I'm in the early stages of building a new engine for my '76 Blazer.  I'm really leaning towards a 406 like in the Impersonator articles.  Questions:  is the cam too much for my Blazer (daily driver, tow rig) - .480 lift, 230 deg., 110?  Is 9.5:1 comp too much to run on pump gas even if I back the timing down a couple of degrees?  I've heard some stories about cooling issues with 400's - how much of a problem is this and can it be solved by a good (4-core?) radiator?  Is there really much difference in performance between the AirGap and standard RPM manifolds, paricularly in a relatively low rpm applicaiton?  I'm really wanting to stick to an almost identical build-up as in the article because I like the torque figures the engine produced with the Vortec heads.

Truck has stock gearing (3.08's?), 4-wheel drive, 33" tall tires, stock converter.

Thanks, OM Gang

 is the cam too much for my Blazer (daily driver, tow rig)
I wouldnt believe so you can see from the dyno charts if the torque is @ a low enough RPM for you, with that low of lift mileage wont be outrageously low and as the article shows it will still make some good torque

Is 9.5:1 comp too much to run on pump gas even if I back the timing down a couple of degrees?
Backing off the timing from a optimal spot with vortec chambers is defeating your purpose of mileage and towing, if you really want to pump 91-94 octane premium fuel into a daily driver it will be probably be okay, yet if you really want to run regular (i would with a daily driver!) 87 octane id back off the c/r .5-1 point trying to not sacrifice too much piston to head clearance (quench clearance)

I've heard some stories about cooling issues with 400's - how much of a problem is this and can it be solved by a good (4-core?) radiator?
i dont see it as much of a problem i think your right and it's a fairly easy fix, but others may have some opinions

Is there really much difference in performance between the AirGap and standard RPM manifolds, paricularly in a relatively low rpm applicaiton?
Flywheel Dyno #'s show 7-8 ft lbs more torque at most RPM points with the air-gap, i suppose some chassis dynos might show slightly more, because underhood temps are factored in, but i dont really belive it justifies the extra cost especially since it eliminates the exhaust crossover which is needed for engine that must start in cold weather and where mileage is of some concern

Thanks for your quick reply!  I guess there's nothing left to do but start building.

OM Gang

If memory serves the Impersonator used Vortec heads. These do not provide exhaust heat to the intake manifold. Therefore, whichever, your choice you’re stuck with all the usual cold engine problems that go with an unheated manifold. On the street that can be a real pain especially if you live in cool, cold and wet country. If you live where cool/cold/wet ambient air is common; I’d highly recommend that you use a factory air cleaner from carbureted or TBI engines with the external exhaust manifold “hot stove” assembly to preheat the incoming air  These come with a thermostatically controlled door that cuts off the heated air when the engine warms up. This combined with a cool air source from behind the grill and a K&N replacement filter will provide plenty of intake air at temperatures the engine likes. This isn’t as good as exhaust heat but will go a long way toward reducing carb icing and let you run a leaner start up mixture which is a lot easier on top end cylinder lube.

A cam with .48 lift and 230 degrees of duration presumably measured from .050 inch lift will announce its presence.  A nine and a half compression ratio with this cam shouldn’t be a problem. Rebuilding with say Keith Black “D” dish pistons will help by keeping surfaces in close proximity to each other on the squish/quench side of the combustion chamber. This really helps detonation resistance, which you don’t get with a full dish piston

The 400’s cooling problems are mostly related to insufficient radiator in passenger car installations the typical 19 by 26 inch opening is right on the edge for a 350 in warm weather and is insufficient for a 400. You’ve got a truck which has a lot more space for something like a 31 by 19 inch radiator or something larger which should be sufficient. Don’t forget that Vortec heads need additional cooling holes if you’re building on a 400 or another block with siamesed bores. Basically you do six holes per head, use the 400 head gasket as a guide. There are 3 outboard (toward the exhaust side of the head) and 3 inboard (toward the intake side of the head). The three outboard (exhaust side) are drilled straight in at 90 degrees to the deck surface. The three inboard holes (intake side) are drilled at 45 degrees to the deck surface angled toward the exhaust side of the head. You only drill till you penetrate into the water passage. This lets coolant pass from either side of the siamesed cylinder walls into the cooling passages of the head preventing the formation of a pocket of non heat conductive gas (steam) under the head deck. Use a sharp drill, new if you doubt your sharpening abilities. Use a good quality center punch and place a punch mark where each hole will be drilled to prevent the bit from wandering off on to the machined surface. A 1/8th to 3/16s inch hole is perfectly adequate; no chamfering is required, nor desirable. The edges of each hole need to be lightly deburred to insure there are no raised or sharp edges that could compromise sealing.

Bogie

If memory serves the Impersonator used Vortec heads. These do not provide exhaust heat to the intake manifold.
Guess i never realized that, so scratch my idea of using a exhaust crossover with the regular RPM manifold, makes it more of a toss-up on which to buy but i believe that the air-gap will of course give up mileage to the regular manifold, if this is of no concern maybe the extra money spent on the air-gapper is a good idea

Any opinions on what switching cams to something like a Comp Cams 268 (.454 lift, 218 deg @ .050) or 270 (.470 lift, 224 deg @ .050) (both @ 110 lobe sep.) will do to the output of this engine?  I'm building the motor for a K5 Blazer that will see a pretty decent amount of daily driver duty and really don't want something that'll be hard to live with.  Am I worrying too much?  FYI, specs for cam in the Impersonator article - .480 lift, 230 deg @ .050, 109 deg lobe sep.) 

Thanks, OM Gang

i think that a extreme energy is preferred (dual pattern and faster ramp rate) so id say the 270 seems fine, the 268 seems pretty small, remember until you get to a duration of 236 @.050 your torque peak will increase, the high end of that spectrum might be a little higher RPM than needed though for a street motor with a stock stall, but your not talking about the high end duration you have already kept at a good balanced point i think

id say your motor will be a little more mild mannered than the impersonator for a engine that is a steady street driver this is not a bad thing and more efficiency at just off idle RPM will help your driveability and mileage

Thanks Gibs.  Not sure if I understand the first part or your post (about the dual pattern cam being preffered) but you think the 270 Magnum cam would be suitable for my application?  I really like the numbers the Impersonator generated in the article and am trying to stay as close to spec as possible (and maintain as much of that torque as possible).  I've run a 280 Magnum in a 355 years ago and it was relatively mild but that was in a Camaro with a manual trans and 3.73 gears.  I really don't have any experience to judge how it will be in my Blazer with stock gears, tall tires and an automatic (thus my question).

The Lunati cam in the article seems to only differ from a Comp 280 magnum in lobe sep. (109 deg. for the Lunati and 110 deg. for the Comp).  Lift and duration at .050 are the same.  Everything else staying the same, should I expect a drop in torque of 5% going with a cam like the 270 Magnum?  More?  Less?  The Impersonator put out 520-something lbs.-ft. of torque - I'd like to keep the number in the neighborhood of 500.

excuse me, i thought that you were talking of a 270 extreme energy cam. I see a dual pattern (more duration on the exhaust than intake) as fitting because vortec exhaust ports are poor and many dyno sheets i have seen have used dual pattern cams with vortec heads sucessfully

but if it interests you, a single pattern cam will almost always produce better mileage and low speed torque but will give up top end torque and fall off the peak faster, since the dual pattern cam among other things opens the exhaust earlier which as RPM climb engines need to start getting rid of the exhaust earlier since there is less time to pump it out. So especially if these vortec heads have been ported a single pattern cam might interest you this way, if it does go for it, the only thing i can recommend for people picking cams is to get a knowledge about it themselves and pick themself, because i dont know how you want the vehicle to act! but i can say a single pattern cam might not be a bad idea for a blazer since it wont be a top end ET machine anyway, and it is heavily daily driver based

compared to the impersonator, i think your engine will see less peak torque but you might have better just off idle torque since your engine will have less seat and .050 duration and 1 degree spread LCA, it will have less overlap area and especially if your compression is a little lower than you would like, this would help keep the engine idle smoothly and at least keep your off idle torque the same if not more than the comparison engine

P.S. i say good choice on going with vortec heads, after looking at the article again i cant believe that the AFR heads didnt out perform the vortecs till after 4000 RPM and were giving up in some places around 30 ft lbs of torque, for a street engine the smart choice is a vortec head

Thanks again Gibs.  Looking at the dyno chart from the article the engine was making over 470 lbs-ft at 2300 rpm and that's what I am really looking for.  If peak torque drops a bit but off-idle torque remains (or increases slightly) with the 270 Magnum cam that'll be just fine with me.

I also noticed that the Vortec's outperformed the AFR's down low.  The price of the Vortec's is icing on the cake too.  I can honestly say that my Blazer hasn't seen 5000 rpm in.....well maybe never.  I see it spending most of it's time below 4000.

I'm really looking forward to the new motor.

OM Gang

sounds great, i think you have made some great choices for the engine, and keep me filled in on the progess!

Can anyone point in a good direction for finding pistons for this motor?  I haven't been able to find many listings for 400 sbc w/5.7 rod pistons listed on the internet.

Also, seems like a 30cc dish will yield approx. 9.5 cr with the Vortec heads (58cc chamber).  Are there 35-36 cc dish pistons available that will bring the cr down near 9.0?  Is going to a deeper dish a bad idea for how the combustion process will perform?

Thanks,

OM Gang

vortec heads have a blueprint cc of 64, are you sure you have vortec heads? for some reason there is common confusion about what is considered high performance vortec heads, so you better check casting numbers

Keith Black PN 126030-8 seems good to me from a performance standpoint, even though they use 5/64 rings it has a d-shaped dish of 30 cc's. And they are hyperetectic and are $245. my calculations put your static compression at 9.0:1 with a piston to head clearance of .040, and you could even use a clearance there of .050-.060 to be safe with 87 octane and bring it between 8.75-8.9:1

Thanks for correcting me.  I'm not sure where I got 58cc from - I started off this whole project by looking at the Vortec heads and the specs say 64cc chambers.  I'm starting to think I should just send you a check and have you build the motor for me.  I really appreciate all the feedback.

OM Gang

you had said that to be a true vortec head they have to be 64cc well i must say i use to think the same untill i found a set of 68cc vortecs that are off a 96' chevy truck the cast # of these heads are 10239906 and chevy did make a 58cc vortec head but they are alum. and they are off the new corrvettes the cast # i do not have at this time but i will find out and get back to you ok john but as far as the best vortec head are the 64cc heads so they say but i really think it all depends on what you want out of your motor