My 79 has a 290 HP Chevy Performance crate engine with 76 cc combustion chambers and mild cam http://paceperformance.com/i-6255330...te-engine.html. I have been researching head/cam combinations that would up the hp to something like 325. Has anyone put together a combo that just did not work? Maybe a roller cam with flat tappet heads, or a combo that did not create enough vacuum, etc. I just don't want to learn the hard way if someone else has already paved the way. Thanks.

 

There is not such a thing as flat tappet heads or roller tappet heads. Why not just buy a top end package that is matched from a source such as www.summitracing.com or www.jegs.com

 

Mel,

Here are the advertised specs for Dart SHPs - they specify the cam type to be used:

PAIR of DART SHP Aluminum Cylinder Heads
Small Block Chevy 327, 350, 400
64cc/200cc
Solid Flat Tappet or Hydraulic Roller Cam
Fully Assembled

 

Understood but you want something more specific, which roller or flat tappet to use. Thus I suggested a pre-paired package from one of the two sites. Here is an example of a pre-matched set

http://www.summitracing.com/parts/tf...make/chevrolet

 

I appreciate the link, but my question is can you mess things up if you do not choose a pre-matched set. I was thinking of just replacing the heads and keeping the hydraulic flat tappet cam for now. Could the Dart SHP heads work with that cam?

 

What is your budget. What gear do you have in the rear, auto or manual? Is 325 all your looking to achieve? A set of vortecs and a small hydraulic roller would get you there for a low cost upgrade. I made 260 rwhp with edelbrock performer heads, hooker comp headers, comp xe262h, wieand action plus intake and a Holley 600 vacuum secondary. It drove good, better with a 2400 rpm stall, but if I were doing that combo over again I'd go afr heads. The vortecs flow about the same as that particular set of edelbrock.

 

290/325 You will hardly notice it and for such a small hp increase on that specific block I would not dump a top end on it . Look for a better intake and 1.6 rockers and a free flowing exhaust and call it a day.

 

The "prematched" sets can be good or bad. The above might work great on an engine with flat top pistons, 3.70 gears and a 4 speed and be a horrible mismatch on a dish piston, 3.08 gear and a stock auto in an otherwise similar car.

The 200 CC dart heads are too big for a base small block. The solid flat tappet or hydraulic roller refers to the open and closed spring pressures of the springs included on the heads. This is a poor way to select proper springs, they should be matched to your specific cam requirements.

Your best bet is to start a thread with budget range, rear gear ratio, trans, intended use and expected power. Then you will still get a wide range of recommendations but at least anyone making those recommendations will be able to base them on real information. Matching the above parameters with your new parts choices to make the combination as well matched as possible is your best option to achieve the end result you really want.

Be very careful who's advice you take. There are plenty that have done mild upgrades with great results that don't break the bank but I have also seen some terrible advise given to those asking similar questions on here recently. If your only looking for a 10% increase in seat of the pants acceleration a set of headers, free flowing true dual exhaust, performance distributor recurve and a intake upgrade will get you that without opening the engine up and really need to be addressed before anything else is changed out anyway.

 

I have the same motor I used dart shp heads Comp 280 cam Rpm intake Holley 750 Headers Recurve ignition Roller rockers Runs great
And a stall converter 2300 I think

 

350 GM Goodwrench Target Crate
185 Patriot Heads
2012 Car Craft Budget SB Chevy ShootOut.
PUmp gas
422HP

 

All great advice. My only concern was that a mismatched set could do some damage. Sounds like there are endless combinations that all work to some extent.

By the way, I have block hugger headers with dual exhaust and a new Pertronics distributor. The vette is an automatic with the 3.55 rear diff.

Thanks

 

we put a street warrior intake, edelbrock 750, and a voodoo 60103lk cam in my friends 77 L82, with long tube headers and full exhaust that thing would fly! i think he eather had 3.55's or 3.70 gears, and we dident have to change out the heads or converter. made tons of vacuum

 

Looking at the specs on that GM engine it looks like it would be a real dog down low with that cam the heads provided, and resultant CR. GM is optimistic in their CR estimates. My 8.5:1 '77 L-48 was more like 7.66:1 after measuring out the heads and pistons.

If this engine is similar to the L-48 (I think it is) then going to a 64cc head with a felpro .015" gasket would net you about 9.0:1 CR. That's a lot better and may work just ok with the provided cam. Not ideal IMO, likely weak off idle, but better than it is currently.

I agree that a 200cc head is too big for your purposes here. 180cc or less would be better for throttle response.
The cam is a 222@.050 on a 112 lsa and off the seat duration is unknown. Probably something around 285*or more assuming it is an old school grind. This is a bit long for 9.0:1 compression. Problem is that your DCR gets really low which is an indicator of your cylinder pressure. Less cylinder pressure = less torque. A cam change would help a lot with the head change.
I have a set of Dart SHP 180cc heads on my engine now. The 180cc is not accurate. Mine cc'd out to 195 to 197cc's.

 

Chris do you have flow numbers and prices for these heads? Are they cnc runners/ chambers? screw in studs? Have you built any engines with these, if so how did they do?

 

This is all real good advice.

What I wanted to know is:

Has anyone set up a combination that just did not work?

something like " I tried xxx heads with xxxx cam and it just did not perform like I thought it would."

 

i had a 307 head and a 350 head, dont remember casting numbers with flat top pistons with 4 valve reliefs on a 355 and an edelbrock RPM cam and it was a dog off the line till about 30mph, that was in a 77 Monte Carlo with a TH350, 1500 stall, and 3.42 gears, weighed about 4300lbs

 

It's not really the heads that determine the cam type, it's the valve springs. Dart is saying that the springs that are included with these heads are suitable for a solid flat tappet or hydraulic roller. A hydraulic flat tappet would want softer springs. A solid roller wants stiffer (as well as handling higher lift which is common with solid rollers).

 

With a stock stall I can see an RPM intake, cam, and a heavy car having a negative effect. A 3,000 stall is recommended for that cam.

(The small valve 307 heads would give alittle better off idle response, but fall off faster toward top-end).

A good example of a not so great combo

 

I have had a lot of poor combos. I used to overcam and overcarb everything. In the 70's the knowledge base was not as easily accessible. It was all trial and error and learning at the track, swap parts, run it again, talk to the guys in the pits who might not know more than the 20 year old kid asking the questions. In 40 years I have learned a lot of what not to do from mistakes, a lot of them expensive mistakes. Got it dialed in pretty good now but still learning all the time.

 

This ^ Pay attention to this guy! Ask him what cam he uses with this combo?