 will make more power than 2 bbl cam or even a 066 in a 350. With a 4 bbl it is likely a 20-30 hp jump with decent exhaust over a 2 bbl cam, and 10-15 over a 066. The 2800 is not a very good cam for a 2 bbl engine though, it is big enough it needs a 4 bbl.

Agree with Tom…Hard to make an argument not to change out the 2 bbl for a 4 bbl first to some immediate power gains. Would definitely be worth the effort. My 326 example earlier was pretty shot in addition to poor gearing. Lol

[pastry_chef]

Originally Posted by Stan Weiss

Mike,
For the cams you show. What does Dynomation show for estimated idle vacuum?

Stan

Hi Stan, unfortunately Dynomation does not provide output on estimated idle vacuum.

[Jay S]

Originally Posted by Jay S

The ICL number for the intake closing is IRC 58.5*, but I add 2* for timing chain slack which is getting close to that 61* numbers Pastry posted. Pontiac heads flow enough at low lifts you can get by pretty well with fairly late intake closings. The 068 ICL number, using it’s actual .006” tappet duration and install dot to dot as it is ground the ICL is close to 70*. Plus the exhaust opens really early too, nearly 80* if I remember correctly. It would work very well with 9.5+ compression 350 but for a low sub 9.0 compression engine it is really a poor choice.

Sorry, should have added that 58.5* intake closing @.006” tappet is for the 2800. Installed dot to dot it will usually run 59*-60*, I often check the intake closing down at the cam when I build engines. It has various ICL positions for different engine makes. 107-108 is pretty common. When we started building a lot of engines I recall TRW use to sell some type of Power pack efficiency performance overhaul set which always included that 2800 grind cam, i don’t recall one for a 350 Pontiac, but 270-280 HP was pretty common dyno results on all the other 350-360 cid engines with their “kit”. I would expect similar results in a 350 pontiac. The next cam bigger (2801) works well with lower compression engine to but have found it doesn’t offer that much over a 2800 until you add higher stall converter, headers and gearing.

[Shiny]

Jay,

Thank you for taking the time to interpret my questions and respond. It's very useful.

I was trying to understand why a 70 350 would be rated 255 hp yet the 73 would be rated 150. I always assumed it followed the advertised CR of 8.8 vs 7.6.

That previous thread showed my assumption followed lies from credible sources! Your comments regarding scallops are even more insightful.

Now that I see the TRUE CR difference between these two engines is MUCH less, the ratings may also be lies or they result from other differences.

Are these engines actually producing the same hp or is the 73 555 cam MUCH less efficient than the 70 054?

If so, could the OP gain some power by using the 054 cam?

Not to detract from the OP, but I am glad to hear my choice of a 2800 cam, 4-bbl, and 3:55 rear may work out with my 11 heads. After hearing they were only 90 cc, I thought they might have to go away. I appreciate all the discussion as it helps me learn.

Is the inexpensive Desktop Dyno software worth buying to gain more understanding?

Mike

[77 TRASHCAN]

Originally Posted by Jay S

Sorry, should have added that 58.5* intake closing @.006” tappet is for the 2800. Installed dot to dot it will usually run 59*-60*, I often check the intake closing down at the cam when I build engines. It has various ICL positions for different engine makes. 107-108 is pretty common. When we started building a lot of engines I recall TRW use to sell some type of Power pack efficiency performance overhaul set which always included that 2800 grind cam, i don’t recall one for a 350 Pontiac, but 270-280 HP was pretty common dyno results on all the other 350-360 cid engines with their “kit”. I would expect similar results in a 350 pontiac. The next cam bigger (2801) works well with lower compression engine to but have found it doesn’t offer that much over a 2800 until you add higher stall converter, headers and gearing.

Jay,
Have you measured the combustion chamber volume on many 350 (specific) heads? I have a set of 17's that measure 83.5, on both heads...I have a 70 350 in my TA now (o66 cam) with the 11 heads. It runs considerably better with the Quadrajet on it, than the 2 Bbl did. I did not measure the 11 chamber volumes, BUT I'm think they are larger. I've had 44 degrees total timing in it, couldn't get it to ping, if I wanted it to....

[PONTIAC LARRY]

I stand with just using a new # 066 cam in current engine if its getting 4v swap etc and hope when it gets a 4v swap that it gets a set of 68 small valve #17 or 68 small valve #15 heads at same time. You get the compression up where it needs to be and has all the exhaust holes unlike the 69 46/47 heads .. We did a old 68 used 066 cam in a junk std re ring 73-78 350 short block and stuck a set of 69 #62 heads with 69 intake log A body manifolds stock converter th350 into a 78 Grand Am with a open 3.73 7.5 rear and it still managed a respectable 14.3@95 in the 1/4.. Our open 2.56 gear original 84k mile 69 3502v 47 head Lemans with stock stall th350 and only a 4v swap and duals and shifting very low3800-4200 went 15's already .. Same buddy has a 2.93 posi 65 Tempest running a un-rebuilt 72 350 short block with a tiny 112 lsa cam and a set of 62 or 16 heads and it is in the 9's 1/8 , 14's 1/4 mile. I do recall another buddy did a Sum 2801 in a 68 Tempest 17 head 350 rebuilt that had 4v swap etc and it lacked low end. 2801 is a no brainer in a 389/400 though, Cam needs to stay 200-210 @050 intake side IMO .. a Old school Cam Dynamics Energizer 210 210 110 cam or old High Energy Comp 260 210 210 110 would be good if ran across a NOS one

[Jay S]

Shiny, the 1970 350 had a Gross HP rating which is power measure with the dyno right up to the flywheel with no accessories, the 1973 had a SAE rating which is taken from the back of the transmission with the accessories on. 1972 on had SAE ratings, some books for 1971 list the power both ways. Some Engine manuals had both ratings listed for 71. The biggest difference between the HP was the methods. There likely is not much actual hp difference between the any of the two bbl cams in power from 1970 up unless it came from emissions equipment. The 2 bbl engines only had about .37 ish lift. I would have to look at those 2 cams you mentioned, but i recall they moved the LSA around and shortened the timing over on the exhaust side on the later 2 bbl engines. They had close to 250* or slightly less than that down at .006” tappet, very small cams. But most of the changes came with how the exhaust profile was positioned.

Jeff, I haven’t checked many 350 heads, and if I did they were all 71 and newer. I think from what I have read that is correct the 68-69 are smaller chambers in the lower to mid 80s. I don’t think the 066 with a little lower compression would have any trouble out muscling one of the stock 2 bbl cams and a half to a point to point more of compression. 066 is a good step over a 2 bbl grinds, the 2 bbl cam limits what can be done for performance usage. I have built some small cam engines up over 11 compression, often on propane. While they do well for tq off idle thru cruising speeds (good for towing)it is pretty difficult path trying to make hp to compete with a bigger cams.