Bottom end just completed. See my sig for top end. Bottom end consists of stock block bored to 383, spayed caps, forged crank, forged I-beam rods, forged Ross flat top pistons. Goes on the Mustang dyno and makes a wopping 276 hp at 5500 and 300 lb ft starting at about 2000 and staying flat to almost 5500. Seems rich on the bottom, lean on top. However, even with chip adjustments, I feel like I am way off. If so, where do I start looking for the power? The only thing left stock on this engine is the HEI including distributor. The rest is the best of the best. I am disappointed in the outcome. I am seeing similar combos on this board at or around 400rwhp. TIA

 

heads are tooo big not enough cam too much injector you didnt mention what intake if you need help i can give some help email me i am in the process of doing a 383 motor and it should be in the 400 rwhp when done :cheers:

 

Your almost there with all those components, but lack a solid lifter camshaft to be able to get the horsepower of a 7000+ engine. It could have with stood some more compression also. But put a good solid lifter cam in it and watch the improvement. :thumbs:

 

You have just discovered that bigger is not always better. You'd recover a lot of the lost torque if you just got a set of GM Vortec heads and had them machined for better springs. Torque is what builds power. Charge speed and swirl and compression, (among other things) builds torque. Huge heads equal less intake charge speed, which equals drastically lower torque...for example. The combination is important, and your combination is not right.

Also, 400 rear wheel horsepower is probably unrealistic. After you factor in a 20% driveline loss, that engine would have to make 500 horsepower. From 383 cubic inches? I don't think so...not without forced induction.


[Modified by Bearcat, 11:48 PM 11/25/2003]

 

Here is an engine dyno from Air Flow Research's Website.

AFR 190 heads
9.5:1 compression
AFR version of Performer RPM manifold
1-3/4" Headers
Comp Cam: 236/242 duration @ 0.05 & 0.520/0.540 lift. 110/106

 

I never did see you final compression ratio. I could tell you if you know the head chamber cc size and what type of heads gasket you used.

Your cam is on the milder side, but it's much bigger than the LPE 219 that are solid performers in 383 ci. I would check on the fuel map, total spark advance, and ensure that the cam is degreed in.

Borrow a complete ignition. Your TQ value is like it's only running on 6-7 cylinders.




[Modified by gkull, 8:47 AM 11/29/2003]

 

gkull, the chamber is 64cc. I am not sure of the gasket thickness but I believe I am at 10.25 to 10.5 CR. The fuel map is way off all through the range. I am waiting for a reprogrammed chip to arrive that should correct the Maps.

 

Flat tops and 64 cc in a 383 put's you in the high 10's for compression ratio. With a thin quench area I'm getting 11.2

Having chips burnt has always seemed like a bad deal to me. Years ago this forum had someone who was doing custom chips.

 

Actually, the pistons are -15cc domed top. I just need to learn to burn my own chips or suck it up and get a DFI, Halltech etc...

 

Domed piston are race gas only with 64 cc chambers. Maybe that's why your not making any power.

Now I see 15 cc dished is what you meant to say. Yes that would bring it down to low 10's on the compression.


[Modified by gkull, 11:49 AM 12/1/2003]

 

Aside from the tuning issues, the problem is the heads and the cam. Out-of-the-box Dart 215cc Pro1's have a 600HP cross-section, 500HP high-lift flow, and 400HP low and mid-lift flow. With your cam and 10:1 compression you will get a little over 400HP from 5000-6500RPM (depending on the success of your porting job).

The Darts are race heads and require professional port preparation combined with aggressive high-lift race cams and high compression to see great results. Your cam uses the CompCams 3051 intake lobe I think (274/220/134/0.512" w/ 1.6's). It is quite mild. People with 500HP LT1's frequently use the XE3192 as an intake (276/224/152/0.605" w/ 1.6's). The 150+ degrees of duration at 0.200" tappet lift is the key to getting the power out of the heads.

 

Great stuff. Keep it coming! The heads have 40hrs of porting by MORE performance and are also matched to the Miniram. MORE put the pkg together for my stock 350 bottom end. If I can't make what they claimed and (still claim) on their website and talking with them, then I will send the car to Charlotte for them to figure it out!!!! :mad MORE custome grinds their cams to match their packages they sell. I am not sure which Comp Cam this started out as. I believe the .510 lift was based on stock rockers so It should be better with the 1.6 rollers. I am quickly losing faith in these folks. I will reserve final judgement until I receive my new chip. I know I won't find 80rwhp in a chip change though.

 

You're right about the lobes. I looked at an old job where the guy wanted to get rid of the More cam. I looks like intake was 3109 (276/220/138/0.544" w/ 1.6's) and exhaust 3112 (290/230/143/0.544" w/ 1.6's). It was an attempt to copy the HotCam specs.

40 hours of porting? Did they give you the final cross-sectional area profile and flow data? Also, with the weak midrange volumetric efficiency of the LT1 style intake, you should have built as much compression ratio into the engine as you could. -5cc flat tops would have given you 11.1:1 or so.

Also, what was your collector configuration downstream of those intermediate length headers? The sizes and lengths to intersection points will have influence on the shape of the torque curve. The most common header configuration that I see on C4's is 20"-26" 1 3/4" primaries into 30+" by 3" collectors to a crossover detail. This puts a sag in the midrange with LT1 sytle intakes because of out-of-tune wave action from the header. Lower midrange and top-end benefit from the second returning and first returning scavenging waves respectively. Maybe one day someone will mass produce full-length headers for the C4.

 

I am sure my exhaust configuration is not optimal. Even though I went with the miniram that has no EGR, I wanted the exhaust semi legal. I wanted 3" all the way but the guy who put it in said the best he could fit was 2.5 (that's after I bought the 3" flows and 3" cat. So, after the collectors, there's a 2.5 Y pipe to a single 3" high flow converter back to 2.5" Y to 3" Flows. I wanted to go true duals but was told there is no room. Is that correct?

 

You can design your exhaust system on my website if you sign up. Run the header design program. Then read the instructions for designing the tailpipes, and locating and selecting the cats. In general you want the cats to flow 2CFM per HP or more. The 3" high flow cats generally flow 500+CFM each, so two of them are suitable for a 500HP engine.

There is nothing wrong with the Y-pipe detail for the collector termination (expansion detail), but reducing the 3" collectors to 2 1/2" collectors effectively reflects some of the blowdown wave and reduces scavenging wave strength. It also retards it. If you can get your output to exceed 450HP, the proper size system would be more like 1 3/4" header into 2 3/4" collector into 3 1/2" single, or most likely into an x-pipe arrangement with twin cats. You will probably need to ceramic coat the inside of the headers to make the cats work their best that far downstream.

Don't be afraid to cut your headers apart and make them right for the engine (before you ceramic coat them). There should be room to fit the right thing. Custom race header builders get it done.

 

I am amazed yet again at the science of something I thought to be pretty simple. Thanks for all of your help. Once I get the engine running better, I can concentrate on the exhaust. I will definately be visiting your website.

 

As a note, dual 3" exhaust fits under the C4

 

your comp ratio works out to 9.4 to 1 with the 15 cc dish piston :cheers:

 

You are right. I am trying to find the thickness of the Felpro 7733PT2 gasket but assuming its around .051 it puts it at 9.4 to 1. I have found out (by opening up the oil fill cap on the manifold cover and seeing a casting #) that my Darts are actually 200cc, not the 215cc. I feel pretty stupid that I did not notice it before but at least my heads are not as oversized as I thought!

 

Hey Corky, my gasket is .0039". Wouldn't that give me 10.3 to 1?