jmccart

I am kind of new to this site. I have asked this question on dieselplace.com-gmgassers and received some quality answers from some cool guys. I just want to hear as many opinions as possible.

I am curious if anyone has any experience with the 264. I believe I have read from 2 guys who opted for the 258 "tow" cam. They both said they would go bigger if they ever did it again. Guys with the 270 all love it, but say they did not get much more power under 3500 RPM's.

I contacted Compcams too. I told them I don't tow that heavy (10k max, I would guess?) and not that often. I just need to get the job done a few times a year. He suggested the 270. But he also said that his push-rods are the correct ones, when I shared with him that every 8.1 cam guy says they are totally short.

Thank you.

Kerr

i have a comp cam, 270hr.. its nice, but if i was to do it again id do a custom grind, only problem is i get lost in the duration X lift x flux capasator navigator X 88 mph and marty never tells the answer.

Dont get there push rods, they do not fit. and they will argue with you on the phone, you can even send them a freaking photo and they dont refund your money. I tried there push rods, and they didnt come out of the head.. stopped about middle way in the watter passage ways or what ever you call them.. com was all well you just have to bolt them on right.. Drew was like how the hell do you bolt the rocker arms on inside the water port.. lol..

I cant chime in on the power gain, because i did the cam and supercharger at the same time. i can tell that with just the cam in it, when you revve it, it rocks like a old muscle car which it didnt do before.

ive heard that cam has taken 2 seconds off some trucks, and some guys said they picked up 50-70 whp, which seems a little high with out going crazy..

Id say do the big one, even comps "big" cam isnt really that big. i think my card read 510 510 or something like that.

hog

450hp 8.1 496

http://www.youtube.com/watch?v=gxb_L5cA1rw

Better vid

http://www.youtube.com/watch?v=C39NKezowNM


525hp-560hp with exhaust/cam/springs/headporting on 87 octane.

peace
Hog

Kerr

awsome but boat stuff isnt the same as the 8.1L truck stuff. or at least thats what everyone said a few years ago... something about compression, timing, water is a lot cooler and the boats run more consistant rpm..

hog

the tune would be a bit different due to some temp differences, but the intakes, heads, blocks, cranks, pistons etc etc are exactly the same as the truck stuff. Some of these engines use a closed cooling system that doesnt run much cooler than auto applications.

The HP3 8.1 is a truck engine with ported heads, cam, springs and higher pressure FPR. That was teh purpose of teh HP3, to show that the Vortec "truck" engine could be competitive against big dollar "race" engines. This was the reason the HP3 crate engine was not released to teh public. Mercury didnt want their "race" 502's being beaten up on by a mostly "stock" 87 octane truck engine. Since Mercury was GM's largest buyer of SBC and BBC engines, GM dropped the 8.1 HP3 version.
A differnt company tried to keep the 8.1 in competition, and got up to 560hp on 87 octane before the stock hypereutectic pistons became an issue.

Guys are now getting 575hp and over 600 lb/ft torque with the new dart GEN 7 8.1 heads out of the box on 91 octane, a virgin marine/truck intake manifold was used.
A 630 cubic inch version was built and 830 lb/ft torque at 2800rpm was produced with a dual plane intake witha 650cfm carb on top.
The Dart iron 8.1 heads are $654 a piece bare, 26 pairs are being machined, 16 are spoken for, orders are being taken.

Flow numbers on the 8.1 heads with porting as used for the HP3 engines
Intake valve 2.250 ex 1.820. These hads made 600hp in 2006, backed off to 590hp tune wise. The new Dart heads will flow closer to 400cfm at 0.700" lift.

Lift..............CFM...............Exh.CFM

.2................157.................141
.3................230.................190
.4................292.................221
.5................330.................238
.6................348.................249
.65..............353.................251




If it will survive in a performance marine application, it will more than survive in a performance truck application.

peace
Hog

jmccart

Good information guys. Thanx. Good head flow info. Do you know what stock heads flow? I have been reading about the Dart heads, they sound totally awesome. I really would like to have a set for when I put in a cam. The price is not that bad, like $1300 for a bare set. Do bare heads come w/valve guides installed?. Even if I get a great deal on valves from ebay or something, and springs/locks/retainers/cam from Comp-cams (a guy w/an ebay store quoted me $450 shipped for all that stuff), I don't know if I can spring for the heads right now. But I like the idea of having the engine apart, and swapping heads while I am in there.

1BadAction

iTrader: (10)

I think a mild port job on stock heads and a towing/street cam should be good for 5 to 550hp at the crank. Around 1hp per cube is very mild. Question is, who in the truck world really pays attention to these things in a performance sense? And don't say Raylar, every time I have seen Ray talk about these engines, he dismisses any parts or modifications except for the ones he sells.

lawdog49

iTrader: (2)

ok, so let's get back to the point and talk about what could be accomplished in a truck. Dart heads, one of the comp cams(which one?), along with otherwise stock 8.1 in a truck- and what kind of improvement versus stock are we talking about? And would this combo still yield good 87 octane, everyday driving and some towing positive results?

TieRod

Don't forget a 200hp shot!!!!!!!!!!!!

BetMinesFaster

270 is a nice cam. I wont look back. Truck snorts right off idle and pulls hard till 5k+

Valves are a bit noisey but tolerable.

Towing is better than ever with this cam. Converter locked in 5th and it will stay locked and no downshifts on moderate long grades with 9K behind you and still maintain speed.

The downer is i havent beaten 9 to the gallon since the install and retune, used to get 10.5-11 when on the highway, havent gotten better than 9 since the install

It is by the far the largest power gain I have personally experianced with doing the cam only.

As Kerr said, Comps supporting parts dont fit (push rods and adjustable conversion kit) So measure and order custom pushrods.