So I have a rather long story that I wont tell here (another thread), but the long of the short is that I live in west Denver (insert, "Dude, this whole town is High" joke here ) at an altitude of approximately 6,000 feet and I am having a engine built. What have people who live and drive at altitude found that works well? I know that any build won't have the same power as at sea level, but what head/cam/intake combinations have people used with good success at these types of altitudes? Issues with detonation?

Car info:
1977 with rebuilt TH350 (2,000 or so converter)
3.08 rear gears
building 383 roller cam
I could be sold on another carb, but for now lets assume nice rebuilt Q-Jet and lets not get into another Holley vs. E vs. Q-jet discussion here.

I want a fun street car. Something in the 450 hp range with good low end torque. Stop light to stop light kind of thing. May see the drag strip once or twice a year, but not its intended use.

I know gears would really help, so lets assume that in the future I will add 3.55 gears and a 700Rr, but I want it to run strong now and then really strong once gears and trans are done. Based on budget, this may be a little while (i.e. years).

I could easily change out torque converter when engine is out also.

Thanks in advance.

Brad

 

Do you plan on living there for the rest of your life?

 

If the shop that is building the engine is located in Denver wouldn't they have some recommendations based on prior experience?

 

I've lived in Denver and understand your challenges. You can add a good bit of compression to help it out.

I would reach out to Mark Jones "VortecPro" in Co Springs. He builds lots of killer combinations that capitalize on mid range TQ without breaking the bank...and is a meticulous builder that will walk you through the whole combination to get what you want.

JIM

 

Yes, I do plan on being here for a long time. Long enough that I may need a new engine if I ever moved. I have not had the car out of state in 10 years. I drive the car from home to work (at 7,200 ft) and around town.

The builder is not here in Denver. There is a long story here, but what's done is done and I have to make the best out of the situation. Lessons learned......

Thanks Jim! I will give him a call. I grew up in the Springs and will be there tomorrow.

 

I have one of his engines, and

 

Lars the expert QuadraJet rebuilder lives in Broomfield. He rebuilt mine this spring. Nite and day diff!!

 

Yep I have had the pleasure of meeting him at his garage. I have tried to contact but haven't heard back as of yet. I hope to consult with him. Unfortunately, he is no longer rebuilding carbs. I missed it by a couple of months. Bummer.

 

Your 80 Miles from Mark Jones "VortecPro"

 

How much of a do yourself kind of a guy are you?

I knew nothing about the Q-jet until I read Cliff Ruggles' book. I took that book and rebuilt as well as modded my Q-jet to the point that it runs so well it may as well be fuel injection. Still subject to Carb jetting changes with changing temps and altitudes of course, but you get what I mean.



I did find that I had to jet leaner than his book called for due to my altitude. Still a great book to learn from.

 

I got some pointers from Lars when I was watching him rebuild mine about 4 years ago and have read his papers multiple times. I have seen that book, and once I get the motor sorted, I am going to dig into it to squeeze every bit of performance I can get out of the new engine. I feel very confident about rebuilding and adjusting the carb and timing including re-curving distributor.

Cam/heads/intake selection..... still a little over my head, but I am learning. I still have the old L48 from the car, and this whole mess has spurred me to one day build that one. The engineer in me has to know how to do this now.

 

I have lived at sea level and high altitude in Utah so on my car I have had to tune for different altitudes. You need really good heads and a decent amount of compression. You also need more timing than what a sea level car uses and of course fuel mixture has to be correct. I have a quick fuel carb because it is very adjustable. To get the fuel mixture correct it's more than just changing the main jets. You will need to also be able to change Idle feed restrictors and air bleeds to get it right. Not sure how this is done on a qjet.
I have a 350 with AFR heads 10:1 compression and a comp xr 276. Runs really well but when in Utah I wished it had more compression but in Texas it needs 93 octane and carefull timing adjustment or it will ping.

 

I gave you a few details to my build in your last thread but though I'd go ahead and give the rest. I did build my 350 with altitude in mind. I figured an average of 5000 ft density altitude for operation. As high as 8000 ft and as low as 3000 ft.
I took the advice of a member here and built it to no more than 8.2:1 on the DCR. I ended up with a 9.9 CR to achieve that with the cam I chose. Strike one for my intake velocity.

In hind sight I would have been better served had I built it for 10.5 CR and about 8.5 DCR.

I have Dart SHP aluminum 180 heads with 64 cc combustion chambers and 11.5 cc dish Keith black pistons.

The 180cc's on the intake runner on the Darts are not accurate. They turned out to be an average of 195cc's. Strike two for velocity of my intake charge.
The 64 cc chambers are in reality 67cc's. So I had the heads shaved to get the chamber down to 61cc's and reduce some valve shrouding.

I ported the heads myself after reading from several sources on how to do it but primarily from David Vizard's book on head porting. Mostly I cleaned up the ports, bowls and thinned down the valve bosses. I also spent a little effort on the exhaust side to provide greater volume for the exhaust to hopefully increase the exhaust volume.

The cam I used was a retro roller with 270/270 duration at .006 and a 219/219 @ .050 with 108 LSA and .549" of lift on both the intake and exhaust. I am running side pipes so I figured minimal exhaust back pressure. The 108 LSA does give a bit more overlap but makes for better intake filling and slightly more peak power. It also gives it a great lopey idle as a side effect. The higher lift for the valves allows for better filling of the cylinder and effectively increases the duration slightly, as does having a roller cam vs a flat tappet.

Tuning the carb for this cam at idle does take some doing but it can be done if you understand the carb.

My timing is set @ 19* intial, 34* all in and 51* at cruise. This took some modification of the stock mechanical advance and the vacuum advance to achieve. Another high altitude issue that has to be addressed. I never could get the engine to ping by increasing the timing just a loss of performance.

If I were to build an engine for your altitudes I would figure 6500ft as my base operational altitude with as high as 10,000ft on a hottish day.

This would mean about 11.5:1 CR with a 9.62 DCR, however an effective 8.3 DCR at 6500ft using my same cam. This would require a 59cc combustion chamber and a max of 7cc flat top piston with a .040 quench distance. .025 down the hole and a .015 felpro shim head gasket.
http://www.jeepstrokers.com/calculator/
Quench in my opinion is very important. Don't give it up for less CR with a thicker head gasket.

My quench is .038. I can run 85 octane fuel with no pinging. Just shows I could have gone quite a bit higher with the CR and DCR.

I usually mix fuel on the hottest days to achieve around 86 octane. About 1.5 gallons of 91 for every 10 gallons of fuel total.

With bad valve spring geometry and loss of valve spring control I was at 377 HP on this engine or 262 hp at the wheels. Now with fixes to springs, installed valve height and full roller rockers my seat-of-the-pants dyno says a bit more.
My wife's Mustang which is 292 at the wheels looses every time to either a rolling start or from a stop start race to my corvette. So I guess I may be somewhere north of 292hp at the wheels. The Corvette is also heavier than the Mustang.

 

Did you run it on both the engine and chasis dyno?

 

No I didn't. Didn't mean for that to be misleading. I just back figured the crank HP approx a 30% loss as near as I can figure from reading different crank vs wheel HP on dyno's with automatic and stall converters.

I wish I could run have run it on an engine dyno. There are none in my area and only one chassis dyno.

I have a Th-350 with a 3.08 rear end, 2600 stall torque converter. It was run on a Mustang dyno. I've read that the Mustang dyno's give lower numbers vs a Dynajet. Could be that the Mustang dyno's are just more realistic. Don't really know for sure.

I'm not seeing any real responses for high altitude NA builds.

Even with a google search there seems to be quite a void for this kind of information with mostly vague hints at how to do it. Most just recommend turbo or super charge to make up the difference.

 

With an altitude build you want a head that flows air very quickly at low lift. You want to get as much air in as you can and shut the valve. Cam profile needs to be moderate on duration and to the aggressive side with lift. This will get you the best performance with engines built for elevation.

I would error to the smaller side on the heads and concentrate on velocity.

 

So would you say 170-180 cc's intake runner?
What would you do with the CR?
How about exhaust?
Restriction to exhaust flow out the pipe would be... less? at altitude vs at sea level?
LSA on the cam narrower?

 

Around 175 to 185cc runner. .300 to .500" flow numbers would be what I look at. The head the flows the most the quickest fills the cylinder fastest.

CR. If OP is going to live in CO I would not be afraid of 12 to 1.

Since your limited on what air and fuel can get in the exhaust size will not need to be as large. A 1 5/8" header will get it done.

Valve events would be so to take advantage of the heads.

 

Thanks everyone for their input. I am working with the builder this week and this information helps.

The heads that are specified now are 205cc intake runners. From a previous thread and this one, I am thinking these are too big. If I am stuck with those, is there anything that can be done with the cam to compensate? I am not sure I can get different heads or not. I will try, but I would like to have a backup if I cannot get those changed.

Cheers
Brad

 

I was thinking more along the lines of not being able to reduce the size of the headers but of eliminating the need for greater duration on the exhaust side of the cam and keep larger headers.
Of course it would depend on the head but given the same head that might otherwise require more duration on the exhaust, is that a reasonable conclusion?
I'm just thinking (could be wrong here) that if a guy could eliminate unwanted or excessive overlap then why not do it.
Then you could use that to increase the lift or duration with no more penalty to low end torque than a lesser lift or duration cam with extended duration on the exhaust.

What's your opinion on .050 to zero lift on flow importance to cylinder filling?

Seriously? These guys want to increase the intake port size? Based on what?
My vote is no. Like Straub is pointing out, port velocity is key at your altitude. Keep it smaller and faster.
I'm no expert, Straub however, does this for a living.