Engine questions
 

Hello. I currently have a 68 265HP 350 with 17 heads (8.6:1 CR) with a TH350 in my 66 Lemans. It has a Holley 600, HEI, headers and flowmasters. So pretty much a stock engine with a few add ons. It runs OK but I'm looking for a little more.

I have an opportunity to pick up (cheaply I might add) a stock 69 290HP 400 with 46 heads (10:1CR). It already has a Pontiac 4bbl intake on it. I know the guy that has it and he says its a good engine

Questions:
With that CR on the 400 will I have trouble with pump gas?
I want to swap in a 2801 cam. Good choice? Will that help with the pump gas thing?
Probably would do a 2500 stall with the 2801.

Thanks for your help
Jeff

All good stuff!

I'm no expert so these are just my opinions not my experiences. I would use the 2802 at least and this may still be close to detonation the 2801 is too small and would build too much cranking compression. Personally I would get the new engine and then swap the heads. If they cc to the specs listed at PDudes website, https://sites.google.com/site/ksmsin...ontiac-head-id
the 17 heads are 72cc and the 46 heads cc at 68cc. A stock 400 with 72cc heads will come in just under 10:1 at 9.96:1scr. With the 2802 this will give you a dcr of 7.32:1 and a cranking compression of about 179psi. This is the highest cranking compression I would want with a stock engine that old and it may be a bit high. If you can rebuild the engine and deck the block or use longer rods/ higher compression height pistons to get close to zero deck then 180psi would be a good thing.

Karl

:usflag:

I'd bet that either set of heads would currently measure out to about 78cc's, and will be at 75cc's after a cleanup cut. You will have too much compression on a 400 (probably an honest 9.8:1 after the heads are done) to run the 2801 cam. Both heads have small valves and pressed in rocker studs. The pressed in studs would be iffy with the duration and lift of the 2802 cam.

You're between a rock and a hard place with your current heads. When you start paying a machine shop for the labor and materials to bring a set of heads up to par, the heads themselves become the cheapest part of the operation. I'd start with a set of heads that already had the large valves and screw in studs, and I would also choose a head with a large chamber that could be milled down to achieve between 82 to 84cc's to keep the compression ratio at 9.3:1 or a little below. Then all you have to do is select the proper springs and installed height to keep the 2802's .488" lift away from coil bind. Replacing all the valves is also a must. Way too many engines have been destroyed with the false economy of keeping the original 2-piece valves. While they seem to last forever in a stock engine, increasing spring pressure and kicking up the valve action all too often has the valve heads breaking off and causing cataclysmic destruction.

Dont just conclued that the 400 is running good now and can jst be dropped in, as I have purchased many running motors that if I did not pull the oil pan and check things out I would have been broken down on the road within the first 29 miles of driving.
One thing for sure is that the 290 HP motor has a 50 lb small pick up tube oil pump, and you need to step up to the 60 lb 3/4" pick up tube pump just for starters!
I would pull the pan and check all the bearings and pull the fuel pump and check for more than 1/2" of play in the timing chain also.

Steve 25, I do plan on pulling the pan. I had planned on a new oil pump and will step up to the 60lb (good idea!). I will also add a new timing set when I do the cam.

now to throw a curveball into the mix!!!

I just picked up a set of 68 #16 heads (2.11/1.77) that have been gone through and have new valves and springs. The price was right so I couldn't pass them up!

My understanding is that they are 72-75 cc heads.

How does this change the combination of cam etc I can use and still use pump gas??

Jeff

Daily driver?
weekend warrior?
Street/strip?

Completely rebuilt Pontiac 455 heads (4X casting, C223 date code, cleaned, magnafluxed, etc. ) all machine work complete and fully assembled, bronze guides, performance 3-angle valve cut, screw-in studs, new valves, springs, push rods, spark plugs, etc. Over $650 in machine work alone. Wrapped in plastic with dessicant since picked up from machine shop in late fall. Stored in temperature-controlled office. Better than it came out of the factory. $375. Tony (231) 937-4113 (see Grand Rapids, MI craigslist).

These heads would certainly be pump gas safe for a 400- you could easily and cheaply whack them down to meet your compression needs. The owner is wanting to sell these...

Blued, it is a weekend car. I do drive it a lot though.

TPS..thanks for the heads up (no pun intended :) ) I already pulled the trigger on the 16's so I'd like to make them work if I can.

I would get a set of dished pistons to get you to 9.5 to 1 and go from there.

Depends on if you want a max effort street engine or low-buck chuck. This board tends to go into the "full $5,000 rebuild" mode every time somebody comes in here with a stock 400. By the time you get dish pistons, forged rods, machine work, expensive valvetrain parts, etc that are recommended for a street/strip engine, the bill is 5 grand plus. By then you realize you could have a real engine with a stroker kit and aluminum heads, so the total project snowballs to 7 grand.

For low buck, take that 400, give it a set of rings/bearings, oil pump and cam/lifter set. Reuse stock rods/pistons if bore is still within service limits. Throw a set of 90-100 CC heads on it and let it ride. Look for 6X-4, 5C-4, 4X-4, 96, etc heads from '72-76. It'll run on 87 octane, be easy to tune and dead reliable.

You could build a basic 400 like that for $1500 in parts/labor. It would make an honest 350 HP pretty easily. Just don't revv it over 5200 and it'll live. Save up and build a more powerful engine later.

Jeff, I have no knowledge about engines, but can tell you what I experienced first hand. I had a set of 68 #16 heads on my 428 with a fairly mild cam, and had to add 2 1/2 gallons of 108 racing fuel to a tank of 93 octane gas to keep it from pinging. I went to a set of 6 x 4 heads and have been very happy with them

69farburd...with every thing I'm hearing on here, that's exactly what I'm afraid of. I think I'll start looking for the 6x4's.

TPS... Wonder what shipping would be from michigan :) ??

Thanks everyone!

cfd2bc,

I don't know about shipping these- I'm estimating they are about 70 lbs. each-I'm guessing $90 to ship both? Maybe someone can chime in here...

Tony

Just thought of a dumb question...my 350 is really a pretty good engine. I'm not unhappy with it. I have 17's on it now that are 72 cc's. Could I throw the 16's , also 72cc, on there with a 2801 cam and pick up a little power. Would the big valves throw it off so to speak?

if they are 4X-1h, i would not put them on a 400, talk about down on compression, they are 114cc chambers.

i would run the 16's with something like a 2802, (224/234 @050) or go bigger on the cam if it's one with short Advertised duration.

this is not a bad idea either. pontiac did it in 1969 with the 350 HO.

This is a simulation power curve for a 400ci with 10:1scr and the Summit 2802HFT cam.

Karl

:usflag:

My first pontiac was a 350 in my 67 LeMans. I found that large valve heads and headers don't help unless you've got the cam and compression to take advantage of it.

My engine was a stock '70 lemans 350 with 46 heads and the stock 254 cam. I swapped on a set of 17s and a comp XE256 cam. It would run 9s in the 1/8 mile with log manifolds and performer intake. I swapped to a set of 670 big-valve heads and headers. It picked up about 2-3 tenths. This is with a stock converter and 3.23 gears. A bigger cam and more gear would have helped. The 350s can be made to run well. Like any engine, you've got to match the overall combo.

The stock 350 cam was T-I-N-Y. I'd swap in that 2800 or 2801 in the 350 with a set of 72CC big valve heads like the 16s. Add a converter and 3.23-3.55s and it'd scoot.

Here is the simulated power curve of a 350HO with the 068 cam over laid on the 400 with the Summit 2802 cam.

Karl

:usflag:

You know for a FACT that this 400 has never been rebuilt? It's been rodding around for 40 years and now has a 4bl intake?

I'll bet you pull the heads off of it and it'll have some replacement pistons in it. :)

Yeah. You are probably right. I need to check that out for sure!!